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D W Raible

Publications and source records attributed to D W Raible.

At least 19 recordsLinked to original sources
PubMed2001

Duplicate mitf genes in zebrafish: complementary expression and conservation of melanogenic potential.

Mutations in the zebrafish nacre/mitfa gene, expressed in all embryonic melanogenic cells, perturb only neural crest melanocytes, suggesting redundancy of mitfa with another gene in the zebrafish retinal pigment epithelium (RPE). Here, we describe a second zebrafish mitf gene, mitfb, which may fulfill this role. The proteins encoded by the two zebrafish mitf genes appear homologous to distinct isoforms generated by alternately spliced mRNAs of the single mammalian Mitf gene, suggesting specialization of the two zebrafish genes following a duplication event. Consistent with this hypothesis, expression of mitfa and mitfb is partially overlapping. mitfb is coexpressed with mitfa in the RPE at an appropriate time to compensate for loss of mitfa function in the nacre mutant but is not expressed in neural crest melanoblasts. Additionally, mitfb is expressed in the epiphysis and olfactory bulb where mitfa is not, and where Mitf expression has not previously been reported in other species. mitfb, but not a zebrafish ortholog of the closely related gene tfe3, can rescue neural crest melanophore development in nacre/mitfa mutant embryos when expressed via the mitfa promoter. These data suggest that mitfa and mitfb together may recapitulate the expression and functions of a single ancestral Mitf gene, and that mitfb may serve additional novel functions.

3T3 Cells↗
PubMed2001

Functional analysis of zebrafish GDNF.

We have identified zebrafish orthologues of glial cell line-derived neurotrophic factor (GDNF) and the ligand-binding component of its receptor GFRalpha1. We examined the mRNA expression pattern of these genes in the developing spinal cord primary motor neurons (PMN), kidney, and enteric nervous systems (ENS) and have identified areas of correlated expression of the ligand and the receptor that suggest functional significance. Many aspects of zebrafish GDNF expression appear conserved with those reported in mouse, rat, and avian systems. In the zebrafish PMN, GFRalpha1 is only expressed in the CaP motor neuron while GDNF is expressed in the ventral somitic muscle that it innervates. To test the functional significance of this correlated expression pattern, we ectopically overexpressed GDNF in somitic muscle during the period of motor axon outgrowth and found specific perturbations in the pattern of CaP axon growth. We also depleted GDNF protein in zebrafish embryos using morpholino antisense oligos and found that GDNF protein is critical for the development of the zebrafish ENS but appears dispensable for the development of the kidney and PMN.

Amino Acid Sequence↗
PubMed2000

Organization of the lateral line system in embryonic zebrafish.

We describe the organization of lateral line nerves and ganglia in the embryonic zebrafish, Danio rerio. Two lateral line nerves are found anterior to the otic vesicle: the anterodorsal nerve innervates neuromasts of the supraorbital, infraorbital, and otic lines, whereas the anteroventral nerve innervates the mandibular and opercular lines. An additional two lateral line nerves are found posterior to the otic vesicle: the middle lateral line nerve innervates the middle line, whereas the posterior nerve innervates the occipital dorsal and posterior trunk lines. Preotic nerves converge on a single entry zone into the central nervous system at the facial motor root (mVII), as do axons of the octaval nerve. Postotic nerves converge to a posterior entry zone at the glossopharyngeal root. Both lateral line ganglia and neuromasts develop on a stereotypical schedule. To examine the segmental relationships among cranial ganglia, neural crest, and hindbrain, lateral line organization was analyzed in valentino mutants, which have disruptions in the development of rhombomeres 5-7 and in the third arch neural crest, and are missing glossopharyngeal motor neurons. The proposed corresponding lateral line nerve for this head segment, the middle lateral line, appears to develop normally. However, the middle and posterior nerves do not form a posterior entry zone in the absence of a glossopharyngeal root in val mutants, but instead course anteriorly to join the preotic nerves.

Animals↗
PubMed2000

Direct regulation of nacre, a zebrafish MITF homolog required for pigment cell formation, by the Wnt pathway.

We have shown that Wnt signals are necessary and sufficient for neural crest cells to adopt pigment cell fates. nacre, a zebrafish homolog of MITF, is required for pigment cell differentiation. We isolated a promoter region of nacre that contains Tcf/Lef binding sites, which can mediate Wnt responsiveness. This promoter binds to zebrafish Lef1 protein in vitro, and a nacre reporter construct is strongly repressed by dominant-negative Tcf in melanoma cells. Mutation of Tcf/Lef sites abolishes Lef1 binding and reporter function in vivo. Wnt signaling therefore directly activates nacre, which in turn leads to pigment cell differentiation.

Animals↗
PubMed2000

Environmental signals and cell fate specification in premigratory neural crest.

Neural crest cells are multipotent progenitors, capable of producing diverse cell types upon differentiation. Recent studies have identified significant heterogeneity in both the fates produced and genes expressed by different premigratory crest cells. While these cells may be specified toward particular fates prior to migration, transplant studies show that some may still be capable of respecification at this time. Here we summarize evidence that extracellular signals in the local environment may act to specify premigratory crest and thus generate diversity in the population. Three main classes of signals-Wnts, BMP2/BMP4 and TGFbeta1,2,3-have been shown to directly influence the production of particular neural crest cell fates, and all are expressed near the premigratory crest. This system may therefore provide a good model for integration of multiple signaling pathways during embryonic cell fate specification.

Animals↗
PubMed1999

Maternal and embryonic expression of zebrafish lef1.

Transcription factors of the TCF/LEF family interact with the Wnt signaling pathway to control transcription of downstream genes (Clevers, H., van de Wetering, M., 1997. TCF/LEF factor earn their wings. Trends Genet. 13, 485-489). We were interested in cloning family members which were expressed in zebrafish neural crest, because Wnt signaling modulates specification of neural crest fate (Dorsky, R.I., Moon, R.T., Raible, D.W., 1998. Control of neural crest cell fate by the Wnt signalling pathway. Nature 396, 370-373). We cloned a zebrafish homolog of lef1 and localized its chromosomal position by radiation hybrid mapping. lef1 is expressed in the neural crest as well as the tailbud and developing mesoderm, and is maternally expressed in zebrafish, unlike mouse and Xenopus homologs. In addition, we cloned two tcf3 genes and a homolog of tcf4, neither of which were strongly expressed in premigratory neural crest.

Amino Acid Sequence↗
PubMed1999

nacre encodes a zebrafish microphthalmia-related protein that regulates neural-crest-derived pigment cell fate.

We report the isolation and identification of a new mutation affecting pigment cell fate in the zebrafish neural crest. Homozygous nacre (nac(w2)) mutants lack melanophores throughout development but have increased numbers of iridophores. The non-crest-derived retinal pigment epithelium is normal, suggesting that the mutation does not affect pigment synthesis per se. Expression of early melanoblast markers is absent in nacre mutants and transplant experiments suggested a cell-autonomous function in melanophores. We show that nac(w2) is a mutation in a zebrafish gene encoding a basic helix-loop-helix/leucine zipper transcription factor related to microphthalmia (Mitf), a gene known to be required for development of eye and crest pigment cells in the mouse. Transient expression of the wild-type nacre gene restored melanophore development in nacre(-/-) embryos. Furthermore, misexpression of nacre induced the formation of ectopic melanized cells and caused defects in eye development in wild-type and mutant embryos. These results demonstrate that melanophore development in fish and mammals shares a dependence on the nacre/Mitf transcription factor, but that proper development of the retinal pigment epithelium in the fish is not nacre-dependent, suggesting an evolutionary divergence in the function of this gene.

Amino Acid Sequence↗
PubMed1998

Control of neural crest cell fate by the Wnt signalling pathway.

Environmental signals are important in the development of neural crest, during which process multipotent progenitor must choose from several fates. However, the nature of these environmental signals is unknown. A previous fate map of zebrafish cranial neural crest showed that lineage-restricted clones of pigment cells arise from medial cells near the neural keel, and that clones of neurons arise from lateral cells farther from the neural keel. Wnt-1 and Wnt-3a are candidate genes for influencing neural crest fate, as they are expressed next to medial, but not lateral, crest cells. Here we determine the role of Wnt signals in modulating the fate of neural crest by injecting messenger RNAs into single, premigratory neural crest cells of zebrafish. Lineage analysis of injected cells shows that activation of Wnt signalling by injection of mRNA encoding cytoplasmic beta-catenin promotes pigment-cell formation at the expense of neurons and glia. Conversely, inhibition of the Wnt pathway, by injection of mRNAs encoding either a truncated form of the transcription factor Tcf-3 or a dominant-negative Wnt, promotes neuronal fates at the expense of pigment cells. We conclude that endogenous Wnt signalling normally promotes pigment-cell formation by medial crest cells and thereby contributes to the diversity of neural crest cell fates.

Animals↗
PubMed1997

Expression of c-ret in the zebrafish embryo: potential roles in motoneuronal development.

We have isolated and characterized the zebrafish ortholog of c-ret, a gene essential for renal organogenesis and enteric nervous system development in mammals. During zebrafish embryogenesis c-ret transcripts are expressed in a number of tissues including spinal motoneurons, pronephric ducts, cranial ganglia, pharyngeal arches, and the enteric nervous system. We have examined in detail the expression of c-ret during the development of identified spinal primary motoneurons. c-ret expression is regulated in a cell type-specific manner among the three primary motoneurons. c-ret is expressed at its highest levels in caudal primary (CaP) motoneurons and transcripts can be detected shortly before the expression of the CaP-specific gene, islet2. We suggest that c-ret may play a role in specifying CaP cell identity. c-ret is expressed at low levels in the other primary motoneurons and also in a subset of secondary motoneurons, suggesting that it may also play a broader role in motoneuronal survival or maintenance.

Amino Acid Sequence↗
PubMed1996

Screen for mutations affecting development of Zebrafish neural crest.

The neural crest provides a useful model to learn how cell fate diversification is regulated during vertebrate development. Our approach is to isolate zebrafish mutations in which the development of neural crest derivatives is disrupted, in order to learn about the underlying genetic mechanisms. We describe a screen in which parthenogenetic diploid embryos are examined both for visible phenotypes and for cellular defects in neural crest-derived sensory neurons recognized immunohistochemically. We present preliminary results from this screen and briefly describe a few representative mutations. We also discuss the general utility of our strategy and comment on the future directions of this approach.

Animals↗
PubMed1996

Regulative interactions in zebrafish neural crest.

Zebrafish trunk neural crest cells that migrate at different times have different fates: early-migrating crest cells produce dorsal root ganglion neurons as well as glia and pigment cells, while late-migrating crest cells produce only non-neuronal derivatives. When presumptive early-migrating crest cells were individually transplanted into hosts such that they migrated late, they retained the ability to generate neurons. In contrast, late-migrating crest cells transplanted under the same conditions never generated neurons. These results suggest that, prior to migration, neural crest cells have intrinsic biases in the types of derivatives they will produce. Transplantation of presumptive early-migrating crest cells does not result in production of dorsal root ganglion neurons under all conditions suggesting that these cells require appropriate environmental factors to express these intrinsic biases. When early-migrating crest cells are ablated, late-migrating crest cells gain the ability to produce neurons, even when they migrate on their normal schedule. Interactions among neural crest cells may thus regulate the types of derivatives neural crest cells produce, by establishing or maintaining intrinsic differences between individual cells.

Animals↗
PubMed1995

Lateral specification of cell fate during vertebrate development.

Cells within equivalence groups interact via lateral specification to determine cell fates during development in Caenorhabditis elegans and other invertebrates. Populations of cells within the developing zebrafish have features similar to those of invertebrate equivalence groups. In a simple example, two identified zebrafish motoneurons behave as an equivalence pair in which one cell adopts a primary fate and interactions between the cells assign the other cell to a secondary fate. A more complicated situation exists for two initially equivalent populations of zebrafish neural crest cells. We consider whether mechanisms similar to those involved in fate specification within invertebrate equivalence groups also function furing fate specification in vertebrates.

Animals↗
PubMed1994

Rin, a novel cell-surface protein that labels reticular neurons early in chick neurogenesis.

Rin is a large cell-surface glycoprotein that we have recently purified from chick brain, with a molecular weight of approximately 200 kD. Protein microsequence obtained from immunopurified rin does not match any sequences in the Genbank data base. Based on the sequence information and on its localization in the early chick embryo, rin is a novel cell-surface protein. Rin is expressed on the surface of many, but not all, axons in the developing chick nervous system. In the chick hindbrain, rin is expressed on reticular neurons, the first neurons to extend axons within the brain. Cranial motoneurons, which extend axons just a few stages later, do not express rin. Rin-positive axons pioneer the caudal section of the medial longitudinal fasciculus. The very first rin-positive axons that reach the floorplate do not enter the floorplate, but remain ipsilateral. Some of the next immunopositive axons to reach the floorplate do cross the midline, often with an alteration in trajectory, and often extending within the floorplate for some distance before reaching the other side. The failure of the very first rin-positive axons to cross the floorplate, and the changes in trajectory observed when the next axons extend onto the floorplate, suggests that early differentiating neurons cross the midline with some difficulty.

Amino Acid Sequence↗
PubMed1994

Restriction of neural crest cell fate in the trunk of the embryonic zebrafish.

To learn when cell fate differences first arise in the zebrafish trunk neural crest, individual premigratory crest cells were labeled intracellularly with fluorescent vital dyes, followed in living embryos and complete lineages recorded. Although some of the earliest cells to migrate produced derivatives of multiple phenotypes, most zebrafish trunk neural crest cells appear to be lineage-restricted, generating type-restricted precursors that produce single kinds of derivatives. Further, cells that produce derivatives of multiple phenotypes appear to do so by first generating type-restricted precursors. Among the various types of derivatives, sensory and sympathetic cells arise only from early migrating crest cells. Some type-restricted precursors display cell-type-specific characteristics while still migrating. Taken together, these observations suggest that some trunk neural crest cells are specified before reaching their final locations.

Animals↗
PubMed1993

Oligodendrocyte differentiation and progenitor cell proliferation are independently regulated by cyclic AMP.

Oligodendrocytes, the glial cells specialized to synthesize myelin in the central nervous system, differentiate in primary rat brain cell cultures on a schedule similar to that observed in vivo. The schedule of oligodendrocyte differentiation and the rate of oligodendroglial progenitor cell proliferation in vitro are both modulated by 3',5'-cyclic AMP (cAMP). A 24-hour exposure to 1 mM N6,2'O-dibutyryladenosine 3',5'-cyclic monophosphate (dbcAMP) induced a wave of oligodendrocyte differentiation but inhibited proliferation of oligodendroglial progenitors, and reduced by 30-fold the proliferation of progenitors in response to platelet-derived growth factor (PDGF). When cells were grown in the presence of maximally stimulating concentrations of PDGF, the inhibitory effect of cAMP on progenitor cell proliferation was abolished while the stimulatory effect of cAMP on oligodendrocyte differentiation remained, demonstrating that these two cAMP-regulated events are independent.

Animals↗
PubMed1992

Segregation and early dispersal of neural crest cells in the embryonic zebrafish.

We have exploited our ability to visualize and follow individual cells in situ, in the living embryo, to study the development of trunk neural crest in the embryonic zebrafish. In most respects, the development of zebrafish trunk neural crest is similar to the development of trunk neural crest in other species: zebrafish trunk neural crest cells segregate from the dorsal neural keel in a rostrocaudal sequence, migrate ventrally along two pathways, and give rise to neurons of the peripheral nervous system, Schwann cells, and pigment cells. However, some aspects of the development of zebrafish trunk neural crest differ from those of other vertebrates: zebrafish trunk neural crest cells are significantly larger and fewer in number than those in avian embryos and the locations of their migratory pathways are slightly different. This initial description of neural crest development in the zebrafish embryo provides the foundation for future experimental studies.

Animals↗
PubMed1990

Induction of oligodendrocyte differentiation by activators of adenylate cyclase.

Oligodendrocyte differentiation is accelerated by analogs of cyclic AMP (cAMP), such as N6,2-'O-dibutyryladenosine 3',5'-cyclic monophosphate (dbcAMP) or 8-bromo cAMP, in developing rat glial cell cultures (Raible and McMorris, 1989). However, it is not known whether the immature developing oligodendrocytes have G protein-coupled adenylate cyclase capable of generating cAMP, as would be required if development of the cells is normally regulated by endogenous cAMP. In the present study, we demonstrate that the diterpene forskolin, a potent activator of adenylate cyclase, or cholera toxin, which activates adenylate cyclase through G protein modification, can induce a precocious increase in oligodendrocyte number. When both forskolin and cholera toxin are added together, oligodendrocyte differentiation is induced to a level similar to that observed in response to cAMP analogs. These results establish for the first time that modulation of the endogenous cAMP regulatory system alters the schedule of oligodendrocyte differentiation.

Adenylyl Cyclases↗