151
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Vanderlaan G, Tyurina OV, Karlstrom RO, Chandrasekhar A. Gli function is essential for motor neuron induction in zebrafish. Dev Biol 2005; 282:550-70. [PMID: 15890329 PMCID: PMC2219918 DOI: 10.1016/j.ydbio.2005.04.010] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2004] [Revised: 04/08/2005] [Accepted: 04/08/2005] [Indexed: 12/30/2022]
Abstract
The Gli family of zinc-finger transcription factors mediates Hedgehog (Hh) signaling in all vertebrates. However, their roles in ventral neural tube patterning, in particular motor neuron induction, appear to have diverged across species. For instance, cranial motor neurons are essentially lost in zebrafish detour (gli1(-)) mutants, whereas motor neuron development is unaffected in mouse single gli and some double gli knockouts. Interestingly, the expression of some Hh-regulated genes (ptc1, net1a, gli1) is mostly unaffected in the detour mutant hindbrain, suggesting that other Gli transcriptional activators may be involved. To better define the roles of the zebrafish gli genes in motor neuron induction and in Hh-regulated gene expression, we examined these processes in you-too (yot) mutants, which encode dominant repressor forms of Gli2 (Gli2(DR)), and following morpholino-mediated knockdown of gli1, gli2, and gli3 function. Motor neuron induction at all axial levels was reduced in yot (gli2(DR)) mutant embryos. In addition, Hh target gene expression at all axial levels except in rhombomere 4 was also reduced, suggesting an interference with the function of other Glis. Indeed, morpholino-mediated knockdown of Gli2(DR) protein in yot mutants led to a suppression of the defective motor neuron phenotype. However, gli2 knockdown in wild-type embryos generated no discernable motor neuron phenotype, while gli3 knockdown reduced motor neuron induction in the hindbrain and spinal cord. Significantly, gli2 or gli3 knockdown in detour (gli1(-)) mutants revealed roles for Gli2 and Gli3 activator functions in ptc1 expression and spinal motor neuron induction. Similarly, gli1 or gli3 knockdown in yot (gli2(DR)) mutants resulted in severe or complete loss of motor neurons, and of ptc1 and net1a expression, in the hindbrain and spinal cord. In addition, gli1 expression was greatly reduced in yot mutants following gli3, but not gli1, knockdown, suggesting that Gli3 activator function is specifically required for gli1 expression. These observations demonstrate that Gli activator function (encoded by gli1, gli2, and gli3) is essential for motor neuron induction and Hh-regulated gene expression in zebrafish.
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Affiliation(s)
- Gary Vanderlaan
- Division of Biological Sciences, University of Missouri, Columbia, MO 65211, USA
- Molecular Biology Program, University of Missouri, Columbia, MO 65211, USA
| | - Oksana V. Tyurina
- Department of Biology, University of Massachusetts, Amherst, MA 01003, USA
| | - Rolf O. Karlstrom
- Department of Biology, University of Massachusetts, Amherst, MA 01003, USA
| | - Anand Chandrasekhar
- Division of Biological Sciences, University of Missouri, Columbia, MO 65211, USA
- Molecular Biology Program, University of Missouri, Columbia, MO 65211, USA
- Interdisciplinary Neuroscience Program, University of Missouri, Columbia, MO 65211, USA
- Genetics Area Program, University of Missouri, Columbia, MO 65211, USA
- * Corresponding author. Division of Biological Sciences, Room 205 Lefevre Hall, University of Missouri, Columbia, MO 65211, USA. Fax: +1 573 884 5020. E-mail address: (A. Chandrasekhar)
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152
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Zilinski CA, Shah R, Lane ME, Jamrich M. Modulation of zebrafish pitx3 expression in the primordia of the pituitary, lens, olfactory epithelium and cranial ganglia by hedgehog and nodal signaling. Genesis 2005; 41:33-40. [PMID: 15645439 DOI: 10.1002/gene.20094] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
In this article we report the isolation of a novel zebrafish gene, pitx3, which plays an important role in the formation of several placode-derived structures. In wildtype embryos, pitx3 is first expressed in a crescent-shaped area in the anterior end of the embryo. At later stages, the primordia of the anterior pituitary, the lens, the olfactory sensory epithelium, and cranial ganglia express this gene. Pitx3 is not expressed in the more posterior preplacodal region that gives rise to the epibranchial, otic, and lateral line placodes. The dynamics of pitx3 in the anterior region of wildtype embryos suggests that pitx3 expression marks a common step in the formation of the pituitary, lens, olfactory placode as well as the trigeminal placode. Analysis of pitx3 expression in mutants lacking the hedgehog or nodal function demonstrates the differential dependence of pitx3 expression in these structures on nodal and hedgehog signaling. While the lens and trigeminal placodes express pitx3 in the absence of hedgehog and nodal signaling, there is no expression of pitx3 in the anteriormost ectoderm adjacent to the neural plate from which the anterior pituitary would derive. In mutants with impaired hedgehog signaling, the lens placode frequently extends into more anterior ventral regions of the embryo.
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MESH Headings
- Amino Acid Motifs
- Amino Acid Sequence
- Animals
- Embryo, Nonmammalian
- Embryonic Development
- Ganglia/cytology
- Ganglia/embryology
- Ganglia/metabolism
- Gene Expression Regulation, Developmental
- Head
- Hedgehog Proteins
- Homeodomain Proteins/chemistry
- Homeodomain Proteins/metabolism
- In Situ Hybridization
- Lens, Crystalline/cytology
- Lens, Crystalline/embryology
- Lens, Crystalline/metabolism
- Molecular Sequence Data
- Morphogenesis
- Mutation
- Nodal Protein
- Olfactory Mucosa/cytology
- Olfactory Mucosa/embryology
- Olfactory Mucosa/metabolism
- Phylogeny
- Pituitary Gland, Anterior/cytology
- Pituitary Gland, Anterior/embryology
- Pituitary Gland, Anterior/metabolism
- Protein Structure, Tertiary
- Sequence Homology, Amino Acid
- Trans-Activators/genetics
- Trans-Activators/metabolism
- Transforming Growth Factor beta/genetics
- Transforming Growth Factor beta/metabolism
- Zebrafish/embryology
- Zebrafish/metabolism
- Zebrafish Proteins/chemistry
- Zebrafish Proteins/metabolism
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Affiliation(s)
- Carolyn A Zilinski
- Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, Texas 77030, USA
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153
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Stevens CB, Halloran MC. Developmental expression of sema3G, a novel zebrafish semaphorin. Gene Expr Patterns 2005; 5:647-53. [PMID: 15939377 DOI: 10.1016/j.modgep.2005.02.009] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2005] [Revised: 02/27/2005] [Accepted: 02/28/2005] [Indexed: 11/29/2022]
Abstract
The semaphorins are a large, evolutionarily conserved family of signaling molecules with broad functions during development. The class 3 semaphorins are a subclass of secreted semaphorins found in vertebrates. There have been six class 3 semaphorins identified to date (sema3A to sema3F) and some have been shown to function in axon guidance and cardiovascular development. However, the functions of many class 3 semaphorins and their potential interactions in vivo are still not well understood. As a step toward understanding the actions of all class 3 semaphorins in vivo, we have cloned and analyzed the developmental expression pattern of a novel zebrafish class 3 semaphorin, sema3H [corrected] sema3H [corrected] is expressed in a dynamic pattern throughout the first 3 days of development. It is expressed in the adaxial cells of the somite during somitogenesis. In the brain, sema3H [corrected] is expressed in cell clusters in the midbrain and diencephalon, and is expressed in the telencephalon in close proximity to the olfactory epithelium. sema3H [corrected] also is expressed in the pharyngeal arches, the pectoral fin bud, and the developing pronephros. These results provide a basis for studying how expression of multiple semaphorins could be essential for aspects of early development.
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Affiliation(s)
- Craig B Stevens
- Department of Zoology, University of Wisconsin, Madison, 53706, USA
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154
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Ingham PW, Kim HR. Hedgehog signalling and the specification of muscle cell identity in the Zebrafish embryo. Exp Cell Res 2005; 306:336-42. [PMID: 15925589 DOI: 10.1016/j.yexcr.2005.03.019] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2005] [Revised: 03/01/2005] [Accepted: 03/14/2005] [Indexed: 11/29/2022]
Abstract
Signalling by members of the Hedgehog family of secreted proteins plays a central role in the development of many animal species. In the zebrafish embryo, the specification of myoblast fates is controlled by Hedgehog signals emanating from axial midline structures. Distinct muscle cell identities are induced by varying levels of signalling activity. The SET domain transcription factor, Blimp1, is a key target of Hedgehog signalling in this process.
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Affiliation(s)
- Phillip W Ingham
- Centre for Developmental and Biomedical Genetics, University of Sheffield, Firth Court, Western Bank, Sheffield, S10 2TN, UK.
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155
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Birely J, Schneider VA, Santana E, Dosch R, Wagner DS, Mullins MC, Granato M. Genetic screens for genes controlling motor nerve-muscle development and interactions. Dev Biol 2005; 280:162-76. [PMID: 15766756 DOI: 10.1016/j.ydbio.2005.01.012] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2004] [Revised: 01/10/2005] [Accepted: 01/12/2005] [Indexed: 11/16/2022]
Abstract
Motor growth cones navigate long and complex trajectories to connect with their muscle targets. Experimental studies have shown that this guidance process critically depends on extrinsic cues. In the zebrafish embryo, a subset of mesodermal cells, the adaxial cells, delineates the prospective path of pioneering motor growth cones. Genetic ablation of adaxial cells causes profound pathfinding defects, suggesting the existence of adaxial cell derived guidance factors. Intriguingly, adaxial cells are themselves migratory, and as growth cones approach they migrate away from the prospective axonal path to the lateral surface of the myotome, where they develop into slow-twitching muscle fibers. Genetic screens in embryos stained with an antibody cocktail identified mutants with specific defects in differentiation and migration of adaxial cells/slow muscle fibers, as well as mutants with specific defects in axonal pathfinding, including exit from the spinal cord and pathway selection. Together, the genes underlying these mutant phenotypes define pathways essential for nerve and muscle development and interactions between these two cell types.
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Affiliation(s)
- Joanne Birely
- Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6058, USA
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156
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Cheesman SE, Eisen JS. gsh1 demarcates hypothalamus and intermediate spinal cord in zebrafish. Gene Expr Patterns 2005; 5:107-12. [PMID: 15533825 DOI: 10.1016/j.modgep.2004.05.006] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2003] [Revised: 04/22/2004] [Accepted: 05/24/2004] [Indexed: 11/24/2022]
Abstract
We have cloned and characterized the expression of zebrafish genetic screen homeobox 1 (gsh1). Early expression is confined to hindbrain rhombomeres; by mid-somitogenesis gsh1 is expressed in precise domains within the mesencephalon and diencephalon, as well as in intermediate spinal cord. Double-label experiments revealed that the diencephalic domain is coincident with hypothalamus and that spinal cord expression is in a region that generates interneurons. These data suggest gsh1 may play a role in patterning cell types generated in these domains.
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Affiliation(s)
- Sarah E Cheesman
- Institute of Neuroscience, 1254 University of Oregon, Eugene, OR 97403-1254, USA.
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157
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Nixon SJ, Wegner J, Ferguson C, Méry PF, Hancock JF, Currie PD, Key B, Westerfield M, Parton RG. Zebrafish as a model for caveolin-associated muscle disease; caveolin-3 is required for myofibril organization and muscle cell patterning. Hum Mol Genet 2005; 14:1727-43. [PMID: 15888488 DOI: 10.1093/hmg/ddi179] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Caveolae are an abundant feature of many animal cells. However, the exact function of caveolae remains unclear. We have used the zebrafish, Danio rerio, as a system to understand caveolae function focusing on the muscle-specific caveolar protein, caveolin-3 (Cav3). We have identified caveolin-1 (alpha and beta), caveolin-2 and Cav3 in the zebrafish. Zebrafish Cav3 has 72% identity to human CAV3, and the amino acids altered in human muscle diseases are conserved in the zebrafish protein. During embryonic development, cav3 expression is apparent by early segmentation stages in the first differentiating muscle precursors, the adaxial cells and slightly later in the notochord. cav3 expression appears in the somites during mid-segmentation stages and then later in the pectoral fins and facial muscles. Cav3 and caveolae are located along the entire sarcolemma of late stage embryonic muscle fibers, whereas beta-dystroglycan is restricted to the muscle fiber ends. Down-regulation of Cav3 expression causes gross muscle abnormalities and uncoordinated movement. Ultrastructural analysis of isolated muscle fibers reveals defects in myoblast fusion and disorganized myofibril and membrane systems. Expression of the zebrafish equivalent to a human muscular dystrophy mutant, CAV3P104L, causes severe disruption of muscle differentiation. In addition, knockdown of Cav3 resulted in a dramatic up-regulation of eng1a expression resulting in an increase in the number of muscle pioneer-like cells adjacent to the notochord. These studies provide new insights into the role of Cav3 in muscle development and demonstrate its requirement for correct intracellular organization and myoblast fusion.
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Affiliation(s)
- Susan J Nixon
- Institute for Molecular Bioscience, Universitky of Queensland, Brisbane 4072, Australia
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158
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Scott A, Stemple DL. Zebrafish notochordal basement membrane: signaling and structure. Curr Top Dev Biol 2005; 65:229-53. [PMID: 15642386 DOI: 10.1016/s0070-2153(04)65009-5] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Affiliation(s)
- Annabelle Scott
- Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge CB10 1SA, United Kingdom
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159
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Tyurina OV, Guner B, Popova E, Feng J, Schier AF, Kohtz JD, Karlstrom RO. Zebrafish Gli3 functions as both an activator and a repressor in Hedgehog signaling. Dev Biol 2005; 277:537-56. [PMID: 15617692 DOI: 10.1016/j.ydbio.2004.10.003] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2004] [Revised: 09/13/2004] [Accepted: 10/07/2004] [Indexed: 01/11/2023]
Abstract
Hedgehog (Hh) signaling regulates cell differentiation and patterning in a wide variety of embryonic tissues. In vertebrates, at least three Gli transcription factors (Gli1, Gli2, and Gli3) are involved in Hh signal transduction. Comparative studies have revealed divergent requirements for Gli1 and Gli2 in zebrafish and mouse. Here, we address the question of whether Gli3 function has also diverged in zebrafish and analyze the regulatory interactions between Hh signaling and Gli activity. We find that zebrafish Gli3 has an early function as an activator of Hh target genes that overlaps with Gli1 activator function in the ventral neural tube. In vitro reporter analysis shows that Gli3 cooperates with Gli1 to activate transcription in the presence of high concentrations of Hh. During late somitogenesis stages, Gli3 is required as a repressor of the Hh response. Gli3 shares this repressor activity with Gli2 in the dorsal spinal cord, hindbrain, and midbrain, but not in the forebrain. Consistently, zebrafish Gli3 blocks Gli1-mediated activation of a reporter gene in the absence of Hh in vitro. In the eye, Gli3 is also required for proper ath5 expression and the differentiation of retinal ganglion cells (RGCs). These results reveal a conserved role for Gli3 in vertebrate development and uncover novel regional functions and regulatory interactions among gli genes.
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Affiliation(s)
- Oksana V Tyurina
- Department of Biology, University of Massachusetts, Amherst, MA 01003-9297, USA
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160
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Shindo N, Sakai A, Arai D, Matsuoka O, Yamasaki Y, Higashinakagawa T. The ESC-E(Z) complex participates in the hedgehog signaling pathway. Biochem Biophys Res Commun 2005; 327:1179-87. [PMID: 15652519 DOI: 10.1016/j.bbrc.2004.12.125] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2004] [Indexed: 11/22/2022]
Abstract
Polycomb group (PcG) genes are required for stable inheritance of epigenetic states throughout development, a phenomenon termed cellular memory. In Drosophila and mice, the product of the E(z) gene, one of the PcG genes, constitutes the ESC-E(Z) complex and specifically methylates histone H3. It has been argued that this methylation sets the stage for appropriate repression of certain genes. Here, we report the isolation of a well-conserved homolog of E(z), olezh2, in medaka. Hypomorphic knock-down of olezh2 resulted in a cyclopia phenotype and markedly perturbed hedgehog signaling, consistent with our previous report on oleed, a medaka esc. We also found cyclopia in embryos treated with trichostatin A, an inhibitor of histone deacetylase, which is a transient component of the ESC-E(Z) complex. The level of tri-methylation at lysine 27 of histone H3 was substantially decreased in both olezh2 and oleed knock-down embryos, and in embryos with hedgehog signaling perturbed by forskolin. We conclude that the ESC-E(Z) complex per se participates in hedgehog signaling.
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Affiliation(s)
- Norihisa Shindo
- Department of Biology, Faculty of Education and Integrated Arts and Sciences, Major in Integrated Bioscience and Biomedical Engineering, Graduate School of Science and Engineering, Waseda University, 1-6-1 Nishi-Waseda, Shinjuku-ku, Tokyo 169-8050, Japan
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161
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Gering M, Patient R. Hedgehog Signaling Is Required for Adult Blood Stem Cell Formation in Zebrafish Embryos. Dev Cell 2005; 8:389-400. [PMID: 15737934 DOI: 10.1016/j.devcel.2005.01.010] [Citation(s) in RCA: 249] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2004] [Revised: 11/25/2004] [Accepted: 01/04/2005] [Indexed: 11/19/2022]
Abstract
Studies with embryonic explants and embryonic stem cells have suggested a role for Hedgehog (Hh) signaling in hematopoiesis. However, targeted deletion of Hh pathway components in the mouse has so far failed to provide in vivo evidence. Here we show that zebrafish embryos mutant in the Hh pathway or treated with the Hh signaling inhibitor cyclopamine display defects in adult hematopoietic stem cell (HSC) formation but not in primitive hematopoiesis. Hh is required in the trunk at three consecutive stages during vascular development: for the medial migration of endothelial progenitors of the dorsal aorta (DA), for arterial gene expression, and for the formation of intersomitic vessel sprouts. Interference with Hh signaling during the first two stages also interferes with HSC formation. Furthermore, HSC and DA formation also share Vegf and Notch requirements, which further distinguishes them from primitive hematopoiesis and underlines their close relationship during vertebrate development.
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Affiliation(s)
- Martin Gering
- Institute of Genetics, University of Nottingham, Queen's Medical Centre, Nottingham, NG7 2UH, United Kingdom
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162
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Kitagawa D, Watanabe T, Saito K, Asaka S, Sasado T, Morinaga C, Suwa H, Niwa K, Yasuoka A, Deguchi T, Yoda H, Hirose Y, Henrich T, Iwanami N, Kunimatsu S, Osakada M, Winkler C, Elmasri H, Wittbrodt J, Loosli F, Quiring R, Carl M, Grabher C, Winkler S, Del Bene F, Momoi A, Katada T, Nishina H, Kondoh H, Furutani-Seiki M. Genetic dissection of the formation of the forebrain in Medaka, Oryzias latipes. Mech Dev 2005; 121:673-85. [PMID: 15210176 DOI: 10.1016/j.mod.2004.03.010] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2004] [Revised: 03/16/2004] [Accepted: 03/18/2004] [Indexed: 01/12/2023]
Abstract
The forebrain, consisting of the telencephalon and diencephalon, is essential for processing sensory information. To genetically dissect formation of the forebrain in vertebrates, we carried out a systematic screen for mutations affecting morphogenesis of the forebrain in Medaka. Thirty-three mutations defining 25 genes affecting the morphological development of the forebrain were grouped into two classes. Class 1 mutants commonly showing a decrease in forebrain size, were further divided into subclasses 1A to 1D. Class 1A mutation (1 gene) caused an early defect evidenced by the lack of bf1 expression, Class 1B mutations (6 genes) patterning defects revealed by the aberrant expression of regional marker genes, Class 1C mutation (1 gene) a defect in a later stage, and Class 1D (3 genes) a midline defect analogous to the zebrafish one-eyed pinhead mutation. Class 2 mutations caused morphological abnormalities in the forebrain without considerably affecting its size, Class 2A mutations (6 genes) caused abnormalities in the development of the ventricle, Class 2B mutations (2 genes) severely affected the anterior commissure, and Class 2C (6 genes) mutations resulted in a unique forebrain morphology. Many of these mutants showed the compromised sonic hedgehog expression in the zona-limitans-intrathalamica (zli), arguing for the importance of this structure as a secondary signaling center. These mutants should provide important clues to the elucidation of the molecular mechanisms underlying forebrain development, and shed new light on phylogenically conserved and divergent functions in the developmental process.
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Affiliation(s)
- Daiju Kitagawa
- Department of Physiological Chemistry, Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo 113-0033, Japan
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163
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Chen W, Ren XR, Nelson CD, Barak LS, Chen JK, Beachy PA, de Sauvage F, Lefkowitz RJ. Activity-dependent internalization of smoothened mediated by beta-arrestin 2 and GRK2. Science 2005; 306:2257-60. [PMID: 15618519 DOI: 10.1126/science.1104135] [Citation(s) in RCA: 225] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Binding of Sonic Hedgehog (Shh) to Patched (Ptc) relieves the latter's tonic inhibition of Smoothened (Smo), a receptor that spans the cell membrane seven times. This initiates signaling which, by unknown mechanisms, regulates vertebrate developmental processes. We find that two molecules interact with mammalian Smo in an activation-dependent manner: G protein-coupled receptor kinase 2 (GRK2) leads to phosphorylation of Smo, and beta-arrestin 2 fused to green fluorescent protein interacts with Smo. These two processes promote endocytosis of Smo in clathrin-coated pits. Ptc inhibits association of beta-arrestin 2 with Smo, and this inhibition is relieved in cells treated with Shh. A Smo agonist stimulated and a Smo antagonist (cyclopamine) inhibited both phosphorylation of Smo by GRK2 and interaction of beta-arrestin 2 with Smo. beta-Arrestin 2 and GRK2 are thus potential mediators of signaling by activated Smo.
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Affiliation(s)
- Wei Chen
- Department of Medicine, Duke University Medical Center, Durham, NC 27710, USA.
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164
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Wilbanks AM, Fralish GB, Kirby ML, Barak LS, Li YX, Caron MG. Beta-arrestin 2 regulates zebrafish development through the hedgehog signaling pathway. Science 2005; 306:2264-7. [PMID: 15618520 DOI: 10.1126/science.1104193] [Citation(s) in RCA: 97] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
beta-arrestins are multifunctional proteins that act as scaffolds and transducers of intracellular signals from heptahelical transmembrane-spanning receptors (7TMR). Hedgehog (Hh) signaling, which uses the putative 7TMR, Smoothened, is established as a fundamental pathway in development, and unregulated Hh signaling is associated with certain malignancies. Here, we show that the functional knockdown of beta-arrestin 2 in zebrafish embryos recapitulates the many phenotypes of Hh pathway mutants. Expression of wild-type beta-arrestin 2, or constitutive activation of the Hh pathway downstream of Smoothened, rescues the phenotypes caused by beta-arrestin 2 deficiency. These results suggest that a functional interaction between beta-arrestin 2 and Smoothened may be critical to regulate Hh signaling in zebrafish development.
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Affiliation(s)
- Alyson M Wilbanks
- Department of Cell Biology, Center for Models of Human Disease, Institute for Genome Science and Policy, Duke University Medical Center, Durham, NC 27710, USA
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165
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Henry CA, Amacher SL. Zebrafish slow muscle cell migration induces a wave of fast muscle morphogenesis. Dev Cell 2005; 7:917-23. [PMID: 15572133 DOI: 10.1016/j.devcel.2004.09.017] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2004] [Revised: 08/25/2004] [Accepted: 09/23/2004] [Indexed: 11/25/2022]
Abstract
The specification and morphogenesis of slow and fast twitch muscle fibers are crucial for muscle development. In zebrafish, Hedgehog is required for slow muscle fiber specification. However, less is known about signals that promote development of fast muscle fibers, which constitute the majority of somitic cells. We show that when Hedgehog signaling is blocked, fast muscle cell elongation is disrupted. Using genetic mosaics, we show that Hedgehog signal perception is required by slow muscle cells but not by fast muscle cells for fast muscle cell elongation. Furthermore, we show that slow muscle cells are sufficient to pattern the medial to lateral wave of fast muscle fiber morphogenesis even when fast muscle cells cannot perceive the Hedgehog signal. Thus, the medial to lateral migration of slow muscle fibers through the somite creates a morphogenetic signal that patterns fast muscle fiber elongation in its wake.
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Affiliation(s)
- Clarissa A Henry
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720 USA
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166
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Jin H, Xu J, Qian F, Du L, Tan CY, Lin Z, Peng J, Wen Z. The 5′ zebrafishscl promoter targets transcription to the brain, spinal cord, and hematopoietic and endothelial progenitors. Dev Dyn 2005; 235:60-7. [PMID: 16258937 DOI: 10.1002/dvdy.20613] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
The stem cell leukemia (SCL) gene encodes a basic helix-loop-helix transcription factor and is essential for embryonic angiogenesis, hematopoietic stem cell specification, and erythrocyte maturation. Here, we report the isolation and characterization of the zebrafish scl promoter. We show that a 5-kilobase (kb) genomic fragment immediately upstream of the translation start site is capable of targeting the enhanced green fluorescence protein (EGFP) expression to the anterior and posterior lateral mesoderm where the endogenous scl normally expresses. Detailed analysis of the stable transgenic fish reveals that this 5-kb upstream sequence is sufficient to direct the EGFP transcription to the brain, spinal cord, and hematopoietic-endothelial progenitors, possibly the hemangioblast, but not primitive erythrocyte, suggesting that the zebrafish scl transcription in hematopoietic-endothelial progenitors and erythrocyte is regulated by distinct cis element(s). Our study has defined the cis regulatory element(s) for zebrafish scl expression in the brain, spinal cord, and hematopoietic-endothelial progenitors and established a valuable transgenic line Tg(5'5kbscl:EGFP) for studying hematopoietic lineage development.
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Affiliation(s)
- Hao Jin
- Laboratory of Molecular and Developmental Immunology, Institute of Molecular and Cell Biology, Proteos, Singapore
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167
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Hirsinger E, Stellabotte F, Devoto SH, Westerfield M. Hedgehog signaling is required for commitment but not initial induction of slow muscle precursors. Dev Biol 2004; 275:143-57. [PMID: 15464578 DOI: 10.1016/j.ydbio.2004.07.030] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2004] [Revised: 07/22/2004] [Accepted: 07/26/2004] [Indexed: 11/19/2022]
Abstract
In zebrafish, skeletal muscle precursors can adopt at least three distinct fates: fast, non-pioneer slow, or pioneer slow muscle fibers. Slow muscle fibers develop from adaxial cells and depend on Hedgehog signaling. We analyzed when precursors become committed to their fates and the step(s) along their differentiation pathway affected by Hedgehog. Unexpectedly, we find that embryos deficient in Hedgehog signaling still contain postmitotic adaxial cells that differentiate into fast muscle fibers instead of slow. We show that by the onset of gastrulation, slow and fast muscle precursors are already spatially segregated but uncommitted to their fates until much later, in the segmental plate when slow precursors become independent of Hedgehog. In contrast, pioneer and non-pioneer slow muscle precursors share a common lineage from the onset of gastrulation. Our results demonstrate that slow muscle precursors form independently of Hedgehog signaling and further provide direct evidence for a multipotent muscle precursor population whose commitment to the slow fate depends on Hedgehog at a late stage of development when postmitotic adaxial cells differentiate into slow muscle fibers.
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Affiliation(s)
- Estelle Hirsinger
- Institute of Neuroscience, University of Oregon, Eugene, OR 97403-1254, USA
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168
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Pinheiro P, Gering M, Patient R. The basic helix-loop-helix transcription factor, Tal2, marks the lateral floor plate of the spinal cord in zebrafish. Gene Expr Patterns 2004; 4:85-92. [PMID: 14678833 DOI: 10.1016/s1567-133x(03)00145-5] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Basic helix-loop-helix (bHLH) transcription factors play key roles in the development of the central nervous system. Here we report the isolation of a zebrafish gene that encodes a homologue of the mammalian bHLH transcription factor, Tal2. In zebrafish embryos, tal2, like its mammalian homologue, is strongly expressed in the diencephalon and the mesencephalon, with the latter expression located in post-mitotic cells of the tectum. However, in addition to this conserved brain expression, we also detect expression in the floor plate of the spinal cord. By the location of this expression relative to other genes expressed in the floor plate and by analysing expression in a selection of midline mutants, we reveal that tal2 is expressed within the lateral floor plate as opposed to the medial floor plate, and also in more dorsal cells which are distinct from motorneurons and depend on either sonic hedgehog signalling or a signal coming from the lateral floor plate. This is to our knowledge the first report of a gene expressed specifically in lateral cells of the floor plate in the spinal cord.
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Affiliation(s)
- Philip Pinheiro
- Institute of Genetics, Queens Medical Centre, University of Nottingham, Nottingham NG7 2UH, UK
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169
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López-Schier H, Starr CJ, Kappler JA, Kollmar R, Hudspeth AJ. Directional cell migration establishes the axes of planar polarity in the posterior lateral-line organ of the zebrafish. Dev Cell 2004; 7:401-12. [PMID: 15363414 DOI: 10.1016/j.devcel.2004.07.018] [Citation(s) in RCA: 112] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2004] [Revised: 06/30/2004] [Accepted: 07/06/2004] [Indexed: 10/26/2022]
Abstract
The proper orientation of mechanosensory hair cells along the lateral-line organ of a fish or amphibian is essential for the animal's ability to sense directional water movements. Within the sensory epithelium, hair cells are polarized in a stereotyped manner, but the mechanisms that control their alignment relative to the body axes are unknown. We have found, however, that neuromasts can be oriented either parallel or perpendicular to the anteroposterior body axis. By characterizing the strauss mutant zebrafish line and by tracking labeled cells, we have demonstrated that neuromasts of these two orientations originate from, respectively, the first and second primordia. Furthermore, altering the migratory pathway of a primordium reorients a neuromast's axis of planar polarity. We propose that the global orientation of hair cells relative to the body axes is established through an interaction between directional movement by primordial cells and the timing of neuromast maturation.
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Affiliation(s)
- Hernán López-Schier
- Laboratory of Sensory Neuroscience, The Rockefeller University, 1230 York Avenue, New York, NY 10021, USA
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170
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Teraoka H, Russell C, Regan J, Chandrasekhar A, Concha ML, Yokoyama R, Higashi K, Take-Uchi M, Dong W, Hiraga T, Holder N, Wilson SW. Hedgehog and Fgf signaling pathways regulate the development of tphR-expressing serotonergic raphe neurons in zebrafish embryos. ACTA ACUST UNITED AC 2004; 60:275-88. [PMID: 15281067 PMCID: PMC2789256 DOI: 10.1002/neu.20023] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Serotonin (5HT) plays major roles in the physiological regulation of many behavioral processes, including sleep, feeding, and mood, but the genetic mechanisms by which serotonergic neurons arise during development are poorly understood. In the present study, we have investigated the development of serotonergic neurons in the zebrafish. Neurons exhibiting 5HT-immunoreactivity (5HT-IR) are detected from 45 h postfertilization (hpf) in the ventral hindbrain raphe, the hypothalamus, pineal organ, and pretectal area. Tryptophan hydroxylases encode rate-limiting enzymes that function in the synthesis of 5HT. As part of this study, we cloned and analyzed a novel zebrafish tph gene named tphR. Unlike two other zebrafish tph genes (tphD1 and tphD2), tphR is expressed in serotonergic raphe neurons, similar to tph genes in mammalian species. tphR is also expressed in the pineal organ where it is likely to be involved in the pathway leading to synthesis of melatonin. To better understand the signaling pathways involved in the induction of the serotonergic phenotype, we analyzed tphR expression and 5HT-IR in embryos in which either Hh or Fgf signals are abrogated. Hindbrain 5HT neurons are severely reduced in mutants lacking activity of either Ace/Fgf8 or the transcription factor Noi/Pax2.1, which regulates expression of ace/fgf8, and probably other genes encoding signaling proteins. Similarly, serotonergic raphe neurons are absent in embryos lacking Hh activity confirming a conserved role for Hh signals in the induction of these cells. Conversely, over-activation of the Hh pathway increases the number of serotonergic neurons. As in mammals, our results are consistent with the transcription factors Nk2.2 and Gata3 acting downstream of Hh activity in the development of serotonergic raphe neurons. Our results show that the pathways involved in induction of hindbrain serotonergic neurons are likely to be conserved in all vertebrates and help establish the zebrafish as a model system to study this important neuronal class.
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Affiliation(s)
- H Teraoka
- Department of Anatomy & Developmental Biology, University College London, Gower Street, London, WC1E 6BT, United Kingdom.
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171
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Shook DR, Majer C, Keller R. Pattern and morphogenesis of presumptive superficial mesoderm in two closely related species, Xenopus laevis and Xenopus tropicalis. Dev Biol 2004; 270:163-85. [PMID: 15136148 DOI: 10.1016/j.ydbio.2004.02.021] [Citation(s) in RCA: 104] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2003] [Revised: 02/20/2004] [Accepted: 02/20/2004] [Indexed: 11/26/2022]
Abstract
The mesoderm, comprising the tissues that come to lie entirely in the deep layer, originates in both the superficial epithelial and the deep mesenchymal layers of the early amphibian embryo. Here, we characterize the mechanisms by which the superficial component of the presumptive mesoderm ingresses into the underlying deep mesenchymal layer in Xenopus tropicalis and extend our previous findings for Xenopus laevis. Fate mapping the superficial epithelium of pregastrula stage embryos demonstrates ingression of surface cells into both paraxial and axial mesoderm (including hypochord), in similar patterns and amounts in both species. Superficial presumptive notochord lies medially, flanked by presumptive hypochord and both overlie the deep region of the presumptive notochord. These tissues are flanked laterally by superficial presumptive somitic mesoderm, the anterior tip of which also appears to overlay the presumptive deep notochord. Time-lapse recordings show that presumptive somitic and notochordal cells move out of the roof of the gastrocoel and into the deep region during neurulation, whereas hypochordal cells ingress after neurulation. Scanning electron microscopy at the stage and position where ingression occurs suggests that superficial presumptive somitic cells in X. laevis ingress into the deep region as bottle cells whereas those in X. tropicalis ingress by "relamination" (e.g., [Dev. Biol. 174 (1996) 92]). In both species, the superficially derived presumptive somitic cells come to lie in the medial region of the presumptive somites during neurulation. By the early tailbud stages, these cells lie at the horizontal myoseptum of the somites. The morphogenic pathway of these cells strongly resembles that of the primary slow muscle pioneer cells of the zebrafish. We present a revised fate map of Xenopus, and we discuss the conservation of superficial mesoderm within amphibians and across the chordates and its implications for the role of this tissue in patterning the mesoderm.
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Affiliation(s)
- David R Shook
- Department of Biology, University of Virginia, Gilmer Hall, Charlottesville, VA 22903, USA.
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172
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Nakano Y, Kim HR, Kawakami A, Roy S, Schier AF, Ingham PW. Inactivation of dispatched 1 by the chameleon mutation disrupts Hedgehog signalling in the zebrafish embryo. Dev Biol 2004; 269:381-92. [PMID: 15110707 DOI: 10.1016/j.ydbio.2004.01.022] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2003] [Revised: 01/07/2004] [Accepted: 01/12/2004] [Indexed: 10/26/2022]
Abstract
Searches of zebrafish EST and whole genome shotgun sequence databases for sequences encoding the sterol-sensing domain (SSD) protein motif identified two sets of DNA sequences with significant homology to the Drosophila dispatched gene required for release of secreted Hedgehog protein. Using morpholino antisense oligonucleotides, we found that inhibition of one of these genes, designated Disp1, results in a phenotype similar to that of the "you-type" mutants, previously implicated in signalling by Hedgehog proteins in the zebrafish embryo. Injection of disp1 mRNA into embryos homozygous for one such mutation, chameleon (con) results in rescue of the mutant phenotype. Radiation hybrid mapping localised disp1 to the same region of LG20 to which the con mutation was mapped by meiotic recombination analysis. Sequence analysis of disp1 cDNA derived from homozygous con mutant embryos revealed that both mutant alleles are associated with premature termination codons in the disp1 coding sequence. By analysing the expression of markers of specific cell types in the neural tube, pancreas and myotome of con mutant and Disp1 morphant embryos, we conclude that Disp1 activity is essential for the secretion of lipid-modified Hh proteins from midline structures.
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Affiliation(s)
- Y Nakano
- Department of Biomedical Science, University of Sheffield, Sheffield S10 2TN, UK
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173
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Affiliation(s)
- Jennifer O Liang
- Department of Embryology, Carnegie Institution of Washington, Baltimore, Maryland 21210, USA
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174
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Abstract
p53, p63 and p73 are related transcription factors involved in the regulation of cell proliferation, survival and differentiation. Here, we report the isolation and characterization of p73 from zebrafish. While for zebrafish p63 only N-terminally truncated isoforms (DeltaNp63) have been reported, p73 appears to be predominantly or exclusively present in transactivating isoforms (TAp73). p73 shows a very restricted expression pattern during zebrafish development. Transcripts are found in a subset of cells of the olfactory system, the telencephalon, the dorsal diencephalon, and the pronephric ducts. In addition, p73 is expressed in differentiating slow muscle cells of the somites, and in the pharyngeal endoderm. We carried out TAp73 gain- and loss-of-function experiments, injecting either TAp73alpha mRNA, or antisense morpholino oligonucleotides to suppress translation of TAp73 transcripts. The overexpression studies indicate that in contrast to p53, TAp73alpha has no pro-apoptotic effect in zebrafish embryos. However, TAp73 appears to be required for specific processes during the development of the olfactory system, the telencephalon and the pharyngeal arches. Together, our data point to both conserved and class-specific roles of p73 during vertebrate development.
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Affiliation(s)
- Fabian Rentzsch
- Max-Planck-Institute for Immunobiology, Stuebeweg 51, D-79108, Freiburg, Germany
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175
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176
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Abstract
Similar to other vertebrate species, the zebrafish retina is simpler than other regions of the central nervous system (CNS). Relative simplicity, rapid development, and accessibility to genetic analysis make the zebrafish retina an excellent model system for the studies of neurogenesis in the vertebrate CNS. Numerous genetic screens have led to isolation of an impressive collection of mutations affecting the retina and the retinotectal projection in zebrafish. Mutant phenotypes are being studied using a rich variety of markers: antibodies, RNA probes, retrograde and anterograde tracers, as well as transgenic lines. Particularly impressive progress has been made in the characterization of the zebrafish genome. Consequently, positional and candidate cloning of mutant genes are now fairly easy to accomplish in zebrafish. Many mutant genes have, in fact, already been cloned and their analysis has provided important insights into the gene circuitry that regulates retinal neurogenesis. Genetic screens for visual system defects will continue in the future and progressively more sophisticated screening approaches will make it possible to detect a variety of subtle mutant phenotypes in retinal development. The remarkable evolutionary conservation of the vertebrate eye provides the basis for the use of the zebrafish retina as a model of human disorders. Some of the genetic defects of the zebrafish retina indeed resemble human retinopathies. As new techniques are being introduced and improved at a rapid pace, the zebrafish will continue to be an important organism for the studies of the vertebrate visual system.
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Affiliation(s)
- Andrei Avanesov
- Department of Ophthalmology, Harvard Medical School, Boston, Massachusetts 02114, USA
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177
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Affiliation(s)
- Yashar Javidan
- Department of Developmental and Cell Biology, University of California, Irvine, Irvine, California 92697, USA
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178
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Baxendale S, Davison C, Muxworthy C, Wolff C, Ingham PW, Roy S. The B-cell maturation factor Blimp-1 specifies vertebrate slow-twitch muscle fiber identity in response to Hedgehog signaling. Nat Genet 2003; 36:88-93. [PMID: 14702044 DOI: 10.1038/ng1280] [Citation(s) in RCA: 147] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2003] [Accepted: 11/24/2003] [Indexed: 11/08/2022]
Abstract
Vertebrate skeletal muscles comprise distinct fiber types that differ in their morphology, contractile function, mitochondrial content and metabolic properties. Recent studies identified the transcriptional coactivator PGC-1alpha as a key mediator of the physiological stimuli that modulate fiber-type plasticity in postembryonic development. Although myoblasts become fated to differentiate into distinct kinds of fibers early in development, the identities of regulatory proteins that determine embryonic fiber-type specification are still obscure. Here we show that the gene u-boot (ubo), a mutation in which disrupts the induction of embryonic slow-twitch fibers, encodes the zebrafish homolog of Blimp-1, a SET domain-containing transcription factor that promotes the terminal differentiation of B lymphocytes in mammals. Expression of ubo is induced by Hedgehog (Hh) signaling in prospective slow muscle precursors, and its activity alone is sufficient to direct slow-twitch fiber-specific development by naive myoblasts. Our data provide the first molecular insight into the mechanism by which a specific group of muscle precursors is driven along a distinct pathway of fiber-type differentiation in response to positional cues in the vertebrate embryo.
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Affiliation(s)
- Sarah Baxendale
- MRC Intercellular Signaling Group, Center for Developmental Genetics, School of Medicine and Biomedical Sciences, University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, UK
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179
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Tallafuss A, Adolf B, Bally-Cuif L. Selective control of neuronal cluster size at the forebrain/midbrain boundary by signaling from the prechordal plate. Dev Dyn 2003; 227:524-35. [PMID: 12889061 DOI: 10.1002/dvdy.10329] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Within the vertebrate embryonic neural plate, the first neuronal clusters often differentiate at the border of patterning identities. Whether the information inherent in the intersection of patterning identities alone controls all aspects of neuronal cluster development (location, identity, and size) is unknown. Here, we focus on the cluster of the medial longitudinal fascicle (nMLF) and posterior commissure (nPC), located at the forebrain/midbrain (fore/mid) boundary, to address this issue. We first identify expression of the transcription factor Six3 as a common and distinct molecular signature of nMLF and nPC neurons in zebrafish, and we use this marker to monitor mechanisms controlling the location and number of nMLF/nPC neurons. We demonstrate that six3 expression is induced at the fore/mid boundary in pax2.1/no-isthmus and smoothened/slow muscle omitted mutants, where identities adjacent to the six3 cluster are altered; however, in these mutants, the subpopulation of six3-positive cells located within the mispatterned territory is reduced. These results show that induction of the six3 cluster is triggered by the information derived from the intersection in patterning identities alone, whereas correct cluster size depends, in a modular manner, on the identities themselves. The size of the six3 cluster is also controlled independently of neural tube patterning: we demonstrate that the prechordal plate (PCP) is impaired in mixer/bonnie and clyde mutants and that this phenotype secondarily results in an increased production of six3-positive cells at the fore/mid boundary, without correlatively affecting patterning in this area. Thus, a signaling process originating from the PCP distinguishes between neural patterning and the control of six3 cluster size at the fore/mid junction in vivo. Together, our results suggest that a combination of patterning-related and -unrelated mechanisms specifically controls the size of individual early neuronal clusters within the anterior neural plate.
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Affiliation(s)
- Alexandra Tallafuss
- Zebrafish Neurogenetics Junior Research Group, Institute of Virology, Technical University-Munich, Munich, Germany
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180
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Wolff C, Roy S, Ingham PW. Multiple muscle cell identities induced by distinct levels and timing of hedgehog activity in the zebrafish embryo. Curr Biol 2003; 13:1169-81. [PMID: 12867027 DOI: 10.1016/s0960-9822(03)00461-5] [Citation(s) in RCA: 228] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
BACKGROUND In the zebrafish embryo, the differentiation of distinct muscle fiber types has been shown to require the activity of members of the Hedgehog (Hh) family of secreted proteins. Evidence from other systems suggests that Hh behaves as a morphogen, inducing cell fates in a concentration-dependent manner. Exactly how Hh signaling contributes to the generation of the correct pattern of cells within the zebrafish myotome, however, has remained obscure. RESULTS Here, we distinguish four distinct myotomal cell identities in the zebrafish embryo on the basis of their position, morphology, and gene expression patterns. Using morpholino oligonucleotides (MOs) to diminish the activities of the Hh pathway components Patched (Ptc), Fused (Fu), and Suppressor of Fused (Su(fu)), and the teratogen cyclopamine to inhibit the Hh transducer Smoothened (Smo), we show that the appropriate differentiation of each cell type depends upon the levels and range of Hh signaling within the myotome. In addition, by transiently modulating Hh activity by using cyclopamine and a heat-inducible transgene, we demonstrate that the competence of myotomal cells to respond to Hh changes with time. Finally, we show that the Gli1 and Gli2 transcription factors mediate most of the response of myotomal cells to Hh. CONCLUSIONS Hh signaling acts in a dosage-dependent manner to specify cell fate in the zebrafish myotome. Allocation of the correct number of cells to a specific fate depends upon the range of Hh activity. The timing of exposure to Hh determines the response of cells to the signal.
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Affiliation(s)
- Christian Wolff
- MRC Intercellular Signalling Group, Centre for Developmental Genetics, University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, United Kingdom
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181
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Abstract
Cell signaling plays a key role in the development of all multicellular organisms. Numerous studies have established the importance of Hedgehog signaling in a wide variety of regulatory functions during the development of vertebrate and invertebrate organisms. Several reviews have discussed the signaling components in this pathway, their various interactions, and some of the general principles that govern Hedgehog signaling mechanisms. This review focuses on the developing systems themselves, providing a comprehensive survey of the role of Hedgehog signaling in each of these. We also discuss the increasing significance of Hedgehog signaling in the clinical setting.
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Affiliation(s)
- Andrew P McMahon
- Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
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182
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Pownall ME, Gustafsson MK, Emerson CP. Myogenic regulatory factors and the specification of muscle progenitors in vertebrate embryos. Annu Rev Cell Dev Biol 2003; 18:747-83. [PMID: 12142270 DOI: 10.1146/annurev.cellbio.18.012502.105758] [Citation(s) in RCA: 415] [Impact Index Per Article: 19.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Embryological and genetic studies of mouse, bird, zebrafish, and frog embryos are providing new insights into the regulatory functions of the myogenic regulatory factors, MyoD, Myf5, Myogenin, and MRF4, and the transcriptional and signaling mechanisms that control their expression during the specification and differentiation of muscle progenitors. Myf5 and MyoD genes have genetically redundant, but developmentally distinct regulatory functions in the specification and the differentiation of somite and head muscle progenitor lineages. Myogenin and MRF4 have later functions in muscle differentiation, and Pax and Hox genes coordinate the migration and specification of somite progenitors at sites of hypaxial and limb muscle formation in the embryo body. Transcription enhancers that control Myf5 and MyoD activation in muscle progenitors and maintain their expression during muscle differentiation have been identified by transgenic analysis. In epaxial, hypaxial, limb, and head muscle progenitors, Myf5 is controlled by lineage-specific transcription enhancers, providing evidence that multiple mechanisms control progenitor specification at different sites of myogenesis in the embryo. Developmental signaling ligands and their signal transduction effectors function both interactively and independently to control Myf5 and MyoD activation in muscle progenitor lineages, likely through direct regulation of their transcription enhancers. Future investigations of the signaling and transcriptional mechanisms that control Myf5 and MyoD in the muscle progenitor lineages of different vertebrate embryos can be expected to provide a detailed understanding of the developmental and evolutionary mechanisms for anatomical muscles formation in vertebrates. This knowledge will be a foundation for development of stem cell therapies to repair diseased and damaged muscles.
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183
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Ju B, Chong SW, He J, Wang X, Xu Y, Wan H, Tong Y, Yan T, Korzh V, Gong Z. Recapitulation of fast skeletal muscle development in zebrafish by transgenic expression of GFP under the mylz2 promoter. Dev Dyn 2003; 227:14-26. [PMID: 12701095 DOI: 10.1002/dvdy.10273] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
A 1,934-bp muscle-specific promoter from the zebrafish mylz2 gene was isolated and characterized by transgenic analysis. By using a series of 5' promoter deletions linked to the green fluorescent protein (gfp) reporter gene, transient transgenic analysis indicated that the strength of promoter activity appeared to correlate to the number of muscle cis-elements in the promoter and that a minimal -77-bp region was sufficient for a relatively strong promoter activity in muscle cells. Stable transgenic lines were obtained from several mylz2-gfp constructs. GFP expression in the 1,934-bp promoter transgenic lines mimicked well the expression pattern of endogenous mylz2 mRNA in both somitic muscle and nonsomitic muscles, including fin, eye, jaw, and gill muscles. An identical pattern of GFP expression, although at a much lower level, was observed from a transgenic line with a shorter 871-bp promoter. Our observation indicates that there is no distinct cis-element for activation of mylz2 in different skeletal muscles. Furthermore, RNA encoding a dominant negative form of cAMP-dependent protein kinase A was injected into mylz2-gfp transgenic embryos and GFP expression was significantly reduced due to an expanded slow muscle development at the expense of GFP-expressing fast muscle. The mylz2-gfp transgene was also transferred into two zebrafish mutants, spadetail and chordino, and several novel phenotypes in muscle development in these mutants were discovered.
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Affiliation(s)
- Bensheng Ju
- Department of Biological Sciences, National University of Singapore, Singapore
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184
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Lam CS, Sleptsova-Friedrich I, Munro AD, Korzh V. SHH and FGF8 play distinct roles during development of noradrenergic neurons in the locus coeruleus of the zebrafish. Mol Cell Neurosci 2003; 22:501-15. [PMID: 12727446 DOI: 10.1016/s1044-7431(03)00031-9] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Several signaling pathways have been implicated in the development of dopaminergic and serotonergic neurons. Here, we analyzed the formation of noradrenergic (NAergic) cells in the locus coeruleus (LC) of zebrafish. In the sonic hedgehog (shh) mutant, cells positive for tyrosine hydroxylase, a marker for putative NAergic cells in the LC were reduced. Similarly, the inhibition of translation of all hh genes and the perturbation of Shh signaling by forskolin resulted in a decrease in the number of cells. Conversely, when SHH was overexpressed, an increase in number was observed. Thus, Shh is involved in maintaining the appropriate number of cells in the LC. While elevated levels of bone morphogenetic protein 4 (BMP4) did not attenuate tyrosine hydroxylase-positive cells, exogenous fibroblast growth factor 8 (FGF8) rescued NAergic neurons in the acerebellar (ace) mutant, providing direct in vivo evidence that Fgf8 is required for the induction of NAergic neurons in the LC.
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Affiliation(s)
- Chen Sok Lam
- Institute of Molecular and Cell Biology, National University of Singapore, Singapore, Republic of Singapore
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185
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Abstract
The ability of an animal to carry out its normal behavioral repertoire requires generation of an enormous diversity of neurons and glia. The relative simplicity of the spinal cord makes this an especially attractive part of the nervous system for addressing questions about the development of vertebrate neural specification and function. The last decade has witnessed an explosion in our understanding of spinal cord development and the functional interactions among spinal cord neurons and glia. Cellular, genetic, molecular, physiological and behavioral studies in zebrafish have all been important in providing insights into questions that remained unanswered by studies from other vertebrate model organisms. This is the case because many zebrafish spinal neurons can be individually identified and followed over time in living embryos and larvae. In this review, we discuss what is currently known about the cellular, genetic and molecular mechanisms involved in specifying distinct cell types in the zebrafish spinal cord and how these cells establish the functional circuitry that mediates particular behaviors. We start by describing the early signals and morphogenetic movements that form the nervous system, and in particular, the spinal cord. We then provide an overview of the cell types within the spinal cord and describe how they are specified and patterned. We begin ventrally with floor plate and proceed dorsally, through motoneurons and oligodendrocytes, interneurons, astrocytes and radial glia, spinal sensory neurons and neural crest. We next describe axon pathfinding of spinal neurons. Finally, we discuss the roles of particular spinal cord neurons in specific behaviors.
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Affiliation(s)
- Katharine E Lewis
- Institute of Neuroscience, 1254 University of Oregon, Eugene, OR 97403, USA.
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186
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Lo J, Lee S, Xu M, Liu F, Ruan H, Eun A, He Y, Ma W, Wang W, Wen Z, Peng J. 15000 unique zebrafish EST clusters and their future use in microarray for profiling gene expression patterns during embryogenesis. Genome Res 2003; 13:455-66. [PMID: 12618376 PMCID: PMC430290 DOI: 10.1101/gr.885403] [Citation(s) in RCA: 201] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
A total of 15590 unique zebrafish EST clusters from two cDNA libraries have been identified. Most significantly, only 22% (3437) of the 15590 unique clusters matched 2805 (of 15200) clusters in the Danio rerio UniGene database, indicating that our EST set is complementary to the existing ESTs in the public database and will be invaluable in assisting the annotation of genes based on the upcoming zebrafish genome sequence. Blast search showed that 7824 of our unique clusters matched 6710 known or predicted proteins in the nonredundant database. A cDNA microarray representing approximately 3100 unique zebrafish cDNA clusters has been generated and used to profile the gene expression patterns across six different embryonic stages (cleavage, blastula, gastrula, segmentation, pharyngula, and hatching). Analysis of expression data using K-means clustering revealed that genes coding for muscle-specific proteins displayed similar expression patterns, confirming that the coordinate gene expression is important for myogenesis. Our results demonstrate that the combination of microarray technology with the zebrafish model system can provide useful information on how genes are coordinated in a genetic network to control zebrafish embryogenesis and can help to identify novel genes that are important for organogenesis.
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Affiliation(s)
- Jane Lo
- Functional Genomics Lab, Institute of Molecular and Cell Biology, Singapore 117609
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187
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Abstract
Although the development of the digestive system of humans and vertebrate model organisms has been well characterized, relatively little is known about how the zebrafish digestive system forms. We define developmental milestones during organogenesis of the zebrafish digestive tract, liver, and pancreas and identify important differences in the way the digestive endoderm of zebrafish and amniotes is organized. Such differences account for the finding that the zebrafish digestive system is assembled from individual organ anlagen, whereas the digestive anlagen of amniotes arise from a primitive gut tube. Despite differences of organ morphogenesis, conserved molecular programs regulate pharynx, esophagus, liver, and pancreas development in teleosts and mammals. Specifically, we show that zebrafish faust/gata-5 is a functional ortholog of gata-4, a gene that is essential for the formation of the mammalian and avian foregut. Further, extraembryonic gata activity is required for this function in zebrafish as has been shown in other vertebrates. We also show that a loss-of-function mutation that perturbs sonic hedgehog causes defects in the development of the esophagus that parallel those associated with targeted disruption of this gene in mammals. Perturbation of sonic hedgehog also affects zebrafish liver and pancreas development, and these effects occur in a reciprocal fashion, as has been described during mammalian liver and ventral pancreas development. Together, these data define aspects of digestive system development necessary for the characterization of zebrafish mutants. Given the similarities of teleost and mammalian digestive physiology and anatomy, these findings have implications for developmental and evolutionary studies as well as research of human diseases, such as diabetes, liver cirrhosis, and cancer.
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Affiliation(s)
- Kenneth N Wallace
- Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA
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188
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Sbrogna JL, Barresi MJF, Karlstrom RO. Multiple roles for Hedgehog signaling in zebrafish pituitary development. Dev Biol 2003; 254:19-35. [PMID: 12606279 DOI: 10.1016/s0012-1606(02)00027-1] [Citation(s) in RCA: 96] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The endocrine-secreting lobe of the pituitary gland, or adenohypophysis, forms from cells at the anterior margin of the neural plate through inductive interactions involving secreted morphogens of the Hedgehog (Hh), fibroblast growth factor (FGF), and bone morphogenetic protein (BMP) families. To better understand when and where Hh signaling influences pituitary development, we have analyzed the effects of blocking Hh signaling both pharmacologically (cyclopamine treatments) and genetically (zebrafish Hh pathway mutants). While current models state that Shh signaling from the oral ectoderm patterns the pituitary after placode induction, our data suggest that Shh plays a direct early role in both pituitary induction and patterning, and that early Hh signals comes from adjacent neural ectoderm. We report that Hh signaling is necessary between 10 and 15 h of development for induction of the zebrafish adenohypophysis, a time when shh is expressed only in neural tissue. We show that the Hh responsive genes ptc1 and nk2.2 are expressed in preplacodal cells at the anterior margin of the neural tube at this time, indicating that these cells are directly receiving Hh signals. Later (15-20 h) cyclopamine treatments disrupt anterior expression of nk2.2 and Prolactin, showing that early functional patterning requires Hh signals. Consistent with a direct role for Hh signaling in pituitary induction and patterning, overexpression of Shh results in expanded adenohypophyseal expression of lim3, expansion of nk2.2 into the posterior adenohypophysis, and an increase in Prolactin- and Somatolactin-secreting cells. We also use the zebrafish Hh pathway mutants to document the range of pituitary defects that occur when different elements of the Hh signaling pathway are mutated. These defects, ranging from a complete loss of the adenohypophysis (smu/smo and yot/gli2 mutants) to more subtle patterning defects (dtr/gli1 mutants), may correlate to human Hh signaling mutant phenotypes seen in Holoprosencephaly and other congenital disorders. Our results reveal multiple and distinct roles for Hh signaling in the formation of the vertebrate pituitary gland, and suggest that Hh signaling from neural ectoderm is necessary for induction and functional patterning of the vertebrate pituitary gland.
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Affiliation(s)
- Jennifer L Sbrogna
- Department of Biology, University of Massachusetts, Amherst, MA 01003, USA
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189
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Abstract
Myogenesis has been a system central to investigations on mechanisms of diversification within groups of differentiating cells. Diversity among cell types has been well described in striated muscle tissue at the protein and enzymatic-function levels for decades, but it is only in recent years that some understanding of the molecular mechanisms responsible for this diversity has begun to emerge. Study of the expression of the slow isoforms of the myosin heavy chain has contributed to our understanding of how cell diversity arises within skeletal and cardiac muscle. Slow MyHc isoforms are developmentally responsive to a number of cues provided by the nervous systems, the endocrine system and, later in development, to functional demands on these developing tissues. Perhaps most informative have been studies on the mechanism for regulation of slow MyHc expression in mammals and birds where studies on the calcineurin-NF-AT pathways and nuclear hormone action have been shown to control MyHC gene expression in skeletal muscle and in the developing heart. The mechanisms involved in cell diversification in myogenesis are undoubtedly more varied and complex than those currently offered to explain cell diversification, but these recent studies have broadened our understanding of the interplay between the nervous system, the endocrine system and cell lineages in controlling cell diversification. Greater focus on the first fibers and cardiomyocytes to form in the embryo are likely to bring additional insights into the mechanism crucial for establishing the patterns of diversity required for successful formation of embryonic tissues.
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Affiliation(s)
- Frank E Stockdale
- Stanford Medical Center, CCSR 1145, Stanford, California 94305-5151, USA
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190
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Albert S, Müller F, Fischer N, Biellmann D, Neumann C, Blader P, Strähle U. Cyclops-independent floor plate differentiation in zebrafish embryos. Dev Dyn 2003; 226:59-66. [PMID: 12508225 DOI: 10.1002/dvdy.10211] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
In zebrafish, development of the ventral neural tube depends on the Nodal-related signal Cyclops (Cyc). One-day-old cyc mutant embryos lack the medial floor plate (MFP). We show here that cells expressing MFP marker genes differentiate gradually in cyc mutant embryos in a delayed manner during the second day of development. This late differentiation is restricted to the hindbrain and spinal cord and depends on an intact Hedgehog (Hh) signalling pathway. Cells expressing MFP marker genes in cyc mutant embryos appear to be derived from lateral floor plate (LFP) cells as they coexpress LFP and MFP marker genes. This finding suggests that the correct temporal development of the MFP is required for the distinction of LFP and MFP cells in wild-type embryos.
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Affiliation(s)
- Stéphanie Albert
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS/INSERM/ULP, C.U. de Strasbourg, France
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191
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David NB, Sapède D, Saint-Etienne L, Thisse C, Thisse B, Dambly-Chaudière C, Rosa FM, Ghysen A. Molecular basis of cell migration in the fish lateral line: role of the chemokine receptor CXCR4 and of its ligand, SDF1. Proc Natl Acad Sci U S A 2002; 99:16297-302. [PMID: 12444253 PMCID: PMC138605 DOI: 10.1073/pnas.252339399] [Citation(s) in RCA: 241] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Cell migration plays an essential role in many morphogenetic processes, and its deregulation has many dramatic consequences. Yet how migration is controlled during normal development is still a largely unresolved question. We examined this process in the case of the posterior lateral line (PLL), a mechanosensory system present in fish and amphibians. In zebrafish, the embryonic PLL comprises seven to eight sense organs (neuromasts) aligned from head to tail along the flank of the animal and is formed by a primordium that originates from a cephalic placode. This primordium migrates along a stereotyped pathway toward the tip of the tail and deposits in its wake discrete groups of cells, each of which will become a neuromast. We show that a trail of SDF1-like chemokine is present along the pathway of the primordium and that a CXCR4-like chemokine receptor is expressed by the migrating cells. The inactivation of either the ligand or its receptor blocks migration, whereas in mutants in which the normal SDF1 trail is absent, the primordium path is redirected to the next, more ventral sdf1 expression domain. In all cases, the sensory axons remain associated to the primordium, indicating that the extension of the neurites to form the PLL nerve depends on the movement of the primordium. We conclude that both the formation and the innervation of this system depend on the SDF1-CXCR4 system, which has also been implicated in several migration events in humans, including metastasis formation and lymphocyte homing.
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Affiliation(s)
- Nicolas B David
- Groupe Danio, Institut National de la Santé et de la Recherche Médicale U368, Ecole Normale Supérieure, 46 Rue d'Ulm, 75230 Paris, France
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192
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Wigmore PM, Evans DJR. Molecular and cellular mechanisms involved in the generation of fiber diversity during myogenesis. INTERNATIONAL REVIEW OF CYTOLOGY 2002; 216:175-232. [PMID: 12049208 DOI: 10.1016/s0074-7696(02)16006-2] [Citation(s) in RCA: 84] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
Abstract
Skeletal muscles have a characteristic proportion and distribution of fiber types, a pattern which is set up early in development. It is becoming clear that different mechanisms produce this pattern during early and late stages of myogenesis. In addition, there are significant differences between the formation of muscles in head and those found in rest of the body. Early fiber type differentiation is dependent upon an interplay between patterning systems which include the Wnt and Hox gene families and different myoblast populations. During later stages, innervation, hormones, and functional demand increasingly act to determine fiber type, but individual muscles still retain an intrinsic commitment to form particular fiber types. Head muscle is the only muscle not derived from the somites and follows a different development pathway which leads to the formation of particular fiber types not found elsewhere. This review discusses the formation of fiber types in both head and other muscles using results from both chick and mammalian systems.
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Affiliation(s)
- Peter M Wigmore
- School of Biomedical Sciences, Queen's Medical Centre, Nottingham, United Kingdom
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193
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Abstract
Genetic screens in zebrafish have identified a large number of mutations that affect neural connectivity in the developing visual system. These mutants define genes essential for accurate retinal axon guidance in the eye and brain and the characterization of these mutants is helping to define the cellular and molecular mechanisms that guide axons in the vertebrate embryo. The combination of zebrafish genetic and embryological approaches promises to greatly increase our understanding of how multiple guidance mechanisms establish the complex neural interconnectivity of the vertebrate brain.
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Affiliation(s)
- James Culverwell
- Department of Biology, University of Massachusetts, Amherst, MA 01003, USA
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194
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Rastegar S, Albert S, Le Roux I, Fischer N, Blader P, Müller F, Strähle U. A floor plate enhancer of the zebrafish netrin1 gene requires Cyclops (Nodal) signalling and the winged helix transcription factor FoxA2. Dev Biol 2002; 252:1-14. [PMID: 12453456 DOI: 10.1006/dbio.2002.0837] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The floor plate is an organising centre that controls neural differentiation and axonogenesis in the neural tube. The axon guidance molecule Netrin1 is expressed in the floor plate of zebrafish embryos. To elucidate the regulatory mechanisms underlying expression in the floor plate, we scanned the netrin1 locus for regulatory regions and identified an enhancer that drives expression in the floor plate and hypochord of transgenic embryos. The expression of the transgene is ectopically activated by Cyclops (Nodal) signals but does not respond to Hedgehog signals. The winged-helix transcription factor foxA2 (also HNF3beta, axial) is expressed in the notochord and floor plate. We show that knock-down of FoxA2 leads to loss of floor plate, while notochord and hypochord development is unaffected, suggesting a specific requirement of FoxA2 in the floor plate. The transgene is ectopically activated by FoxA2, and expression of FoxA2 leads to rescue of floor plate differentiation in mutant embryos that are deficient in Cyclops signalling. Zebrafish and mouse use different signalling systems to specify floor plate. The zebrafish netrin1 regulatory region also drives expression in the floor plate of mouse and chicken embryos. This suggests that components of the regulatory circuits controlling expression in the floor plate are conserved and that FoxA2-given its importance for midline development also in the mouse-may be one such component.
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Affiliation(s)
- Sepand Rastegar
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS/INSERM/ULP, B.P. 10142, 67404, Illkirch Cedex, C.U. de Strasbourg, France
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195
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Chen JK, Taipale J, Young KE, Maiti T, Beachy PA. Small molecule modulation of Smoothened activity. Proc Natl Acad Sci U S A 2002; 99:14071-6. [PMID: 12391318 PMCID: PMC137838 DOI: 10.1073/pnas.182542899] [Citation(s) in RCA: 782] [Impact Index Per Article: 35.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/06/2002] [Indexed: 12/13/2022] Open
Abstract
Smoothened (Smo), a distant relative of G protein-coupled receptors, mediates Hedgehog (Hh) signaling during embryonic development and can initiate or transmit ligand-independent pathway activation in tumorigenesis. Although the cellular mechanisms that regulate Smo function remain unclear, the direct inhibition of Smo by cyclopamine, a plant-derived steroidal alkaloid, suggests that endogenous small molecules may be involved. Here we demonstrate that SAG, a chlorobenzothiophene-containing Hh pathway agonist, binds to the Smo heptahelical bundle in a manner that antagonizes cyclopamine action. In addition, we have identified four small molecules that directly inhibit Smo activity but are structurally distinct from cyclopamine. Functional and biochemical studies of these compounds provide evidence for the small molecule modulation of Smo through multiple mechanisms and yield insights into the physiological regulation of Smo activity. The mechanistic differences between the Smo antagonists may be useful in the therapeutic manipulation of Hh signaling.
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Affiliation(s)
- James K Chen
- Department of Molecular Biology and Genetics, Howard Hughes Medical Institute, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
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196
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Drapeau P, Saint-Amant L, Buss RR, Chong M, McDearmid JR, Brustein E. Development of the locomotor network in zebrafish. Prog Neurobiol 2002; 68:85-111. [PMID: 12450489 DOI: 10.1016/s0301-0082(02)00075-8] [Citation(s) in RCA: 259] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
The zebrafish is a leading model for studies of vertebrate development and genetics. Its embryonic motor behaviors are easy to assess (e.g. for mutagenic screens), the embryos develop rapidly (hatching as larvae at 2 days) and are transparent, permitting calcium imaging and patch clamp recording in vivo. We review primarily the recent advances in understanding the cellular basis for the development of motor activities in the developing zebrafish. The motor activities are generated largely in the spinal cord and hindbrain. In the embryo these segmented structures possess a relatively small number of repeating sets of identifiable neurons. Many types of neurons as well as the two types of muscle cells have been classified based on their morphologies. Some of the molecular signals for cellular differentiation have been identified recently and mutations affecting cell development have been isolated. Embryonic motor behaviors appear in sequence and consist of an early period of transient spontaneous coiling contractions, followed by the emergence of twitching responses to touch, and later by the ability to swim. Coiling contractions are generated by an electrically coupled network of a subset of spinal neurons whereas a chemical (glutamatergic and glycinergic) synaptic drive underlies touch responses and swimming. Swimming becomes sustained in larvae once the neuromodulatory serotonergic system develops. These results indicate many similarities between developing zebrafish and other vertebrates in the properties of the synaptic drive underlying locomotion. Therefore, the zebrafish is a useful preparation for gaining new insights into the development of the neural control of vertebrate locomotion. As the types of neurons, transmitters, receptors and channels used in the locomotor network are being defined, this opens the possibility of combining cellular neurophysiology with forward and reverse molecular genetics to understand the principles of locomotor network assembly and function.
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Affiliation(s)
- Pierre Drapeau
- McGill Centre for Research in Neuroscience and Department of Biology, McGill University, Que., Montreal, Canada.
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197
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Chen YH, Tsai HJ. Treatment with Myf5-morpholino results in somite patterning and brain formation defects in zebrafish. Differentiation 2002; 70:447-56. [PMID: 12366382 DOI: 10.1046/j.1432-0436.2002.700807.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Myf-5 is a stage-dependent transcription factor associated with somitogenesis. To study its biological functions in zebrafish, we injected the Myf5-morpholinos ZMF-MO (antisense nucleotides 28 to 52) and ZMF-OTHER (antisense nucleotides 3 to 27) into zebrafish embryos to establish a myf-5 gene knockdown. No phenotypic abnormalities were observed following injection with 0.2 ng of ZMF-MO, but defects were displayed in 2 of 118 (1.7%) surviving embryos injected with 1 ng ZMF-MO. Morphological defects became more severe with increased dosages: 105 of 270 (38.9%) surviving embryos injected with 4.5 ng of ZMF-MO displayed such abnormalities as the absence of eyes or brains in addition to the following low-dosage defects in 24 hpf embryos: longitudinal yolk sacs, incomplete epiboly coverage, abnormal and suspended tail buds, diffused somite boundaries, and head shrinkage. Similar results were observed in the 4.5 ng ZMF-OTHER injection group. However, when fish were co-injected with 4.5 ng ZMF-MO and 4.5 ng myf-5 mRNA, abnormality rates decreased from 49.6% to 5.5%. Our results show that the brain krox20 gene was down-regulated at rhombomere 3; the pax2.1 gene was completely down-regulated; myoD was expressed normally; myogenin was substantially down-regulated in whole somites; and desmin was partly inhibited in newly forming somites. Our conclusion is that zebrafish Myf-5 may play important roles in brain formation and in the convergence and extension of shield epiblasts and tail buds during early embryogenesis, in addition to its well-understood role as a muscle regulatory factor in somites.
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Affiliation(s)
- Yau-Hung Chen
- Institute of Fisheries Science, National Taiwan University,1 Roosevelt Road, Sec 4, Taipei, Taiwan
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198
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Park HC, Mehta A, Richardson JS, Appel B. olig2 is required for zebrafish primary motor neuron and oligodendrocyte development. Dev Biol 2002; 248:356-68. [PMID: 12167410 DOI: 10.1006/dbio.2002.0738] [Citation(s) in RCA: 243] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Oligodendrocytes are produced from the same region of the ventral spinal cord that earlier generated motor neurons in bird and rodent embryos. Motor neuron and oligodendrocyte precursor cells express Olig genes, which encode basic helix-loop-helix transcription factors that play important roles in the development of both motor neurons and oligodendrocytes. We found that oligodendrocytes develop similarly in zebrafish embryos, in that they arise from ventral spinal cord and migrate to new positions. Developing primary motor neurons and oligodendrocytes express olig2 as do neural plate cells that give rise to both primary motor neurons and oligodendrocytes. Loss of olig2 function prevented primary motor neuron and oligodendrocyte development, whereas olig2 overexpression promoted formation of excess primary motor neurons and oligodendrocytes. We provide genetic evidence that Hedgehog signaling is required for zebrafish olig2 expression and oligodendrocyte development. However, olig2 overexpression did not promote primary motor neuron or oligodendrocyte development in embryos with reduced Hedgehog signaling activity. One possibility consistent with these data is that Hedgehog signaling, partly by inducing olig2 expression, specifies neural precursor cells that have potential for primary motor neuron or oligodendrocyte fate.
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Affiliation(s)
- Hae-Chul Park
- Department of Biological Sciences, Vanderbilt University, Nashville, TN 37235, USA
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199
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Etheridge L, Diiorio P, Sagerström CG. A zebrafish unc-45-related gene expressed during muscle development. Dev Dyn 2002; 224:457-60. [PMID: 12203738 DOI: 10.1002/dvdy.10123] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We report the isolation and expression pattern of zebrafish unc45r, a gene related to Caenorhabditis elegans unc-45. UNC-45 is a muscle-specific protein thought to interact with myosin and promote the assembly of muscle thick filaments during C. elegans development. Zebrafish Unc45r shares sequence features with C. elegans UNC-45, including three tetratricopeptide repeats and a CRO1/She4p homology domain. unc45r is expressed in mesoderm adjacent to the dorsal midline during late gastrula stages and is coexpressed with muscle specific genes in somitic mesoderm during development of trunk skeletal muscle. unc45r is also expressed in cranial skeletal muscle as well as in cardiac and smooth muscle. The isolation of a muscle-specific unc-45 related gene from zebrafish suggests a common mechanism for muscle filament assembly between vertebrates and invertebrates.
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Affiliation(s)
- Letitiah Etheridge
- Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, Massachusetts 01605, USA
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200
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diIorio PJ, Moss JB, Sbrogna JL, Karlstrom RO, Moss LG. Sonic hedgehog is required early in pancreatic islet development. Dev Biol 2002; 244:75-84. [PMID: 11900460 DOI: 10.1006/dbio.2002.0573] [Citation(s) in RCA: 90] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Pancreatic organogenesis relies on a complex interplay of cell-autonomous and extracellular signals. We demonstrate that the morphogen sonic hedgehog (Shh) is required for pancreatic development in zebrafish. Genetic mutants of Shh and its signaling pathway establish this dependence as specific to endocrine, but not exocrine, pancreas. Using cyclopamine to inhibit hedgehog signaling, we show that transient Shh signaling is necessary during gastrulation for subsequent differentiation of endoderm into islet tissue. A second hedgehog-dependent activity occurring later in development was also identified and may be analogous to the known action of Shh in gut endoderm to direct localization of pancreatic development. The early action of Shh may be part of a more general process allowing neuroendocrine cells to originate in nonneuroectodermally derived tissues.
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Affiliation(s)
- Philip J diIorio
- Department of Medicine, Tufts University School of Medicine, Boston, Massachusetts 02111, USA
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