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Chang Y, Yang B, Zhang Y, Dong C, Liu L, Zhao X, Wang G. Identification of sex-biased and neurodevelopment genes via brain transcriptome in Ostrinia furnacalis. Front Physiol 2022; 13:953538. [PMID: 36003649 PMCID: PMC9393524 DOI: 10.3389/fphys.2022.953538] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2022] [Accepted: 07/01/2022] [Indexed: 11/16/2022] Open
Abstract
Insect brains play important roles in the regulation of sex-biased behaviors such as mating and oviposition. The neural structure and function of brain differences between males and females have been identified, in which the antenna lobes (AL) showed the most discrepancy, however, the whole repertoire of the genes expressed in the brains and the molecular mechanism of neural signaling and structural development are still unclear. In this study, high-throughput transcriptome analysis of male and female brains was carried on in the Asia corn borer, Ostrinia furnacalis, and a total of 39.23 Gb data and 34,092 unigenes were obtained. Among them, 276 genes displayed sex-biased expression by DEG analysis, of which 125 genes were highly expressed in the males and 151 genes were highly expressed in the females. Besides, by homology analysis against genes that have been confirmed to be related to brain neurodevelopment, a total of 24 candidate genes were identified in O. furnacalis. In addition, to further screen the core genes that may be important for sex-biased nerve signaling and neurodevelopment, protein-protein interaction networks were constructed for the sex-biased genes and neurodevelopment genes. We identified 10 (Mhc, Mlc1, Mlc2, Prm, Mf, wupA, TpnC25D, fln, l(2)efl, and Act5C), 11 (PPO2, GNBP3, Spn77Ba, Ppn, yellow-d2, PGRP-LB, PGRP-SD, PGRP-SC2, Hml, Cg25C, and vkg) and 8 (dac, wg, hh, ci, run, Lim1, Rbp9, and Bx) core hub genes that may be related to brain neural development from male-biased, female-biased, and neurodevelopment gene groups. Our results provide a reference for further analysis of the dimorphism of male and female brain structures in agricultural pests.
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Affiliation(s)
- Yajun Chang
- State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, China
- Department of Entomology, College of Plant Protection, Henan Agricultural University, Zhengzhou, China
| | - Bin Yang
- State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, China
- *Correspondence: Guirong Wang, ; Bin Yang,
| | - Yu Zhang
- Key Laboratory of Biohazard Monitoring, Green Prevention and Control for Artificial Grassland, Ministry of Agriculture and Rural Affairs, Institute of Grassland Research of Chinese Academy of Agricultural Sciences, Hohhot, China
| | - Chenxi Dong
- State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, China
| | - Lei Liu
- State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, China
| | - Xincheng Zhao
- Department of Entomology, College of Plant Protection, Henan Agricultural University, Zhengzhou, China
| | - Guirong Wang
- State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, China
- *Correspondence: Guirong Wang, ; Bin Yang,
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Chowdhury R, Roure A, le Pétillon Y, Mayeur H, Daric V, Darras S. Highly distinct genetic programs for peripheral nervous system formation in chordates. BMC Biol 2022; 20:152. [PMID: 35761237 PMCID: PMC9238270 DOI: 10.1186/s12915-022-01355-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2021] [Accepted: 06/20/2022] [Indexed: 11/10/2022] Open
Abstract
Abstract
Background
Vertebrates develop their peripheral nervous system (PNS) from transient unique embryonic structures, the neural crest, and the ectodermal placodes that are located at the border of the forming central nervous system. By contrast, in the invertebrate chordates, amphioxus and ascidians, a large part of the PNS originates at the opposite of the embryo, in the ventral ectoderm. In both groups, a biphasic mechanism regulates ventral PNS formation: high BMP levels specify a neurogenic territory within which glutamatergic epidermal sensory neuron formation is controlled by the Notch pathway. Given these similarities and the phylogenetic relationships within chordates, it is likely that ventral PNS is an ancestral feature in chordates and that it has been lost in vertebrates.
Results
In order to get insights into the molecular control of ventral PNS formation and to test the hypothesis of their homology and potential contribution to the emergence of vertebrate PNS, we undertook a close comparison of ventral PNS formation in the ascidian Phallusia mammillata and the amphioxus Branchiostoma lanceolatum. Using timed RNA-seq series, we identified novel markers of the ventral PNS during different phases of its development in both species. By extensively determining the expression of paralogous and orthologous genes, we observed that only a minority of genes have a shared expression in the ventral PNS. However, a large fraction of ventral PNS orthologous genes are expressed in the dorsally forming PNS of vertebrates.
Conclusions
Our work has significantly increased the molecular characterization of ventral PNS formation in invertebrate chordates. The low observed conservation of gene expression in the ventral PNS suggests that the amphioxus and ascidian ventral PNS are either not homologous, or alternatively extensive drift has occurred in their regulatory mechanisms following a long period (600 My) of separate evolution and accelerated evolution in the ascidian lineage. The homology to genes expressed in the dorsally forming PNS of vertebrates suggests that ancestral sensory neurons gene networks have been redeployed in vertebrates.
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Ma P, Liu X, Xu Z, Liu H, Ding X, Huang Z, Shi C, Liang L, Xu L, Li X, Li G, He Y, Ding Z, Chai C, Wang H, Qiu J, Zhu J, Wang X, Ding P, Zhou S, Yuan Y, Wu W, Wan C, Yan Y, Zhou Y, Zhou QJ, Wang GD, Zhang Q, Xu X, Li G, Zhang S, Mao B, Chen D. Joint profiling of gene expression and chromatin accessibility during amphioxus development at single-cell resolution. Cell Rep 2022; 39:110979. [PMID: 35732129 DOI: 10.1016/j.celrep.2022.110979] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2021] [Revised: 03/21/2022] [Accepted: 05/27/2022] [Indexed: 11/03/2022] Open
Abstract
Vertebrate evolution was accompanied by two rounds of whole-genome duplication followed by functional divergence in terms of regulatory circuits and gene expression patterns. As a basal and slow-evolving chordate species, amphioxus is an ideal paradigm for exploring the origin and evolution of vertebrates. Single-cell sequencing has been widely used to construct the developmental cell atlas of several representative species of vertebrates (human, mouse, zebrafish, and frog) and tunicates (sea squirts). Here, we perform single-nucleus RNA sequencing (snRNA-seq) and single-cell assay for transposase accessible chromatin sequencing (scATAC-seq) for different stages of amphioxus (covering embryogenesis and adult tissues). With the datasets generated, we constructed a developmental tree for amphioxus cell fate commitment and lineage specification and characterize the underlying key regulators and genetic regulatory networks. The data are publicly available on the online platform AmphioxusAtlas.
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Affiliation(s)
- Pengcheng Ma
- State Key Laboratory of Genetic Resources and Evolution, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming 650223, China
| | - Xingyan Liu
- Academy of Mathematics and Systems Science, Chinese Academy of Science, Beijing 100190, China; School of Mathematical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Zaoxu Xu
- BGI-Shenzhen, Shenzhen 518083, China; College of Life Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Huimin Liu
- State Key Laboratory of Cellular Stress Biology, School of Life Sciences, Xiamen University, Xiangan District, Xiamen, Fujian 361102, China
| | - Xiangning Ding
- BGI-Shenzhen, Shenzhen 518083, China; College of Life Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Zhen Huang
- Fujian Key Laboratory of Special Marine Bio-resources Sustainable Utilization, College of Life Sciences, Fujian Normal University, Fuzhou, 350117 Fujian, China; Fuzhou Institute of Oceanography, Minjiang University, Fuzhou 350108, China; Fujian Key Laboratory on Conservation and Sustainable Utilization of Marine Biodiversity, Minjiang University, Fuzhou 350108, China
| | - Chenggang Shi
- State Key Laboratory of Cellular Stress Biology, School of Life Sciences, Xiamen University, Xiangan District, Xiamen, Fujian 361102, China
| | - Langchao Liang
- BGI-Shenzhen, Shenzhen 518083, China; College of Life Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Luohao Xu
- Key Laboratory of Freshwater Fish Reproduction and Development (Ministry of Education), Key Laboratory of Aquatic Science of Chongqing, School of Life Sciences, Southwest University, Chongqing, China
| | - Xiaolu Li
- Genome Center of Biodiversity, Kunming Institute of Zoology, Chinese Academy of Science, Kunming 650223, China
| | - Guimei Li
- State Key Laboratory of Genetic Resources and Evolution, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming 650223, China
| | - Yuqi He
- Genome Center of Biodiversity, Kunming Institute of Zoology, Chinese Academy of Science, Kunming 650223, China
| | - Zhaoli Ding
- Genome Center of Biodiversity, Kunming Institute of Zoology, Chinese Academy of Science, Kunming 650223, China
| | - Chaochao Chai
- BGI-Shenzhen, Shenzhen 518083, China; College of Life Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Haoyu Wang
- BGI-Shenzhen, Shenzhen 518083, China; College of Life Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Jiaying Qiu
- BGI-Shenzhen, Shenzhen 518083, China; College of Life Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Jiacheng Zhu
- BGI-Shenzhen, Shenzhen 518083, China; College of Life Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | | | - Peiwen Ding
- BGI-Shenzhen, Shenzhen 518083, China; College of Life Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Si Zhou
- BGI-Shenzhen, Shenzhen 518083, China
| | | | - Wendi Wu
- BGI-Shenzhen, Shenzhen 518083, China
| | - Cen Wan
- Fujian Key Laboratory of Special Marine Bio-resources Sustainable Utilization, College of Life Sciences, Fujian Normal University, Fuzhou, 350117 Fujian, China
| | - Yanan Yan
- Fujian Key Laboratory of Special Marine Bio-resources Sustainable Utilization, College of Life Sciences, Fujian Normal University, Fuzhou, 350117 Fujian, China
| | - Yitao Zhou
- Fujian Key Laboratory of Special Marine Bio-resources Sustainable Utilization, College of Life Sciences, Fujian Normal University, Fuzhou, 350117 Fujian, China
| | - Qi-Jun Zhou
- State Key Laboratory of Genetic Resources and Evolution, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming 650223, China
| | - Guo-Dong Wang
- State Key Laboratory of Genetic Resources and Evolution, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming 650223, China; Genome Center of Biodiversity, Kunming Institute of Zoology, Chinese Academy of Science, Kunming 650223, China; Center for Excellence in Animal Evolution and Genetics, Chinese Academy of Sciences, Kunming 650223, China
| | - Qiujin Zhang
- Fujian Key Laboratory of Special Marine Bio-resources Sustainable Utilization, College of Life Sciences, Fujian Normal University, Fuzhou, 350117 Fujian, China.
| | - Xun Xu
- BGI-Shenzhen, Shenzhen 518083, China.
| | - Guang Li
- State Key Laboratory of Cellular Stress Biology, School of Life Sciences, Xiamen University, Xiangan District, Xiamen, Fujian 361102, China.
| | - Shihua Zhang
- Academy of Mathematics and Systems Science, Chinese Academy of Science, Beijing 100190, China; Center for Excellence in Animal Evolution and Genetics, Chinese Academy of Sciences, Kunming 650223, China; Key Laboratory of Systems Biology, Hangzhou Institute for Advanced Study, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Hangzhou 310024, China.
| | - Bingyu Mao
- State Key Laboratory of Genetic Resources and Evolution, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming 650223, China; Center for Excellence in Animal Evolution and Genetics, Chinese Academy of Sciences, Kunming 650223, China.
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Bozzo M, Costa S, Obino V, Bachetti T, Marcenaro E, Pestarino M, Schubert M, Candiani S. Functional Conservation and Genetic Divergence of Chordate Glycinergic Neurotransmission: Insights from Amphioxus Glycine Transporters. Cells 2021; 10:cells10123392. [PMID: 34943900 PMCID: PMC8699752 DOI: 10.3390/cells10123392] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2021] [Revised: 11/22/2021] [Accepted: 11/25/2021] [Indexed: 11/24/2022] Open
Abstract
Glycine is an important neurotransmitter in vertebrates, performing both excitatory and inhibitory actions. Synaptic levels of glycine are tightly controlled by the action of two glycine transporters, GlyT1 and GlyT2, located on the surface of glial cells and neurons, respectively. Only limited information is available on glycinergic neurotransmission in invertebrates, and the evolution of glycinergic neurotransmission is poorly understood. Here, by combining phylogenetic and gene expression analyses, we characterized the glycine transporter complement of amphioxus, an important invertebrate model for studying the evolution of chordates. We show that amphioxus possess three glycine transporter genes. Two of these (GlyT2.1 and GlyT2.2) are closely related to GlyT2 of vertebrates, whereas the third (GlyT) is a member of an ancestral clade of deuterostome glycine transporters. GlyT2.2 expression is predominantly non-neural, whereas GlyT and GlyT2.1 are widely expressed in the amphioxus nervous system and are differentially expressed, respectively, in neurons and glia. Vertebrate glycinergic neurons express GlyT2 and glia GlyT1, suggesting that the evolution of the chordate glycinergic system was accompanied by a paralog-specific inversion of gene expression. Despite this genetic divergence between amphioxus and vertebrates, we found strong evidence for conservation in the role glycinergic neurotransmission plays during larval swimming, the implication being that the neural networks controlling the rhythmic movement of chordate bodies may be homologous.
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Affiliation(s)
- Matteo Bozzo
- Dipartimento di Scienze della Terra, dell’Ambiente e della Vita (DISTAV), Università degli Studi di Genova, 16132 Genoa, Italy; (S.C.); (T.B.); (M.P.)
- Dipartimento di Medicina Sperimentale (DIMES), Università degli Studi di Genova, 16132 Genoa, Italy; (V.O.); (E.M.)
- Correspondence: (M.B.); (S.C.); Tel.: +39-010-335-8043 (M.B.); +39-010-335-8051 (S.C.)
| | - Simone Costa
- Dipartimento di Scienze della Terra, dell’Ambiente e della Vita (DISTAV), Università degli Studi di Genova, 16132 Genoa, Italy; (S.C.); (T.B.); (M.P.)
| | - Valentina Obino
- Dipartimento di Medicina Sperimentale (DIMES), Università degli Studi di Genova, 16132 Genoa, Italy; (V.O.); (E.M.)
| | - Tiziana Bachetti
- Dipartimento di Scienze della Terra, dell’Ambiente e della Vita (DISTAV), Università degli Studi di Genova, 16132 Genoa, Italy; (S.C.); (T.B.); (M.P.)
| | - Emanuela Marcenaro
- Dipartimento di Medicina Sperimentale (DIMES), Università degli Studi di Genova, 16132 Genoa, Italy; (V.O.); (E.M.)
| | - Mario Pestarino
- Dipartimento di Scienze della Terra, dell’Ambiente e della Vita (DISTAV), Università degli Studi di Genova, 16132 Genoa, Italy; (S.C.); (T.B.); (M.P.)
| | - Michael Schubert
- Laboratoire de Biologie du Développement de Villefranche-sur-Mer (LBDV), Institut de la Mer de Villefranche, Sorbonne Université, CNRS, 06230 Villefranche-sur-Mer, France;
| | - Simona Candiani
- Dipartimento di Scienze della Terra, dell’Ambiente e della Vita (DISTAV), Università degli Studi di Genova, 16132 Genoa, Italy; (S.C.); (T.B.); (M.P.)
- Correspondence: (M.B.); (S.C.); Tel.: +39-010-335-8043 (M.B.); +39-010-335-8051 (S.C.)
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5
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Bozzo M, Lacalli TC, Obino V, Caicci F, Marcenaro E, Bachetti T, Manni L, Pestarino M, Schubert M, Candiani S. Amphioxus neuroglia: Molecular characterization and evidence for early compartmentalization of the developing nerve cord. Glia 2021; 69:1654-1678. [PMID: 33624886 DOI: 10.1002/glia.23982] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2020] [Revised: 02/02/2021] [Accepted: 02/09/2021] [Indexed: 12/19/2022]
Abstract
Glial cells play important roles in the development and homeostasis of metazoan nervous systems. However, while their involvement in the development and function in the central nervous system (CNS) of vertebrates is increasingly well understood, much less is known about invertebrate glia and the evolutionary history of glial cells more generally. An investigation into amphioxus glia is therefore timely, as this organism is the best living proxy for the last common ancestor of all chordates, and hence provides a window into the role of glial cell development and function at the transition of invertebrates and vertebrates. We report here our findings on amphioxus glia as characterized by molecular probes correlated with anatomical data at the transmission electron microscopy (TEM) level. The results show that amphioxus glial lineages express genes typical of vertebrate astroglia and radial glia, and that they segregate early in development, forming what appears to be a spatially separate cell proliferation zone positioned laterally, between the dorsal and ventral zones of neural cell proliferation. Our study provides strong evidence for the presence of vertebrate-type glial cells in amphioxus, while highlighting the role played by segregated progenitor cell pools in CNS development. There are implications also for our understanding of glial cells in a broader evolutionary context, and insights into patterns of precursor cell deployment in the chordate nerve cord.
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Affiliation(s)
- Matteo Bozzo
- Department of Earth, Environment and Life Sciences, University of Genoa, Genoa, Italy
| | - Thurston C Lacalli
- Biology Department, University of Victoria, Victoria, British Columbia, Canada
| | - Valentina Obino
- Department of Experimental Medicine, University of Genoa, Genoa, Italy
| | | | - Emanuela Marcenaro
- Department of Experimental Medicine, University of Genoa, Genoa, Italy.,Centre of Excellence for Biomedical Research, University of Genoa, Genoa, Italy
| | - Tiziana Bachetti
- Department of Earth, Environment and Life Sciences, University of Genoa, Genoa, Italy
| | - Lucia Manni
- Centre of Excellence for Biomedical Research, University of Genoa, Genoa, Italy
| | - Mario Pestarino
- Department of Earth, Environment and Life Sciences, University of Genoa, Genoa, Italy
| | - Michael Schubert
- Sorbonne Université, CNRS, Laboratoire de Biologie du Développement de Villefranche-sur-Mer, Villefranche-sur-Mer, France
| | - Simona Candiani
- Department of Earth, Environment and Life Sciences, University of Genoa, Genoa, Italy
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Holland ND. Hunting needles in a haystack: Migrating precursors of epidermal sensory neurons in amphioxus found with serial blockface scanning electron microscopy (SBSEM). ACTA ZOOL-STOCKHOLM 2020. [DOI: 10.1111/azo.12324] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Affiliation(s)
- Nicholas D. Holland
- Marine Biology Research Division Scripps Institution of Oceanography University of California at San Diego San Diego California
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7
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Zieger E, Garbarino G, Robert NSM, Yu JK, Croce JC, Candiani S, Schubert M. Retinoic acid signaling and neurogenic niche regulation in the developing peripheral nervous system of the cephalochordate amphioxus. Cell Mol Life Sci 2018; 75:2407-2429. [PMID: 29387904 PMCID: PMC11105557 DOI: 10.1007/s00018-017-2734-3] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2017] [Accepted: 12/19/2017] [Indexed: 10/18/2022]
Abstract
The retinoic acid (RA) signaling pathway regulates axial patterning and neurogenesis in the developing central nervous system (CNS) of chordates, but little is known about its roles during peripheral nervous system (PNS) formation and about how these roles might have evolved. This study assesses the requirement of RA signaling for establishing a functional PNS in the cephalochordate amphioxus, the best available stand-in for the ancestral chordate condition. Pharmacological manipulation of RA signaling levels during embryogenesis reduces the ability of amphioxus larvae to respond to sensory stimulation and alters the number and distribution of ectodermal sensory neurons (ESNs) in a stage- and context-dependent manner. Using gene expression assays combined with immunohistochemistry, we show that this is because RA signaling specifically acts on a small population of soxb1c-expressing ESN progenitors, which form a neurogenic niche in the trunk ectoderm, to modulate ESN production during elongation of the larval body. Our findings reveal an important role for RA signaling in regulating neurogenic niche activity in the larval amphioxus PNS. Although only few studies have addressed this issue so far, comparable RA signaling functions have been reported for neurogenic niches in the CNS and in certain neurogenic placode derivatives of vertebrates. Accordingly, the here-described mechanism is likely a conserved feature of chordate embryonic and adult neural development.
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Affiliation(s)
- Elisabeth Zieger
- Laboratoire de Biologie du Développement de Villefranche-sur-Mer, Observatoire Océanologique de Villefranche-sur-Mer, Sorbonne Universités, UPMC Université Paris 06, CNRS, 181 Chemin du Lazaret, 06230, Villefranche-sur-Mer, France
| | - Greta Garbarino
- Department of Earth, Environment and Life Sciences (Dipartimento di Scienze della Terra dell'Ambiente e della Vita, DISTAV), University of Genoa, Viale Benedetto XV 5, 16132, Genoa, Italy
| | - Nicolas S M Robert
- Laboratoire de Biologie du Développement de Villefranche-sur-Mer, Observatoire Océanologique de Villefranche-sur-Mer, Sorbonne Universités, UPMC Université Paris 06, CNRS, 181 Chemin du Lazaret, 06230, Villefranche-sur-Mer, France
| | - Jr-Kai Yu
- Institute of Cellular and Organismic Biology, Academia Sinica, Taipei, 11529, Taiwan
| | - Jenifer C Croce
- Laboratoire de Biologie du Développement de Villefranche-sur-Mer, Observatoire Océanologique de Villefranche-sur-Mer, Sorbonne Universités, UPMC Université Paris 06, CNRS, 181 Chemin du Lazaret, 06230, Villefranche-sur-Mer, France
| | - Simona Candiani
- Department of Earth, Environment and Life Sciences (Dipartimento di Scienze della Terra dell'Ambiente e della Vita, DISTAV), University of Genoa, Viale Benedetto XV 5, 16132, Genoa, Italy
| | - Michael Schubert
- Laboratoire de Biologie du Développement de Villefranche-sur-Mer, Observatoire Océanologique de Villefranche-sur-Mer, Sorbonne Universités, UPMC Université Paris 06, CNRS, 181 Chemin du Lazaret, 06230, Villefranche-sur-Mer, France.
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Abstract
The foundation of the diverse metazoan nervous systems is laid by embryonic patterning mechanisms, involving the generation and movement of neural progenitors and their progeny. Here we divide early neurogenesis into discrete elements, including origin, pattern, proliferation, and movement of neuronal progenitors, which are controlled by conserved gene cassettes. We review these neurogenetic mechanisms in representatives of the different metazoan clades, with the goal to build a conceptual framework in which one can ask specific questions, such as which of these mechanisms potentially formed part of the developmental "toolkit" of the bilaterian ancestor and which evolved later.
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Affiliation(s)
- Volker Hartenstein
- Department of Molecular Cell and Developmental Biology, University of California, Los Angeles, Los Angeles, CA 90095, USA.
| | - Angelika Stollewerk
- School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London E1 4NS, UK.
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Soukup V, Yong LW, Lu TM, Huang SW, Kozmik Z, Yu JK. The Nodal signaling pathway controls left-right asymmetric development in amphioxus. EvoDevo 2015; 6:5. [PMID: 25954501 PMCID: PMC4423147 DOI: 10.1186/2041-9139-6-5] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2014] [Accepted: 01/27/2015] [Indexed: 11/24/2022] Open
Abstract
Background Nodal is an important determinant of the left-right (LR) body axis in bilaterians, specifying the right side in protostomes and non-chordate deuterostomes as opposed to the left side in chordates. Amphioxus represents an early-branching chordate group, rendering it especially useful for studying the character states that predate the origin of vertebrates. However, its anatomy, involving offset arrangement of axial structures, marked asymmetry of the oropharyngeal region, and, most notably, a mouth positioned on the left side, contrasts with the symmetric arrangement of the corresponding regions in other chordates. Results We show that the Nodal signaling pathway acts to specify the LR axis in the cephalochordate amphioxus in a similar way as in vertebrates. At early neurula stages, Nodal switches from initial bilateral to the left-sided expression and subsequently specifies the left embryonic side. Perturbation of Nodal signaling with small chemical inhibitors (SB505124 and SB431542) alters expression of other members of the pathway and of left/right-sided, organ-specific genes. Upon inhibition, larvae display loss of the innate alternation of both somites and axons of peripheral nerves and loss of left-sided pharyngeal structures, such as the mouth, the preoral pit, and the duct of the club-shaped gland. Concomitantly, the left side displays ectopic expression of otherwise right-sided genes, and the larvae exhibit bilaterally symmetrical morphology, with duplicated endostyle and club-shaped gland structures. Conclusions We demonstrate that Nodal signaling is necessary for establishing the LR embryonic axis and for developing profound asymmetry in amphioxus. Our data suggest that initial symmetry breaking in amphioxus and propagation of the pathway on the left side correspond with the situation in vertebrates. However, the organs that become targets of the pathway differ between amphioxus and vertebrates, which may explain the pronounced asymmetry of its oropharyngeal and axial structures and the left-sided position of the mouth. Electronic supplementary material The online version of this article (doi:10.1186/2041-9139-6-5) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Vladimir Soukup
- Institute of Molecular Genetics, Academy of Sciences of the Czech Republic, Videnska 1083, Prague, 14220 Czech Republic
| | - Luok Wen Yong
- Institute of Cellular and Organismic Biology, Academia Sinica, 128 Academia Road, Section 2, Nankang, Taipei 11529 Taiwan
| | - Tsai-Ming Lu
- Institute of Cellular and Organismic Biology, Academia Sinica, 128 Academia Road, Section 2, Nankang, Taipei 11529 Taiwan
| | - Song-Wei Huang
- Institute of Cellular and Organismic Biology, Academia Sinica, 128 Academia Road, Section 2, Nankang, Taipei 11529 Taiwan
| | - Zbynek Kozmik
- Institute of Molecular Genetics, Academy of Sciences of the Czech Republic, Videnska 1083, Prague, 14220 Czech Republic
| | - Jr-Kai Yu
- Institute of Cellular and Organismic Biology, Academia Sinica, 128 Academia Road, Section 2, Nankang, Taipei 11529 Taiwan ; Institute of Oceanography, National Taiwan University, 1 Roosevelt Road, Section 4, Taipei, 10617 Taiwan
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10
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Schlosser G. Vertebrate cranial placodes as evolutionary innovations--the ancestor's tale. Curr Top Dev Biol 2015; 111:235-300. [PMID: 25662263 DOI: 10.1016/bs.ctdb.2014.11.008] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Evolutionary innovations often arise by tinkering with preexisting components building new regulatory networks by the rewiring of old parts. The cranial placodes of vertebrates, ectodermal thickenings that give rise to many of the cranial sense organs (ear, nose, lateral line) and ganglia, originated as such novel structures, when vertebrate ancestors elaborated their head in support of a more active and exploratory life style. This review addresses the question of how cranial placodes evolved by tinkering with ectodermal patterning mechanisms and sensory and neurosecretory cell types that have their own evolutionary history. With phylogenetic relationships among the major branches of metazoans now relatively well established, a comparative approach is used to infer, which structures evolved in which lineages and allows us to trace the origin of placodes and their components back from ancestor to ancestor. Some of the core networks of ectodermal patterning and sensory and neurosecretory differentiation were already established in the common ancestor of cnidarians and bilaterians and were greatly elaborated in the bilaterian ancestor (with BMP- and Wnt-dependent patterning of dorsoventral and anteroposterior ectoderm and multiple neurosecretory and sensory cell types). Rostral and caudal protoplacodal domains, giving rise to some neurosecretory and sensory cells, were then established in the ectoderm of the chordate and tunicate-vertebrate ancestor, respectively. However, proper cranial placodes as clusters of proliferating progenitors producing high-density arrays of neurosecretory and sensory cells only evolved and diversified in the ancestors of vertebrates.
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Affiliation(s)
- Gerhard Schlosser
- School of Natural Sciences & Regenerative Medicine Institute (REMEDI), National University of Ireland, Galway, Ireland.
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Li KL, Lu TM, Yu JK. Genome-wide survey and expression analysis of the bHLH-PAS genes in the amphioxus Branchiostoma floridae reveal both conserved and diverged expression patterns between cephalochordates and vertebrates. EvoDevo 2014; 5:20. [PMID: 24959341 PMCID: PMC4066832 DOI: 10.1186/2041-9139-5-20] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2014] [Accepted: 05/07/2014] [Indexed: 01/13/2023] Open
Abstract
Background The bHLH-PAS transcription factors are found in both protostomes and deuterostomes. They are involved in many developmental and physiological processes, including regional differentiation of the central nervous system, tube-formation, hypoxia signaling, aromatic hydrocarbon sensing, and circadian rhythm regulation. To understand the evolution of these genes in chordates, we analyzed the bHLH-PAS genes of the basal chordate amphioxus (Branchiostoma floridae). Results From the amphioxus draft genome database, we identified ten bHLH-PAS genes, nine of which could be assigned to known orthologous families. The tenth bHLH-PAS gene could not be assigned confidently to any known bHLH family; however, phylogenetic analysis clustered this gene with arthropod Met family genes and two spiralian bHLH-PAS-containing sequences, suggesting that they may share the same ancestry. We examined temporal and spatial expression patterns of these bHLH-PAS genes in developing amphioxus embryos. We found that BfArnt, BfNcoa, BfSim, and BfHifα were expressed in the central nervous system in patterns similar to those of their vertebrate homologs, suggesting that their functions may be conserved. By contrast, the amphioxus BfAhr and BfNpas4 had expression patterns distinct from those in vertebrates. These results imply that there were changes in gene regulation after the divergence of cephalochordates and vertebrates. Conclusions We have identified ten bHLH-PAS genes from the amphioxus genome and determined the embryonic expression profiles for these genes. In addition to the nine currently recognized bHLH-PAS families, our survey suggests that the BfbHLHPAS-orphan gene along with arthropod Met genes and the newly identified spiralian bHLH-PAS-containing sequences represent an ancient group of genes that were lost in the vertebrate lineage. In a comparison with the expression patterns of the vertebrate bHLH-PAS paralogs, which are the result of whole-genome duplication, we found that although several members seem to retain conserved expression patterns during chordate evolution, many duplicated paralogs may have undergone subfunctionalization and neofunctionalization in the vertebrate lineage. In addition, our survey of amphioxus bHLH-PAS gene models from genome browser with experimentally verified cDNA sequences calls into question the accuracy of the current in silico gene annotation of the B. floridae genome.
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Affiliation(s)
- Kun-Lung Li
- Institute of Cellular and Organismic Biology, Academia Sinica, 128 Academia Road, Section 2, Nankang, Taipei 11529, Taiwan ; Institute of Oceanography, National Taiwan University, Taipei 10617, Taiwan
| | - Tsai-Ming Lu
- Institute of Cellular and Organismic Biology, Academia Sinica, 128 Academia Road, Section 2, Nankang, Taipei 11529, Taiwan
| | - Jr-Kai Yu
- Institute of Cellular and Organismic Biology, Academia Sinica, 128 Academia Road, Section 2, Nankang, Taipei 11529, Taiwan ; Institute of Oceanography, National Taiwan University, Taipei 10617, Taiwan
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Schlosser G, Patthey C, Shimeld SM. The evolutionary history of vertebrate cranial placodes II. Evolution of ectodermal patterning. Dev Biol 2014; 389:98-119. [PMID: 24491817 DOI: 10.1016/j.ydbio.2014.01.019] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2013] [Revised: 01/21/2014] [Accepted: 01/24/2014] [Indexed: 12/12/2022]
Abstract
Cranial placodes are evolutionary innovations of vertebrates. However, they most likely evolved by redeployment, rewiring and diversification of preexisting cell types and patterning mechanisms. In the second part of this review we compare vertebrates with other animal groups to elucidate the evolutionary history of ectodermal patterning. We show that several transcription factors have ancient bilaterian roles in dorsoventral and anteroposterior regionalisation of the ectoderm. Evidence from amphioxus suggests that ancestral chordates then concentrated neurosecretory cells in the anteriormost non-neural ectoderm. This anterior proto-placodal domain subsequently gave rise to the oral siphon primordia in tunicates (with neurosecretory cells being lost) and anterior (adenohypophyseal, olfactory, and lens) placodes of vertebrates. Likewise, tunicate atrial siphon primordia and posterior (otic, lateral line, and epibranchial) placodes of vertebrates probably evolved from a posterior proto-placodal region in the tunicate-vertebrate ancestor. Since both siphon primordia in tunicates give rise to sparse populations of sensory cells, both proto-placodal domains probably also gave rise to some sensory receptors in the tunicate-vertebrate ancestor. However, proper cranial placodes, which give rise to high density arrays of specialised sensory receptors and neurons, evolved from these domains only in the vertebrate lineage. We propose that this may have involved rewiring of the regulatory network upstream and downstream of Six1/2 and Six4/5 transcription factors and their Eya family cofactors. These proteins, which play ancient roles in neuronal differentiation were first recruited to the dorsal non-neural ectoderm in the tunicate-vertebrate ancestor but subsequently probably acquired new target genes in the vertebrate lineage, allowing them to adopt new functions in regulating proliferation and patterning of neuronal progenitors.
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Affiliation(s)
- Gerhard Schlosser
- Department of Zoology, School of Natural Sciences & Regenerative Medicine Institute (REMEDI), National University of Ireland, University Road, Galway, Ireland.
| | - Cedric Patthey
- Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, UK
| | - Sebastian M Shimeld
- Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, UK
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Holland LZ, Carvalho JE, Escriva H, Laudet V, Schubert M, Shimeld SM, Yu JK. Evolution of bilaterian central nervous systems: a single origin? EvoDevo 2013; 4:27. [PMID: 24098981 PMCID: PMC3856589 DOI: 10.1186/2041-9139-4-27] [Citation(s) in RCA: 111] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2013] [Accepted: 08/14/2013] [Indexed: 12/21/2022] Open
Abstract
The question of whether the ancestral bilaterian had a central nervous system (CNS) or a diffuse ectodermal nervous system has been hotly debated. Considerable evidence supports the theory that a CNS evolved just once. However, an alternative view proposes that the chordate CNS evolved from the ectodermal nerve net of a hemichordate-like ancestral deuterostome, implying independent evolution of the CNS in chordates and protostomes. To specify morphological divisions along the anterior/posterior axis, this ancestor used gene networks homologous to those patterning three organizing centers in the vertebrate brain: the anterior neural ridge, the zona limitans intrathalamica and the isthmic organizer, and subsequent evolution of the vertebrate brain involved elaboration of these ancestral signaling centers; however, all or part of these signaling centers were lost from the CNS of invertebrate chordates. The present review analyzes the evidence for and against these theories. The bulk of the evidence indicates that a CNS evolved just once - in the ancestral bilaterian. Importantly, in both protostomes and deuterostomes, the CNS represents a portion of a generally neurogenic ectoderm that is internalized and receives and integrates inputs from sensory cells in the remainder of the ectoderm. The expression patterns of genes involved in medio/lateral (dorso/ventral) patterning of the CNS are similar in protostomes and chordates; however, these genes are not similarly expressed in the ectoderm outside the CNS. Thus, their expression is a better criterion for CNS homologs than the expression of anterior/posterior patterning genes, many of which (for example, Hox genes) are similarly expressed both in the CNS and in the remainder of the ectoderm in many bilaterians. The evidence leaves hemichordates in an ambiguous position - either CNS centralization was lost to some extent at the base of the hemichordates, or even earlier, at the base of the hemichordates + echinoderms, or one of the two hemichordate nerve cords is homologous to the CNS of protostomes and chordates. In any event, the presence of part of the genetic machinery for the anterior neural ridge, the zona limitans intrathalamica and the isthmic organizer in invertebrate chordates together with similar morphology indicates that these organizers were present, at least in part, at the base of the chordates and were probably elaborated upon in the vertebrate lineage.
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Affiliation(s)
- Linda Z Holland
- Marine Biology Research Division, Scripps Institution of Oceanography, University of California at San Diego, La Jolla, CA 92093-0202, USA
| | - João E Carvalho
- Laboratoire de Biologie du Développement de Villefranche-sur-Mer (UMR 7009 – CNRS/UPMC), Observatoire Océanologique de Villefranche-sur-Mer, 181 Chemin du Lazaret, B.P. 28, 06230 Villefranche-sur-Mer, France
| | - Hector Escriva
- CNRS, UMR 7232, BIOM, Université Pierre et Marie Curie Paris 06, Observatoire Océanologique, 66650 Banyuls-sur-Mer, France
| | - Vincent Laudet
- Institut de Génomique Fonctionnelle de Lyon (CNRS UMR5242, UCBL, ENS, INRA 1288), Ecole Normale Supérieure de Lyon, 46 allée d’Italie, 69364 Lyon Cedex 07, France
| | - Michael Schubert
- Laboratoire de Biologie du Développement de Villefranche-sur-Mer (UMR 7009 – CNRS/UPMC), Observatoire Océanologique de Villefranche-sur-Mer, 181 Chemin du Lazaret, B.P. 28, 06230 Villefranche-sur-Mer, France
| | - Sebastian M Shimeld
- Department of Zoology, University of Oxford, The Tinbergen Building, South Parks Road, Oxford OX1 3PS, UK
| | - Jr-Kai Yu
- Institute of Cellular and Organismic Biology, Academia Sinica, Taipei 11529, Taiwan
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Candiani S, Moronti L, Ramoino P, Schubert M, Pestarino M. A neurochemical map of the developing amphioxus nervous system. BMC Neurosci 2012; 13:59. [PMID: 22676056 PMCID: PMC3484041 DOI: 10.1186/1471-2202-13-59] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2011] [Accepted: 04/27/2012] [Indexed: 12/27/2022] Open
Abstract
BACKGROUND Amphioxus, representing the most basal group of living chordates, is the best available proxy for the last invertebrate ancestor of the chordates. Although the central nervous system (CNS) of amphioxus comprises only about 20,000 neurons (as compared to billions in vertebrates), the developmental genetics and neuroanatomy of amphioxus are strikingly vertebrate-like. In the present study, we mapped the distribution of amphioxus CNS cells producing distinctive neurochemicals. To this end, we cloned genes encoding biosynthetic enzymes and/or transporters of the most common neurotransmitters and assayed their developmental expression in the embryo and early larva. RESULTS By single and double in situ hybridization experiments, we identified glutamatergic, GABAergic/glycinergic, serotonergic and cholinergic neurons in developing amphioxus. In addition to characterizing the distribution of excitatory and inhibitory neurons in the developing amphioxus CNS, we observed that cholinergic and GABAergic/glycinergic neurons are segmentally arranged in the hindbrain, whereas serotonergic, glutamatergic and dopaminergic neurons are restricted to specific regions of the cerebral vesicle and the hindbrain. We were further able to identify discrete groups of GABAergic and glutamatergic interneurons and cholinergic motoneurons at the level of the primary motor center (PMC), the major integrative center of sensory and motor stimuli of the amphioxus nerve cord. CONCLUSIONS In this study, we assessed neuronal differentiation in the developing amphioxus nervous system and compiled the first neurochemical map of the amphioxus CNS. This map is a first step towards a full characterization of the neurotransmitter signature of previously described nerve cell types in the amphioxus CNS, such as motoneurons and interneurons.
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Affiliation(s)
- Simona Candiani
- Dipartimento per lo Studio del Territorio e delle sue Risorse, Università di Genova, Viale Benedetto XV, 5, 16132 Genoa, Italy.
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Lu TM, Luo YJ, Yu JK. BMP and Delta/Notch signaling control the development of amphioxus epidermal sensory neurons: insights into the evolution of the peripheral sensory system. Development 2012; 139:2020-30. [PMID: 22535413 DOI: 10.1242/dev.073833] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The evolution of the nervous system has been a topic of great interest. To gain more insight into the evolution of the peripheral sensory system, we used the cephalochordate amphioxus. Amphioxus is a basal chordate that has a dorsal central nervous system (CNS) and a peripheral nervous system (PNS) comprising several types of epidermal sensory neurons (ESNs). Here, we show that a proneural basic helix-loop-helix gene (Ash) is co-expressed with the Delta ligand in ESN progenitor cells. Using pharmacological treatments, we demonstrate that Delta/Notch signaling is likely to be involved in the specification of amphioxus ESNs from their neighboring epidermal cells. We also show that BMP signaling functions upstream of Delta/Notch signaling to induce a ventral neurogenic domain. This patterning mechanism is highly similar to that of the peripheral sensory neurons in the protostome and vertebrate model animals, suggesting that they might share the same ancestry. Interestingly, when BMP signaling is globally elevated in amphioxus embryos, the distribution of ESNs expands to the entire epidermal ectoderm. These results suggest that by manipulating BMP signaling levels, a conserved neurogenesis circuit can be initiated at various locations in the epidermal ectoderm to generate peripheral sensory neurons in amphioxus embryos. We hypothesize that during chordate evolution, PNS progenitors might have been polarized to different positions in various chordate lineages owing to differential regulation of BMP signaling in the ectoderm.
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Affiliation(s)
- Tsai-Ming Lu
- Institute of Cellular and Organismic Biology, Academia Sinica, 128 Academia Road, Section 2, Nankang, Taipei, 11529, Taiwan
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Beaster-Jones L. Cis-regulation and conserved non-coding elements in amphioxus. Brief Funct Genomics 2012; 11:118-30. [DOI: 10.1093/bfgp/els006] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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Nakanishi N, Renfer E, Technau U, Rentzsch F. Nervous systems of the sea anemone Nematostella vectensis are generated by ectoderm and endoderm and shaped by distinct mechanisms. Development 2011; 139:347-57. [PMID: 22159579 DOI: 10.1242/dev.071902] [Citation(s) in RCA: 113] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
As a sister group to Bilateria, Cnidaria is important for understanding early nervous system evolution. Here we examine neural development in the anthozoan cnidarian Nematostella vectensis in order to better understand whether similar developmental mechanisms are utilized to establish the strikingly different overall organization of bilaterian and cnidarian nervous systems. We generated a neuron-specific transgenic NvElav1 reporter line of N. vectensis and used it in combination with immunohistochemistry against neuropeptides, in situ hybridization and confocal microscopy to analyze nervous system formation in this cnidarian model organism in detail. We show that the development of neurons commences in the ectoderm during gastrulation and involves interkinetic nuclear migration. Transplantation experiments reveal that sensory and ganglion cells are autonomously generated by the ectoderm. In contrast to bilaterians, neurons are also generated throughout the endoderm during planula stages. Morpholino-mediated gene knockdown shows that the development of a subset of ectodermal neurons requires NvElav1, the ortholog to bilaterian neural elav1 genes. The orientation of ectodermal neurites changes during planula development from longitudinal (in early-born neurons) to transverse (in late-born neurons), whereas endodermal neurites can grow in both orientations at any stage. Our findings imply that elav1-dependent ectodermal neurogenesis evolved prior to the divergence of Cnidaria and Bilateria. Moreover, they suggest that, in contrast to bilaterians, almost the entire ectoderm and endoderm of the body column of Nematostella planulae have neurogenic potential and that the establishment of connectivity in its seemingly simple nervous system involves multiple neurite guidance systems.
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Affiliation(s)
- Nagayasu Nakanishi
- Sars Centre for Marine Molecular Biology, University of Bergen, Thormoehlensgt 55, 5008 Bergen, Norway
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Holland LZ, Onai T. Early development of cephalochordates (amphioxus). WILEY INTERDISCIPLINARY REVIEWS-DEVELOPMENTAL BIOLOGY 2011; 1:167-83. [PMID: 23801434 DOI: 10.1002/wdev.11] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
The Phylum Chordata includes three groups--Vertebrata, Tunicata, and Cephalochordata. In cephalochordates, commonly called amphioxus or lancelets, which are basal in the Chordata, the eggs are small and relatively non-yolky. As in vertebrates, cleavage is indeterminate with cell fates determined gradually as development proceeds. The oocytes are attached to the ovarian follicle at the animal pole, where the oocyte nucleus is located. The cytoplasm at the opposite side of the egg, the vegetal pole, contains the future germ plasm or pole plasm, which includes determinants of the germline. After fertilization, additional asymmetries are established by movements of the egg and sperm nuclei, resulting in a concentration of mitochondria at one side of the animal hemisphere. This may be related to establishment of the dorsal/ventral axis. Patterning along the embryonic axes is mediated by secreted signaling proteins. Dorsal identity is specified by Nodal/Vg1 signaling, while during the gastrula stage, opposition between Nodal/Vg1 and BMP signaling establishes dorsal/anterior (i.e., head) and ventral/posterior (i.e., trunk/tail) identities, respectively. Wnt/β-catenin signaling specifies posterior identity while retinoic acid signaling specifies positions along the anterior/posterior axis. These signals are further modulated by a number of secreted antagonists. This fundamental patterning mechanism is conserved, with some modifications, in vertebrates.
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Affiliation(s)
- Linda Z Holland
- Marine Biology Research Division, Scripps Institution of Oceanography, La Jolla, CA, USA.
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Candiani S, Moronti L, Pennati R, De Bernardi F, Benfenati F, Pestarino M. The synapsin gene family in basal chordates: evolutionary perspectives in metazoans. BMC Evol Biol 2010; 10:32. [PMID: 20113475 PMCID: PMC2825198 DOI: 10.1186/1471-2148-10-32] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2009] [Accepted: 01/29/2010] [Indexed: 01/07/2023] Open
Abstract
Background Synapsins are neuronal phosphoproteins involved in several functions correlated with both neurotransmitter release and synaptogenesis. The comprehension of the basal role of the synapsin family is hampered in vertebrates by the existence of multiple synapsin genes. Therefore, studying homologous genes in basal chordates, devoid of genome duplication, could help to achieve a better understanding of the complex functions of these proteins. Results In this study we report the cloning and characterization of the Ciona intestinalis and amphioxus Branchiostoma floridae synapsin transcripts and the definition of their gene structure using available C. intestinalis and B. floridae genomic sequences. We demonstrate the occurrence, in both model organisms, of a single member of the synapsin gene family. Full-length synapsin genes were identified in the recently sequenced genomes of phylogenetically diverse metazoans. Comparative genome analysis reveals extensive conservation of the SYN locus in several metazoans. Moreover, developmental expression studies underline that synapsin is a neuronal-specific marker in basal chordates and is expressed in several cell types of PNS and in many, if not all, CNS neurons. Conclusion Our study demonstrates that synapsin genes are metazoan genes present in a single copy per genome, except for vertebrates. Moreover, we hypothesize that, during the evolution of synapsin proteins, new domains are added at different stages probably to cope up with the increased complexity in the nervous system organization. Finally, we demonstrate that protochordate synapsin is restricted to the post-mitotic phase of CNS development and thereby is a good marker of postmitotic neurons.
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Affiliation(s)
- Simona Candiani
- Department of Biology, University of Genoa, Viale Benedetto XV5, 16132 Genova, Italy.
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Chordate roots of the vertebrate nervous system: expanding the molecular toolkit. Nat Rev Neurosci 2009; 10:736-46. [PMID: 19738625 DOI: 10.1038/nrn2703] [Citation(s) in RCA: 93] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The vertebrate brain is highly complex with millions to billions of neurons. During development, the neural plate border region gives rise to the neural crest, cranial placodes and, in anamniotes, to Rohon-Beard sensory neurons, whereas the boundary region of the midbrain and hindbrain develops organizer properties. Comparisons of developmental gene expression and neuroanatomy between vertebrates and the basal chordate amphioxus, which has only thousands of neurons and lacks a neural crest, most placodes and a midbrain-hindbrain organizer, indicate that these vertebrate features were built on a foundation already present in the ancestral chordate. Recent advances in genomics have provided insights into the elaboration of the molecular toolkit at the invertebrate-vertebrate transition that may have facilitated the evolution of these vertebrate characteristics.
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Kaltenbach SL, Yu JK, Holland ND. The origin and migration of the earliest-developing sensory neurons in the peripheral nervous system of amphioxus. Evol Dev 2009; 11:142-51. [DOI: 10.1111/j.1525-142x.2009.00315.x] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Meulemans D, Bronner-Fraser M. The amphioxus SoxB family: implications for the evolution of vertebrate placodes. Int J Biol Sci 2007; 3:356-64. [PMID: 17713598 PMCID: PMC1950271 DOI: 10.7150/ijbs.3.356] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2007] [Accepted: 08/05/2007] [Indexed: 01/12/2023] Open
Abstract
Cranial placodes are regions of thickened ectoderm that give rise to sense organs and ganglia in the vertebrate head. Homologous structures are proposed to exist in urochordates, but have not been found in cephalochordates, suggesting the first chordates lacked placodes. SoxB genes are expressed in discrete subsets of vertebrate placodes. To investigate how placodes arose and diversified in the vertebrate lineage we isolated the complete set of SoxB genes from amphioxus and analyzed their expression in embryos and larvae. We find that while amphioxus possesses a single SoxB2 gene, it has three SoxB1 paralogs. Like vertebrate SoxB1 genes, one of these paralogs is expressed in non-neural ectoderm destined to give rise to sensory cells. When considered in the context of other amphioxus placode marker orthologs, amphioxus SoxB1 expression suggests a diversity of sensory cell types utilizing distinct placode-type gene programs was present in the first chordates. Our data supports a model for placode evolution and diversification whereby the full complement of vertebrate placodes evolved by serial recruitment of distinct sensory cell specification programs to anterior pre-placodal ectoderm.
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Affiliation(s)
- Daniel Meulemans
- Division of Biology, Beckman Institute, California Institute of Technology, Pasadena, CA 91125, USA.
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Rasmussen SLK, Holland LZ, Schubert M, Beaster-Jones L, Holland ND. Amphioxus AmphiDelta: evolution of Delta protein structure, segmentation, and neurogenesis. Genesis 2007; 45:113-22. [PMID: 17299746 DOI: 10.1002/dvg.20278] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
The amphioxus genome has a single Delta gene (AmphiDelta) encoding a protein 766 amino acids long. Comparison of Delta proteins of amphioxus and other animals indicates that AmphiDelta retains features of a basal bilaterian Delta protein--in having nine epidermal growth factor (EGF) repeats and also in having characteristic numbers of amino acids separating successive cysteines between and within EGF repeats. During development, AmphiDelta is expressed in the forming somites, in some regions of pharyngeal endoderm, and in cells (presumably differentiating neurons) scattered in both the neural plate and ectoderm. Expression is strongly associated with cells initiating movements to separate themselves from parent epithelia, either en masse by evagination (endoderm and mesoderm) or by delamination as isolated cells (ectoderm). The AmphiDelta-expressing cells delaminating from the ectoderm apparently migrate beneath it as they begin differentiating into probable sensory neurons, suggesting a scenario for the evolutionary origin of the placode-derived neurons of vertebrate cranial ganglia.
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Affiliation(s)
- Stacy L K Rasmussen
- Division of Marine Biology Research, Scripps Institution of Oceanography, University of California at San Diego, La Jolla, CA 92093-0202, USA
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Lamas I, Anadón R, Díaz-Regueira S. Carnosine-like immunoreactivity in neurons of the brain of an advanced teleost, the gray mullet (Chelon labrosus, Risso). Brain Res 2007; 1149:87-100. [PMID: 17425949 DOI: 10.1016/j.brainres.2007.02.070] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2006] [Revised: 02/13/2007] [Accepted: 02/14/2007] [Indexed: 11/26/2022]
Abstract
The distribution of the dipeptide carnosine (beta-alanyl-L-histidine) and the related dipeptides anserine and homocarnosine has been studied by biochemical methods and immunohistochemistry in the brain of mammals and other tetrapods. These studies have indicated the presence of these dipeptides mainly in glial cells and in some neurons (olfactory receptor neurons and certain putative migrating neurons and neuroblasts). Here, we used immunohistochemistry with a polyclonal anti-carnosine antibody and the streptavidin-avidin method to study for the first time the distribution of carnosine/carnosine-related dipeptides in the brain of a teleost fish (the gray mullet Chelon labrosus). In order to assess the neuronal nature of carnosine-immunoreactive cells, we also used double immunofluorescence methods with antibodies to carnosine and to the neuronal protein HuC/D. The results obtained show that carnosine and/or related dipeptides are present in neurons of various brain regions. The carnosine-like-immunoreactive neuronal populations of the optic tectum and cerebellum are described in detail. In the optic tectum, immunoreactivity to carnosine/carnosine-related dipeptides is present in neurons of the stratum album and the stratum griseum centrale. In the cerebellum, immunoreactivity to these dipeptides is localized in Purkinje cells, in putative Golgi and stellate cells, and in many nerve fibers. Carnosine-like immunoreactive cells in mullet brain seem to be specific types of neurons, in line with previous results in a urodele but at variance with previous results in mammals, reptiles and anurans.
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Affiliation(s)
- Iván Lamas
- Department of Cell and Molecular Biology, Faculty of Sciences, University of A Coruña, 15007 A Coruña, Spain
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Pasini A, Amiel A, Rothbächer U, Roure A, Lemaire P, Darras S. Formation of the ascidian epidermal sensory neurons: insights into the origin of the chordate peripheral nervous system. PLoS Biol 2006; 4:e225. [PMID: 16787106 PMCID: PMC1481523 DOI: 10.1371/journal.pbio.0040225] [Citation(s) in RCA: 111] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2006] [Accepted: 05/03/2006] [Indexed: 11/18/2022] Open
Abstract
The vertebrate peripheral nervous system (PNS) originates from neural crest and placodes. While its developmental origin is the object of intense studies, little is known concerning its evolutionary history. To address this question, we analyzed the formation of the larval tail PNS in the ascidian Ciona intestinalis. The tail PNS of Ciona is made of sensory neurons located within the epidermis midlines and extending processes in the overlying tunic median fin. We show that each midline corresponds to a single longitudinal row of epidermal cells and neurons sharing common progenitors. This simple organization is observed throughout the tail epidermis, which is made of only eight single-cell rows, each expressing a specific genetic program. We next demonstrate that the epidermal neurons are specified in two consecutive steps. During cleavage and gastrula stages, the dorsal and ventral midlines are independently induced by FGF9/16/20 and the BMP ligand ADMP, respectively. Subsequently, Delta/Notch-mediated lateral inhibition controls the number of neurons formed within these neurogenic regions. These results provide a comprehensive overview of PNS formation in ascidian and uncover surprising similarities between the fate maps and embryological mechanisms underlying formation of ascidian neurogenic epidermis midlines and the vertebrate median fin.
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Affiliation(s)
- Andrea Pasini
- 1Institut de Biologie du Développement de Marseille-Luminy (IBDML), UMR6216, CNRS/Université de la Méditerranée, Marseille, France
| | - Aldine Amiel
- 1Institut de Biologie du Développement de Marseille-Luminy (IBDML), UMR6216, CNRS/Université de la Méditerranée, Marseille, France
| | - Ute Rothbächer
- 1Institut de Biologie du Développement de Marseille-Luminy (IBDML), UMR6216, CNRS/Université de la Méditerranée, Marseille, France
| | - Agnès Roure
- 1Institut de Biologie du Développement de Marseille-Luminy (IBDML), UMR6216, CNRS/Université de la Méditerranée, Marseille, France
| | - Patrick Lemaire
- 1Institut de Biologie du Développement de Marseille-Luminy (IBDML), UMR6216, CNRS/Université de la Méditerranée, Marseille, France
| | - Sébastien Darras
- 1Institut de Biologie du Développement de Marseille-Luminy (IBDML), UMR6216, CNRS/Université de la Méditerranée, Marseille, France
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Candiani S, Oliveri D, Parodi M, Bertini E, Pestarino M. Expression of AmphiPOU-IV in the developing neural tube and epidermal sensory neural precursors in amphioxus supports a conserved role of class IV POU genes in the sensory cells development. Dev Genes Evol 2006; 216:623-33. [PMID: 16773340 DOI: 10.1007/s00427-006-0083-6] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2006] [Accepted: 05/01/2006] [Indexed: 10/24/2022]
Abstract
POU genes play a prominent role in the nervous system differentiation of several organism models, and in particular, they are involved in the differentiation of sensory neurons in numerous invertebrate and vertebrate species. In the present report, cloning and expression profile of a class IV POU gene in amphioxus was assessed for understanding its role in the sensory systems development. A single class IV gene, AmphiPOU-IV was isolated from the amphioxus Branchiostoma floridae. From a phylogenetic point of view, AmphiPOU-IV appears to be strictly related to the vertebrate one, sharing a high homology ratio especially with all vertebrate POU-IV proteins Brn-3a, Brn-3b, and Brn-3c. AmphiPOU-IV was found in the most anterior neural plate and in scattered ectodermic cells on the flanks of neurula, such ectodermic cells resemble the characteristic morphology and position of AmphiCoe and AmphiTrk developing sensory cells. Later on, the expression was confined in some motoneurons at level of the PMC and in some segmental arranged motoneurons in the hindbrain. Such expression is also maintained in larvae, and a new site of AmphiPOU-IV expression was also found in rostrum and mouth edge epidermal sensory cells of the larva. In conclusion, our data suggest an evolutionary conserved role of POU-IV transcription factors in the specification and differentiation of the sensory system in both vertebrates and invertebrates and underline the importance of amphioxus as linking step between them.
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Affiliation(s)
- Simona Candiani
- Department of Biology, University of Genoa, viale Benedetto XV, 5, Genoa, 16132, Italy
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Benito-Gutiérrez E. A gene catalogue of the amphioxus nervous system. Int J Biol Sci 2006; 2:149-60. [PMID: 16763675 PMCID: PMC1474150 DOI: 10.7150/ijbs.2.149] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2006] [Accepted: 05/21/2006] [Indexed: 12/12/2022] Open
Abstract
The elaboration of extremely complex nervous systems is a major success of evolution. However, at the dawn of the post-genomic era, few data have helped yet to unravel how a nervous system develops and evolves to complexity. On the evolutionary road to vertebrates, amphioxus occupies a key position to tackle this exciting issue. Its “simple” nervous system basically consists of a dorsal nerve cord and a diffuse net of peripheral neurons, which contrasts greatly with the complexity of vertebrate nervous systems. Notwithstanding, increasing data on gene expression has faced up this simplicity by revealing a mounting level of cryptic complexity, with unexpected levels of neuronal diversity, organisation and regionalisation of the central and peripheral nervous systems. Furthermore, recent gene expression data also point to the high neurogenic potential of the epidermis of amphioxus, suggestive of a skin-brain track for the evolution of the vertebrate nervous system. Here I attempt to catalogue and synthesise current gene expression data in the amphioxus nervous system. From this global point of view, I suggest scenarios for the evolutionary origin of complex features in the vertebrate nervous system, with special emphasis on the evolutionary origin of placodes and neural crest, and postulate a pre-patterned migratory pathway of cells, which, in the epidermis, may represent an intermediate state towards the deployment of one of the most striking innovative features of vertebrates: the neural crest and its derivatives.
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Satoh G. Exploring developmental, functional, and evolutionary aspects of amphioxus sensory cells. Int J Biol Sci 2006; 2:142-8. [PMID: 16763674 PMCID: PMC1474149 DOI: 10.7150/ijbs.2.142] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2006] [Accepted: 04/14/2006] [Indexed: 11/15/2022] Open
Abstract
Amphioxus has neither elaborated brains nor definitive sensory organs, so that the two may have evolved in a mutually affecting manner and given rise to the forms seen in extant vertebrates. Clarifying the developmental and functional aspects of the amphioxus sensory system is thus pivotal for inferring the early evolution of vertebrates. Morphological studies have identified and classified amphioxus sensory cells; however, it is completely unknown whether the morphological classification makes sense in functional and evolutionary terms. Molecular markers, such as gene expression, are therefore indispensable for investigating the developmental and functional aspects of amphioxus sensory cells. This article reviews recent molecular studies on amphioxus sensory cells. Increasing evidence shows that the non-neural ectoderm of amphioxus can be subdivided into molecularly distinct subdomains by the combinatorial code of developmental cues involving the RA-dependent Hox code, suggesting that amphioxus epithelial sensory cells developed along positional information. This study focuses particularly on research involving the molecular phylogeny and expression of the seven-transmembrane, G protein-coupled receptor (GPCR) genes and discusses the usefulness of this information for characterizing the sensory cells of amphioxus.
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Affiliation(s)
- Gouki Satoh
- Graduate School of Life and Environmental Sciences, University of Tsukuba, Japan.
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29
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Candiani S, Oliveri D, Parodi M, Pestarino M. Expression of AmphiNaC, a new member of the amiloride-sensitive sodium channel related to degenerins and epithelial sodium channels in amphioxus. Int J Biol Sci 2006; 2:79-86. [PMID: 16733538 PMCID: PMC1458428 DOI: 10.7150/ijbs.2.79] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2006] [Accepted: 03/22/2006] [Indexed: 11/05/2022] Open
Abstract
Degenerins and amiloride-sensitive Na+ channels form a new family of cationic ion channels (DEG/NaC). DEG/NaC family emerged as common denominator within a metazoan mechanosensory apparatus. In this study, we characterized a new member of such family in amphioxus, Branchiostoma floridae. The AmphiNaC cDNA sequence encodes a protein showing amino acid residues characteristic of DEG/NaC family, such as two hydrophobic domains surrounding a large extracellular loop that includes cystein-rich domains; nevertheless its predicted sequence is quite divergent from other family members. AmphiNaC is expressed at early larval stage in some putative sensory epidermal cells in the middle of the body and in neurons of the posterior cerebral vesicle, as well as in some ventrolateral and mediolateral neurons of the neural tube. In late larvae, AmphiNaC expression is maintained in some neurons of the neural tube, and it is expressed in putative sensory epidermal cells of rostrum and mouth. The analysis of AmphiNaC gene expression pattern suggests that it might be involved in neurotransmission and sensory modulation.
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30
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Pezzementi L, Rowland M, Wolfe M, Tsigelny I. Inactivation of an invertebrate acetylcholinesterase by sulfhydryl reagents: the roles of two cysteines in the catalytic gorge of the enzyme. INVERTEBRATE NEUROSCIENCE 2006; 6:47-55. [PMID: 16586114 DOI: 10.1007/s10158-006-0017-z] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/18/2006] [Accepted: 03/08/2006] [Indexed: 10/24/2022]
Abstract
We have used site-directed mutagenesis and molecular modeling to investigate the inactivation of an invertebrate acetylcholinesterase (AChE), ChE2 from amphioxus, by the sulfhydryl reagents 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB) and N-ethylmaleimide (NEM), creating various mutants, including C310A and C466A, and the double mutants C310A/C466A and C310A/F312I, to assess the relative roles of the two cysteines and a proposal that the increased rate of inactivation in the F312I mutant is due to increased access to Cys310. Our results suggest that both cysteines may be involved in inactivation by sulfhydryl reagents, but that the cysteine in the vicinity of the acyl pocket is more accessible. We speculate that the inactivation of aphid AChEs by sulfhydryl reagents is due to the presence of a cysteine homologous to Cys310. We also investigated the effects of various reversible cholinergic ligands, which bind to different subsites of the active site of the enzyme, on the rate of inactivation by DTNB of wild type ChE2 and ChE2 F312I. For the most part the inhibitors protect the enzymes from inactivation by DTNB. However, a notable exception is the peripheral site ligand propidium, which accelerates inactivation in the wild type ChE2, but retards inactivation in the F312I mutant. We propose that these opposing effects are the result of an altered allosteric signal transduction mechanism in the F312I mutant compared to the wild type ChE2.
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Affiliation(s)
- Leo Pezzementi
- Division of Science and Mathematics, Birmingham-Southern College, Birmingham, AL 35222, USA.
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31
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Schlosser G. Evolutionary origins of vertebrate placodes: insights from developmental studies and from comparisons with other deuterostomes. JOURNAL OF EXPERIMENTAL ZOOLOGY PART B-MOLECULAR AND DEVELOPMENTAL EVOLUTION 2005; 304:347-99. [PMID: 16003766 DOI: 10.1002/jez.b.21055] [Citation(s) in RCA: 112] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Ectodermal placodes comprise the adenohypophyseal, olfactory, lens, profundal, trigeminal, otic, lateral line, and epibranchial placodes. The first part of this review presents a brief overview of placode development. Placodes give rise to a variety of cell types and contribute to many sensory organs and ganglia of the vertebrate head. While different placodes differ with respect to location and derivative cell types, all appear to originate from a common panplacodal primordium, induced at the anterior neural plate border by a combination of mesodermal and neural signals and defined by the expression of Six1, Six4, and Eya genes. Evidence from mouse and zebrafish mutants suggests that these genes promote generic placodal properties such as cell proliferation, cell shape changes, and specification of neurons. The common developmental origin of placodes suggests that all placodes may have evolved in several steps from a common precursor. The second part of this review summarizes our current knowledge of placode evolution. Although placodes (like neural crest cells) have been proposed to be evolutionary novelties of vertebrates, recent studies in ascidians and amphioxus have proposed that some placodes originated earlier in the chordate lineage. However, while the origin of several cellular and molecular components of placodes (e.g., regionalized expression domains of transcription factors and some neuronal or neurosecretory cell types) clearly predates the origin of vertebrates, there is presently little evidence that these components are integrated into placodes in protochordates. A scenario is presented according to which all placodes evolved from an adenohypophyseal-olfactory protoplacode, which may have originated in the vertebrate ancestor from the anlage of a rostral neurosecretory organ (surviving as Hatschek's pit in present-day amphioxus).
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32
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Satoh G. A trajectory of increasing activity and the elaboration of chemosensory modality: a new perspective on vertebrate origins. Zoolog Sci 2005; 22:613-26. [PMID: 15988155 DOI: 10.2108/zsj.22.613] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
This article reviews recent advances in comparative biological studies of vertebrate origins, with the aim of revisiting the long-standing controversy concerning these origins. Since early vertebrate evolution is paralleled by an evolutionary trend towards increasing activity, I focus on the evolution of respiratory and circulatory systems and discuss their potential roles in early vertebrate evolution. I give particular attention to the nasohypophyseal duct, an orifice characteristically found in agnathan vertebrates, and hypothesize that this duct originally functioned to convey oxygen dissolved in seawater to the respiratory gills. The chemosensory cell population that originated from the wall of the duct became the incipient olfactory organ and played a role in the organization of feeding behavior. An increase in chemosensory receptor genes via large-scale genomic evolution in the vertebrate lineage caused the repertoire of chemosensory cells to diversify and led to the appearance of the integrative center, including telencephalic structures typically lacking in protochordates.
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Affiliation(s)
- Gouki Satoh
- Seto Marine Biological Laboratory, Field Science Education and Research Center, Kyoto University, Wakayama, Japan.
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33
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Satoh G. Characterization of novel GPCR gene coding locus in amphioxus genome: gene structure, expression, and phylogenetic analysis with implications for its involvement in chemoreception. Genesis 2005; 41:47-57. [PMID: 15682401 DOI: 10.1002/gene.20082] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Chemosensation is the primary sensory modality in almost all metazoans. The vertebrate olfactory receptor genes exist as tandem clusters in the genome, so that identifying their evolutionary origin would be useful for understanding the expansion of the sensory world in relation to a large-scale genomic duplication event in a lineage leading to the vertebrates. In this study, I characterized a novel GPCR (G-protein-coupled receptor) gene-coding locus from the amphioxus genome. The genomic DNA contains an intronless ORF whose deduced amino acid sequence encodes a seven-transmembrane protein with some amino acid residues characteristic of vertebrate olfactory receptors (ORs). Surveying counterparts in the Ciona intestinalis (Asidiacea, Urochordata) genome by querying BLAST programs against the Ciona genomic DNA sequence database resulted in the identification of a remotely related gene. In situ hybridization analysis labeled primary sensory neurons in the rostral epithelium of amphioxus adults. Based on these findings, together with comparison of the developmental gene expression between amphioxus and vertebrates, I postulate that chemoreceptive primary sensory neurons in the rostrum are an ancient cell population traceable at least as far back in phylogeny as the common ancestor of amphioxus and vertebrates.
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Affiliation(s)
- Gouki Satoh
- Department of Zoology, Graduate School of Science, Kyoto University, Kyoto, Japan.
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34
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Benito-Gutiérrez E, Illas M, Comella JX, Garcia-Fernàndez J. Outlining the nascent nervous system of Branchiostoma floridae (amphioxus) by the pan-neural marker AmphiElav. Brain Res Bull 2005; 66:518-21. [PMID: 16144641 DOI: 10.1016/j.brainresbull.2005.03.007] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2004] [Indexed: 11/26/2022]
Abstract
The cephalochordate amphioxus is the closest living relative of the vertebrates. The anatomy and development of the amphioxus nervous system is giving insights into the basic chordate neural organisation, prior to the increase in neural complexity that characterised the origin of vertebrates. We have analysed the expression of the pan-neural marker AmphiElav in the Florida lancelet (Branchiostoma floridae) through development and up to larval stages. AmphiElav is expressed in the developing neural tube with particular temporal and spatial dynamics that correlate with neuronal differentiation. In addition, AmphiElav is expressed in isolated epidermal cells from mid-neurula embryos. This epidermal expression probably corresponds to precursors of sensory neurons. Together with data from other neural markers, we discuss the evolutionary relevance of these neural precursors to the origin of some of the most dramatic vertebrate inventions, neural crests and placodes.
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35
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Benito-Gutiérrez E, Nake C, Llovera M, Comella JX, Garcia-Fernàndez J. The single AmphiTrk receptor highlights increased complexity of neurotrophin signalling in vertebrates and suggests an early role in developing sensory neuroepidermal cells. Development 2005; 132:2191-202. [PMID: 15799999 DOI: 10.1242/dev.01803] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Neurotrophins (Nt) and their tyrosine kinase Trk receptors play an essential role in the development and maintenance of the complex vertebrate nervous system. Invertebrate genome sequencing projects have suggested that the Nt/Trk system is a vertebrate innovation. We describe the isolation and characterisation of the amphioxus Trk receptor, AmphiTrk. Its ancestral link to vertebrate Trk receptors is supported by phylogenetic analysis and domain characterisation. The genomic structure of AmphiTrk strongly suggests that a ProtoTrk gene emerged by means of exon-shuffling prior to the cephalochordate/vertebrate split. We also examined the physiological response of AmphiTrk to vertebrate neurotrophins, and found that despite 500 million years of divergence, AmphiTrk transduces signals mediated by NGF, BDNF, NT3 and NT4. Markedly, AmphiTrk is able to activate survival and differentiation pathways, but fails to activate the PLCgamma pathway, which is involved in synaptic plasticity in higher vertebrates. AmphiTrk is expressed during amphioxus embryogenesis in sensory neural precursors in the epidermis, which possesses single migratory cells. We propose that the duplication and divergence of the Nt/Trk system, in tandem with recruitment of the PLCgamma pathway, may have provided the genetic basis for a key aspect of vertebrate evolution: the complexity of the nervous system.
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Affiliation(s)
- Elia Benito-Gutiérrez
- Departament de Genética, Facultat de Biologia, Universitat de Barcelona, Avinguda Diagonal, 645, E-08028, Barcelona, Spain
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Holland LZ. Non-neural ectoderm is really neural: evolution of developmental patterning mechanisms in the non-neural ectoderm of chordates and the problem of sensory cell homologies. JOURNAL OF EXPERIMENTAL ZOOLOGY PART B-MOLECULAR AND DEVELOPMENTAL EVOLUTION 2005; 304:304-23. [PMID: 15834938 DOI: 10.1002/jez.b.21038] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
In chordates, the ectoderm is divided into the neuroectoderm and the so-called non-neural ectoderm. In spite of its name, however, the non-neural ectoderm contains numerous sensory cells. Therefore, the term "non-neural" ectoderm should be replaced by "general ectoderm." At least in amphioxus and tunicates and possibly in vertebrates as well, both the neuroectoderm and the general ectoderm are patterned anterior/posteriorly by mechanisms involving retinoic acid and Hox genes. In amphioxus and tunicates the ectodermal sensory cells, which have a wide range of ciliary and microvillar configurations, are mostly primary neurons sending axons to the CNS, although a minority lack axons. In contrast, vertebrate mechanosensory cells, called hair cells, are all secondary neurons that lack axons and have a characteristic eccentric cilium adjacent to a group of microvilli of graded lengths. It has been highly controversial whether the ectodermal sensory cells in the oral siphons of adult tunicates are homologous to vertebrate hair cells. In some species of tunicates, these cells appear to be secondary neurons, and microvillar and ciliary configurations of some of these cells approach those of vertebrate hair cells. However, none of the tunicate cells has all the characteristics of a hair cell, and there is a high degree of variation among ectodermal sensory cells within and between different species. Thus, similarities between the ectodermal sensory cells of any one species of tunicate and craniate hair cells may well represent convergent evolution rather than homology.
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Affiliation(s)
- Linda Z Holland
- Marine Biology Research Division, Scripps Institution of Oceanography, University of California San Diego, La Jolla, 92093-0202 USA.
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37
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Mazet F, Masood S, Luke GN, Holland ND, Shimeld SM. Expression of AmphiCoe, an amphioxus COE/EBF gene, in the developing central nervous system and epidermal sensory neurons. Genesis 2004; 38:58-65. [PMID: 14994268 DOI: 10.1002/gene.20006] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The COE/EBF gene family marks a subset of prospective neurons in the vertebrate central and peripheral nervous system, including neurons deriving from some ectodermal placodes. Since placodes are often considered unique to vertebrates, we have characterised an amphioxus COE/EBF gene with the aim of using it as a marker to examine the timing and location of peripheral neuron differentiation. A single COE/EBF family member, AmphiCoe, was isolated from the amphioxus Branchiostoma floridae. AmphiCoe lies basal to the vertebrate COE/EBF genes in molecular phylogenetic analysis, suggesting that the duplications that formed the vertebrate COE/EBF family were specific to the vertebrate lineage. AmphiCoe is expressed in the central nervous system and in a small number of scattered ectodermal cells on the flanks of neurulae stage embryos. These cells become at least largely recessed beneath the ectoderm. Scanning electron microscopy was used to examine embryos in which the ectoderm had been partially peeled away. This revealed that these cells have neuronal morphology, and we infer that they are the precursors of epidermal primary sensory neurons. These characters lead us to suggest that differentiation of some ectodermal cells into sensory neurons with a tendency to sink beneath the embryonic surface represents a primitive feature that has become incorporated into placodes during vertebrate evolution.
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Affiliation(s)
- Françoise Mazet
- School of Animal and Microbial Sciences, The University of Reading, Whiteknights, Reading, UK.
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38
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Abstract
In this review, we outline the gene-regulatory interactions driving neural crest development and compare these to a hypothetical network operating in the embryonic ectoderm of the cephalochordate amphioxus. While the early stages of ectodermal patterning appear conserved between amphioxus and vertebrates, later activation of neural crest-specific factors at the neural plate border appears to be a vertebrate novelty. This difference may reflect co-option of genetic pathways which conferred novel properties upon the evolving vertebrate neural plate border, potentiating the evolution of definitive neural crest.
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Affiliation(s)
- Daniel Meulemans
- California Institute of Technology, 1200 East California Boulevard, Pasadena 91125, USA
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Pezzementi L, Johnson K, Tsigelny I, Cotney J, Manning E, Barker A, Merritt S. Amino acids defining the acyl pocket of an invertebrate cholinesterase. Comp Biochem Physiol B Biochem Mol Biol 2004; 136:813-32. [PMID: 14662305 DOI: 10.1016/s1096-4959(03)00259-8] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Amphioxus (Branchiostoma floridae) cholinesterase 2 (ChE2) hydrolyzes acetylthiocholine (AsCh) almost exclusively. We constructed a homology model of ChE2 on the basis of Torpedo californica acetylcholinesterase (AChE) and found that the acyl pocket of the enzyme resembles that of Drosophila melanogaster AChE, which is proposed to be comprised of Phe330 (Phe290 in T. californica AChE) and Phe440 (Val400), rather than Leu328 (Phe288) and Phe330 (Phe290), as in vertebrate AChE. In ChE2, the homologous amino acids are Phe312 (Phe290) and Phe422 (Val400). To determine if these amino acids define the acyl pocket of ChE2 and its substrate specificity, and to obtain information about the hydrophobic subsite, partially comprised of Tyr352 (Phe330) and Phe353 (Phe331), we performed site-directed mutagenesis and in vitro expression. The aliphatic substitution mutant F312I ChE2 hydrolyzes AsCh preferentially but also butyrylthiocholine (BsCh), and the change in substrate specificity is due primarily to an increase in k(cat) for BsCh; K(m) and K(ss) are also altered. F422L and F422V produce enzymes that hydrolyze BsCh and AsCh equally due to an increase in k(cat) for BsCh and a decrease in k(cat) for AsCh. Our data suggest that Phe312 and Phe422 define the acyl pocket. We also screened mutants for changes in sensitivity to various inhibitors. Y352A increases the sensitivity of ChE2 to the bulky inhibitor ethopropazine. Y352A decreases inhibition by BW284c51, consistent with its role as part of the choline-binding site. Aliphatic replacement mutations produce enzymes that are more sensitive to inhibition by iso-OMPA, presumably by increasing access to the active site serine. Y352A, F353A and F353V make ChE2 considerably more resistant to inhibition by eserine and neostigmine, suggesting that binding of these aromatic inhibitors is mediated by pi-pi or cation-pi interactions at the hydrophobic site. Our results also provide information about the aromatic trapping of the active site histidine and the inactivation of ChE2 by sulfhydryl reagents.
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Affiliation(s)
- Leo Pezzementi
- Division of Science and Mathematics, Birmingham-Southern College, Box 549022, Birmingham, AL 35254, USA.
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40
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Sueiro C, Carrera I, Molist P, Rodríguez-Moldes I, Anadón R. Distribution and development of glutamic acid decarboxylase immunoreactivity in the spinal cord of the dogfishScyliorhinus canicula(elasmobranchs). J Comp Neurol 2004; 478:189-206. [PMID: 15349979 DOI: 10.1002/cne.20285] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The adult distribution and development of gamma-aminobutyric acid (GABA)-synthesizing cells and fibers in the spinal cord of the lesser spotted dogfish (Scyliorhinus canicula L.) was studied by means of immunohistochemistry using antibodies against glutamic acid decarboxylase (GAD). Complementary immunostaining with antibodies against GABA, tyrosine hydroxylase (TH), and HuC/HuD (members of the Hu/Elav family of RNA-associated proteins) and staining with a reduced silver procedure ("en bloc" Bielschowski method), Nissl, and hematoxylin were also used. In adults, GAD-immunoreactive (GAD-ir) cells were observed in the ventral horns, in the spinal nucleus of the dorsal horn, at the base of the dorsal horns, and around the central canal, where some GAD-ir cells were cerebrospinal fluid-contacting (CSF-c). In addition, a few GAD-ir cells were observed in the lateral funiculus between the ventral horn and the marginal nucleus. The adult spinal cord was richly innervated by GAD-ir fibers. Large numbers of GAD-ir fibers and boutons were observed in the dorsal and ventral horns and also interstitially in the dorsal, lateral, and ventral funiculi. In addition, a rich GAD-ir innervation was observed in the marginal nucleus of the spinal cord. In the embryonic spinal cord, GAD-ir cells develop very early: The earliest cells were observed in the very thin mantle/marginal layer of stage 22 embryos in a short length of the spinal cord. At stages 25 and 26, several types of GAD-ir cells (commissural and noncommissural) were distinguished, and two of these cells were of CSF-c type. At stages 28, 30, and 31, the GAD-ir populations exhibited a marked longitudinal columnar organization. Double-immunolabeling experiments in embryos showed the presence of two different GAD-ir CSF-c cell populations, one ventral that is simultaneously TH-ir and other more dorsal that is TH-negative. By stage 33 (prehatching), GAD-expressing cells are present in virtually all loci, as in adults, especially in the ventral horn and base of the dorsal horn. The present results for the lesser spotted dogfish suggest an important role for gamma-aminobutyric acid in sensory and motor circuits of the spinal cord.
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Affiliation(s)
- Catalina Sueiro
- Departamento de Biología Celular y Ecología, Universidad de Santiago de Compostela, 15706-Santiago de Compostela, Spain
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Schubert M, Holland ND, Escriva H, Holland LZ, Laudet V. Retinoic acid influences anteroposterior positioning of epidermal sensory neurons and their gene expression in a developing chordate (amphioxus). Proc Natl Acad Sci U S A 2004; 101:10320-5. [PMID: 15226493 PMCID: PMC478570 DOI: 10.1073/pnas.0403216101] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2003] [Indexed: 11/18/2022] Open
Abstract
In developing chordates, retinoic acid (RA) signaling patterns the rostrocaudal body axis globally and affects gene expression locally in some differentiating cell populations. Here we focus on development of epidermal sensory neurons in an invertebrate chordate (amphioxus) to determine how RA signaling influences their rostrocaudal distribution and gene expression (for AmphiCoe, a neural precursor gene; for amphioxus islet and AmphiERR, two neural differentiation genes; and for AmphiHox1, -3, -4, and -6). Treatments with RA or an RA antagonist (BMS009) shift the distribution of developing epidermal neurons anteriorly or posteriorly, respectively. These treatments also affect gene expression patterns in the epidermal neurons, suggesting that RA levels may influence specification of neuronal subtypes. Although colinear expression of Hox genes is well known for the amphioxus central nervous system, we find an unexpected comparable colinearity for AmphiHox1, -3, -4, and -6 in the developing epidermis; moreover, RA levels affect the anteroposterior extent of these Hox expression domains, suggesting that RA signaling controls a colinear Hox code for anteroposterior patterning of the amphioxus epidermis. Thus, in amphioxus, the developing peripheral nervous system appears to be structured by mechanisms parallel to those that structure the central nervous system. One can speculate that, during evolution, an ancestral deuterostome that structured its panepidermal nervous system with an RA-influenced Hox code gave rise to chordates in which this patterning mechanism persisted within the epidermal elements of the peripheral nervous system and was transferred to the neuroectoderm as the central nervous system condensed dorsally.
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Affiliation(s)
- Michael Schubert
- Laboratoire de Biologie Moléculaire de la Cellule, Centre National de la Recherche Scientifique, Unité Mixte de Recherche 5161, and Institut National de la Recherche Agronomique, Ecole Normale Supérieure de Lyon, 69364 Lyon, France
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Lacalli TC. Sensory Systems in Amphioxus: A Window on the Ancestral Chordate Condition. BRAIN, BEHAVIOR AND EVOLUTION 2004; 64:148-62. [PMID: 15353907 DOI: 10.1159/000079744] [Citation(s) in RCA: 118] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Amphioxus has an assortment of cells and organs for sensing light and mechanical stimuli. Vertebrate counterparts of these structures are not always apparent, and a strong case can be made for homology in only a few instances. For example, amphioxus has anatomically simple but plausible homologs of both the pineal and paired eyes of vertebrates. Placodal and neural crest derivatives are, however, more problematic: the evidence for an olfactory system in amphioxus is only circumstantial and, despite the variety of secondary sensory cell types that occur on the body surface in amphioxus, none are obvious homologs of vertebrate taste buds, neuromasts or acoustic hair cells. A useful perspective can nevertheless be gained by examining differences in amphioxus and vertebrate development, specifically how each specifies and positions sensory precursors, controls their proliferation, and deploys them through the body. The much larger size of vertebrate embryos and the need to cope developmentally with increased scale and cell numbers may account for some key vertebrate innovations, including placodes and neural crest. The presence or absence of specific structural adaptations, like the latter, is therefore less useful for judging homology between amphioxus and vertebrates than shared features of specific cell types. It is also clear that the duration of embryogenesis in vertebrates has been significantly extended in comparison with ancestral chordates so as to incorporate events that would originally have occurred during the post-embryonic growth period, including events of neurogenesis. Consequently, no scenario for the origin of vertebrates can be considered complete unless it deals explicitly with the whole of the life history and changes to it.
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Urano A, Suzuki MM, Zhang P, Satoh N, Satoh G. Expression of muscle-related genes and two MyoD genes during amphioxus notochord development. Evol Dev 2003; 5:447-58. [PMID: 12950624 DOI: 10.1046/j.1525-142x.2003.03051.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The notochord is one of the diagnostic features of the phylum Chordata. Despite the similarities in the early morphogenetic patterns of the notochords of various chordates, they are strikingly distinct from one another at the histological level. The amphioxus notochord is one example of an evolutionary novelty because it is made up of muscle cells. Our previous expressed sequence tag analysis, targeting messenger RNAs expressed in the adult amphioxus notochord, demonstrated that many muscle-related genes are expressed there. To characterize amphioxus notochord cells and to gain insights into the myogenic program in the notochord, we determined the spatial and temporal expre-ssion patterns of these muscle-related genes during amphioxus development. We found that BbNA1 (notochord actin), Amphi-Trop I (troponin I), Amphi-TPmyosin (tropo-myosin), Amphi-MHC2 (myosin heavy chain), Amphi-nMRLC (notochord-specific myosin regulatory light chain), Amphi-nTitin/MLCK (notochord-specific titin/myosin light chain kinase), Amphi-MLP/CRP3 (muscle LIM protein), and Amphi-nCalponin (notochord-specific calponin) are expres-sed with characteristic patterns in notochord cells, including the central cells, dorsally located cells, and ventrally located cells, suggesting that each notochord cell has a unique molecular architecture that may reflect its function. In addition, we characterized two MyoD genes (Amphi-MyoD1 and Amphi-MyoD2) to gain insight into the genetic circuitry governing the formation of the notochord muscle. One of the MyoD genes (Amphi-MyoD2) is expressed in the central notochord cells, and the coexistence of Amphi-MyoD2 transcripts along with the Amphi-MLP/CRP3 transcripts implies the participation of Amphi-MyoD2 in the myogenic program in the notochord muscle.
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Affiliation(s)
- Aki Urano
- Department of Zoology, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
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Holland ND, Yu JK. Epidermal receptor development and sensory pathways in vitally stained amphioxus (Branchiostoma floridae). ACTA ZOOL-STOCKHOLM 2002. [DOI: 10.1046/j.1463-6395.2002.00120.x] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Satoh G, Takeuchi JK, Yasui K, Tagawa K, Saiga H, Zhang P, Satoh N. Amphi-Eomes/Tbr1: an amphioxus cognate of vertebrate Eomesodermin and T-Brain1 genes whose expression reveals evolutionarily distinct domain in amphioxus development. THE JOURNAL OF EXPERIMENTAL ZOOLOGY 2002; 294:136-45. [PMID: 12210114 DOI: 10.1002/jez.10149] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
A cDNA for a novel T-box containing gene was isolated from the amphioxus Branchiostoma belcheri. A molecular phylogenetic tree constructed from the deduced amino acid sequence of the isolated cDNA indicates that this gene belongs to the T-Brain subfamily. In situ hybridization reveals that the expression is first detected in the invaginating archenteron at the early gastrula stage and this expression is down-regulated at the neurula stage. In early larvae, the expression appears again and transcripts are detected exclusively in the pre-oral pit (wheel organ-Hatschek's pit of the adult). In contrast to the vertebrate counterparts, no transcripts are detected in the brain vesicle or nerve cord throughout the development. These results are interpreted to mean that a role of T-Brain products in vertebrate forebrain development was acquired after the amphioxus was split from the lineage leading to the vertebrates. On the other hand, comparison of the tissue-specific expression domain of T-Brain genes and other genes between amphioxus and vertebrates revealed that the pre-oral pit of amphioxus has several molecular features which are comparable to those of the vertebrate olfactory and hypophyseal placode.
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Affiliation(s)
- Gouki Satoh
- Department of Zoology, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
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