1
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Chen X. Reimagining Cortical Connectivity by Deconstructing Its Molecular Logic into Building Blocks. Cold Spring Harb Perspect Biol 2024; 16:a041509. [PMID: 38621822 PMCID: PMC11529856 DOI: 10.1101/cshperspect.a041509] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/17/2024]
Abstract
Comprehensive maps of neuronal connectivity provide a foundation for understanding the structure of neural circuits. In a circuit, neurons are diverse in morphology, electrophysiology, gene expression, activity, and other neuronal properties. Thus, constructing a comprehensive connectivity map requires associating various properties of neurons, including their connectivity, at cellular resolution. A commonly used approach is to use the gene expression profiles as an anchor to which all other neuronal properties are associated. Recent advances in genomics and anatomical techniques dramatically improved the ability to determine and associate the long-range projections of neurons with their gene expression profiles. These studies revealed unprecedented details of the gene-projection relationship, but also highlighted conceptual challenges in understanding this relationship. In this article, I delve into the findings and the challenges revealed by recent studies using state-of-the-art neuroanatomical and transcriptomic techniques. Building upon these insights, I propose an approach that focuses on understanding the gene-projection relationship through basic features in gene expression profiles and projections, respectively, that associate with underlying cellular processes. I then discuss how the developmental trajectories of projections and gene expression profiles create additional challenges and necessitate interrogating the gene-projection relationship across time. Finally, I explore complementary strategies that, together, can provide a comprehensive view of the gene-projection relationship.
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Affiliation(s)
- Xiaoyin Chen
- Allen Institute for Brain Science, Seattle, Washington 98109, USA
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2
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Kratsios P, Hobert O. Almost 40 years of studying homeobox genes in C. elegans. Development 2024; 151:dev204328. [PMID: 39475047 PMCID: PMC11698070 DOI: 10.1242/dev.204328] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2024]
Abstract
Homeobox genes are among the most deeply conserved families of transcription factor-encoding genes. Following their discovery in Drosophila, homeobox genes arrived on the Caenorhabditis elegans stage with a vengeance. Between 1988 and 1990, just a few years after their initial discovery in flies and vertebrates, positional cloning and sequence-based searches showed that C. elegans contains HOX cluster genes, an apparent surprise given the simplicity and non-segmented body plan of the nematode, as well as many other non-clustered homeobox genes of all major subfamilies (e.g. LIM, POU, etc.). Not quite 40 years later, we have an exceptionally deep understanding of homeodomain protein expression and function in C. elegans, revealing their prevalent role in nervous system development. In this Spotlight, we provide a historical perspective and a non-comprehensive journey through the C. elegans homeobox field and discuss open questions and future directions.
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Affiliation(s)
- Paschalis Kratsios
- Department of Neurobiology, University of Chicago, 947 E. 58th St., Chicago, IL 60637, USA
| | - Oliver Hobert
- Department of Biological Sciences, Columbia University, Howard Hughes Medical Institute, 1212 Amsterdam Avenue, New York, NY 10025, USA
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3
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Poole RJ, Flames N, Cochella L. Neurogenesis in Caenorhabditis elegans. Genetics 2024; 228:iyae116. [PMID: 39167071 PMCID: PMC11457946 DOI: 10.1093/genetics/iyae116] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2024] [Accepted: 06/24/2024] [Indexed: 08/23/2024] Open
Abstract
Animals rely on their nervous systems to process sensory inputs, integrate these with internal signals, and produce behavioral outputs. This is enabled by the highly specialized morphologies and functions of neurons. Neuronal cells share multiple structural and physiological features, but they also come in a large diversity of types or classes that give the nervous system its broad range of functions and plasticity. This diversity, first recognized over a century ago, spurred classification efforts based on morphology, function, and molecular criteria. Caenorhabditis elegans, with its precisely mapped nervous system at the anatomical level, an extensive molecular description of most of its neurons, and its genetic amenability, has been a prime model for understanding how neurons develop and diversify at a mechanistic level. Here, we review the gene regulatory mechanisms driving neurogenesis and the diversification of neuron classes and subclasses in C. elegans. We discuss our current understanding of the specification of neuronal progenitors and their differentiation in terms of the transcription factors involved and ensuing changes in gene expression and chromatin landscape. The central theme that has emerged is that the identity of a neuron is defined by modules of gene batteries that are under control of parallel yet interconnected regulatory mechanisms. We focus on how, to achieve these terminal identities, cells integrate information along their developmental lineages. Moreover, we discuss how neurons are diversified postembryonically in a time-, genetic sex-, and activity-dependent manner. Finally, we discuss how the understanding of neuronal development can provide insights into the evolution of neuronal diversity.
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Affiliation(s)
- Richard J Poole
- Department of Cell and Developmental Biology, University College London, London WC1E 6BT, UK
| | - Nuria Flames
- Developmental Neurobiology Unit, Instituto de Biomedicina de Valencia IBV-CSIC, Valencia 46012, Spain
| | - Luisa Cochella
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
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4
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Lee HMT, Lim HY, He H, Lau CY, Zheng C. MBL-1/Muscleblind regulates neuronal differentiation and controls the splicing of a terminal selector in Caenorhabditis elegans. PLoS Genet 2024; 20:e1011276. [PMID: 39423233 PMCID: PMC11524483 DOI: 10.1371/journal.pgen.1011276] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2024] [Revised: 10/30/2024] [Accepted: 10/09/2024] [Indexed: 10/21/2024] Open
Abstract
The muscleblind family of mRNA splicing regulators is conserved across species and regulates the development of muscles and the nervous system. However, how Muscleblind proteins regulate neuronal fate specification and neurite morphogenesis at the single-neuron level is not well understood. In this study, we found that the C. elegans Muscleblind/MBL-1 promotes axonal growth in the touch receptor neurons (TRNs) by regulating microtubule stability and polarity. Transcriptomic analysis identified dozens of MBL-1-controlled splicing events in genes related to neuronal differentiation or microtubule functions. Among the MBL-1 targets, the LIM-domain transcription factor mec-3 is the terminal selector for the TRN fate and induces the expression of many TRN terminal differentiation genes. MBL-1 promotes the splicing of the mec-3 long isoform, which is essential for TRN fate specification, and inhibits the short isoforms that have much weaker activities in activating downstream genes. MBL-1 promotes mec-3 splicing through three "YGCU(U/G)Y" motifs located in or downstream of the included exon, which is similar to the mechanisms used by mammalian Muscleblind and suggests a deeply conserved context-dependency of the splicing regulation. Interestingly, the expression of mbl-1 in the TRNs is dependent on the mec-3 long isoform, indicating a positive feedback loop between the splicing regulator and the terminal selector. Finally, through a forward genetic screen, we found that MBL-1 promotes neurite growth partly by inhibiting the DLK-1/p38 MAPK pathway. In summary, our study provides mechanistic understanding of the role of Muscleblind in regulating cell fate specification and neuronal morphogenesis.
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Affiliation(s)
- Ho Ming Terence Lee
- School of Biological Sciences, The University of Hong Kong, Hong Kong SAR, China
| | - Hui Yuan Lim
- School of Biological Sciences, The University of Hong Kong, Hong Kong SAR, China
| | - Haoming He
- School of Biological Sciences, The University of Hong Kong, Hong Kong SAR, China
| | - Chun Yin Lau
- School of Biological Sciences, The University of Hong Kong, Hong Kong SAR, China
| | - Chaogu Zheng
- School of Biological Sciences, The University of Hong Kong, Hong Kong SAR, China
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5
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Ma F, Zheng C. Single-cell phylotranscriptomics of developmental and cell type evolution. Trends Genet 2024; 40:495-510. [PMID: 38490933 DOI: 10.1016/j.tig.2024.02.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2023] [Revised: 02/16/2024] [Accepted: 02/16/2024] [Indexed: 03/17/2024]
Abstract
Single-cell phylotranscriptomics is an emerging tool to reveal the molecular and cellular mechanisms of evolution. We summarize its utility in studying the hourglass pattern of ontogenetic evolution and for understanding the evolutionary history of cell types. The developmental hourglass model suggests that the mid-embryonic stage is the most conserved period of development across species, which is supported by morphological and molecular studies. Single-cell phylotranscriptomic analysis has revealed previously underappreciated heterogeneity in transcriptome ages among lineages and cell types throughout development, and has identified the lineages and tissues that drive the whole-organism hourglass pattern. Single-cell transcriptome age analyses also provide important insights into the origin of germ layers, the different selective forces on tissues during adaptation, and the evolutionary relationships between cell types.
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Affiliation(s)
- Fuqiang Ma
- School of Biological Sciences, The University of Hong Kong, Hong Kong SAR, China
| | - Chaogu Zheng
- School of Biological Sciences, The University of Hong Kong, Hong Kong SAR, China.
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6
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Xu C, Ramos TB, Rogers EM, Reiser MB, Doe CQ. Homeodomain proteins hierarchically specify neuronal diversity and synaptic connectivity. eLife 2024; 12:RP90133. [PMID: 38180023 PMCID: PMC10942767 DOI: 10.7554/elife.90133] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2024] Open
Abstract
How our brain generates diverse neuron types that assemble into precise neural circuits remains unclear. Using Drosophila lamina neuron types (L1-L5), we show that the primary homeodomain transcription factor (HDTF) brain-specific homeobox (Bsh) is initiated in progenitors and maintained in L4/L5 neurons to adulthood. Bsh activates secondary HDTFs Ap (L4) and Pdm3 (L5) and specifies L4/L5 neuronal fates while repressing the HDTF Zfh1 to prevent ectopic L1/L3 fates (control: L1-L5; Bsh-knockdown: L1-L3), thereby generating lamina neuronal diversity for normal visual sensitivity. Subsequently, in L4 neurons, Bsh and Ap function in a feed-forward loop to activate the synapse recognition molecule DIP-β, thereby bridging neuronal fate decision to synaptic connectivity. Expression of a Bsh:Dam, specifically in L4, reveals Bsh binding to the DIP-β locus and additional candidate L4 functional identity genes. We propose that HDTFs function hierarchically to coordinate neuronal molecular identity, circuit formation, and function. Hierarchical HDTFs may represent a conserved mechanism for linking neuronal diversity to circuit assembly and function.
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Affiliation(s)
- Chundi Xu
- Institute of Neuroscience, Howard Hughes Medical Institute, University of OregonEugeneUnited States
| | - Tyler B Ramos
- Institute of Neuroscience, Howard Hughes Medical Institute, University of OregonEugeneUnited States
| | - Edward M Rogers
- Janelia Research Campus, Howard Hughes Medical Institute, Helix DriveAshburnUnited States
| | - Michael B Reiser
- Janelia Research Campus, Howard Hughes Medical Institute, Helix DriveAshburnUnited States
| | - Chris Q Doe
- Institute of Neuroscience, Howard Hughes Medical Institute, University of OregonEugeneUnited States
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7
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Ma F, Zheng C. Transcriptome age of individual cell types in Caenorhabditis elegans. Proc Natl Acad Sci U S A 2023; 120:e2216351120. [PMID: 36812209 PMCID: PMC9992843 DOI: 10.1073/pnas.2216351120] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2022] [Accepted: 01/27/2023] [Indexed: 02/24/2023] Open
Abstract
The phylotranscriptomic analysis of development in several species revealed the expression of older and more conserved genes in midembryonic stages and younger and more divergent genes in early and late embryonic stages, which supported the hourglass mode of development. However, previous work only studied the transcriptome age of whole embryos or embryonic sublineages, leaving the cellular basis of the hourglass pattern and the variation of transcriptome ages among cell types unexplored. By analyzing both bulk and single-cell transcriptomic data, we studied the transcriptome age of the nematode Caenorhabditis elegans throughout development. Using the bulk RNA-seq data, we identified the morphogenesis phase in midembryonic development as the phylotypic stage with the oldest transcriptome and confirmed the results using whole-embryo transcriptome assembled from single-cell RNA-seq data. The variation in transcriptome ages among individual cell types remained small in early and midembryonic development and grew bigger in late embryonic and larval stages as cells and tissues differentiate. Lineages that give rise to certain tissues (e.g., hypodermis and some neurons) but not all recapitulated the hourglass pattern across development at the single-cell transcriptome level. Further analysis of the variation in transcriptome ages among the 128 neuron types in C. elegans nervous system found that a group of chemosensory neurons and their downstream interneurons expressed very young transcriptomes and may contribute to adaptation in recent evolution. Finally, the variation in transcriptome age among the neuron types, as well as the age of their cell fate regulators, led us to hypothesize the evolutionary history of some neuron types.
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Affiliation(s)
- Fuqiang Ma
- School of Biological Sciences, The University of Hong Kong, Hong Kong SAR, China
| | - Chaogu Zheng
- School of Biological Sciences, The University of Hong Kong, Hong Kong SAR, China
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8
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Widespread employment of conserved C. elegans homeobox genes in neuronal identity specification. PLoS Genet 2022; 18:e1010372. [PMID: 36178933 PMCID: PMC9524666 DOI: 10.1371/journal.pgen.1010372] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2022] [Accepted: 08/03/2022] [Indexed: 11/20/2022] Open
Abstract
Homeobox genes are prominent regulators of neuronal identity, but the extent to which their function has been probed in animal nervous systems remains limited. In the nematode Caenorhabditis elegans, each individual neuron class is defined by the expression of unique combinations of homeobox genes, prompting the question of whether each neuron class indeed requires a homeobox gene for its proper identity specification. We present here progress in addressing this question by extending previous mutant analysis of homeobox gene family members and describing multiple examples of homeobox gene function in different parts of the C. elegans nervous system. To probe homeobox function, we make use of a number of reporter gene tools, including a novel multicolor reporter transgene, NeuroPAL, which permits simultaneous monitoring of the execution of multiple differentiation programs throughout the entire nervous system. Using these tools, we add to the previous characterization of homeobox gene function by identifying neuronal differentiation defects for 14 homeobox genes in 24 distinct neuron classes that are mostly unrelated by location, function and lineage history. 12 of these 24 neuron classes had no homeobox gene function ascribed to them before, while in the other 12 neuron classes, we extend the combinatorial code of transcription factors required for specifying terminal differentiation programs. Furthermore, we demonstrate that in a particular lineage, homeotic identity transformations occur upon loss of a homeobox gene and we show that these transformations are the result of changes in homeobox codes. Combining the present with past analyses, 113 of the 118 neuron classes of C. elegans are now known to require a homeobox gene for proper execution of terminal differentiation programs. Such broad deployment indicates that homeobox function in neuronal identity specification may be an ancestral feature of animal nervous systems.
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9
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Ahn S, Yang H, Son S, Lee HS, Park D, Yim H, Choi HJ, Swoboda P, Lee J. The C. elegans regulatory factor X (RFX) DAF-19M module: A shift from general ciliogenesis to cell-specific ciliary and behavioral specialization. Cell Rep 2022; 39:110661. [PMID: 35417689 DOI: 10.1016/j.celrep.2022.110661] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2021] [Revised: 01/14/2022] [Accepted: 03/18/2022] [Indexed: 12/28/2022] Open
Abstract
Cilia are important for the interaction with environments and the proper function of tissues. While the basic structure of cilia is well conserved, ciliated cells have various functions. To understand the distinctive identities of ciliated cells, the identification of cell-specific proteins and its regulation is essential. Here, we report the mechanism that confers a specific identity on IL2 neurons in Caenorhabditis elegans, neurons important for the dauer larva-specific nictation behavior. We show that DAF-19M, an isoform of the sole C. elegans RFX transcription factor DAF-19, heads a regulatory subroutine, regulating target genes through an X-box motif variant under the control of terminal selector proteins UNC-86 and CFI-1 in IL2 neurons. Considering the conservation of DAF-19M module in IL2 neurons for nictation and in male-specific neurons for mating behavior, we propose the existence of an evolutionarily adaptable, hard-wired genetic module for distinct behaviors that share the feature "recognizing the environment."
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Affiliation(s)
- Soungyub Ahn
- Department of Biological Sciences, Seoul National University, Seoul, Republic of Korea; Institute of Molecular Biology and Genetics, Seoul National University, Seoul, Republic of Korea
| | - Heeseung Yang
- Department of Biological Sciences, Seoul National University, Seoul, Republic of Korea; Institute of Molecular Biology and Genetics, Seoul National University, Seoul, Republic of Korea
| | - Sangwon Son
- Department of Biological Sciences, Seoul National University, Seoul, Republic of Korea; Institute of Molecular Biology and Genetics, Seoul National University, Seoul, Republic of Korea
| | - Hyun Sik Lee
- Department of Biological Sciences, Seoul National University, Seoul, Republic of Korea
| | - Dongjun Park
- Department of Biological Sciences, Seoul National University, Seoul, Republic of Korea; Institute of Molecular Biology and Genetics, Seoul National University, Seoul, Republic of Korea
| | - Hyunsoo Yim
- Department of Biological Sciences, Seoul National University, Seoul, Republic of Korea; Institute of Molecular Biology and Genetics, Seoul National University, Seoul, Republic of Korea
| | - Hee-Jung Choi
- Department of Biological Sciences, Seoul National University, Seoul, Republic of Korea
| | - Peter Swoboda
- Department of Biosciences and Nutrition, Karolinska Institute, Huddinge, Sweden.
| | - Junho Lee
- Department of Biological Sciences, Seoul National University, Seoul, Republic of Korea; Institute of Molecular Biology and Genetics, Seoul National University, Seoul, Republic of Korea.
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10
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Sousa E, Flames N. Transcriptional regulation of neuronal identity. Eur J Neurosci 2021; 55:645-660. [PMID: 34862697 PMCID: PMC9306894 DOI: 10.1111/ejn.15551] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2021] [Revised: 11/22/2021] [Accepted: 11/23/2021] [Indexed: 11/29/2022]
Abstract
Neuronal diversity is an intrinsic feature of the nervous system. Transcription factors (TFs) are key regulators in the establishment of different neuronal identities; how are the actions of different TFs coordinated to orchestrate this diversity? Are there common features shared among the different neuron types of an organism or even among different animal groups? In this review, we provide a brief overview on common traits emerging on the transcriptional regulation of neuron type diversification with a special focus on the comparison between mouse and Caenorhabditis elegans model systems. In the first part, we describe general concepts on neuronal identity and transcriptional regulation of gene expression. In the second part of the review, TFs are classified in different categories according to their key roles at specific steps along the protracted process of neuronal specification and differentiation. The same TF categories can be identified both in mammals and nematodes. Importantly, TFs are very pleiotropic: Depending on the neuron type or the time in development, the same TF can fulfil functions belonging to different categories. Finally, we describe the key role of transcriptional repression at all steps controlling neuronal diversity and propose that acquisition of neuronal identities could be considered a metastable process.
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Affiliation(s)
- Erick Sousa
- Developmental Neurobiology Unit, Instituto de Biomedicina de Valencia IBV-CSIC, Valencia, Spain
| | - Nuria Flames
- Developmental Neurobiology Unit, Instituto de Biomedicina de Valencia IBV-CSIC, Valencia, Spain
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11
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Hobert O. Homeobox genes and the specification of neuronal identity. Nat Rev Neurosci 2021; 22:627-636. [PMID: 34446866 DOI: 10.1038/s41583-021-00497-x] [Citation(s) in RCA: 45] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/06/2021] [Indexed: 12/27/2022]
Abstract
The enormous diversity of cell types that characterizes any animal nervous system is defined by neuron-type-specific gene batteries that endow cells with distinct anatomical and functional properties. To understand how such cellular diversity is genetically specified, one needs to understand the gene regulatory programmes that control the expression of cell-type-specific gene batteries. The small nervous system of the nematode Caenorhabditis elegans has been comprehensively mapped at the cellular and molecular levels, which has enabled extensive, nervous system-wide explorations into whether there are common underlying mechanisms that specify neuronal cell-type diversity. One principle that emerged from these studies is that transcription factors termed 'terminal selectors' coordinate the expression of individual members of neuron-type-specific gene batteries, thereby assigning unique identities to individual neuron types. Systematic mutant analyses and recent nervous system-wide expression analyses have revealed that one transcription factor family, the homeobox gene family, is broadly used throughout the entire C. elegans nervous system to specify neuronal identity as terminal selectors. I propose that the preponderance of homeobox genes in neuronal identity control is a reflection of an evolutionary trajectory in which an ancestral neuron type was specified by one or more ancestral homeobox genes, and that this functional linkage then duplicated and diversified to generate distinct cell types in an evolving nervous system.
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Affiliation(s)
- Oliver Hobert
- Department of Biological Sciences, Columbia University, Howard Hughes Medical Institute, New York, NY, USA.
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12
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Glenwinkel L, Taylor SR, Langebeck-Jensen K, Pereira L, Reilly MB, Basavaraju M, Rafi I, Yemini E, Pocock R, Sestan N, Hammarlund M, Miller DM, Hobert O. In silico analysis of the transcriptional regulatory logic of neuronal identity specification throughout the C. elegans nervous system. eLife 2021; 10:e64906. [PMID: 34165430 PMCID: PMC8225391 DOI: 10.7554/elife.64906] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2020] [Accepted: 05/07/2021] [Indexed: 12/11/2022] Open
Abstract
The generation of the enormous diversity of neuronal cell types in a differentiating nervous system entails the activation of neuron type-specific gene batteries. To examine the regulatory logic that controls the expression of neuron type-specific gene batteries, we interrogate single cell expression profiles of all 118 neuron classes of the Caenorhabditis elegans nervous system for the presence of DNA binding motifs of 136 neuronally expressed C. elegans transcription factors. Using a phylogenetic footprinting pipeline, we identify cis-regulatory motif enrichments among neuron class-specific gene batteries and we identify cognate transcription factors for 117 of the 118 neuron classes. In addition to predicting novel regulators of neuronal identities, our nervous system-wide analysis at single cell resolution supports the hypothesis that many transcription factors directly co-regulate the cohort of effector genes that define a neuron type, thereby corroborating the concept of so-called terminal selectors of neuronal identity. Our analysis provides a blueprint for how individual components of an entire nervous system are genetically specified.
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Affiliation(s)
- Lori Glenwinkel
- Department of Biological Sciences, Columbia University, Howard Hughes Medical InstituteNew YorkUnited States
| | - Seth R Taylor
- Department of Cell and Developmental Biology, Vanderbilt University School of MedicineNashvilleUnited States
| | | | - Laura Pereira
- Department of Biological Sciences, Columbia University, Howard Hughes Medical InstituteNew YorkUnited States
| | - Molly B Reilly
- Department of Biological Sciences, Columbia University, Howard Hughes Medical InstituteNew YorkUnited States
| | - Manasa Basavaraju
- Department of Neurobiology, Yale University School of MedicineNew HavenUnited States
- Department of Genetics, Yale University School of MedicineNew HavenUnited States
| | - Ibnul Rafi
- Department of Biological Sciences, Columbia University, Howard Hughes Medical InstituteNew YorkUnited States
| | - Eviatar Yemini
- Department of Biological Sciences, Columbia University, Howard Hughes Medical InstituteNew YorkUnited States
| | - Roger Pocock
- Biotech Research and Innovation Centre, University of CopenhagenCopenhagenDenmark
- Development and Stem Cells Program, Monash Biomedicine Discovery Institute and Department of Anatomy and Developmental Biology, Monash UniversityMelbourneAustralia
| | - Nenad Sestan
- Department of Neurobiology, Yale University School of MedicineNew HavenUnited States
- Department of Genetics, Yale University School of MedicineNew HavenUnited States
| | - Marc Hammarlund
- Department of Neurobiology, Yale University School of MedicineNew HavenUnited States
- Department of Genetics, Yale University School of MedicineNew HavenUnited States
| | - David M Miller
- Department of Cell and Developmental Biology, Vanderbilt University School of MedicineNashvilleUnited States
| | - Oliver Hobert
- Department of Biological Sciences, Columbia University, Howard Hughes Medical InstituteNew YorkUnited States
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13
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Masoudi N, Yemini E, Schnabel R, Hobert O. Piecemeal regulation of convergent neuronal lineages by bHLH transcription factors in Caenorhabditis elegans. Development 2021; 148:dev199224. [PMID: 34100067 PMCID: PMC8217713 DOI: 10.1242/dev.199224] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2021] [Accepted: 04/29/2021] [Indexed: 11/20/2022]
Abstract
Cells of the same type can be generated by distinct cellular lineages that originate in different parts of the developing embryo ('lineage convergence'). Several Caenorhabditis elegans neuron classes composed of left/right or radially symmetric class members display such lineage convergence. We show here that the C. elegans Atonal homolog lin-32 is differentially expressed in neuronal lineages that give rise to left/right or radially symmetric class members. Loss of lin-32 results in the selective loss of the expression of pan-neuronal markers and terminal selector-type transcription factors that confer neuron class-specific features. Another basic helix-loop-helix (bHLH) gene, the Achaete-Scute homolog hlh-14, is expressed in a mirror image pattern relative to lin-32 and is required to induce neuronal identity and terminal selector expression on the contralateral side of the animal. These findings demonstrate that distinct lineage histories converge via different bHLH factors at the level of induction of terminal selector identity determinants, which thus serve as integrators of distinct lineage histories. We also describe neuron-to-neuron identity transformations in lin-32 mutants, which we propose to also be the result of misregulation of terminal selector gene expression.
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Affiliation(s)
- Neda Masoudi
- Department of Biological Sciences, Columbia University, Howard Hughes Medical Institute, New York, NY 10027, USA
| | - Eviatar Yemini
- Department of Biological Sciences, Columbia University, Howard Hughes Medical Institute, New York, NY 10027, USA
| | - Ralf Schnabel
- Institute of Genetics, Technische Universität Braunschweig, 38106 Braunschweig, Germany
| | - Oliver Hobert
- Department of Biological Sciences, Columbia University, Howard Hughes Medical Institute, New York, NY 10027, USA
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14
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Tournière O, Dolan D, Richards GS, Sunagar K, Columbus-Shenkar YY, Moran Y, Rentzsch F. NvPOU4/Brain3 Functions as a Terminal Selector Gene in the Nervous System of the Cnidarian Nematostella vectensis. Cell Rep 2021; 30:4473-4489.e5. [PMID: 32234481 DOI: 10.1016/j.celrep.2020.03.031] [Citation(s) in RCA: 28] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2019] [Revised: 01/08/2020] [Accepted: 03/11/2020] [Indexed: 12/27/2022] Open
Abstract
Terminal selectors are transcription factors that control the morphological, physiological, and molecular features that characterize distinct cell types. Here, we show that, in the sea anemone Nematostella vectensis, NvPOU4 is expressed in post-mitotic cells that give rise to a diverse set of neural cell types, including cnidocytes and NvElav1-expressing neurons. Morphological analyses of NvPOU4 mutants crossed to transgenic reporter lines show that the loss of NvPOU4 does not affect the initial specification of neural cells. Transcriptomes derived from the mutants and from different neural cell populations reveal that NvPOU4 is required for the execution of the terminal differentiation program of these neural cells. These findings suggest that POU4 genes have ancient functions as terminal selectors for morphologically and functionally disparate types of neurons and they provide experimental support for the relevance of terminal selectors for understanding the evolution of cell types.
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Affiliation(s)
- Océane Tournière
- Sars International Centre for Marine Molecular Biology, University of Bergen, 5006 Bergen, Norway
| | - David Dolan
- Computational Biology Unit, Department for Informatics, University of Bergen, 5006 Bergen, Norway
| | - Gemma Sian Richards
- Sars International Centre for Marine Molecular Biology, University of Bergen, 5006 Bergen, Norway
| | - Kartik Sunagar
- Department of Ecology, Evolution and Behaviour, Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, 9190401 Jerusalem, Israel; Evolutionary Venomics Lab, Centre for Ecological Sciences, Indian Institute of Science, Bangalore 560012, India
| | - Yaara Y Columbus-Shenkar
- Department of Ecology, Evolution and Behaviour, Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, 9190401 Jerusalem, Israel
| | - Yehu Moran
- Department of Ecology, Evolution and Behaviour, Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, 9190401 Jerusalem, Israel
| | - Fabian Rentzsch
- Sars International Centre for Marine Molecular Biology, University of Bergen, 5006 Bergen, Norway; Department for Biological Sciences, University of Bergen, 5006 Bergen, Norway.
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15
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Barrière A, Bertrand V. Neuronal specification in C. elegans: combining lineage inheritance with intercellular signaling. J Neurogenet 2020; 34:273-281. [PMID: 32603241 DOI: 10.1080/01677063.2020.1781850] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The nervous system is composed of a high diversity of neuronal types. How this diversity is generated during development is a key question in neurobiology. Addressing this question is one of the reasons that led Sydney Brenner to develop the nematode C. elegans as a model organism. While there was initially a debate on whether the neuronal specification follows a 'European' model (determined by ancestry) or an 'American' model (determined by intercellular communication), several decades of research have established that the truth lies somewhere in between. Neurons are specified by the combination of transcription factors inherited from the ancestor cells and signaling between neighboring cells (especially Wnt and Notch signaling). This converges to the activation in newly generated postmitotic neurons of a specific set of terminal selector transcription factors that initiate and maintain the differentiation of the neuron. In this review, we also discuss the evolution of these specification mechanisms in other nematodes and beyond.
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Affiliation(s)
- Antoine Barrière
- Aix Marseille University, CNRS, IBDM, Turing Center for Living Systems, Marseille, France
| | - Vincent Bertrand
- Aix Marseille University, CNRS, IBDM, Turing Center for Living Systems, Marseille, France
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16
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Leyva-Díaz E, Masoudi N, Serrano-Saiz E, Glenwinkel L, Hobert O. Brn3/POU-IV-type POU homeobox genes-Paradigmatic regulators of neuronal identity across phylogeny. WILEY INTERDISCIPLINARY REVIEWS-DEVELOPMENTAL BIOLOGY 2020; 9:e374. [PMID: 32012462 DOI: 10.1002/wdev.374] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/21/2019] [Revised: 12/18/2019] [Accepted: 01/07/2020] [Indexed: 02/06/2023]
Abstract
One approach to understand the construction of complex systems is to investigate whether there are simple design principles that are commonly used in building such a system. In the context of nervous system development, one may ask whether the generation of its highly diverse sets of constituents, that is, distinct neuronal cell types, relies on genetic mechanisms that share specific common features. Specifically, are there common patterns in the function of regulatory genes across different neuron types and are those regulatory mechanisms not only used in different parts of one nervous system, but are they conserved across animal phylogeny? We address these questions here by focusing on one specific, highly conserved and well-studied regulatory factor, the POU homeodomain transcription factor UNC-86. Work over the last 30 years has revealed a common and paradigmatic theme of unc-86 function throughout most of the neuron types in which Caenorhabditis elegans unc-86 is expressed. Apart from its role in preventing lineage reiterations during development, UNC-86 operates in combination with distinct partner proteins to initiate and maintain terminal differentiation programs, by coregulating a vast array of functionally distinct identity determinants of specific neuron types. Mouse orthologs of unc-86, the Brn3 genes, have been shown to fulfill a similar function in initiating and maintaining neuronal identity in specific parts of the mouse brain and similar functions appear to be carried out by the sole Drosophila ortholog, Acj6. The terminal selector function of UNC-86 in many different neuron types provides a paradigm for neuronal identity regulation across phylogeny. This article is categorized under: Gene Expression and Transcriptional Hierarchies > Regulatory Mechanisms Invertebrate Organogenesis > Worms Nervous System Development > Vertebrates: Regional Development.
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Affiliation(s)
- Eduardo Leyva-Díaz
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York, New York
| | - Neda Masoudi
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York, New York
| | | | - Lori Glenwinkel
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York, New York
| | - Oliver Hobert
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York, New York
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17
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Feng W, Li Y, Dao P, Aburas J, Islam P, Elbaz B, Kolarzyk A, Brown AE, Kratsios P. A terminal selector prevents a Hox transcriptional switch to safeguard motor neuron identity throughout life. eLife 2020; 9:50065. [PMID: 31902393 PMCID: PMC6944445 DOI: 10.7554/elife.50065] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2019] [Accepted: 12/08/2019] [Indexed: 01/01/2023] Open
Abstract
To become and remain functional, individual neuron types must select during development and maintain throughout life their distinct terminal identity features, such as expression of specific neurotransmitter receptors, ion channels and neuropeptides. Here, we report a molecular mechanism that enables cholinergic motor neurons (MNs) in the C. elegans ventral nerve cord to select and maintain their unique terminal identity. This mechanism relies on the dual function of the conserved terminal selector UNC-3 (Collier/Ebf). UNC-3 synergizes with LIN-39 (Scr/Dfd/Hox4-5) to directly co-activate multiple terminal identity traits specific to cholinergic MNs, but also antagonizes LIN-39’s ability to activate terminal features of alternative neuronal identities. Loss of unc-3 causes a switch in the transcriptional targets of LIN-39, thereby alternative, not cholinergic MN-specific, terminal features become activated and locomotion defects occur. The strategy of a terminal selector preventing a transcriptional switch may constitute a general principle for safeguarding neuronal identity throughout life.
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Affiliation(s)
- Weidong Feng
- Department of Neurobiology, University of Chicago, Chicago, United States.,Committee on Development, Regeneration and Stem Cell Biology, University of Chicago, Chicago, United States
| | - Yinan Li
- Department of Neurobiology, University of Chicago, Chicago, United States.,Committee on Neurobiology, University of Chicago, Chicago, United States
| | - Pauline Dao
- Department of Neurobiology, University of Chicago, Chicago, United States
| | - Jihad Aburas
- Department of Neurobiology, University of Chicago, Chicago, United States
| | - Priota Islam
- MRC London Institute of Medical Sciences, London, United Kingdom.,Institute of Clinical Sciences, Imperial College London, London, United Kingdom
| | - Benayahu Elbaz
- Department of Neurology, Center for Peripheral Neuropathy, University of Chicago, Chicago, United States
| | - Anna Kolarzyk
- Department of Neurology, Center for Peripheral Neuropathy, University of Chicago, Chicago, United States
| | - André Ex Brown
- MRC London Institute of Medical Sciences, London, United Kingdom.,Institute of Clinical Sciences, Imperial College London, London, United Kingdom
| | - Paschalis Kratsios
- Department of Neurobiology, University of Chicago, Chicago, United States.,Committee on Development, Regeneration and Stem Cell Biology, University of Chicago, Chicago, United States.,Committee on Neurobiology, University of Chicago, Chicago, United States.,The Grossman Institute for Neuroscience, Quantitative Biology, and Human Behavior, University of Chicago, Chicago, United States
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18
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Thompson M, Bixby R, Dalton R, Vandenburg A, Calarco JA, Norris AD. Splicing in a single neuron is coordinately controlled by RNA binding proteins and transcription factors. eLife 2019; 8:46726. [PMID: 31322498 PMCID: PMC6641836 DOI: 10.7554/elife.46726] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2019] [Accepted: 06/20/2019] [Indexed: 12/22/2022] Open
Abstract
Single-cell transcriptomes are established by transcription factors (TFs), which determine a cell's gene-expression complement. Post-transcriptional regulation of single-cell transcriptomes, and the RNA binding proteins (RBPs) responsible, are more technically challenging to determine, and combinatorial TF-RBP coordination of single-cell transcriptomes remains unexplored. We used fluorescent reporters to visualize alternative splicing in single Caenorhabditis elegans neurons, identifying complex splicing patterns in the neuronal kinase sad-1. Most neurons express both isoforms, but the ALM mechanosensory neuron expresses only the exon-included isoform, while its developmental sister cell the BDU neuron expresses only the exon-skipped isoform. A cascade of three cell-specific TFs and two RBPs are combinatorially required for sad-1 exon inclusion. Mechanistically, TFs combinatorially ensure expression of RBPs, which interact with sad-1 pre-mRNA. Thus a combinatorial TF-RBP code controls single-neuron sad-1 splicing. Additionally, we find ‘phenotypic convergence,’ previously observed for TFs, also applies to RBPs: different RBP combinations generate similar splicing outcomes in different neurons. All the cells in the human nervous system contain the same genetic information, and yet there are many kinds of neurons, each with different features and roles in the body. Proteins known as transcription factors help to establish this diversity by switching on different genes in different types of cells. A mechanism known as RNA splicing, which is regulated by RNA binding proteins, can also provide another layer of regulation. When a gene is switched on, a faithful copy of its sequence is produced in the form of an RNA molecule, which will then be ‘read’ to create a protein. However, the RNA molecules may first be processed to create templates that can differ between cell types: this means that a single gene can code for slightly different proteins, some of them specific to a given cell type. Yet, very little is known about how RNA splicing can generate more diversity in the nervous system. To investigate, Thompson et al. developed a fluorescent reporter system that helped them track how the RNA of a gene called sad-1 is spliced in individual neurons of the worm Caenorhabditis elegans. This showed that sad-1 was turned on in all neurons, but the particular spliced versions varied widely between different types of nerve cells. Additional experiments combined old school and cutting-edge genetics technics such as CRISPR/Cas9 to identify the proteins that control the splicing of sad-1 in different kinds of neurons. Despite not directly participating in RNA splicing, a number of transcription factors were shown to be involved. These molecular switches were turning on genes that code for RNA binding proteins differently between types of neurons, which in turn led sad-1 to be spliced according to neuron-specific patterns. The findings by Thompson et al. could provide some insight into how mammals can establish many types of neurons; however, a technical hurdle stands in the way of this line of research, as it is still difficult to detect splicing in single neurons in these species.
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Affiliation(s)
- Morgan Thompson
- Biological Sciences, Southern Methodist University, Dallas, United States
| | - Ryan Bixby
- Biological Sciences, Southern Methodist University, Dallas, United States
| | - Robert Dalton
- Biological Sciences, Southern Methodist University, Dallas, United States
| | - Alexa Vandenburg
- Biological Sciences, Southern Methodist University, Dallas, United States
| | - John A Calarco
- Cell & Systems Biology, University of Toronto, Toronto, Canada
| | - Adam D Norris
- Biological Sciences, Southern Methodist University, Dallas, United States
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19
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Stratmann J, Ekman H, Thor S. Branching gene regulatory network dictating different aspects of a neuronal cell identity. Development 2019; 146:dev.174300. [DOI: 10.1242/dev.174300] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2018] [Accepted: 02/22/2019] [Indexed: 12/30/2022]
Abstract
The nervous system displays a daunting cellular diversity. Neuronal sub-types differ from each other in several aspects, including their neurotransmitter expression and axon projection. These aspects can converge, but can also diverge, such that neurons expressing the same neurotransmitter may project axons to different targets. It is not well understood how regulatory programs converge/diverge to associate/dissociate different cell fate features. Studies of the Drosophila Tv1 neurons have identified a regulatory cascade; ladybird early -> collier -> apterous/eyes absent -> dimmed, which specifies Tv1 neurotransmitter expression. Here, we conduct genetic and transcriptome analysis to address how other aspects of Tv1 cell fate is governed. We find that an initiator terminal selector gene triggers a feedforward loop which branches into different subroutines, each of which establishes different features of this one unique neuronal cell fate.
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Affiliation(s)
- Johannes Stratmann
- Department of Clinical and Experimental Medicine, Linkoping University, SE-581 85 Linkoping, Sweden
| | - Helen Ekman
- Department of Clinical and Experimental Medicine, Linkoping University, SE-581 85 Linkoping, Sweden
| | - Stefan Thor
- Department of Clinical and Experimental Medicine, Linkoping University, SE-581 85 Linkoping, Sweden
- School of Biomedical Sciences, University of Queensland, St Lucia QLD 4072, Australia
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20
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Serrano-Saiz E, Leyva-Díaz E, De La Cruz E, Hobert O. BRN3-type POU Homeobox Genes Maintain the Identity of Mature Postmitotic Neurons in Nematodes and Mice. Curr Biol 2018; 28:2813-2823.e2. [PMID: 30146154 DOI: 10.1016/j.cub.2018.06.045] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2018] [Revised: 06/08/2018] [Accepted: 06/19/2018] [Indexed: 11/28/2022]
Abstract
Many distinct regulatory factors have been shown to be required for the proper initiation of neuron-type-specific differentiation programs, but much less is known about the regulatory programs that maintain the differentiated state in the adult [1-3]. One possibility is that regulatory factors that initiate a terminal differentiation program during development are continuously required to maintain the differentiated state. Here, we test this hypothesis by investigating the function of two orthologous POU homeobox genes in nematodes and mice. The C. elegans POU homeobox gene unc-86 is a terminal selector that is required during development to initiate the terminal differentiation program of several distinct neuron classes [4-13]. Through post-developmental removal of unc-86 activity, we show here that unc-86 is also continuously required throughout the life of many neuron classes to maintain neuron-class-specific identity features. Similarly, the mouse unc-86 ortholog Brn3a/POU4F1 has been shown to control the initiation of the terminal differentiation program of distinct neuron types across the mouse brain, such as the medial habenular neurons [14-20]. By conditionally removing Brn3a in the adult mouse central nervous system, we show that, like its invertebrate ortholog unc-86, Brn3a is also required for the maintenance of terminal identity features of medial habenular neurons. In addition, Brn3a is required for the survival of these neurons, indicating that identity maintenance and survival are genetically linked. We conclude that the continuous expression of transcription factors is essential for the active maintenance of the differentiated state of a neuron across phylogeny.
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Affiliation(s)
- Esther Serrano-Saiz
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York, NY, USA.
| | - Eduardo Leyva-Díaz
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York, NY, USA
| | - Estanislao De La Cruz
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York, NY, USA
| | - Oliver Hobert
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York, NY, USA.
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21
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Bhati M, Llamosas E, Jacques DA, Jeffries CM, Dastmalchi S, Ripin N, Nicholas HR, Matthews JM. Interactions between LHX3- and ISL1-family LIM-homeodomain transcription factors are conserved in Caenorhabditis elegans. Sci Rep 2017; 7:4579. [PMID: 28676648 PMCID: PMC5496915 DOI: 10.1038/s41598-017-04587-8] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2017] [Accepted: 05/17/2017] [Indexed: 02/07/2023] Open
Abstract
LIM-Homeodomain (LIM-HD) transcription factors are highly conserved in animals where they are thought to act in a transcriptional ‘LIM code’ that specifies cell types, particularly in the central nervous system. In chick and mammals the interaction between two LIM-HD proteins, LHX3 and Islet1 (ISL1), is essential for the development of motor neurons. Using yeast two-hybrid analysis we showed that the Caenorhabditis elegans orthologs of LHX3 and ISL1, CEH-14 and LIM-7 can physically interact. Structural characterisation of a complex comprising the LIM domains from CEH-14 and a LIM-interaction domain from LIM-7 showed that these nematode proteins assemble to form a structure that closely resembles that of their vertebrate counterparts. However, mutagenic analysis across the interface indicates some differences in the mechanisms of binding. We also demonstrate, using fluorescent reporter constructs, that the two C. elegans proteins are co-expressed in a small subset of neurons. These data show that the propensity for LHX3 and Islet proteins to interact is conserved from C. elegans to mammals, raising the possibility that orthologous cell specific LIM-HD-containing transcription factor complexes play similar roles in the development of neuronal cells across diverse species.
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Affiliation(s)
- Mugdha Bhati
- School of Life and Environmental Sciences, University of Sydney, NSW, 2006, Australia.,Teva Pharmaceuticals Australia Pty Ltd, Macquarie Park, NSW, 2113, Australia
| | - Estelle Llamosas
- School of Life and Environmental Sciences, University of Sydney, NSW, 2006, Australia.,School of Women's and Children's Health, University of New South Wales, NSW, Australia
| | - David A Jacques
- School of Life and Environmental Sciences, University of Sydney, NSW, 2006, Australia.,iThree Institute, University of Technology, NSW, 2007, Australia
| | - Cy M Jeffries
- School of Life and Environmental Sciences, University of Sydney, NSW, 2006, Australia.,European Molecular Biology Laboratory (EMBL) Hamburg Outstation, c/o DESY, Notkestrasse 85, 22607, Hamburg, Germany
| | - Siavoush Dastmalchi
- Biotechnology Research Center and School of Pharmacy, Tabritz Univeristy of Medical Science, Tabritz, Iran
| | - Nina Ripin
- School of Life and Environmental Sciences, University of Sydney, NSW, 2006, Australia.,Department of Biology, ETH, Zurich, 8093, Switzerland
| | - Hannah R Nicholas
- School of Life and Environmental Sciences, University of Sydney, NSW, 2006, Australia.
| | - Jacqueline M Matthews
- School of Life and Environmental Sciences, University of Sydney, NSW, 2006, Australia.
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22
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Costa A, Powell LM, Lowell S, Jarman AP. Atoh1 in sensory hair cell development: constraints and cofactors. Semin Cell Dev Biol 2017; 65:60-68. [DOI: 10.1016/j.semcdb.2016.10.003] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2016] [Revised: 09/26/2016] [Accepted: 10/13/2016] [Indexed: 11/28/2022]
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23
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Rhee HS, Closser M, Guo Y, Bashkirova EV, Tan GC, Gifford DK, Wichterle H. Expression of Terminal Effector Genes in Mammalian Neurons Is Maintained by a Dynamic Relay of Transient Enhancers. Neuron 2016; 92:1252-1265. [PMID: 27939581 PMCID: PMC5193225 DOI: 10.1016/j.neuron.2016.11.037] [Citation(s) in RCA: 64] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2016] [Revised: 10/31/2016] [Accepted: 11/17/2016] [Indexed: 11/22/2022]
Abstract
Generic spinal motor neuron identity is established by cooperative binding of programming transcription factors (TFs), Isl1 and Lhx3, to motor-neuron-specific enhancers. How expression of effector genes is maintained following downregulation of programming TFs in maturing neurons remains unknown. High-resolution exonuclease (ChIP-exo) mapping revealed that the majority of enhancers established by programming TFs are rapidly deactivated following Lhx3 downregulation in stem-cell-derived hypaxial motor neurons. Isl1 is released from nascent motor neuron enhancers and recruited to new enhancers bound by clusters of Onecut1 in maturing neurons. Synthetic enhancer reporter assays revealed that Isl1 operates as an integrator factor, translating the density of Lhx3 or Onecut1 binding sites into transient enhancer activity. Importantly, independent Isl1/Lhx3- and Isl1/Onecut1-bound enhancers contribute to sustained expression of motor neuron effector genes, demonstrating that outwardly stable expression of terminal effector genes in postmitotic neurons is controlled by a dynamic relay of stage-specific enhancers.
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Affiliation(s)
- Ho Sung Rhee
- Departments of Pathology and Cell Biology, Neuroscience, and Neurology, Center for Motor Neuron Biology and Disease, Columbia Stem Cell Initiative, Columbia University Medical Center, New York, NY 10032, USA
| | - Michael Closser
- Departments of Pathology and Cell Biology, Neuroscience, and Neurology, Center for Motor Neuron Biology and Disease, Columbia Stem Cell Initiative, Columbia University Medical Center, New York, NY 10032, USA
| | - Yuchun Guo
- Computer Science and Artificial Intelligence Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Elizaveta V Bashkirova
- Departments of Pathology and Cell Biology, Neuroscience, and Neurology, Center for Motor Neuron Biology and Disease, Columbia Stem Cell Initiative, Columbia University Medical Center, New York, NY 10032, USA
| | - G Christopher Tan
- Departments of Pathology and Cell Biology, Neuroscience, and Neurology, Center for Motor Neuron Biology and Disease, Columbia Stem Cell Initiative, Columbia University Medical Center, New York, NY 10032, USA
| | - David K Gifford
- Computer Science and Artificial Intelligence Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Hynek Wichterle
- Departments of Pathology and Cell Biology, Neuroscience, and Neurology, Center for Motor Neuron Biology and Disease, Columbia Stem Cell Initiative, Columbia University Medical Center, New York, NY 10032, USA.
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24
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Abstract
Cell types are the basic building blocks of multicellular organisms and are extensively diversified in animals. Despite recent advances in characterizing cell types, classification schemes remain ambiguous. We propose an evolutionary definition of a cell type that allows cell types to be delineated and compared within and between species. Key to cell type identity are evolutionary changes in the 'core regulatory complex' (CoRC) of transcription factors, that make emergent sister cell types distinct, enable their independent evolution and regulate cell type-specific traits termed apomeres. We discuss the distinction between developmental and evolutionary lineages, and present a roadmap for future research.
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25
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Arlotta P, Hobert O. Homeotic Transformations of Neuronal Cell Identities. Trends Neurosci 2016; 38:751-762. [PMID: 26596501 DOI: 10.1016/j.tins.2015.10.005] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2015] [Revised: 10/13/2015] [Accepted: 10/18/2015] [Indexed: 11/20/2022]
Abstract
Homeosis is classically defined as the transformation of one body part into something that resembles another body part. We propose here to broaden the concept of homeosis to the many neuronal cell identity transformations that have been uncovered over the past few years upon removal of specific regulatory factors in organisms from Caenorhabditis elegans to Drosophila, zebrafish, and mice. The concept of homeosis provides a framework for the evolution of cell type diversity in the brain.
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Affiliation(s)
- Paola Arlotta
- Department of Stem Cell and Regenerative Biology, Harvard University, Cambridge, MA 02138, USA.
| | - Oliver Hobert
- Department of Biology and Department of Biochemistry and Molecular Biophysics, Howard Hughes Medical Institute, Columbia University, New York, NY, USA.
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26
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Corty MM, Tam J, Grueber WB. Dendritic diversification through transcription factor-mediated suppression of alternative morphologies. Development 2016; 143:1351-62. [PMID: 27095495 DOI: 10.1242/dev.130906] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2015] [Accepted: 02/25/2016] [Indexed: 01/23/2023]
Abstract
Neurons display a striking degree of functional and morphological diversity, and the developmental mechanisms that underlie diversification are of significant interest for understanding neural circuit assembly and function. We find that the morphology of Drosophila sensory neurons is diversified through a series of suppressive transcriptional interactions involving the POU domain transcription factors Pdm1 (Nubbin) and Pdm2, the homeodomain transcription factor Cut, and the transcriptional regulators Scalloped and Vestigial. Pdm1 and Pdm2 are expressed in a subset of proprioceptive sensory neurons and function to inhibit dendrite growth and branching. A subset of touch receptors show a capacity to express Pdm1/2, but Cut represses this expression and promotes more complex dendritic arbors. Levels of Cut expression are diversified in distinct sensory neurons by selective expression of Scalloped and Vestigial. Different levels of Cut impact dendritic complexity and, consistent with this, we show that Scalloped and Vestigial suppress terminal dendritic branching. This transcriptional hierarchy therefore acts to suppress alternative morphologies to diversify three distinct types of somatosensory neurons.
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Affiliation(s)
- Megan M Corty
- Department of Neuroscience, Columbia University Medical Center, 630 W. 168th St. P&S 12-403, New York, NY 10032, USA Department of Physiology and Cellular Biophysics, Columbia University Medical Center, 630 W. 168th St. P&S 12-403, New York, NY 10032, USA
| | - Justina Tam
- Department of Physiology and Cellular Biophysics, Columbia University Medical Center, 630 W. 168th St. P&S 12-403, New York, NY 10032, USA
| | - Wesley B Grueber
- Department of Neuroscience, Columbia University Medical Center, 630 W. 168th St. P&S 12-403, New York, NY 10032, USA Department of Physiology and Cellular Biophysics, Columbia University Medical Center, 630 W. 168th St. P&S 12-403, New York, NY 10032, USA
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27
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Kodama H, Miyata Y, Kuwajima M, Izuchi R, Kobayashi A, Gyoja F, Onuma TA, Kumano G, Nishida H. Redundant mechanisms are involved in suppression of default cell fates during embryonic mesenchyme and notochord induction in ascidians. Dev Biol 2016; 416:162-172. [PMID: 27265866 DOI: 10.1016/j.ydbio.2016.05.033] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2016] [Revised: 05/28/2016] [Accepted: 05/30/2016] [Indexed: 11/30/2022]
Abstract
During embryonic induction, the responding cells invoke an induced developmental program, whereas in the absence of an inducing signal, they assume a default uninduced cell fate. Suppression of the default fate during the inductive event is crucial for choice of the binary cell fate. In contrast to the mechanisms that promote an induced cell fate, those that suppress the default fate have been overlooked. Upon induction, intracellular signal transduction results in activation of genes encoding key transcription factors for induced tissue differentiation. It is elusive whether an induced key transcription factor has dual functions involving suppression of the default fates and promotion of the induced fate, or whether suppression of the default fate is independently regulated by other factors that are also downstream of the signaling cascade. We show that during ascidian embryonic induction, default fates were suppressed by multifold redundant mechanisms. The key transcription factor, Twist-related.a, which is required for mesenchyme differentiation, and another independent transcription factor, Lhx3, which is dispensable for mesenchyme differentiation, sequentially and redundantly suppress the default muscle fate in induced mesenchyme cells. Similarly in notochord induction, Brachyury, which is required for notochord differentiation, and other factors, Lhx3 and Mnx, are likely to suppress the default nerve cord fate redundantly. Lhx3 commonly suppresses the default fates in two kinds of induction. Mis-activation of the autonomously executed default program in induced cells is detrimental to choice of the binary cell fate. Multifold redundant mechanisms would be required for suppression of the default fate to be secure.
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Affiliation(s)
- Hitoshi Kodama
- Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
| | - Yoshimasa Miyata
- Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
| | - Mami Kuwajima
- Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
| | - Ryoichi Izuchi
- Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
| | - Ayumi Kobayashi
- Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
| | - Fuki Gyoja
- Marine Genomics Unit, Okinawa Institute of Science and Technology Graduate University, 1919-1 Tancha, Onna, Okinawa 904-0495, Japan
| | - Takeshi A Onuma
- Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
| | - Gaku Kumano
- Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
| | - Hiroki Nishida
- Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan.
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28
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Hobert O. A map of terminal regulators of neuronal identity in Caenorhabditis elegans. WILEY INTERDISCIPLINARY REVIEWS-DEVELOPMENTAL BIOLOGY 2016; 5:474-98. [PMID: 27136279 PMCID: PMC4911249 DOI: 10.1002/wdev.233] [Citation(s) in RCA: 69] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/02/2016] [Revised: 02/07/2016] [Accepted: 02/21/2016] [Indexed: 12/31/2022]
Abstract
Our present day understanding of nervous system development is an amalgam of insights gained from studying different aspects and stages of nervous system development in a variety of invertebrate and vertebrate model systems, with each model system making its own distinctive set of contributions. One aspect of nervous system development that has been among the most extensively studied in the nematode Caenorhabditis elegans is the nature of the gene regulatory programs that specify hardwired, terminal cellular identities. I first summarize a number of maps (anatomical, functional, and molecular) that describe the terminal identity of individual neurons in the C. elegans nervous system. I then provide a comprehensive summary of regulatory factors that specify terminal identities in the nervous system, synthesizing these past studies into a regulatory map of cellular identities in the C. elegans nervous system. This map shows that for three quarters of all neurons in the C. elegans nervous system, regulatory factors that control terminal identity features are known. In-depth studies of specific neuron types have revealed that regulatory factors rarely act alone, but rather act cooperatively in neuron-type specific combinations. In most cases examined so far, distinct, biochemically unlinked terminal identity features are coregulated via cooperatively acting transcription factors, termed terminal selectors, but there are also cases in which distinct identity features are controlled in a piecemeal fashion by independent regulatory inputs. The regulatory map also illustrates that identity-defining transcription factors are reemployed in distinct combinations in different neuron types. However, the same transcription factor can drive terminal differentiation in neurons that are unrelated by lineage, unrelated by function, connectivity and neurotransmitter deployment. Lastly, the regulatory map illustrates the preponderance of homeodomain transcription factors in the control of terminal identities, suggesting that these factors have ancient, phylogenetically conserved roles in controlling terminal neuronal differentiation in the nervous system. WIREs Dev Biol 2016, 5:474-498. doi: 10.1002/wdev.233 For further resources related to this article, please visit the WIREs website.
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Affiliation(s)
- Oliver Hobert
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York, NY, USA
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Stefanakis N, Carrera I, Hobert O. Regulatory Logic of Pan-Neuronal Gene Expression in C. elegans. Neuron 2015; 87:733-50. [PMID: 26291158 DOI: 10.1016/j.neuron.2015.07.031] [Citation(s) in RCA: 104] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2015] [Revised: 07/01/2015] [Accepted: 07/20/2015] [Indexed: 01/03/2023]
Abstract
While neuronal cell types display an astounding degree of phenotypic diversity, most if not all neuron types share a core panel of terminal features. However, little is known about how pan-neuronal expression patterns are genetically programmed. Through an extensive analysis of the cis-regulatory control regions of a battery of pan-neuronal C. elegans genes, including genes involved in synaptic vesicle biology and neuropeptide signaling, we define a common organizational principle in the regulation of pan-neuronal genes in the form of a surprisingly complex array of seemingly redundant, parallel-acting cis-regulatory modules that direct expression to broad, overlapping domains throughout the nervous system. These parallel-acting cis-regulatory modules are responsive to a multitude of distinct trans-acting factors. Neuronal gene expression programs therefore fall into two fundamentally distinct classes. Neuron-type-specific genes are generally controlled by discrete and non-redundantly acting regulatory inputs, while pan-neuronal gene expression is controlled by diverse, coincident and seemingly redundant regulatory inputs.
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Affiliation(s)
- Nikolaos Stefanakis
- Department of Biochemistry and Molecular Biophysics, Howard Hughes Medical Institute, Columbia University Medical Center, New York, NY, USA
| | - Ines Carrera
- Department of Biochemistry and Molecular Biophysics, Howard Hughes Medical Institute, Columbia University Medical Center, New York, NY, USA
| | - Oliver Hobert
- Department of Biochemistry and Molecular Biophysics, Howard Hughes Medical Institute, Columbia University Medical Center, New York, NY, USA.
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Alqadah A, Hsieh YW, Vidal B, Chang C, Hobert O, Chuang CF. Postmitotic diversification of olfactory neuron types is mediated by differential activities of the HMG-box transcription factor SOX-2. EMBO J 2015; 34:2574-89. [PMID: 26341465 DOI: 10.15252/embj.201592188] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2015] [Accepted: 08/06/2015] [Indexed: 12/23/2022] Open
Abstract
Diversification of neuron classes is essential for functions of the olfactory system, but the underlying mechanisms that generate individual olfactory neuron types are only beginning to be understood. Here we describe a role of the highly conserved HMG-box transcription factor SOX-2 in postmitotic specification and alternative differentiation of the Caenorhabditis elegans AWC and AWB olfactory neurons. We show that SOX-2 partners with different transcription factors to diversify postmitotic olfactory cell types. SOX-2 functions cooperatively with the OTX/OTD transcription factor CEH-36 to specify an AWC "ground state," and functions with the LIM homeodomain factor LIM-4 to suppress this ground state and drive an AWB identity instead. Our findings provide novel insights into combinatorial codes that drive terminal differentiation programs in the nervous system and reveal a biological function of the deeply conserved Sox2 protein that goes beyond its well-known role in stem cell biology.
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Affiliation(s)
- Amel Alqadah
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL, USA Molecular and Developmental Biology Graduate Program, University of Cincinnati, Cincinnati, OH, USA
| | - Yi-Wen Hsieh
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL, USA
| | - Berta Vidal
- Department of Biological Sciences, Department of Biochemistry and Molecular Biophysics, Howard Hughes Medical Institute Columbia University, New York, NY, USA
| | - Chieh Chang
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL, USA
| | - Oliver Hobert
- Department of Biological Sciences, Department of Biochemistry and Molecular Biophysics, Howard Hughes Medical Institute Columbia University, New York, NY, USA
| | - Chiou-Fen Chuang
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL, USA
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