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Assaying Optic Nerve Regeneration in Larval Zebrafish. Methods Mol Biol 2023; 2636:191-203. [PMID: 36881301 DOI: 10.1007/978-1-0716-3012-9_10] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/08/2023]
Abstract
Zebrafish have a remarkable capacity for spontaneously regenerating their central nervous system. Larval zebrafish are optically transparent and therefore are widely used to dynamically visualize cellular processes in vivo, such as nerve regeneration. Regeneration of retinal ganglion cell (RGC) axons within the optic nerve has been previously studied in adult zebrafish. In contrast, assays of optic nerve regeneration have previously not been established in larval zebrafish. In order to take advantage of the imaging capabilities in the larval zebrafish model, we recently developed an assay to physically transect RGC axons and monitor optic nerve regeneration in larval zebrafish. We found that RGC axons rapidly and robustly regrow to the optic tectum. Here, we describe the methods for performing the optic nerve transections, as well as methods for visualizing RGC regeneration in larval zebrafish.
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Lloyd E, McDole B, Privat M, Jaggard JB, Duboué ER, Sumbre G, Keene AC. Blind cavefish retain functional connectivity in the tectum despite loss of retinal input. Curr Biol 2022; 32:3720-3730.e3. [PMID: 35926509 DOI: 10.1016/j.cub.2022.07.015] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2021] [Revised: 04/07/2022] [Accepted: 07/07/2022] [Indexed: 11/26/2022]
Abstract
Sensory systems display remarkable plasticity and are under strong evolutionary selection. The Mexican cavefish, Astyanax mexicanus, consists of eyed river-dwelling surface populations and multiple independent cave populations that have converged on eye loss, providing the opportunity to examine the evolution of sensory circuits in response to environmental perturbation. Functional analysis across multiple transgenic populations expressing GCaMP6s showed that functional connectivity of the optic tectum largely did not differ between populations, except for the selective loss of negatively correlated activity within the cavefish tectum, suggesting positively correlated neural activity is resistant to an evolved loss of input from the retina. Furthermore, analysis of surface-cave hybrid fish reveals that changes in the tectum are genetically distinct from those encoding eye loss. Together, these findings uncover the independent evolution of multiple components of the visual system and establish the use of functional imaging in A. mexicanus to study neural circuit evolution.
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Affiliation(s)
- Evan Lloyd
- Department of Biological Science, Florida Atlantic University, Jupiter, FL 33458, USA; Department of Biology, Texas A&M University, College Station, TX 77843, USA; Harriet Wilkes Honors College, Florida Atlantic University, Jupiter, FL 33458, USA
| | - Brittnee McDole
- Department of Biological Science, Florida Atlantic University, Jupiter, FL 33458, USA
| | - Martin Privat
- Institut de Biologie de l'ENS (IBENS), Département de Biologie, École Normale Supérieure, CNRS, INSERM, Université PSL, 75005 Paris, France
| | - James B Jaggard
- Department of Biological Science, Florida Atlantic University, Jupiter, FL 33458, USA; Department of Psychiatry and Behavioral Sciences, Stanford University School of Medicine, Stanford, CA 94305, USA
| | - Erik R Duboué
- Department of Psychiatry and Behavioral Sciences, Stanford University School of Medicine, Stanford, CA 94305, USA
| | - German Sumbre
- Institut de Biologie de l'ENS (IBENS), Département de Biologie, École Normale Supérieure, CNRS, INSERM, Université PSL, 75005 Paris, France.
| | - Alex C Keene
- Department of Biology, Texas A&M University, College Station, TX 77843, USA.
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Harvey BM, Baxter M, Granato M. Optic nerve regeneration in larval zebrafish exhibits spontaneous capacity for retinotopic but not tectum specific axon targeting. PLoS One 2019; 14:e0218667. [PMID: 31220164 PMCID: PMC6586344 DOI: 10.1371/journal.pone.0218667] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2018] [Accepted: 06/06/2019] [Indexed: 01/28/2023] Open
Abstract
In contrast to mammals, retinal ganglion cells (RGC) axons of the optic nerve even in mature zebrafish exhibit a remarkable capacity for spontaneous regeneration. One constraint of using adult zebrafish is the limited ability to visualize the regeneration process in live animals. To dynamically visualize and trace the degree of target specific optic nerve regeneration, we took advantage of the optical transparency still preserved in post developmental larval zebrafish. We developed a rapid and robust assay to physically transect the larval optic nerve and find that by 96 hours post injury RGC axons have robustly regrown onto the optic tectum. We observe functional regeneration by 8 days post injury, and demonstrate that similar to adult zebrafish, optic nerve transection in larval zebrafish does not prominently induce cell death or proliferation of RGC neurons. Furthermore, we find that partial optic nerve transection results in axonal growth predominantly to the original, contralateral tectum, while complete transection results in innervation of both the correct contralateral and ‘incorrect’ ipsilateral tectum. Axonal tracing reveals that although regenerating axons innervate the ‘incorrect’ ipsilateral tectum, they successfully target their topographically appropriate synaptic areas. Combined, our results validate post developmental larval zebrafish as a powerful model for optic nerve regeneration, and reveal intricate mechanistic differences between axonal growth, midline guidance and synaptic targeting during zebrafish optic nerve regeneration.
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Affiliation(s)
- Beth M. Harvey
- Department of Cell and Developmental Biology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, United States of America
| | - Melissa Baxter
- Department of Cell and Developmental Biology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, United States of America
| | - Michael Granato
- Department of Cell and Developmental Biology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, United States of America
- * E-mail:
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Samuel A, Rubinstein AM, Azar TT, Ben-Moshe Livne Z, Kim SH, Inbal A. Six3 regulates optic nerve development via multiple mechanisms. Sci Rep 2016; 6:20267. [PMID: 26822689 PMCID: PMC4731751 DOI: 10.1038/srep20267] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2015] [Accepted: 12/30/2015] [Indexed: 12/05/2022] Open
Abstract
Malformations of the optic nerve lead to reduced vision or even blindness. During optic nerve development, retinal ganglion cell (RGC) axons navigate across the retina, exit the eye to the optic stalk (OS), and cross the diencephalon midline at the optic chiasm en route to their brain targets. Many signalling molecules have been implicated in guiding various steps of optic nerve pathfinding, however much less is known about transcription factors regulating this process. Here we show that in zebrafish, reduced function of transcription factor Six3 results in optic nerve hypoplasia and a wide repertoire of RGC axon pathfinding errors. These abnormalities are caused by multiple mechanisms, including abnormal eye and OS patterning and morphogenesis, abnormal expression of signalling molecules both in RGCs and in their environment and anatomical deficiency in the diencephalic preoptic area, where the optic chiasm normally forms. Our findings reveal new roles for Six3 in eye development and are consistent with known phenotypes of reduced SIX3 function in humans. Hence, the new zebrafish model for Six3 loss of function furthers our understanding of the mechanisms governing optic nerve development and Six3-mediated eye and forebrain malformations.
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Affiliation(s)
- Anat Samuel
- Department of Medical Neurobiology, Institute for Medical Research - Israel-Canada, The Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Ariel M. Rubinstein
- Department of Medical Neurobiology, Institute for Medical Research - Israel-Canada, The Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Tehila T. Azar
- Department of Medical Neurobiology, Institute for Medical Research - Israel-Canada, The Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Zohar Ben-Moshe Livne
- Department of Neurobiology, The George S. Wise Faculty of Life Sciences and Sagol School of Neuroscience, Tel Aviv University, Tel Aviv, Israel
| | - Seok-Hyung Kim
- Department of Biological Sciences, Vanderbilt University, Nashville, Tennessee, USA
| | - Adi Inbal
- Department of Medical Neurobiology, Institute for Medical Research - Israel-Canada, The Hebrew University-Hadassah Medical School, Jerusalem, Israel
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5
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Kita EM, Scott EK, Goodhill GJ. Topographic wiring of the retinotectal connection in zebrafish. Dev Neurobiol 2015; 75:542-56. [PMID: 25492632 DOI: 10.1002/dneu.22256] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2014] [Revised: 12/03/2014] [Accepted: 12/08/2014] [Indexed: 11/08/2022]
Abstract
The zebrafish retinotectal projection provides an attractive model system for studying many aspects of topographic map formation and maintenance. Visual connections initially start to form between 3 and 5 days postfertilization, and remain plastic throughout the life of the fish. Zebrafish are easily manipulated surgically, genetically, and chemically, and a variety of molecular tools exist to enable visualization and control of various aspects of map development. Here, we review zebrafish retinotectal map formation, focusing particularly on the detailed structure and dynamics of the connections, the molecules that are important in map creation, and how activity regulates the maintenance of the map.
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Affiliation(s)
- Elizabeth M Kita
- Queensland Brain Institute, The University of Queensland, Brisbane QLD 4072, Australia
| | - Ethan K Scott
- School of Biomedical Sciences, The University of Queensland, Brisbane QLD 4072, Australia
| | - Geoffrey J Goodhill
- Queensland Brain Institute, The University of Queensland, Brisbane QLD 4072, Australia.,School of Mathematics and Physics, The University of Queensland, Brisbane QLD 4072, Australia
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Atkinson-Leadbeater K, McFarlane S. Extrinsic factors as multifunctional regulators of retinal ganglion cell morphogenesis. Dev Neurobiol 2011; 71:1170-85. [DOI: 10.1002/dneu.20924] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
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Barresi MJF, Burton S, Dipietrantonio K, Amsterdam A, Hopkins N, Karlstrom RO. Essential genes for astroglial development and axon pathfinding during zebrafish embryogenesis. Dev Dyn 2011; 239:2603-18. [PMID: 20806318 DOI: 10.1002/dvdy.22393] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The formation of the central nervous system depends on the coordinated development of neural and glial cell types that arise from a common precursor. Using an existing group of zebrafish mutants generated by viral insertion, we performed a "shelf-screen" to identify genes necessary for astroglial development and axon scaffold formation. We screened 274 of 315 viral insertion lines using antibodies that label axons (anti-Acetylated Tubulin) and astroglia (anti-Gfap) and identified 25 mutants with defects in gliogenesis, glial patterning, neurogenesis, and axon guidance. We also identified a novel class of mutants affecting radial glial cell numbers. Defects in astroglial patterning were always associated with axon defects, supporting an important role for axon-glial interactions during axon scaffold development. The genes disrupted in these viral lines have all been identified, providing a powerful new resource for the study of axon guidance, glio- and neurogenesis, and neuron-glial interactions during development of the vertebrate CNS.
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Bergeron SA, Tyurina OV, Miller E, Bagas A, Karlstrom RO. Brother of cdo (umleitung) is cell-autonomously required for Hedgehog-mediated ventral CNS patterning in the zebrafish. Development 2010; 138:75-85. [PMID: 21115611 DOI: 10.1242/dev.057950] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The transmembrane protein Brother of Cdo (Boc) has been implicated in Shh-mediated commissural axon guidance, and can both positively and negatively regulate Hedgehog (Hh) target gene transcription, however, little is known about in vivo requirements for Boc during vertebrate embryogenesis. The zebrafish umleitung (uml(ty54)) mutant was identified by defects in retinotectal axon projections. Here, we show that the uml locus encodes Boc and that Boc function is cell-autonomously required for Hh-mediated neural patterning. Our phenotypic analysis suggests that Boc is required as a positive regulator of Hh signaling in the spinal cord, hypothalamus, pituitary, somites and upper jaw, but that Boc might negatively regulate Hh signals in the lower jaw. This study reveals a role for Boc in ventral CNS cells that receive high levels of Hh and uncovers previously unknown roles for Boc in vertebrate embryogenesis.
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Affiliation(s)
- Sadie A Bergeron
- Department of Biology, University of Massachusetts, Amherst, MA 01003, USA
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Sánchez-Camacho C, Bovolenta P. Autonomous and non-autonomous Shh signalling mediate the in vivo growth and guidance of mouse retinal ganglion cell axons. Development 2008; 135:3531-41. [PMID: 18832395 DOI: 10.1242/dev.023663] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
In non-mammalian vertebrates, the relatively homogeneous population of retinal ganglion cells (RGCs) differentiates and projects entirely to the contralateral side of the brain under the influence of sonic hedgehog (Shh). In mammals, by contrast, there are two different RGC types: the Zic2-positive ipsilateral projecting and the Isl2-positive contralateral projecting. We asked whether the axons of these two populations respond to Shh and if their response differs. We have also analysed whether midline- and RGC-derived Shh contributes to the growth of the axons in the proximal visual pathway. We show that these two RGC types are characterised by a differential expression of Shh signalling components and that they respond differently to Shh when challenged in vitro. In vivo blockade of Shh activity, however, alters the path and distribution mostly of the contralateral projecting RGC axons at the chiasm, indicating that midline-derived Shh participates in funnelling contralateral visual fibres in this region. Furthermore, interference with Shh signalling in the RGCs themselves causes abnormal growth and navigation of contralateral projecting axons in the proximal portion of the pathway, highlighting a novel cell-autonomous mechanism by which Shh can influence growth cone behaviour.
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Affiliation(s)
- Cristina Sánchez-Camacho
- Departamento de Neurobiología Molecular Celular y del Desarrollo, Instituto Cajal, CSIC and CIBER de Enfermedades Raras (CIBERER) 37, Madrid 28002, Spain
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Ott M, Walz BC, Paulsen UJ, Mack AF, Wagner HJ. Retinotectal ganglion cells in the zebrafish, Danio rerio. J Comp Neurol 2007; 501:647-58. [PMID: 17278143 DOI: 10.1002/cne.21269] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
The morphology of retinotectal ganglion cells was investigated by retrograde transport of dextran amines applied into the optic tectum in vitro. Based on criteria such as stratification pattern and size of the dendritic processes, as well as the shape and position of the soma within the dendritic field, three main groups of ganglion cell types with a total of nine different types were identified. The first group included monostratified cells, of which two types (Ma(2) and Mb(5)) may be ON- and OFF-variants, and the third (Mb(6)) had its dendritic field as a narrow band at the inner border of the inner plexiform layer. These three cells had the largest dendritic fields, with areas exceeding 40,000 microm(2). In two additional monostratified cells the dendrites were spread over the entire width of either sublamina a or sublamina b of the inner plexiform layer (Ma, Mb). They were of intermediate size with mean dendritic field areas between 10,000 and 20,000 microm(2). The second group contained two types of bistratified cells (Bb(4/5) and Bb(4,5/5,6)) with two distinct bands of dendritic stratifications in sublamina b. One of them had the smallest dendritic field (below 5,000,mm(2)) of all cell types in the sample. The diffuse cells of the third group had their dendrites across the entire width of the inner plexiform layer. The sample of retinotectal cells investigated in this study included types described previously (Mangrum et al. [2002] Vis Neurosci 19:767-779) but also new types not described previously.
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Affiliation(s)
- Matthias Ott
- Anatomisches Institut, Universität Tübingen, Germany.
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12
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Fuccillo M, Joyner AL, Fishell G. Morphogen to mitogen: the multiple roles of hedgehog signalling in vertebrate neural development. Nat Rev Neurosci 2006; 7:772-83. [PMID: 16988653 DOI: 10.1038/nrn1990] [Citation(s) in RCA: 339] [Impact Index Per Article: 18.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Sonic hedgehog has received an enormous amount of attention since its role as a morphogen that directs ventral patterning in the spinal cord was discovered a decade ago. Since that time, a bewildering array of information has been generated concerning both the components of the hedgehog signalling pathway and the remarkable number of contexts in which it functions. Nowhere is this more evident than in the nervous system, where hedgehog signalling has been implicated in events as disparate as axonal guidance and stem cell maintenance. Here we review our present knowledge of the hedgehog signalling pathway and speculate about areas in which further insights into this versatile pathway might be forthcoming.
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Affiliation(s)
- Marc Fuccillo
- Developmental Genetics Program and the Department of Cell Biology, Skirball Institute of Biomolecular Medicine, New York University Medical Center, 540 First Avenue, New York, NY 10016, USA
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13
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Seth A, Culverwell J, Walkowicz M, Toro S, Rick JM, Neuhauss SCF, Varga ZM, Karlstrom RO. belladonna/(Ihx2) is required for neural patterning and midline axon guidance in the zebrafish forebrain. Development 2006; 133:725-35. [PMID: 16436624 DOI: 10.1242/dev.02244] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Some of the earliest axon pathways to form in the vertebrate forebrain are established as commissural and retinal axons cross the midline of the diencephalon and telencephalon. To better understand axon guidance in the forebrain, we characterized the zebrafish belladonna (bel) mutation, which disrupts commissural and retinal axon guidance in the forebrain. Using a positional cloning strategy, we determined that the bel locus encodes zebrafish Lhx2, a lim-homeodomain transcription factor expressed in the brain, eye and fin buds. We show that bel(Ihx2) function is required for patterning in the ventral forebrain and eye, and that loss of bel function leads to alterations in regulatory gene expression, perturbations in axon guidance factors, and the absence of an optic chiasm and forebrain commissures. Our analysis reveals new roles for Ihx2 in midline axon guidance, forebrain patterning and eye morphogenesis.
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Affiliation(s)
- Anandita Seth
- Biology Department, University of Massachusetts, Amherst, MA 01003-9297, USA
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Muto A, Orger MB, Wehman AM, Smear MC, Kay JN, Page-McCaw PS, Gahtan E, Xiao T, Nevin LM, Gosse NJ, Staub W, Finger-Baier K, Baier H. Forward genetic analysis of visual behavior in zebrafish. PLoS Genet 2005; 1:e66. [PMID: 16311625 PMCID: PMC1287954 DOI: 10.1371/journal.pgen.0010066] [Citation(s) in RCA: 206] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2005] [Accepted: 10/19/2005] [Indexed: 11/19/2022] Open
Abstract
The visual system converts the distribution and wavelengths of photons entering the eye into patterns of neuronal activity, which then drive motor and endocrine behavioral responses. The gene products important for visual processing by a living and behaving vertebrate animal have not been identified in an unbiased fashion. Likewise, the genes that affect development of the nervous system to shape visual function later in life are largely unknown. Here we have set out to close this gap in our understanding by using a forward genetic approach in zebrafish. Moving stimuli evoke two innate reflexes in zebrafish larvae, the optomotor and the optokinetic response, providing two rapid and quantitative tests to assess visual function in wild-type (WT) and mutant animals. These behavioral assays were used in a high-throughput screen, encompassing over half a million fish. In almost 2,000 F2 families mutagenized with ethylnitrosourea, we discovered 53 recessive mutations in 41 genes. These new mutations have generated a broad spectrum of phenotypes, which vary in specificity and severity, but can be placed into only a handful of classes. Developmental phenotypes include complete absence or abnormal morphogenesis of photoreceptors, and deficits in ganglion cell differentiation or axon targeting. Other mutations evidently leave neuronal circuits intact, but disrupt phototransduction, light adaptation, or behavior-specific responses. Almost all of the mutants are morphologically indistinguishable from WT, and many survive to adulthood. Genetic linkage mapping and initial molecular analyses show that our approach was effective in identifying genes with functions specific to the visual system. This collection of zebrafish behavioral mutants provides a novel resource for the study of normal vision and its genetic disorders.
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Affiliation(s)
- Akira Muto
- Department of Physiology, Programs in Neuroscience, Genetics, and Developmental Biology, Center for Human Genetics, University of California, San Francisco, California, United States of America
| | - Michael B Orger
- Department of Physiology, Programs in Neuroscience, Genetics, and Developmental Biology, Center for Human Genetics, University of California, San Francisco, California, United States of America
| | - Ann M Wehman
- Department of Physiology, Programs in Neuroscience, Genetics, and Developmental Biology, Center for Human Genetics, University of California, San Francisco, California, United States of America
| | - Matthew C Smear
- Department of Physiology, Programs in Neuroscience, Genetics, and Developmental Biology, Center for Human Genetics, University of California, San Francisco, California, United States of America
| | - Jeremy N Kay
- Department of Physiology, Programs in Neuroscience, Genetics, and Developmental Biology, Center for Human Genetics, University of California, San Francisco, California, United States of America
| | - Patrick S Page-McCaw
- Department of Physiology, Programs in Neuroscience, Genetics, and Developmental Biology, Center for Human Genetics, University of California, San Francisco, California, United States of America
| | - Ethan Gahtan
- Department of Physiology, Programs in Neuroscience, Genetics, and Developmental Biology, Center for Human Genetics, University of California, San Francisco, California, United States of America
| | - Tong Xiao
- Department of Physiology, Programs in Neuroscience, Genetics, and Developmental Biology, Center for Human Genetics, University of California, San Francisco, California, United States of America
| | - Linda M Nevin
- Department of Physiology, Programs in Neuroscience, Genetics, and Developmental Biology, Center for Human Genetics, University of California, San Francisco, California, United States of America
| | - Nathan J Gosse
- Department of Physiology, Programs in Neuroscience, Genetics, and Developmental Biology, Center for Human Genetics, University of California, San Francisco, California, United States of America
| | - Wendy Staub
- Department of Physiology, Programs in Neuroscience, Genetics, and Developmental Biology, Center for Human Genetics, University of California, San Francisco, California, United States of America
| | - Karin Finger-Baier
- Department of Physiology, Programs in Neuroscience, Genetics, and Developmental Biology, Center for Human Genetics, University of California, San Francisco, California, United States of America
| | - Herwig Baier
- Department of Physiology, Programs in Neuroscience, Genetics, and Developmental Biology, Center for Human Genetics, University of California, San Francisco, California, United States of America
- * To whom correspondence should be addressed. E-mail:
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Stadler JA, Shkumatava A, Neumann CJ. The role of hedgehog signaling in the development of the zebrafish visual system. Dev Neurosci 2005; 26:346-51. [PMID: 15855763 DOI: 10.1159/000082276] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2004] [Accepted: 07/20/2004] [Indexed: 11/19/2022] Open
Abstract
The vertebrate visual system is a region of the nervous system that is characterized by relative simplicity, and its development has hence been studied intensively, to serve as a paradigm for the rest of the central nervous system. The zebrafish model organism offers an impressive array of tools to dissect this process experimentally, and in recent years has helped to significantly deepen our understanding of the development of the visual system. A number of these studies have focused on the role of the Hedgehog family of secreted signaling molecules in eye development, and this is the main topic of this review. Hedgehog signaling plays an important role in all major steps of visual system development, starting with the regionalization of the eye primordium into proximal and distal territories, continuing with the control of cellular differentiation in the retina, and ending with the guidance of axonal projections from the retina to the optic centers of the brain.
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Affiliation(s)
- Jochen A Stadler
- EMBL, Developmental Biology Programme, Meyerhofstrasse 1, DE-69117 Heidelberg, Germany
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Barresi MJF, Hutson LD, Chien CB, Karlstrom RO. Hedgehog regulated Slit expression determines commissure and glial cell position in the zebrafish forebrain. Development 2005; 132:3643-56. [PMID: 16033800 DOI: 10.1242/dev.01929] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Three major axon pathways cross the midline of the vertebrate forebrain early in embryonic development: the postoptic commissure (POC), the anterior commissure (AC) and the optic nerve. We show that a small population of Gfap+ astroglia spans the midline of the zebrafish forebrain in the position of, and prior to, commissural and retinal axon crossing. These glial ;bridges' form in regions devoid of the guidance molecules slit2 and slit3, although a subset of these glial cells express slit1a. We show that Hh signaling is required for commissure formation, glial bridge formation, and the restricted expression of the guidance molecules slit1a, slit2, slit3 and sema3d, but that Hh does not appear to play a direct role in commissural and retinal axon guidance. Reducing Slit2 and/or Slit3 function expanded the glial bridges and caused defasciculation of the POC, consistent with a ;channeling' role for these repellent molecules. By contrast, reducing Slit1a function led to reduced midline axon crossing, suggesting a distinct role for Slit1a in midline axon guidance. Blocking Slit2 and Slit3, but not Slit1a, function in the Hh pathway mutant yot (gli2DR) dramatically rescued POC axon crossing and glial bridge formation at the midline, indicating that expanded Slit2 and Slit3 repellent function is largely responsible for the lack of midline crossing in these mutants. This analysis shows that Hh signaling helps to pattern the expression of Slit guidance molecules that then help to regulate glial cell position and axon guidance across the midline of the forebrain.
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Xiao T, Roeser T, Staub W, Baier H. A GFP-based genetic screen reveals mutations that disrupt the architecture of the zebrafish retinotectal projection. Development 2005; 132:2955-67. [PMID: 15930106 DOI: 10.1242/dev.01861] [Citation(s) in RCA: 239] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The retinotectal projection is a premier model system for the investigation of molecular mechanisms that underlie axon pathfinding and map formation. Other important features, such as the laminar targeting of retinal axons, the control of axon fasciculation and the intrinsic organization of the tectal neuropil, have been less accessible to investigation. In order to visualize these processes in vivo, we generated a transgenic zebrafish line expressing membrane-targeted GFP under control of the brn3c promoter/enhancer. The GFP reporter labels a distinct subset of retinal ganglion cells (RGCs), which project mainly into one of the four retinorecipient layers of the tectum and into a small subset of the extratectal arborization fields. In this transgenic line, we carried out an ENU-mutagenesis screen by scoring live zebrafish larvae for anatomical phenotypes. Thirteen recessive mutations in 12 genes were discovered. In one mutant, ddl, the majority of RGCs fail to differentiate. Three of the mutations, vrt, late and tard, delay the orderly ingrowth of retinal axons into the tectum. Two alleles of drg disrupt the layer-specific targeting of retinal axons. Three genes, fuzz, beyo and brek, are required for confinement of the tectal neuropil. Fasciculation within the optic tract and adhesion within the tectal neuropil are regulated by vrt, coma, bluk, clew and blin. The mutated genes are predicted to encode molecules essential for building the intricate neural architecture of the visual system.
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Affiliation(s)
- Tong Xiao
- Department of Physiology, University of California, San Francisco, Programs in Neuroscience, Genetics, Human Genetics, and Developmental Biology, 1550 4th Street, San Francisco, CA 94158-2722, USA
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Gahtan E, Baier H. Of lasers, mutants, and see-through brains: functional neuroanatomy in zebrafish. ACTA ACUST UNITED AC 2004; 59:147-61. [PMID: 15007833 DOI: 10.1002/neu.20000] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Behavioral functions are carried out by localized circuits in the brain. Although this modular principle is clearly established, the boundaries of modules, and sometimes even their existence, are still debated. Zebrafish might offer distinct advantages in localizing behaviors to discrete brain regions because of the ability to visualize, record from, and lesion precisely identified populations of neurons in the brain. In addition, genetic screens in zebrafish enable the isolation of mutations that disrupt neural pathways and/or behaviors, as an alternative lesioning technique with complementary strengths to laser ablations. For example, the Mauthner cell, a large identified neuron in the hindbrain, has been postulated to be both necessary and sufficient for the execution of escapes. We discuss in this review how experiments, using laser ablations, calcium imaging, and mutants have eroded this notion. Even in a simple behavior, such as escape, many parallel pathways appear to be involved with no single one being absolutely necessary. Lesion studies and the analysis of behavioral mutants are now also beginning to elucidate the functional architecture of the zebrafish visual system. Although still in an embryonic stage, the neuroanatomy of behaviors in zebrafish has a bright future.
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Affiliation(s)
- Ethan Gahtan
- UCSF Department of Physiology, Program in Neuroscience, 513 Parnassus Avenue, Room S-762, San Francisco, California 94143-0444, USA
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Affiliation(s)
- Lara D Hutson
- Department of Biology, Williams College, Williamstown, Massachusetts 01267, USA
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