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Johnson CJ, Razy-Krajka F, Zeng F, Piekarz KM, Biliya S, Rothbächer U, Stolfi A. Specification of distinct cell types in a sensory-adhesive organ important for metamorphosis in tunicate larvae. PLoS Biol 2024; 22:e3002555. [PMID: 38478577 PMCID: PMC10962819 DOI: 10.1371/journal.pbio.3002555] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2023] [Revised: 03/25/2024] [Accepted: 02/21/2024] [Indexed: 03/22/2024] Open
Abstract
The papillae of tunicate larvae contribute sensory, adhesive, and metamorphosis-regulating functions that are crucial for the biphasic lifestyle of these marine, non-vertebrate chordates. We have identified additional molecular markers for at least 5 distinct cell types in the papillae of the model tunicate Ciona, allowing us to further study the development of these organs. Using tissue-specific CRISPR/Cas9-mediated mutagenesis and other molecular perturbations, we reveal the roles of key transcription factors and signaling pathways that are important for patterning the papilla territory into a highly organized array of different cell types and shapes. We further test the contributions of different transcription factors and cell types to the production of the adhesive glue that allows for larval attachment during settlement, and to the processes of tail retraction and body rotation during metamorphosis. With this study, we continue working towards connecting gene regulation to cellular functions that control the developmental transition between the motile larva and sessile adult of Ciona.
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Affiliation(s)
- Christopher J Johnson
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, Georgia, United States of America
| | - Florian Razy-Krajka
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, Georgia, United States of America
| | - Fan Zeng
- Department of Zoology, University of Innsbruck, Innsbruck, Austria
| | - Katarzyna M Piekarz
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, Georgia, United States of America
| | - Shweta Biliya
- Molecular Evolution Core, Petit H. Parker Institute for Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, Georgia, United States of America
| | - Ute Rothbächer
- Department of Zoology, University of Innsbruck, Innsbruck, Austria
| | - Alberto Stolfi
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, Georgia, United States of America
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Gigante ED, Piekarz KM, Gurgis A, Cohen L, Razy-Krajka F, Popsuj S, Ali HS, Sundaram SM, Stolfi A. Specification and survival of post-metamorphic branchiomeric neurons in the hindbrain of a non-vertebrate chordate. bioRxiv 2023:2023.06.16.545305. [PMID: 37645866 PMCID: PMC10461979 DOI: 10.1101/2023.06.16.545305] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/31/2023]
Abstract
Tunicates are the sister group to the vertebrates, yet most species have a life cycle split between swimming larva and sedentary adult phases. During metamorphosis, larval neurons are largely replaced by adult-specific ones. Yet the regulatory mechanisms underlying this neural replacement remain largely unknown. Using tissue-specific CRISPR/Cas9-mediated mutagenesis in the tunicate Ciona, we show that orthologs of conserved hindbrain and branchiomeric neuron regulatory factors Pax2/5/8 and Phox2 are required to specify the "Neck", a compartment of cells set aside in the larva to give rise to cranial motor neuron-like neurons in the adult. Using bulk and single-cell RNAseq analyses, we also characterize the transcriptome of the Neck downstream of Pax2/5/8. Surprisingly, we find that Neck-derived adult ciliomotor neurons begin to differentiate in the larva, contrary to the long-held assumption that the adult nervous system is formed only after settlement and the death of larval neurons during metamorphosis. Finally, we show that manipulating FGF signaling during the larval phase alters the patterning of the Neck and its derivatives. Suppression of FGF converts Neck cells into larval neurons that fail to survive metamorphosis, while prolonged FGF signaling promotes an adult neural stem cell-like fate instead.
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Affiliation(s)
- Eduardo D Gigante
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA, 30332; USA
| | - Katarzyna M Piekarz
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA, 30332; USA
| | - Alexandra Gurgis
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA, 30332; USA
- Department of Biology, Case Western Reserve University, Cleveland, OH, 44106; USA
| | - Leslie Cohen
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA, 30332; USA
| | - Florian Razy-Krajka
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA, 30332; USA
| | - Sydney Popsuj
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA, 30332; USA
| | - Hussan S Ali
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA, 30332; USA
| | | | - Alberto Stolfi
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA, 30332; USA
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Johnson CJ, Razy-Krajka F, Stolfi A. Expression of smooth muscle-like effectors and core cardiomyocyte regulators in the contractile papillae of Ciona. EvoDevo 2020; 11:15. [PMID: 32774829 PMCID: PMC7397655 DOI: 10.1186/s13227-020-00162-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2020] [Accepted: 07/22/2020] [Indexed: 01/19/2023] Open
Abstract
BACKGROUND The evolution of vertebrate smooth muscles is obscured by lack of identifiable smooth muscle-like cells in tunicates, the invertebrates most closely related to vertebrates. A recent evolutionary model was proposed in which smooth muscles arose before the last bilaterian common ancestor, and were later diversified, secondarily lost or modified in the branches leading to extant animal taxa. However, there is currently no data from tunicates to support this scenario. METHODS AND RESULTS Here, we show that the axial columnar cells, a unique cell type in the adhesive larval papillae of the tunicate Ciona, are enriched for orthologs of vertebrate smooth/non-muscle-specific effectors of contractility, in addition to developing from progenitors that express conserved cardiomyocyte regulatory factors. We show that these cells contract during the retraction of the Ciona papillae during larval settlement and metamorphosis. CONCLUSIONS We propose that the axial columnar cells of Ciona are a myoepithelial cell type required for transducing external stimuli into mechanical forces that aid in the attachment of the motile larva to its final substrate. Furthermore, they share developmental and functional features with vertebrate myoepithelial cells, vascular smooth muscle cells, and cardiomyocytes. We discuss these findings in the context of the proposed models of vertebrate smooth muscle and cardiomyocyte evolution.
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Kim K, Gibboney S, Razy-Krajka F, Lowe EK, Wang W, Stolfi A. Regulation of Neurogenesis by FGF Signaling and Neurogenin in the Invertebrate Chordate Ciona. Front Cell Dev Biol 2020; 8:477. [PMID: 32656209 PMCID: PMC7324659 DOI: 10.3389/fcell.2020.00477] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2020] [Accepted: 05/21/2020] [Indexed: 12/22/2022] Open
Abstract
Neurogenesis is a complex sequence of cellular processes and behaviors driven by the coordinated expression of conserved effectors. The bipolar tail neurons (BTNs) of Ciona develop according to a highly dynamic, yet highly stereotyped developmental program and thus could serve as an accessible model system for neurogenesis, including underlying cell behaviors like neuronal delamination, migration, and polarized axon outgrowth. Here we investigate both the upstream events that shape BTN neurogenesis through spatiotemporal regulation of the conserved proneural factor Neurog, spatiotemporal, and the gene expression profile of differentiating BTNs downstream of Neurog activity. We show that, although early FGF signaling is required for Neurog expression and BTN specification, Fgf8/17/18 is expressed in tail tip cells at later stages and suppresses sustained Neurog expression in the anterior BTN (aBTN) lineage, such that only one cell (the one furthest from the source of Fgf8/17/18) maintains Neurog expression and becomes a neuron. Curiously, Fgf8/17/18 might not affect neurogenesis of the posterior BTNs (pBTNs), which are in direct contact with the Fgf8/17/18-expressing cells. Finally, to profile gene expression associated with BTN neurogenesis we performed RNAseq of isolated BTN lineage cells in which BTN neurogenesis was enhanced or suppressed by perturbing Neurog function. This allowed us to identify several candidate genes that might play conserved roles in neurogenesis and neuronal migration in other animals, including mammals.
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Affiliation(s)
- Kwantae Kim
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA, United States
| | - Susanne Gibboney
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA, United States
| | - Florian Razy-Krajka
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA, United States
| | - Elijah K. Lowe
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA, United States
| | - Wei Wang
- Department of Biology, New York University, New York, NY, United States
| | - Alberto Stolfi
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA, United States
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Abstract
For more than a century, studies on tunicate muscle formation have revealed many principles of cell fate specification, gene regulation, morphogenesis, and evolution. Here, we review the key studies that have probed the development of all the various muscle cell types in a wide variety of tunicate species. We seize this occasion to explore the implications and questions raised by these findings in the broader context of muscle evolution in chordates.
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Affiliation(s)
- Florian Razy-Krajka
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, USA
| | - Alberto Stolfi
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, USA
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Razy-Krajka F, Gravez B, Kaplan N, Racioppi C, Wang W, Christiaen L. An FGF-driven feed-forward circuit patterns the cardiopharyngeal mesoderm in space and time. eLife 2018; 7:e29656. [PMID: 29431097 PMCID: PMC5809146 DOI: 10.7554/elife.29656] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2017] [Accepted: 01/26/2018] [Indexed: 12/16/2022] Open
Abstract
In embryos, multipotent progenitors divide to produce distinct progeny and express their full potential. In vertebrates, multipotent cardiopharyngeal progenitors produce second-heart-field-derived cardiomyocytes, and branchiomeric skeletal head muscles. However, the mechanisms underlying these early fate choices remain largely elusive. The tunicate Ciona emerged as an attractive model to study early cardiopharyngeal development at high resolution: through two asymmetric and oriented divisions, defined cardiopharyngeal progenitors produce distinct first and second heart precursors, and pharyngeal muscle (aka atrial siphon muscle, ASM) precursors. Here, we demonstrate that differential FGF-MAPK signaling distinguishes between heart and ASM precursors. We characterize a feed-forward circuit that promotes the successive activations of essential ASM determinants, Hand-related, Tbx1/10 and Ebf. Finally, we show that coupling FGF-MAPK restriction and cardiopharyngeal network deployment with cell divisions defines the timing of gene expression and permits the emergence of diverse cell types from multipotent progenitors.
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Affiliation(s)
- Florian Razy-Krajka
- Center for Developmental Genetics, Department of BiologyCollege of Arts and Science, New York UniversityNew YorkUnited States
| | - Basile Gravez
- Center for Developmental Genetics, Department of BiologyCollege of Arts and Science, New York UniversityNew YorkUnited States
| | - Nicole Kaplan
- Center for Developmental Genetics, Department of BiologyCollege of Arts and Science, New York UniversityNew YorkUnited States
| | - Claudia Racioppi
- Center for Developmental Genetics, Department of BiologyCollege of Arts and Science, New York UniversityNew YorkUnited States
| | - Wei Wang
- Center for Developmental Genetics, Department of BiologyCollege of Arts and Science, New York UniversityNew YorkUnited States
| | - Lionel Christiaen
- Center for Developmental Genetics, Department of BiologyCollege of Arts and Science, New York UniversityNew YorkUnited States
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Abstract
Clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 has emerged as a revolutionary tool for fast and efficient targeted gene knockouts and genome editing in almost any organism. The laboratory model tunicate Ciona is no exception. Here, we describe our latest protocol for the design, implementation, and evaluation of successful CRISPR/Cas9-mediated gene knockouts in somatic cells of electroporated Ciona embryos. Using commercially available reagents, publicly accessible plasmids, and free web-based software applications, any Ciona researcher can easily knock out any gene of interest in their favorite embryonic cell lineage.
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Affiliation(s)
- Shashank Gandhi
- Center for Developmental Genetics, Department of Biology, New York University, New York, NY, USA
| | - Florian Razy-Krajka
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, USA
| | - Lionel Christiaen
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, USA.
| | - Alberto Stolfi
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA, USA.
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Gandhi S, Haeussler M, Razy-Krajka F, Christiaen L, Stolfi A. Evaluation and rational design of guide RNAs for efficient CRISPR/Cas9-mediated mutagenesis in Ciona. Dev Biol 2017; 425:8-20. [PMID: 28341547 PMCID: PMC5502750 DOI: 10.1016/j.ydbio.2017.03.003] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2016] [Revised: 02/06/2017] [Accepted: 03/05/2017] [Indexed: 12/26/2022]
Abstract
The CRISPR/Cas9 system has emerged as an important tool for various genome engineering applications. A current obstacle to high throughput applications of CRISPR/Cas9 is the imprecise prediction of highly active single guide RNAs (sgRNAs). We previously implemented the CRISPR/Cas9 system to induce tissue-specific mutations in the tunicate Ciona. In the present study, we designed and tested 83 single guide RNA (sgRNA) vectors targeting 23 genes expressed in the cardiopharyngeal progenitors and surrounding tissues of Ciona embryo. Using high-throughput sequencing of mutagenized alleles, we identified guide sequences that correlate with sgRNA mutagenesis activity and used this information for the rational design of all possible sgRNAs targeting the Ciona transcriptome. We also describe a one-step cloning-free protocol for the assembly of sgRNA expression cassettes. These cassettes can be directly electroporated as unpurified PCR products into Ciona embryos for sgRNA expression in vivo, resulting in high frequency of CRISPR/Cas9-mediated mutagenesis in somatic cells of electroporated embryos. We found a strong correlation between the frequency of an Ebf loss-of-function phenotype and the mutagenesis efficacies of individual Ebf-targeting sgRNAs tested using this method. We anticipate that our approach can be scaled up to systematically design and deliver highly efficient sgRNAs for the tissue-specific investigation of gene functions in Ciona.
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Affiliation(s)
| | - Maximilian Haeussler
- Santa Cruz Genomics Institute, University of California, MS CBSE, Santa Cruz, USA
| | | | | | - Alberto Stolfi
- Department of Biology, New York University, New York, USA.
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Razy-Krajka F, Lam K, Wang W, Stolfi A, Joly M, Bonneau R, Christiaen L. Collier/OLF/EBF-dependent transcriptional dynamics control pharyngeal muscle specification from primed cardiopharyngeal progenitors. Dev Cell 2014; 29:263-76. [PMID: 24794633 DOI: 10.1016/j.devcel.2014.04.001] [Citation(s) in RCA: 70] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2013] [Revised: 01/26/2014] [Accepted: 04/01/2014] [Indexed: 01/09/2023]
Abstract
In vertebrates, pluripotent pharyngeal mesoderm progenitors produce the cardiac precursors of the second heart field as well as the branchiomeric head muscles and associated stem cells. However, the mechanisms underlying the transition from multipotent progenitors to distinct muscle precursors remain obscured by the complexity of vertebrate embryos. Using Ciona intestinalis as a simple chordate model, we show that bipotent cardiopharyngeal progenitors are primed to activate both heart and pharyngeal muscle transcriptional programs, which progressively become restricted to corresponding precursors. The transcription factor COE (Collier/OLF/EBF) orchestrates the transition to pharyngeal muscle fate both by promoting an MRF-associated myogenic program in myoblasts and by maintaining an undifferentiated state in their sister cells through Notch-mediated lateral inhibition. The latter are stem cell-like muscle precursors that form most of the juvenile pharyngeal muscles. We discuss the implications of our findings for the development and evolution of the chordate cardiopharyngeal mesoderm.
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Affiliation(s)
- Florian Razy-Krajka
- Center for Developmental Genetics, Department of Biology, New York University, New York, NY 10003, USA
| | - Karen Lam
- Center for Developmental Genetics, Department of Biology, New York University, New York, NY 10003, USA; Center for Genomics and Systems Biology, Department of Biology, New York University, New York, NY 10003, USA; Courant Institute of Mathematical Sciences, New York University, New York, NY 10012, USA
| | - Wei Wang
- Center for Developmental Genetics, Department of Biology, New York University, New York, NY 10003, USA
| | - Alberto Stolfi
- Center for Developmental Genetics, Department of Biology, New York University, New York, NY 10003, USA
| | - Marine Joly
- Center for Developmental Genetics, Department of Biology, New York University, New York, NY 10003, USA
| | - Richard Bonneau
- Center for Genomics and Systems Biology, Department of Biology, New York University, New York, NY 10003, USA; Courant Institute of Mathematical Sciences, New York University, New York, NY 10012, USA
| | - Lionel Christiaen
- Center for Developmental Genetics, Department of Biology, New York University, New York, NY 10003, USA.
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Wang W, Razy-Krajka F, Siu E, Ketcham A, Christiaen L. NK4 antagonizes Tbx1/10 to promote cardiac versus pharyngeal muscle fate in the ascidian second heart field. PLoS Biol 2013; 11:e1001725. [PMID: 24311985 PMCID: PMC3849182 DOI: 10.1371/journal.pbio.1001725] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2013] [Accepted: 10/23/2013] [Indexed: 12/27/2022] Open
Abstract
Cross inhibition between NK4 and TBX1 transcription factors specifies heart versus pharyngeal muscle fates by promoting the activation of tissue-specific regulators in distinct precursors within the cardiopharyngeal lineage of the ascidian, Ciona intestinalis. The heart and head muscles share common developmental origins and genetic underpinnings in vertebrates, including humans. Parts of the heart and cranio-facial musculature derive from common mesodermal progenitors that express NKX2-5, ISL1, and TBX1. This ontogenetic kinship is dramatically reflected in the DiGeorge/Cardio-Velo-Facial syndrome (DGS/CVFS), where mutations of TBX1 cause malformations in the pharyngeal apparatus and cardiac outflow tract. Cardiac progenitors of the first heart field (FHF) do not require TBX1 and segregate precociously from common progenitors of the second heart field (SHF) and pharyngeal muscles. However, the cellular and molecular mechanisms that govern heart versus pharyngeal muscle specification within this lineage remain elusive. Here, we harness the simplicity of the ascidian larva to show that, following asymmetric cell division of common progenitors, NK4/NKX2-5 promotes GATAa/GATA4/5/6 expression and cardiac specification in the second heart precursors by antagonizing Tbx1/10-mediated inhibition of GATAa and activation of Collier/Olf/EBF (COE), the determinant of atrial siphon muscle (ASM) specification. Our results uncover essential regulatory connections between the conserved cardio-pharyngeal factor Tbx1/10 and muscle determinant COE, as well as a mutual antagonism between NK4 and Tbx1/10 activities upstream of GATAa and COE. The latter cross-antagonism underlies a fundamental heart versus pharyngeal muscle fate choice that occurs in a conserved lineage of cardio-pharyngeal progenitors. We propose that this basic ontogenetic motif underlies cardiac and pharyngeal muscle development and evolution in chordates. Mutations in the regulatory genes encoding the transcription factors NKX2-5 and TBX1, which govern heart and head muscle development, cause prevalent congenital defects. Recent studies using vertebrate models have shown that the heart and pharyngeal head muscle cells derive from common progenitors in the early embryo. To better understand the genetic mechanisms by which these progenitors select one of the two developmental trajectories, we studied the activity of these transcription factors in a simple invertebrate chordate model, the sea squirt Ciona intestinalis. We show that the sea squirt homolog of NKX2-5 promotes early heart specification by inhibiting the formation of pharyngeal muscles. Conversely, the TBX1 homolog determines pharyngeal muscle fate by inhibiting GATAa and thereby the heart program it instructs, as well as promoting the pharyngeal muscle program through activation of COE (Collier/Olf-1/EBF), a recently identified regulator of skeletal muscle differentiation. Finally, we show that the NKX2-5 homolog protein directly binds to the COE gene to repress its activity. Notably, these antagonistic interactions occur in heart and pharyngeal precursors immediately following the division of their pluripotent mother cells, thus contributing to their respective fate choice. These mechanistic insights into the process of early heart versus head muscle specification in this simple chordate provide the grounds for establishing the etiology of human congenital cardio-craniofacial defects.
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Affiliation(s)
- Wei Wang
- Department of Biology, New York University, New York, New York, United States of America
| | - Florian Razy-Krajka
- Department of Biology, New York University, New York, New York, United States of America
| | - Eric Siu
- Department of Biology, New York University, New York, New York, United States of America
| | - Alexandra Ketcham
- Department of Biology, New York University, New York, New York, United States of America
| | - Lionel Christiaen
- Department of Biology, New York University, New York, New York, United States of America
- * E-mail:
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Razy-Krajka F, Brown ER, Horie T, Callebert J, Sasakura Y, Joly JS, Kusakabe TG, Vernier P. Monoaminergic modulation of photoreception in ascidian: evidence for a proto-hypothalamo-retinal territory. BMC Biol 2012; 10:45. [PMID: 22642675 PMCID: PMC3414799 DOI: 10.1186/1741-7007-10-45] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2012] [Accepted: 05/29/2012] [Indexed: 12/12/2022] Open
Abstract
Background The retina of craniates/vertebrates has been proposed to derive from a photoreceptor prosencephalic territory in ancestral chordates, but the evolutionary origin of the different cell types making the retina is disputed. Except for photoreceptors, the existence of homologs of retinal cells remains uncertain outside vertebrates. Methods The expression of genes expressed in the sensory vesicle of the ascidian Ciona intestinalis including those encoding components of the monoaminergic neurotransmission systems, was analyzed by in situ hybridization or in vivo transfection of the corresponding regulatory elements driving fluorescent reporters. Modulation of photic responses by monoamines was studied by electrophysiology combined with pharmacological treatments. Results We show that many molecular characteristics of dopamine-synthesizing cells located in the vicinity of photoreceptors in the sensory vesicle of the ascidian Ciona intestinalis are similar to those of amacrine dopamine cells of the vertebrate retina. The ascidian dopamine cells share with vertebrate amacrine cells the expression of the key-transcription factor Ptf1a, as well as that of dopamine-synthesizing enzymes. Surprisingly, the ascidian dopamine cells accumulate serotonin via a functional serotonin transporter, as some amacrine cells also do. Moreover, dopamine cells located in the vicinity of the photoreceptors modulate the light-off induced swimming behavior of ascidian larvae by acting on alpha2-like receptors, instead of dopamine receptors, supporting a role in the modulation of the photic response. These cells are located in a territory of the ascidian sensory vesicle expressing genes found both in the retina and the hypothalamus of vertebrates (six3/6, Rx, meis, pax6, visual cycle proteins). Conclusion We propose that the dopamine cells of the ascidian larva derive from an ancestral multifunctional cell population located in the periventricular, photoreceptive field of the anterior neural tube of chordates, which also gives rise to both anterior hypothalamus and the retina in craniates/vertebrates. It also shows that the existence of multiple cell types associated with photic responses predates the formation of the vertebrate retina.
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Affiliation(s)
- Florian Razy-Krajka
- Neurobiology and Development, UPR, Institut de Neurobiologie Alfred Fessard, Centre National de la Recherche Scientifique, Gif-sur-Yvette, France
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