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At least 595 records · Page 33Linked to original sources
PubMed1999

Origin and development of the zebrafish endoderm.

The segregation of cells into germ layers is one of the earliest events in the establishment of cell fate in the embryo. In the zebrafish, endoderm and mesoderm are derived from cells that involute into an internal layer, the hypoblast, whereas ectoderm is derived from cells that remain in the outer layer, the epiblast. In this study, we examine the origin of the zebrafish endoderm and its separation from the mesoderm. By labeling individual cells located at the margin of the blastula, we demonstrate that all structures that are endodermal in origin are derived predominantly from the more dorsal and lateral cells of the blastoderm margin. Frequently marginal cells give rise to both endodermal and mesodermal derivatives, demonstrating that these two lineages have not yet separated. Cells located farther than 4 cell diameters from the margin give rise exclusively to mesoderm, and not to endoderm. Following involution, we see a variety of cellular changes indicating the differentiation of the two germ layers. Endodermal cells gradually flatten and extend filopodial processes forming a noncontiguous inner layer of cells against the yolk. At this time, they also begin to express Forkhead-domain 2 protein. Mesodermal cells form a coherent layer of round cells separating the endoderm and ectoderm. In cyclops-mutant embryos that have reduced mesodermal anlage, we demonstrate that by late gastrulation not only mesodermal but also endodermal cells are fewer in number. This suggests that a common pathway initially specifies germ layers together before a progressive sequence of determinative events segregate endoderm and mesoderm into morphologically distinct germ layers.

Animals↗
PubMed2003

Genetic dissection of thymus development in mouse and zebrafish.

Lymphoid organs represent a specialized microenvironment for interaction of stromal and lymphoid cells. In primary lymphoid organs, these interactions are required to establish a self-tolerant repertoire of lymphocytes. While detailed information is available about the genes that control lymphocyte differentiation, little is known about the genes that direct the establishment and differentiation of principal components of such microenvironments. Here, we discuss genetic studies addressing the role of thymic epithelial cells (TECs) during thymopoiesis. We have identified an evolutionarily conserved key regulator of TEC differentiation, Foxn1, that is required for the immigration of prothymocytes into the thymic primordium. Because Foxn1 specifies the prospective endodermal domain that gives rise to thymic epithelial cells, it can be used to identify the evolutionary origins of this specialized cell type. In the course of these studies, we have found that early steps of thymus development in zebrafish are very similar to those in mice. Subsequently, we have used chemical mutagenesis to derive zebrafish lines with aberrant thymus development. Strengths and weaknesses of mouse and zebrafish models are largely complementary such that genetic analysis of mouse and zebrafish mutants may lead to a better understanding of thymus development.

Adaptation, Biological↗
PubMedDate not supplied

Ventromedial focus of cell death is absent during development of Xenopus and zebrafish inner ears.

We present the normal patterns of programmed cell death in the developing inner ears of a primitive anuran, Xenopus laevis, and an ostariophysan fish, Danio rerio. A prominent ventromedial focus of cell death was described previously in the developing chicken and mouse otocysts. We hypothesize that this focus of cell death might be associated with a signaling center that directs morphogenesis of the surrounding tissue. Amphibian and fish ear anatomies differ considerably from those of birds and mammals, particularly in the structures derived from the ventral part (pars inferior) of the otic vesicle. We reasoned that these anatomical differences between species might result from a difference in the size, location, or presence of a putative morphogenetic signaling center. Using in situ terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick-end labeling (TUNEL) to detect apoptotic cells, we show that developing Xenopus and zebrafish ears have apoptotic cells in the eighth cranial ganglia, the developing sensory patches, and in various positions in the otocyst wall. However, both species lack the persistent ventromedial hot spot of cell death that is prominently situated between the pars superior and pars inferior in the chicken and mouse otocysts.

Anatomy, Comparative↗
PubMed2004

Development of the zebrafish lateral line.

The lateral line system is simple (comprising six cell types), its sense organs form according to a defined and reproducible pattern, and its neurons are easily visualized. In the zebrafish, these advantages can be combined with a wealth of genetic tools, making this system ideally suited to a combined molecular, cellular and genetic analysis. Recent progress has taken advantage of these various qualities to elucidate the mechanism that drives the migration from head to tail of the sense organ precursor cells, and to approach the questions surrounding axonal guidance and target recognition.

Animals↗
PubMed2006

Dynamic expression of the osmosensory channel trpv4 in multiple developing organs in zebrafish.

Transient receptor potential channels function in a wide spectrum of tissues and transduce sensory stimuli. The vanilloid (capsaicin) channel TRPV4 is sensitive to osmotic changes and plays a central role in osmoregulatory responses in a variety of organisms. We cloned a zebrafish trpv4 cDNA and assayed its expression during embryogenesis. trpv4 is expressed as maternal mRNA in 4-cell embryos and later zygotic expression is first observed in the forming notochord at the one somite stage. Notochord expression persists to 24 hpf when broad expression in the brain is observed. At 32 hpf trpv4 expression is observed in the endocardium, restricted primarily to the ventricular endothelium. Low level expression of trpv4 is also seen from 32-48 hpf in the pronephric kidney with strongest expression in the most distal nephron segment and in the cloaca. Expression is also observed in lateral line organs starting at 32 hpf, primarily in the hair cells. At 72 hpf, expression of trpv4 in heart, kidney, brain, and lateral line organs persists while expression in the notochord is down-regulated.

Amino Acid Sequence↗
PubMed2002

B cells develop in the zebrafish pancreas.

The zebrafish, with its transparent free-living embryo, is a useful organism for investigating early stages in lymphopoiesis. Previously, we showed that T cells differentiate in the thymus by day 4, but no sites for B cell differentiation were seen until 3 weeks. We report here that on day 4, we detect rearrangements of genes encoding B cell receptors in DNA extracted from whole fish. Also by day 4, rag1 transcripts are seen in the pancreas, an organ not previously associated with lymphopoiesis; by day 10, Igmu transcripts are detected here. Thus, in zebrafish, the pancreas assumes the role of both the liver in fetal mice and the spleen in neonatal mice.

Animals↗
PubMed1999

Early postembryonic neural development in the zebrafish: a 3-D reconstruction of forebrain proliferation zones shows their relation to prosomeres.

Based on a section-by-section analysis of the morphology (combined silver/Nissl stain) and of the distribution of proliferation zones (immunohistochemical detection of the proliferating cell nuclear antigen) in the zebrafish (Danio rerio) forebrain at 5 days postfertilization, we created a three-dimensional reconstruction of proliferation zones of that developmental stage. The resulting model visualizes the size, number, location and morphology of forebrain proliferation zones. The latter foreshadow closely adult neuroanatomical forebrain entities. Furthermore, the detailed distribution of proliferation zones in the posterior forebrain - but not in the more anterior secondary prosencephalon - supports a segmental prosomeric organization.

Animals↗
PubMed2004

Met and Hgf signaling controls hypaxial muscle and lateral line development in the zebrafish.

Somites give rise to a number of different embryonic cell types, including the precursors of skeletal muscle populations. The lateral aspect of amniote and fish somites have been shown to give rise specifically to hypaxial muscle, including the appendicular muscle that populates fins and limbs. We have investigated the morphogenetic basis for formation of specific hypaxial muscles within the zebrafish embryo and larvae. Transplantation experiments have revealed a developmentally precocious commitment of cells derived from pectoral fin level somites to forming hypaxial and specifically appendicular muscle. The fate of transplanted somites cannot be over-ridden by local inductive signals, suggesting that somitic tissue may be fixed at an early point in their developmental history to produce appendicular muscle. We further show that this restriction in competence is mirrored at the molecular level, with the exclusive expression of the receptor tyrosine kinase met within somitic regions fated to give rise to appendicular muscle. Loss-of-function experiments reveal that Met and its ligand, hepatocyte growth factor, are required for the correct morphogenesis of the hypaxial muscles in which met is expressed. Furthermore, we demonstrate a requirement for Met signaling in the process of proneuromast deposition from the posterior lateral line primordia.

Animals↗
PubMed1993

Cardiovascular development in the zebrafish. I. Myocardial fate map and heart tube formation.

We have analyzed the origin of cardiac progenitors in the zebrafish embryo by injection of single blastomeres with a lineage tracer dye, and examined the formation of the zebrafish heart tube by serial sectioning of immunostained embryos. At the 512-cell stage (early blastula), most cardiac progenitors lie in a marginal zone that extends from 90 degrees longitude (midway between the future dorsal and ventral axis) through 180 degrees longitude (the future ventral axis) to 270 degrees longitude. By focusing on myocardial progenitors located at 90 degrees (and 270 degrees) longitude, we found that a single cell injected in the early blastula can contribute progeny to both the atrium and ventricle. A cell injected in the midblastula contributes progeny to either the atrium or ventricle, but not both. This analysis suggests that, at least for these myocardial progenitors, the atrial and ventricular lineages separate in the midblastula. Precardiac cells involute early during gastrulation and turn towards the animal pole with other early involuting cells. These cardiogenic cells reach the embryonic axis around the 8-somite stage, and there they coalesce to form a pair of myocardial tubular primordia on either side of the midline. By the 21-somite stage, the tropomyosin-immunoreactive myocardial tubes have moved closer to each other, and a distinct group of cells, the endocardial progenitor cells, sits medially between them. The myocardial tubes then fuse to enclose the endocardial cells and form the definitive heart tube. By 22 hours postfertilization (26-somite stage), the heart tube is clearly beating. The regionalization of cardiac myosin heavy chain expression distinguishes the cardiac chambers at this stage, although they are not morphologically delineated until 36 hours. This work shows that cardiogenic regions can be identified in the early blastula, and that chamber restriction seems to arise in the midblastula. Additionally, it provides the basis for embryological perturbation at the single cell level, as well as for the genetic analysis of heart tube formation in the zebrafish.

Animals↗
PubMed1994

Cardiovascular development in the zebrafish. II. Endocardial progenitors are sequestered within the heart field.

We have examined the zebrafish embryo to ascertain the location of endocardial and myocardial progenitors prior to gastrulation, in an attempt to define the earliest stages of cardiac patterning. Currently there is uncertainty as to the spatial and lineage relationship of the progenitors for these two phenotypically distinct cell types that form the two concentric layers of the primitive heart tube. By single-cell injection and tracking, we distinguish a region in the early and midblastula which has the properties of a heart field, in that it defines a zone of cardiac progenitors within which there is a spatial gradient of propensity to generate heart cells, and which regulates, in the sense of adapting to the transplantation of pluripotential cells. This zone extends from the future ventral axis dorsally along the margin, with cardiogenic propensity tapering off laterally and dorsally. Myocardial progenitors are spread throughout this region, but endocardial precursors are restricted to the ventral marginal region. The cardiovascular progeny of the ventral cells include, in addition to endocardium and myocardium, cells in the endothelium and blood.

Animals↗
PubMed1994

Segment and cell type lineage restrictions during pharyngeal arch development in the zebrafish embryo.

In zebrafish, the segmental series of pharyngeal arches is formed predominantly by two migratory cell types, neural crest and paraxial mesoderm, which arise in the early embryo. Neural crest cells migrate ventrally out of the neuroepithelium and into the arches to form cartilage, neurons, glia and pigment cells. Surrounding mesoderm generates muscles and endothelia. We labeled individual pharyngeal precursor cells with fluorescent dyes and found that their clonal progeny were confined to single segments and generated single cell types. When a neural crest or mesodermal cell was marked before migration into the pharynx, its progeny dispersed but generally remained confined to a single arch primordium. Such segmental restrictions arose first in the most rostral arches, mandibular and hyoid, and progressed caudally. The phenotypes of progeny generated by single cells were examined in the mandibular arch. Clones derived from premigratory neural crest cells generally did not contribute to more than one cell type. Further, the progenitors of some cell types were spatially separated in the premigratory crest. In particular, neurogenic crest cells were situated further laterally than cells that generate cartilage and connective tissues, while pigment and glial cell progenitors were more evenly distributed. Based on these results we suggest that arch precursors may be specified as to their eventual fates before the major morphogenetic movements that form the arch primordia. Further, cell movements are restricted during segmentation establishing a group of arch precursors as a unit of developmental patterning, as in the fashion of vertebrate rhombomeres or segmental lineage compartments in Drosophila.

Animals↗
PubMed1996

Genes involved in forebrain development in the zebrafish, Danio rerio.

We identified four zebrafish mutants with defects in forebrain induction and patterning during embryogenesis. The four mutants define three genes: masterblind (mbl), silberblick (slb), and knollnase (kas). In mbl embryos, the anterior forebrain acquires posterior forebrain characteristics: anterior structures such as the eyes, olfactory placodes and the telencephalon are missing, whereas the epiphysis located in the posterior forebrain is expanded. In slb embryos, the extension of the embryonic axis is initially delayed and eventually followed by a partial fusion of the eyes. Finally, in kas embryos, separation of the telencephalic primordia is incomplete and dorsal midline cells fail to form a differentiated roof plate. Analysis of the mutant phenotypes indicates that we have identified genes essential for the specification of the anterior forebrain (mbl), positioning of the eyes (slb) and differentiation of the roof plate (kas). In an appendix to this study we list mutants showing alterations in the size of the eyes and abnormal differentiation of the lenses.

Animals↗