SEARCH · PubMed Health

Results for “zebrafish”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,153 records · Page 64Linked to original sources

PubMed2004

Zebrafish Dapper1 and Dapper2 play distinct roles in Wnt-mediated developmental processes.

Wnt signaling pathways in vertebrates use the phosphoprotein Dishevelled (Dvl). The cellular responses to Wnt signaling may in part be modulated by Dvl-associated proteins, including Dapper (Dpr). We have cloned and characterized the zebrafish Dpr paralogs Dpr1 and Dpr2. Loss-of-function studies reveal that endogenous Dpr1 but not Dpr2 is required to enhance Wnt/beta-catenin activity in zebrafish embryos that are hypomorphic for Wnt8. Conversely, Dpr2 but not Dpr1 is required for normal convergence extension movements in embryos that are hypomorphic for Stbm or Wnt11, supporting a functional interaction of Dpr2 with Wnt/Ca2+-PCP signaling. In gain-of-function experiments, Dpr1 but not Dpr2 induces Wnt/beta-catenin target genes. Dpr1 synergizes with zebrafish Dvl2, and with the Dvl-interacting kinases CK1epsilon, Par1 and CK2, in activating target genes. We conclude that two Dvl-associated paralogs, Dpr1 and Dpr2, participate in distinct Wnt-dependent developmental processes.

Adaptor Proteins, Signal Transducing↗

PubMed2005

Robo2 is required for establishment of a precise glomerular map in the zebrafish olfactory system.

Olfactory sensory neurons (OSNs) expressing a given odorant receptor project their axons to specific glomeruli, creating a topographic odor map in the olfactory bulb (OB). The mechanisms underlying axonal pathfinding of OSNs to their precise targets are not fully understood. Here, we demonstrate that Robo2/Slit signaling functions to guide nascent olfactory axons to the OB primordium in zebrafish. robo2 is transiently expressed in the olfactory placode during the initial phase of olfactory axon pathfinding. In the robo2 mutant, astray (ast), early growing olfactory axons misroute ventromedially or posteriorly, and often penetrate into the diencephalon without reaching the OB primordium. Four zebrafish Slit homologs are expressed in regions adjacent to the olfactory axon trajectory, consistent with their role as repulsive ligands for Robo2. Masking of endogenous Slit gradients by ubiquitous misexpression of Slit2 in transgenic fish causes posterior pathfinding errors that resemble the ast phenotype. We also found that the spatial arrangement of glomeruli in OB is perturbed in ast adults, suggesting an essential role for the initial olfactory axon scaffold in determining a topographic glomerular map. These data provide functional evidence for Robo2/Slit signaling in the establishment of olfactory neural circuitry in zebrafish.

Animals↗

PubMed2005

Wnt/beta-catenin regulation of the Sp1-related transcription factor sp5l promotes tail development in zebrafish.

Tail formation in vertebrates involves the specification of a population of multipotent precursors, the tailbud, which will give rise to all of the posterior structures of the embryo. Wnts are signaling proteins that are candidates for promoting tail outgrowth in zebrafish, although which Wnts are involved, what genes they regulate, and whether Wnts are required for initiation or maintenance steps in tail formation has not been resolved. We show here that both wnt3a and wnt8 are expressed in the zebrafish tailbud and that simultaneous inhibition of both wnt3a and wnt8 using morpholino oligonucleotides can completely block tail formation. In embryos injected with wnt3a and wnt8 morpholinos, expression of genes in undifferentiated presomitic mesoderm is initiated, but not maintained. To identify genes that might function downstream of Wnts in tail formation, a DNA microarray screen was conducted, revealing that sp5l, a member of the Sp1 family of zinc-finger transcription factors, is activated by Wnt signaling. Moreover, we show that sp5l expression in the developing tail is dependent on both wnt3a and wnt8 function. Supporting a role for sp5l in tail formation, we find that inhibition of sp5l strongly enhances the effects of wnt3a inhibition, and overexpression of sp5l RNA is able to completely restore normal tail development in wnt3a morphants. These data place sp5l downstream of wnt3a and wnt8 in a Wnt/beta-catenin signaling pathway that controls tail development in zebrafish.

Animals↗

PubMed2005

AP2-dependent signals from the ectoderm regulate craniofacial development in the zebrafish embryo.

AP2 transcription factors regulate many aspects of embryonic development. Studies of AP2a (Tfap2a) function in mice and zebrafish have demonstrated a role in patterning mesenchymal cells of neural crest origin that form the craniofacial skeleton, while the mammalian Tfap2b is required in both the facial skeleton and kidney. Here, we show essential functions for zebrafish tfap2a and tfap2b in development of the facial ectoderm, and for signals from this epithelium that induce skeletogenesis in neural crest cells (NCCs). Zebrafish embryos deficient for both tfap2a and tfap2b show defects in epidermal cell survival and lack NCC-derived cartilages. We show that cartilage defects arise after NCC migration during skeletal differentiation, and that they can be rescued by transplantation of wild-type ectoderm. We propose a model in which AP2 proteins play two distinct roles in cranial NCCs: an early cell-autonomous function in cell specification and survival, and a later non-autonomous function regulating ectodermal signals that induce skeletogenesis.

Animals↗

PubMed2005

A genetic screen in zebrafish identifies the mutants vps18, nf2 and foie gras as models of liver disease.

Hepatomegaly is a sign of many liver disorders. To identify zebrafish mutants to serve as models for hepatic pathologies, we screened for hepatomegaly at day 5 of embryogenesis in 297 zebrafish lines bearing mutations in genes that are essential for embryonic development. Seven mutants were identified, and three have phenotypes resembling different liver diseases. Mutation of the class C vacuolar protein sorting gene vps18 results in hepatomegaly associated with large, vesicle-filled hepatocytes, which we attribute to the failure of endosomal-lysosomal trafficking. Additionally, these mutants develop defects in the bile canaliculi and have marked biliary paucity, suggesting that vps18 also functions to traffic vesicles to the hepatocyte apical membrane and may play a role in the development of the intrahepatic biliary tree. Similar findings have been reported for individuals with arthrogryposis-renal dysfunction-cholestasis (ARC) syndrome, which is due to mutation of another class C vps gene. A second mutant, resulting from disruption of the tumor suppressor gene nf2, develops extrahepatic choledochal cysts in the common bile duct, suggesting that this gene regulates division of biliary cells during development and that nf2 may play a role in the hyperplastic tendencies observed in biliary cells in individuals with choledochal cysts. The third mutant is in the novel gene foie gras, which develops large, lipid-filled hepatocytes, resembling those in individuals with fatty liver disease. These mutants illustrate the utility of zebrafish as a model for studying liver development and disease, and provide valuable tools for investigating the molecular pathogenesis of congenital biliary disorders and fatty liver disease.

Animals↗

PubMed2006

lessen encodes a zebrafish trap100 required for enteric nervous system development.

The zebrafish enteric nervous system (ENS), like those of all other vertebrate species, is principally derived from the vagal neural crest. The developmental controls that govern the specification and patterning of the ENS are not well understood. To identify genes required for the formation of the vertebrate ENS, we preformed a genetic screen in zebrafish. We isolated the lessen (lsn) mutation that has a significant reduction in the number of ENS neurons as well as defects in other cranial neural crest derived structures. We show that the lsn gene encodes a zebrafish orthologue of Trap100, one of the subunits of the TRAP/mediator transcriptional regulation complex. A point mutation in trap100 causes a premature stop codon that truncates the protein, causing a loss of function. Antisense-mediated knockdown of trap100 causes an identical phenotype to lsn. During development trap100 is expressed in a dynamic tissue-specific expression pattern consistent with its function in ENS and jaw cartilage development. Analysis of neural crest markers revealed that the initial specification and migration of the neural crest is unaffected in lsn mutants. Phosphohistone H3 immunocytochemistry revealed that there is a significant reduction in proliferation of ENS precursors in lsn mutants. Using cell transplantation studies, we demonstrate that lsn/trap100 acts cell autonomously in the pharyngeal mesendoderm and influences the development of neural crest derived cartilages secondarily. Furthermore, we show that endoderm is essential for ENS development. These studies demonstrate that lsn/trap100 is not required for initial steps of cranial neural crest development and migration, but is essential for later proliferation of ENS precursors in the intestine.

Animals↗

PubMed2006

Differentiation of cerebellar cell identities in absence of Fgf signalling in zebrafish Otx morphants.

Although the secreted molecule Fgf8 is a key player of the isthmic organiser function, the mechanisms by which it acts remain unclear. Here, we present evidence indicating that Fgf8 is not instructive in establishing zebrafish cerebellar cell identities, although it is required for proliferation and morphogenesis of this territory. We first show that, as in mouse, lack of Otx function in zebrafish leads to transformation of the presumptive mesencephalon into an extended rhombomere 1 (r1). Expanded Fgf8 expression was proposed to be the cause of this fate transformation. However, this report demonstrates that zebrafish embryos lacking both Otx and fgf8 functions retain an extended r1 and display differentiation of at least two cerebellar cell fates. We show that this is not caused by presence of other Fgfs, which implies that in absence of Otx, Fgf function is not necessary for the differentiation of cerebellar cell types. Otx proteins are therefore potent repressors of cerebellar fates, kept out of r1 progeny by Fgf8. Because Otx transcripts are not present in presumptive r1 territory prior to fgf8 expression, Fgf8 is required to maintain, rather than induce, the posterior boundary of Otx expression. This maintenance is enough to allow cerebellar differentiation.

Animals↗

PubMed2006

her5 expression reveals a pool of neural stem cells in the adult zebrafish midbrain.

Current models of vertebrate adult neural stem cells are largely restricted to the rodent forebrain. To extract the general mechanisms of neural stem cell biology, we sought to identify new adult stem cell populations, in other model systems and/or brain areas. The teleost zebrafish appears to be an ideal system, as cell proliferation in the adult zebrafish brain is found in many more niches than in the mammalian brain. As a starting point towards identifying stem cell populations in this system, we used an embryonic neural stem cell marker, the E(spl) bHLH transcription factor Her5. We demonstrate that her5 expression is not restricted to embryonic neural progenitors, but also defines in the adult zebrafish brain a new proliferation zone at the junction between the mid- and hindbrain. We show that adult her5-expressing cells proliferate slowly, self-renew and express neural stem cell markers. Finally, using in vivo lineage tracing in her5:gfp transgenic animals, we demonstrate that the her5-positive population is multipotent, giving rise in situ to differentiated neurons and glia that populate the basal midbrain. Our findings conclusively identify a new population of adult neural stem cells, as well as their fate and their endogenous environment, in the intact vertebrate brain. This cell population, located outside the forebrain, provides a powerful model to assess the general mechanisms of vertebrate neural stem cell biology. In addition, the first transcription factor characteristic of this cell population, Her5, points to the E(Spl) as a promising family of candidate adult neural stem cell regulators.

Animals↗

PubMed2006

Zebrafish atoh1 genes: classic proneural activity in the inner ear and regulation by Fgf and Notch.

Hair cells of the inner ear develop from an equivalence group marked by expression of the proneural gene Atoh1. In mouse, Atoh1 is necessary for hair cell differentiation, but its role in specifying the equivalence group (proneural function) has been questioned and little is known about its upstream activators. We have addressed these issues in zebrafish. Two zebrafish homologs, atoh1a and atoh1b, are together necessary for hair cell development. These genes crossregulate each other but are differentially required during distinct developmental periods, first in the preotic placode and later in the otic vesicle. Interactions with the Notch pathway confirm that atoh1 genes have early proneural function. Fgf3 and Fgf8 are upstream activators of atoh1 genes during both phases, and foxi1, pax8 and dlx genes regulate atoh1b in the preplacode. A model is presented in which zebrafish atoh1 genes operate in a complex network leading to hair cell development.

Animals↗

PubMed1995

Nodal induces ectopic goosecoid and lim1 expression and axis duplication in zebrafish.

One of the first intercellular signalling events in the vertebrate embryo leads to mesoderm formation and axis determination. In the mouse, a gene encoding a new member of the TGF-beta superfamily, nodal, is disrupted in a mutant deficient in mesoderm formation (Zhou et al., 1993, Nature 361, 543). nodal mRNA is found in prestreak mouse embryos, consistent with a role in the development of the dorsal axis. To examine the biological activities of nodal, we have studied the action of this factor in eliciting axis determination in the zebrafish, Danio rerio. Injection of nodal mRNA into zebrafish embryos caused the formation of ectopic axes that included notochord and somites. Axis duplication was preceded by the generation of an apparent ectopic shield (organizer equivalent) in nodal-injected embryos, as indicated by the appearance of a region over-expressing gsc and lim1; isolation and expression in the shield of the lim1 gene is reported here. These results suggest a role for a nodal-like factor in pattern formation in zebrafish.

Amino Acid Sequence↗

PubMed1996

Specification of cell fates at the dorsal margin of the zebrafish gastrula.

Using fate mapping techniques, we have analyzed development of cells of the dorsal marginal region in wild-type and mutant zebrafish. We define a domain in the early gastrula that is located just at the margin and centered on the dorsal midline, in which most cells generate clones that develop exclusively as notochord. The borders of the notochord domain are sharp at the level of single cells, and coincide almost exactly with the border of the expression domain of the homeobox gene floating head (flh; zebrafish homologue of Xnot), a gene essential for notochord development. In flh mutants, cells in the notochord domain generate clones of muscle cells. In contrast, notochord domain cells form mesenchyme in embryos mutant for no tail (ntl; zebrafish homologue of Brachyury). A minority of cells in the notochord domain in wild-type embryos develop as unrestricted mesoderm, invariably located in the tail, suggesting that early gastrula expression of flh does not restrict cellular potential to the notochord fate. The unrestricted tail mesodermal fate is also expressed by the forerunner cells, a cluster of cells located outside the blastoderm, adjacent to the notochord domain. We show that cells can leave the dorsal blastoderm to join the forerunners, suggesting that relocation between fate map domains might respecify notochord domain cells to the tail mesodermal fate. An intermediate fate of the forerunners is to form the epithelial lining of Kupffer's vesicle, a transient structure of the teleost tailbud. The forerunners appear to generate the entire structure of Kupffer's vesicle, which also develops in most flh mutants. Although forerunner cells are present in ntl mutants, Kupffer's vesicle never appears, which is correlated with the later severe disruption of tail development.

Animals↗

PubMed1997

Development of branchiomotor neurons in zebrafish.

The mechanisms underlying neuronal specification and axonogenesis in the vertebrate hindbrain are poorly understood. To address these questions, we have employed anatomical methods and mutational analysis to characterize the branchiomotor neurons in the zebrafish embryo. The zebrafish branchiomotor system is similar to those in the chick and mouse, except for the location of the nVII and nIX branchiomotor neurons. Developmental analyses of genes expressed by branchiomotor neurons suggest that the different location of the nVII neurons in the zebrafish may result from cell migration. To gain insight into the mechanisms underlying the organization and axonogenesis of these neurons, we examined the development of the branchiomotor pathways in neuronal mutants. The valentino b337 mutation blocks the formation of rhombomeres 5 and 6, and severely affects the development of the nVII and nIX motor nuclei. The cyclops b16 mutation deletes ventral midline cells in the neural tube, and leads to a severe disruption of most branchiomotor nuclei and axon pathways. These results demonstrate that rhombomere-specific cues and ventral midline cells play important roles in the development of the branchiomotor pathways.

Animals↗

PubMed1997

GATA-1 expression pattern can be recapitulated in living transgenic zebrafish using GFP reporter gene.

In this study, DNA constructs containing the putative zebrafish promoter sequences of GATA-1, an erythroid-specific transcription factor, and the green fluorescent protein reporter gene, were microinjected into single-cell zebrafish embryos. Erythroid-specific activity of the GATA-1 promoter was observed in living embryos during early development. Fluorescent circulating blood cells were detected in microinjected embryos 24 hours after fertilization and were still present in 2-month-old fish. Germline transgenic fish obtained from the injected founders continued to express green fluorescent protein in erythroid cells in the F1 and F2 generations. The green fluorescent protein expression patterns in transgenic fish were consistent with the pattern of GATA-1 mRNA expression detected by RNA in situ hybridization. These transgenic fish have allowed us to isolate, by fluorescence-activated cell sorting, the earliest erythroid progenitor cells from developing embryos for in vitro studies. By generating transgenic fish using constructs containing other zebrafish promoters and green fluorescent protein reporter gene, it should be possible to visualize the origin and migration of any lineage-specific progenitor cells in a living embryo.

Animals↗

PubMed1998

Sonic hedgehog is not required for the induction of medial floor plate cells in the zebrafish.

Sonic hedgehog (Shh) is a secreted protein that is involved in the organization and patterning of several tissues in vertebrates. We show that the zebrafish sonic-you (syu) gene, a member of a group of five genes required for somite patterning, is encoding Shh. Embryos mutant for a deletion of syu display defects in patterning of the somites, the lateral floor plate cells, the pectoral fins, the axons of motorneurons and the retinal ganglion cells. In contrast to mouse embryos lacking Shh activity, syu mutant embryos do form medial floor plate cells and motorneurons. Since ectopic overexpression of shh in zebrafish embryos does not induce ectopic medial floor plate cells, we conclude that shh is neither required nor sufficient to induce this cell type in the zebrafish.

Animals↗

PubMed1998

Evidence for a frizzled-mediated wnt pathway required for zebrafish dorsal mesoderm formation.

We have used zebrafish as a model system for the study of vertebrate dorsoventral patterning. We isolated a maternally expressed and dorsal organizer localized member of the frizzled family of wnt receptors. Wild-type and dominant, loss-of-function molecules in misexpression studies demonstrate frizzled function is necessary and sufficient for dorsal mesoderm specification. frizzled activity is antagonized by the action of GSK-3, and we show GSK-3 is also required for zebrafish dorsal mesoderm formation. frizzled cooperatively interacts with the maternally encoded zebrafish wnt8 protein in dorsal mesodermal fate determination. This frizzled -mediated wnt pathway for dorsal mesoderm specification provides the first evidence for the requirement of a wnt-like signal in vertebrate axis determination.

Amino Acid Sequence↗

PubMed1998

Regulation of neuronal specification in the zebrafish spinal cord by Delta function.

The vertebrate spinal cord consists of a large number of different cell types in close proximity to one another. The identities of these cells appear to be specified largely by information acquired from their local environments. We report here that local cell-cell interactions, mediated by zebrafish homologues of the Drosophila melanogaster neurogenic gene, Delta, regulate specification of diverse neuronal types in the ventral spinal cord. We describe identification of a novel zebrafish Delta gene expressed specifically in the nervous system and show, by expressing a dominant negative form of Delta protein in embryos, that Delta proteins mediate lateral inhibition in the zebrafish spinal cord. Furthermore, we find that Delta function is important for specification of a variety of spinal cord neurons, suggesting that lateral inhibition serves to diversify neuronal fate during development of the vertebrate spinal cord.

Animals↗

PubMed1999

Zebrafish aussicht mutant embryos exhibit widespread overexpression of ace (fgf8) and coincident defects in CNS development.

During the development of the zebrafish nervous system both noi, a zebrafish pax2 homolog, and ace, a zebrafish fgf8 homolog, are required for development of the midbrain and cerebellum. Here we describe a dominant mutation, aussicht (aus), in which the expression of noi and ace is upregulated. In aus mutant embryos, ace is upregulated at many sites in the embryo, while noi expression is only upregulated in regions of the forebrain and midbrain which also express ace. Subsequent to the alterations in noi and ace expression, aus mutants exhibit defects in the differentiation of the forebrain, midbrain and eyes. Within the forebrain, the formation of the anterior and postoptic commissures is delayed and the expression of markers within the pretectal area is reduced. Within the midbrain, En and wnt1 expression is expanded. In heterozygous aus embryos, there is ectopic outgrowth of neural retina in the temporal half of the eyes, whereas in putative homozygous aus embryos, the ventral retina is reduced and the pigmented retinal epithelium is expanded towards the midline. The observation that aus mutant embryos exhibit widespread upregulation of ace raised the possibility that aus might represent an allele of the ace gene itself. However, by crossing carriers for both aus and ace, we were able to generate homozygous ace mutant embryos that also exhibited the aus phenotype. This indicated that aus is not tightly linked to ace and is unlikely to be a mutation directly affecting the ace locus. However, increased Ace activity may underly many aspects of the aus phenotype and we show that the upregulation of noi in the forebrain of aus mutants is partially dependent upon functional Ace activity. Conversely, increased ace expression in the forebrain of aus mutants is not dependent upon functional Noi activity. We conclude that aus represents a mutation involving a locus normally required for the regulation of ace expression during embryogenesis.

Animals↗

PubMed1999

her1, a zebrafish pair-rule like gene, acts downstream of notch signalling to control somite development.

During vertebrate embryonic development, the paraxial mesoderm becomes subdivided into metameric units known as somites. In the zebrafish embryo, genes encoding homologues of the proteins of the Drosophila Notch signalling pathway are expressed in the presomitic mesoderm and expression is maintained in a segmental pattern during somitogenesis. This expression pattern suggests a role for these genes during somite development. We misexpressed various zebrafish genes of this group by injecting mRNA into early embryos. RNA encoding a constitutively active form of notch1a (notch1a-intra) and a truncated variant of deltaD [deltaD(Pst)], as well as transcripts of deltaC and deltaD, the hairy-E(spl) homologues her1 and her4, and groucho2 were tested for their effects on somite formation, myogenesis and on the pattern of transcription of putative downstream genes. In embryos injected with any of these RNAs, with the exception of groucho2 RNA, the paraxial mesoderm differentiated normally into somitic tissue, but failed to segment correctly. Activation of notch results in ectopic activation of her1 and her4. This misregulation of the expression of her genes might be causally related to the observed mesodermal defects, as her1 and her4 mRNA injections led to effects similar to those seen with notch1a-intra. deltaC and deltaD seem to function after subdivision of the presomitic mesoderm, since the her gene transcription pattern in the presomitic mesoderm remains essentially normal after misexpression of delta genes. Whereas notch signalling alone apparently does not affect myogenesis, zebrafish groucho2 is involved in differentiation of mesodermal derivatives.

Animals↗