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At least 271 records · Page 15Linked to original sources
PubMed2002

Expression pattern of the single-minded gene in zebrafish embryos.

Recently we isolated a homolog of the Drosophila single-minded (sim) gene from a zebrafish cDNA library. The 4380-bp of zebrafish sim cDNA encodes a polypeptide of 585 amino acids with strikingly conserved bHLH and PAS A/B domains in the amino-terminal region. During embryogenesis, sim mRNA appears in the animal hemisphere as early as 3 h post-fertilization and is expressed in a widespread pattern throughout the epiblast at the 75% epiboly stage. During the segmentation stage, sim mRNA is prominently expressed in the primordium of the hindbrain and appears as a transverse stripe in the epithelial layers of the mid-diencephalic boundary (MDB). During the pharyngula stage, sim is no longer expressed in the hindbrain, but continues to be expressed in the MDB and extends to the caudal diencephalon along the ventral midline. In addition, sim mRNA is prominent in the two pharyngeal arches. During the larval stage, sim mRNA is transcribed in the esophagus, liver, pancreas, and intestine. In contrast, sim mRNA is no longer detectable in the forebrain after hatching. In adult fish, sim is widely expressed in brain, eyes, gill, heart, liver, and intestine.

Amino Acid Sequence↗
PubMed2001

Expression of zTlxA, a Hox11-like gene, in early differentiating embryonic neurons and cranial sensory ganglia of the zebrafish embryo.

We have isolated a cDNA encoding a member of the Tlx/Hox11 family of homeodomain factors from the zebrafish, most closely related to the vertebrate Tlx-1/Hox11 and Tlx-3/Hox11L2 proteins. The gene is expressed in a set of early differentiating neurons that project to a common tract, the lateral longitudinal fascicle. We show that the gene is specifically expressed in spinal cord Rohon Beard neurons, in nucleus of the posterior commissure neurons of the midbrain, in a set of hindbrain neurons that include RoL3 reticulospinal interneurons, and in the trigeminal, statoacoustic, anterior lateral line, glossopharyngeal, and vagal cranial sensory ganglia. Timing of expression of the gene in these neurons correlates with the phase of axonal outgrowth and target innervation. Expression of the gene is also observed in several non-neural tissues, including the pharyngeal arches, budding gill filaments, outgrowing semicircular protrusions in the otic vesicle, and in the pectoral fin buds.

Amino Acid Sequence↗
PubMed1998

Ectopic expression of hoxb2 after retinoic acid treatment or mRNA injection: disruption of hindbrain and craniofacial morphogenesis in zebrafish embryos.

To investigate pattern formation in the vertebrate hindbrain, we isolated a full length hoxb2 cDNA clone from zebrafish. In a gene phylogeny, zebrafish hoxb2 clusters with human HOXB2, and it maps on linkage group 3 along with several other loci whose orthologues are syntenic with human HOXB2. In the hindbrain, hoxb2 is expressed at high levels in rhombomere 3 (r3), lower levels in r4, still lower in r5, and at undetectable levels in r6. In r7, r8, and the rostral spinal cord, hoxb2 is expressed at a lower level than in r5. Lateral cells appearing to emanate from r4 express both hoxb2 and dlx2, suggesting that they are neural crest. Overexpression of hoxb2 by mRNA injections into early cleavage stage embryos resulted in abnormal morphogenesis of the midbrain and rostral hindbrain, abnormal patterning in r4, fusion of cartilage elements arising from pharyngeal arches 1 and 2, and ectopic expression of krx20 and valentino (but not pax2, rtk1, or hoxb1) in the rostral hindbrain, midbrain, and, surprisingly, the eye. Treatments with retinoic acid produced a phenotype similar to that of ectopic hoxb2 expression, including ectopic krx20 (but not valentino) expression in the eye, and fusion of cartilages from pharyngeal arches 1 and 2. The results suggest that hoxb2 plays an important role in the patterning of hindbrain and pharyngeal arches in the zebrafish.

Amino Acid Sequence↗
PubMed1990

Organization of hindbrain segments in the zebrafish embryo.

To learn how neural segments are structured in a simple vertebrate, we have characterized the embryonic zebrafish hindbrain with a library of monoclonal antibodies. Two regions repeat in an alternating pattern along a series of seven segments. One, the neuromere centers, contains the first basal plate neurons to develop and the first neuropil. The other region, surrounding the segment boundaries, contains the first neurons to develop in the alar plate. The projection patterns of these neurons differ: those in the segment centers have descending axons, while those in the border regions form ventral commissures. A row of glial fiber bundles forms a curtain-like structure between each center and border region. Specific features of the individual hindbrain segments in the series arise within this general framework. We suggest that a cryptic simplicity underlies the eventual complex structure that develops from this region of the CNS.

Animals↗
PubMed1993

A functionally conserved homolog of the Drosophila segment polarity gene hh is expressed in tissues with polarizing activity in zebrafish embryos.

The segment polarity gene hedgehog (hh) encodes a novel signaling protein that mediates local cell-cell interactions in the developing Drosophila embryo. Here we describe the existence of an hh-related gene family in the zebrafish, Brachydanio rerio. One of these genes, sonic hedgehog (shh), is expressed in the notochord, floor plate, and posterior fin mesoderm, tissues associated with polarizing activities in various vertebrate embryos. The pattern of shh expression in zebra-fish mutants affecting axial structures, together with the consequences of its ectopic expression in normal embryos, is consistent with a role for shh in floor plate induction. By expressing shh in transgenic Drosophila embryos, we also demonstrate a strong functional conservation between the fish and fly hh genes.

Amino Acid Sequence↗
PubMed2006

Two GC-rich boxes in huC promoter play distinct roles in controlling its neuronal specific expression in zebrafish embryos.

HuC, a vertebrate ortholog of Drosophila elav gene, encodes an RNA binding protein and is involved in early neurogenesis. Zebrafish huC is expressed in distinct neurons, including Rohon-Beard (RB) sensory neurons, interneurons and motoneurons, during primary neurogenesis, and in all neurons later during secondary neurogenesis. In this study, we identify two GC-rich box elements, proximal GC (p-GC) box from -172 to -149 and distal GC (d-GC) box from -218 to -208, in zebrafish huC promoter. Using transgenic approach, we demonstrate that deletion of the p-GC box from the promoter results in loss of expression of the reporter GFP in neurons while deletion of the d-GC box leads to GFP expression only in dorsal RB sensory neurons. These results suggest that the p-GC box alone confers transcriptional activity of huC promoter in primary RB neurons and the d-GC is required for huC transcription in the full spectrum of spinal cord neurons. Further studies are needed to identify specific Sp1-like transcription factors that bind to these GC boxes and activate huC transcription.

Animals↗
PubMed1999

The smad5 mutation somitabun blocks Bmp2b signaling during early dorsoventral patterning of the zebrafish embryo.

Signaling by members of the TGFbeta superfamily is thought to be transduced by Smad proteins. Here, we describe a zebrafish mutant in smad5, designated somitabun (sbn). The dominant maternal and zygotic effect of the sbntc24 mutation is caused by a change in a single amino acid in the L3 loop of Smad5 protein which transforms Smad5 into an antimorphic version, inhibiting wild-type Smad5 and related Smad proteins. sbn mutant embryos are strongly dorsalized, similarly to mutants in Bmp2b, its putative upstream signal. Double mutant analyses and RNA injection experiments show that sbn and bmp2b interact and that sbn acts downstream of Bmp2b signaling to mediate Bmp2b autoregulation during early dorsoventral (D-V) pattern formation. Comparison of early marker gene expression patterns, chimera analyses and rescue experiments involving temporally controlled misexpression of bmp or smad in mutant embryos reveal three phases of D-V patterning: an early sbn- and bmp2b-independent phase when a coarse initial D-V pattern is set up, an intermediate sbn- and bmp2b-dependent phase during which the putative morphogenetic Bmp2/4 gradient is established, and a later sbn-independent phase during gastrulation when the Bmp2/4 gradient is interpreted and cell fates are specified.

Amino Acid Sequence↗
PubMed2005

Kupffer's vesicle is a ciliated organ of asymmetry in the zebrafish embryo that initiates left-right development of the brain, heart and gut.

Monocilia have been proposed to establish the left-right (LR) body axis in vertebrate embryos by creating a directional fluid flow that triggers asymmetric gene expression. In zebrafish, dorsal forerunner cells (DFCs) express a conserved ciliary dynein gene (left-right dynein-related1, lrdr1) and form a ciliated epithelium inside a fluid-filled organ called Kupffer's vesicle (KV). Here, videomicroscopy demonstrates that cilia inside KV are motile and create a directional fluid flow just prior to the onset of asymmetric gene expression in lateral cells. Laser ablation of DFCs and surgical disruption of KV provide direct evidence that ciliated KV cells are required during early somitogenesis for subsequent LR patterning in the brain, heart and gut. Antisense morpholinos against lrdr1 disrupt KV fluid flow and perturb LR development. Furthermore, lrdr1 morpholinos targeted to DFC/KV cells demonstrate that Lrdr1 functions in these ciliated cells to control LR patterning. This provides the first direct evidence, in any vertebrate, that impairing cilia function in derivatives of the dorsal organizer, and not in other cells that express ciliogenic genes, alters LR development. Finally, genetic analysis reveals novel roles for the T-box transcription factor no tail and the Nodal signaling pathway as upstream regulators of lrdr1 expression and KV morphogenesis. We propose that KV is a transient embryonic 'organ of asymmetry' that directs LR development by establishing a directional fluid flow. These results suggest that cilia are an essential component of a conserved mechanism that controls the transition from bilateral symmetry to LR asymmetry in vertebrates.

Animals↗
PubMed2002

Reptin and pontin antagonistically regulate heart growth in zebrafish embryos.

Organ size is precisely regulated during development, but the control mechanisms remain obscure. We have isolated a mutation in zebrafish, liebeskummer (lik), which causes development of hyperplastic embryonic hearts. lik encodes Reptin, a component of a DNA-stimulated ATPase complex. The mutation activates ATPase activity of Reptin complexes and causes a cell-autonomous proliferation of cardiomyocytes to begin well after progenitors have fashioned the primitive heart tube. With regard to heart growth, beta-catenin and Pontin, a DNA-stimulated ATPase that is often part of complexes with Reptin, are in the same genetic pathways. Pontin reduction phenocopies the cardiac hyperplasia of the lik mutation. Thus, the Reptin/Pontin ratio serves to regulate heart growth during development, at least in part via the beta-catenin pathway.

ATP-Dependent Proteases↗
PubMed2001

Hematopoietic regulatory domain of gata1 gene is positively regulated by GATA1 protein in zebrafish embryos.

Expression of gata1 is regulated through multiple cis-acting GATA motifs. To elucidate regulatory mechanisms of the gata1 gene, we have used zebrafish. To this end, we isolated and analyzed zebrafish gata1 genomic DNA, which resulted in the discovery of a novel intron that was unknown in previous analyses. This intron corresponds to the first intron of other vertebrate Gata1 genes. GFP reporter analyses revealed that this intron and a distal double GATA motif in the regulatory region are important for the regulation of zebrafish gata1 gene expression. To examine whether GATA1 regulates its own gene expression, we microinjected into embryos a GFP reporter gene linked successively to the gata1 gene regulatory region and to GATA1 mRNA. Surprisingly, ectopic expression of the reporter gene was induced at the site of GATA1 overexpression and was dependent on the distal double GATA motif. Functional domain analyses using transgenic fish lines that harbor the gata1-GFP reporter construct revealed that both the N- and C-terminal zinc-finger domains of GATA1, hence intact GATA1 function, are required for the ectopic GFP expression. These results provide the first in vivo evidence that gata1 gene expression undergoes positive autoregulation.

Animals↗
PubMed2003

Whole-cell patch-clamp recordings from identified spinal neurons in the zebrafish embryo.

We describe a preparation for obtaining patch-clamp recordings from identified embryonic spinal cord interneurons, motoneurons and sensory neurons in an in vivo zebrafish preparation. This preparation is used to study the spatial and temporal patterns of spontaneous and touch-evoked electrical activity during the initial development of circuitry in the spinal cord. The combination of these physiological techniques with the powerful genetic and molecular tools available in the zebrafish has the potential to increase our understanding of the complex interactions between genes and electrical activity during the development of the vertebrate nervous system.

Animals↗
PubMed1996

Expression of axial and sonic hedgehog in wildtype and midline defective zebrafish embryos.

We present a description of the expression of the HNF-3 beta homolog axial (axl) in the developing zebrafish up to larva stages and compare it with that of sonic hedgehog (shh). Both genes are expressed in derivatives of all three germ layers in dynamic patterns that show substantial overlap, consistent with mutual regulatory interactions between the two genes. However, we also describe unique sites of expression of both axl and shh indicating that some aspects of their regulation are independent of one another. In no tail (ntl, zebrafish Brachyury) and floating head (flh, zebrafish Xnot1) mutants, both of which affect notochord development, early expression of axl in the organizer is unaffected, excluding a function for these genes in establishment of axl expression. At later stages, ntl and flh mutants show different effects on the expression of both axl and shh in the neuroectoderm of the trunk and tail reflecting their distinct contributions to the development of the midline mesoderm; in contrast to flh and ntl mutations whose effects are restricted to the trunk and tail, mutation of cyclops (cyc) affects axl and shh expression along the entire midline of the neuroectoderm. Endodermal expression of axl and shh is not affected by the mutations showing that development of the endoderm is under distinct control.

Animals↗
PubMed2005

Integrinalpha5-dependent fibronectin accumulation for maintenance of somite boundaries in zebrafish embryos.

Boundary formation and epithelialization are crucial processes in the morphological segmentation of vertebrate somites. By a genetic screening procedure with zebrafish, we identified two genes, integrinalpha5 (itga5) and fibronectin (fn), required for these processes. Fibronectin proteins accumulate at somite boundaries in accordance with epithelialization of the somites. Both Fibronectin accumulation and the epithelialization are dependent on itga5, which is expressed in the most medial part of somites. Although somite boundaries are initially formed, but not maintained, in the anterior trunk of the mutant embryos deficient in either gene, their maintenance is defective at all axial levels of embryos deficient for both of these genes. Therefore, Integrinalpha5-directed assembly of Fibronectin appears critical for epithelialization and boundary maintenance of somites. Furthermore, with an additional deficiency in ephrin-B2a, the segmental defect in itga5 or fn mutant embryos is expanded posteriorly, indicating that both Integrin-Fibronectin and Eph-Ephrin systems function cooperatively in maintaining somite boundaries.

Animals↗
PubMed2005

Expression analysis of jagged genes in zebrafish embryos.

The interaction of transmembrane Delta and Jagged/Serrate ligands with Notch receptors on neighboring cells is critically involved in cell specification during development. In zebrafish, the early expression of delta but not of jagged genes has been investigated in some detail. We have analyzed the sequence and embryonic expression pattern of the three zebrafish genes jagged1a, jagged1b, and jagged2. These genes, whose transcripts are detectable by in situ hybridization from early somitogenesis, are widely and dynamically expressed in embryos. Coexpression is limited, however, to the notochord and lens (jagged1a and jagged1b) and to the otic vesicle and pronephros (jagged1b and jagged2). Conversely, jagged1a and jagged2, both widely expressed in the central nervous system, are not coexpressed. jagged2 is also detected in the epidermis, newly formed somites, pharyngeal pouches, and pancreatic exocrine anlage and jagged1b in otic placodes and cell clusters close to the pancreatic islet. The similarities of the expression patterns of jagged and delta genes in zebrafish suggest that the Jagged and Delta ligands are functionally redundant or required in specific combinations in many differentiation processes.

Animals↗
PubMed2004

No correlation between multilamellar bodies in the inner ear and further organs of mutant (backstroke, bks) and wildtype zebrafish embryos.

The origin of the proteinacious matrix of the inner ear stones (otoliths) of vertebrates has not yet been clarified. Using the backstroke mutant (bks) of the zebrafish Danio rerio, which is characterized by a complete lack of otoliths, we searched for possibly missing or aberrant structural components within the macular epithelia of the inner ears of embryos on the ultrastructural level. Numerous multilamellar bodies (MLBs) were found. The MLBs were, however, not restricted to the inner ears of mutants but were also found in wildtype individuals and in further organs such as brain and liver. MLBs have hitherto never been described from the inner ear of fish and are generally estimated to be rare structures. Their occurrence in fish liver can, however, be induced by using particular chemical substances, which seem to effect adaptive compensatory processes on the cellular level. Such a chemical treatment also affects the ultrastructure of further organelles. Since the occurrence of MLBs in the liver of zebrafish was not accompanied by an alteration of the morphology of other organelles, their occurrence seems not to be due to environmental stress. The findings indicate that the MLBs cannot be correlated with bks-inherent features as well as with missing otolith development/growth. Since the occurrence of MLBs was independent from the developmental stage of a specimen and its overall tissue preservation, it can moreover be excluded that these MLBs merely represent fixation artifacts. Their presence more likely indicates cellular remodelling processes of hitherto unknown significance.

Acoustic Maculae↗