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Results for “GERM LAYERS”

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At least 19 recordsLinked to original sources

PubMed2000

The role of the yolk syncytial layer in germ layer patterning in zebrafish.

Formation of the three germ layers requires a series of inductive events during early embryogenesis. Studies in zebrafish indicate that the source of these inductive signals may be the extra-embryonic yolk syncytial layer (YSL). The characterization of genes encoding the nodal-related factor, Squint, and homeodomain protein, Bozozok, both of which are expressed in the YSL, suggested that the YSL has a role in mesendoderm induction. However, these genes, and a second nodal-related factor, cyclops, are also expressed in the overlying marginal blastomeres, raising the possibility that the marginal blastomeres can induce mesendodermal genes independently of the YSL. We have developed a novel technique to study signaling from the YSL in which we specifically eliminate RNAs in the YSL, thus addressing the in vivo requirement of RNA-derived signals from this region in mesendoderm induction. We show that injection of RNase into the yolk cell after the 1K cell stage (3 hours) effectively eliminates YSL transcripts without affecting ubiquitously expressed genes in the blastoderm. We also present data that indicate the stability of existing proteins in the YSL is unaffected by RNase injection. Using this technique, we show that RNA in the YSL is required for the formation of ventrolateral mesendoderm and induction of the nodal-related genes in the ventrolateral marginal blastomeres, revealing the presence of an unidentified inducing signal released from the YSL. We also demonstrate that the dorsal mesoderm can be induced independently of signals from the YSL and present evidence that this is due to the stabilization of (&bgr;)-catenin in the dorsal marginal blastomeres. Our results demonstrate that germ layer formation and patterning in zebrafish uses a combination of YSL-dependent and -independent inductive events.

Animals↗

PubMed1983

X-chromosome inactivation mosaicism in the three germ layers and the germ line of the mouse embryo.

Electrophoretic variant forms of the X-linked enzyme phosphoglycerate kinase (PGK-1, E.C.2,7,2,3) have been used to examine X-chromosome mosaicism in tissues from 12 1/2-day post coitum heterozygous female mouse embryos. Samples of yolk-sac endoderm, neural ectoderm, heart (mesoderm), liver (endoderm) and germ cells were analysed from each embryo. In all tissues except yolk-sac endoderm, both PGK-1 isozymes were expressed. The extent of covariance among tissues with respect to the PGK-1 isozyme contribution is consistent with all tissues being derived from the same pool of cells after X-inactivation. The covariance among tissues gives an estimate of the size of this pool (47 cells) and places the earliest time of X-inactivation in epiblast cells between 4 1/2 and 5 1/2 days post coitum. From the independent variance among tissues within an individual, the average primordial precursor pool size for the three germ layers and the germ line itself was estimated as 193 cells.

Animals↗

PubMed1978

[Comparative study of mouse teratoids developed from blastocysts and embryos at the three germ layer stage].

Germs of three stages: blasocyst, three layer germ cylinder, as well as head-fold and neural plate were implanted under the testicular capsule of mice, CBAXC57Bl line. Teratoids developed at the place of implantation are represented by the derivatives of all germ layers, as well as by some organic structures. The method for an experimental production of teratoids by means of transplantation of developing embryos is discussed as one of the methods for experimental histology. At the same time, possible tissue determination in embryos which do not undergo normal gastrulation is considered.

Animals↗

PubMed2025

Foxi2 and Sox3 are master regulators controlling ectoderm germ layer specification.

In vertebrates, germ layer specification represents a critical transition where pluripotent cells acquire lineage-specific identities. We identify the maternal transcription factors Foxi2 and Sox3 to be pivotal master regulators of ectodermal germ layer specification in Xenopus. Ectopic co-expression of Foxi2 and Sox3 in prospective endodermal tissue induces the expression of ectodermal markers while suppressing mesendodermal markers. Transcriptomics analyses reveal that Foxi2 and Sox3 jointly and independently regulate hundreds of ectodermal target genes. During early cleavage stages, Foxi2 and Sox3 pre-bind to key cis-regulatory modules (CRMs), marking sites that later recruit Ep300 and facilitate H3K27ac deposition, thereby shaping the epigenetic landscape of the ectodermal genome. These CRMs are highly enriched within ectoderm-specific super-enhancers (SEs). Our findings highlight the pivotal role of ectodermal SE-associated CRMs in precise and robust ectodermal gene activation, establishing Foxi2 and Sox3 as central architects of ectodermal lineage specification.

Ep300↗

PubMed2025

Foxi2 and Sox3 are master transcription regulators that control ectoderm germ layer specification in Xenopus.

Germ layer specification represents a critical transition where pluripotent cells acquire lineage-specific identities. We identify the maternal transcription factors Foxi2 and Sox3 to be pivotal master regulators of ectodermal germ layer specification in Xenopus. Ectopic co-expression of Foxi2 and Sox3 in prospective endodermal tissue induces the expression of ectodermal markers while suppressing mesendodermal markers. Transcriptomic analyses reveal that Foxi2 and Sox3 jointly and independently regulate hundreds of ectodermal target genes. During early cleavage stages, Foxi2 and Sox3 pre-bind to key cis-regulatory modules (CRMs), marking sites that later recruit Ep300 and facilitate H3K27ac deposition, thereby shaping the epigenetic landscape of the ectodermal genome. These CRMs are highly enriched within ectoderm-specific super-enhancers (SEs). Our findings highlight the pivotal role of ectodermal SE-associated CRMs in precise and robust ectodermal gene activation, establishing Foxi2 and Sox3 as central architects of ectodermal lineage specification.

Animals↗

PubMed2003

Nodal signaling and vertebrate germ layer formation.

The understanding of germ layer formation in vertebrates began with classical experimental embryology. Early in the 20th century, Spemann and Mangold (1924) identified a region of the early embryo capable of inducing an entire embryonic axis. Termed the dorsal organizer, the tissue and the activity have been shown to exist in all vertebrates examined. In mice, for example, the activity resides in a region of the gastrula embryo known as the node. Experiments by the Dutch embryologist Nieuwkoop (1967a, 1967b, 1973, 1977) showed that a signal derived from the vegetal half of the amphibian embryo is responsible for the formation of mesoderm. Nieuwkoop's results allowed the development of in vitro assays that led, in the late 1980s and early 1990s, to the identification of growth factors essential for germ layer formation. Through more recent genetic investigations in mice and zebrafish, we now know that one class of secreted growth factor, called Nodal because of its localized expression in the mouse node, is essential for formation of mesoderm and endoderm and for the morphological rearrangements that occur during gastrulation.

Activins↗

PubMed1999

Anterior patterning by synergistic activity of the early gastrula organizer and the anterior germ layer tissues of the mouse embryo.

Fragments of the germ layer tissues isolated from the early-primitive-streak (early-streak) stage mouse embryos were tested for axis induction activity by transplantation to late-gastrula (late-streak to early-bud) stage host embryos. The posterior epiblast fragment that contains the early gastrula organizer was able to recruit the host tissues to form an ectopic axis. However, the most anterior neural gene that was expressed in the ectopic axis was Krox20 that marks parts of the hindbrain, but markers of the mid- and forebrain (Otx2 and En1) were not expressed. Anterior visceral endoderm or the anterior epiblast alone did not induce any ectopic neural tissue. However, when these two anterior germ layer tissues were transplanted together, they can induce the formation of ectopic host-derived neural tissues but these tissues rarely expressed anterior neural genes and did not show any organization of an ectopic axis. Therefore, although the anterior endoderm and epiblast together may display some inductive activity, they do not act like a classical organizer. Induction of the anterior neural genes in the ectopic axis was achieved only when a combination of the posterior epiblast fragment, anterior visceral endoderm and the anterior epiblast was transplanted to the host embryo. The formation of anterior neural structures therefore requires the synergistic interaction of the early gastrula organizer and anterior germ layer tissues.

Animals↗

PubMed1993

Regional repression of a Drosophila POU box gene in the endoderm involves inductive interactions between germ layers.

An induction process occurring between the mesodermal and the endodermal germ layers has recently been described in the regulation of the Drosophila homeotic gene labial (lab). We report here that proper spatial regulation of the Drosophila POU box gene pdm-1 products also involves interaction between these two germ layers. pdm-1 transcripts are initially present in both the anterior and the posterior endodermal midgut primordia. Upon fusion of the two primordia, transcripts disappear from two regions in the endoderm, a central domain and an anterior domain. The anterior repression domain of pdm-1 is independent of the expression of known homeotic genes and genes encoding secreted signalling molecules in the visceral mesoderm, both for its positioning and its repression. Repression in the central domain requires both the homeotic gene Ultrabithorax (Ubx) and the decapentaplegic (dpp) gene, which encodes a secreted protein. Both of these genes are also required for lab induction. However, the analysis of pdm-1 expression in various mutant backgrounds indicates that the regulation of lab and pdm-1 across germ layers is controlled by different genetic cascades. Our study indicates that dpp is not the signal that dictates central pdm-1 repression across germ layers and suggests that in the same midgut region, different signalling pathways result in the differential activation or repression of potential transcription factors.

Animals↗

PubMed1997

Germ-layer surface tensions and "tissue affinities" in Rana pipiens gastrulae: quantitative measurements.

The morphogenetic properties causing germ-layer spreading and stratification in amphibian gastrulation were called "tissue affinities" by Holtfreter. The differential adhesion hypothesis (DAH) attributes such liquid-like tissue rearrangements to forces generated by intercellular adhesions within and between the migrating cell populations. This theory predicts that, among the primary germ layers, the cohesiveness of deep ectoderm should be the greatest, that of deep mesoderm should be intermediate, and that of deep endoderm should be the least. Also, the cohesiveness of differentiating neural ectoderm should increase after induction, causing it to internalize and segregate from epidermis. The DAH also explains why the cohesiveness of "liquid" tissues, whose cells are free to rearrange, should be measurable as tissue surface tensions. Using a specially designed tissue surface tensiometer, we demonstrate that (i) aggregates of Rana pipiens deep germ layers do possess liquid-like surface tensions, (ii) their surface tension values lie in precisely the sequence necessary to account for germ-layer stratification in vitro and in vivo, and (iii) the surface tension of deep ectoderm just underlain by the archenteron roof is twice that of not-yet-underlain deep ectoderm. These measurements provide direct, quantitative evidence that the "tissue affinities" governing germ-layer flow during early stages of vertebrate morphogenesis are reflected in tissue surface tensions.

Animals↗

PubMed1985

Sequential expression of germ-layer specific molecules in the sea urchin embryo.

Described are two germ-layer specific molecules that appear coincident with the formation of two germ layer cell lineages in the sea urchin embryo. Meso1 is a molecule of 380 kDa that is first detected at the time of primary mesenchyme cell delamination from the wall of the blastula. Endo1 is a molecule of 320 kDa that appears on endoderm cells at the time of archenteron formation a few hours after Meso1 appears. Both antigens are identified by monoclonal antibodies. The appearance of these antigens is described by immunofluorescence microscopy, and quantitative data on their localization has been obtained by ultrastructural immunoelectron microscopy. The synthesis of the molecules has been followed by pulse-chase immunoprecipitation. Meso1 is first expressed in trans Golgi-like saccules, is concentrated in peripheral low electron-dense vesicles, and is found throughout the plasma membrane of the mesenchymal cells and their filopodial extensions. Newly translated Meso1 can first be immunoprecipitated upon differentiation of the mesoderm cell lineage, and pulse-chase studies suggest that the determinant is the result of a post-translational modification. [35S]Methionine pulses early in development followed by a chase to the mesenchyme blastula or prism stage show that at least a portion of the molecule is translated well in advance of the mesenchyme blastula stage. Endo1, in contrast, does not appear to be translated until the onset of gastrulation, just preceding the post-translational expression of the Endo1 determinant. Endo1 is localized to the apical and basolateral cell surfaces of the midgut and hindgut. No label is detected in foregut cells, demonstrating a heterogeneity of cell populations within the endoderm cell lineage corresponding to a difference in morphology. In addition, Endo1 is shown to be the result of new transcription by the embryonic genome. Even though the function of neither molecule is known, together they show the spatial and temporal precision of differentiation that accompanies the formation of germ layers.

Animals↗

PubMed2001

Generation of the germ layers along the animal-vegetal axis in Xenopus laevis.

After completion of gastrulation, typical vertebrate embryos consist of three cell sheets, called germ layers. The outer layer, the ectoderm, which produces the cells of the epidermis and the nervous system; the inner layer, the endoderm, producing the lining of the digestive tube and its associated organs (pancreas, liver, lungs etc.) and the middle layer, the mesoderm, which gives rise to several organs (heart, kidney, gonads), connective tissues (bone, muscles, tendons, blood vessels), and blood cells. The formation of the germ layers is one of the earliest embryonic events to subdivide multicellular embryos into a few compartments. In Xenopus laevis, the spatial domains of three germ layers are largely separated along the animal-vegetal axis even before gastrulation; ectoderm in the animal pole region; mesoderm in the equatorial region and endoderm in the vegetal pole region. In this review, we summarise the recent advances in our understanding of the formation of the germ layers in Xenopus laevis.

Animals↗

PubMed1991

Development of separated germ layers of rodent embryos on ectopic sites: a reappraisal.

The method of separation of germ layers of rodent embryos by treating the embryonic shields with proteolytic enzymes and by microsurgery with the subsequent transplantation to ectopic sites has helped to gain a more detailed insight into what is going on during gastrulation in mammals. The space under the kidney capsule of adult animals seems to be the most appropriate ectopic site for transplantation of early postimplantation rat embryos or separated germ layers. After transplantation the grafts develop into teratomas whose complex histological structure reflects the initial developmental capacities of the graft. At the pre-primitive streak and the early primitive streak stages the primitive ectoderm differentiates into tissue derivatives of all three definitive germ layers, often in complex organotypic combinations. This is indirect evidence that all cells of the embryonic body originate from the primitive embryonic ectoderm. Halves of the primitive ectoderm obtained by a longitudinal or transverse cut through the egg cylinder give the same result. At the head fold stage the capacity for differentiation of the ectoderm is restricted to ectodermal and mesodermal derivatives. One day before gastrulation the isolated primitive ectoderm is not able to differentiate as renal isograft. The mesoderm isolated at the head fold stage and at later stages when its segmentation occurs, differentiates almost exclusively into the brown adipose tissue. The embryonic endoderm differentiates only in combination with the mesoderm. After transplantation the embryonic ectoderm loses its epithelial organization and breaks up into a mass of mesenchyme-like cells in which epithelial structures subsequently appear and differentiate in a way reminiscent of the reaggregation of cells in mixed cell suspension in vitro.

Animals↗

PubMed2006

Identification of regulators of germ layer morphogenesis using proteomics in zebrafish.

During vertebrate gastrulation, a well-orchestrated series of morphogenetic changes leads to the formation of the three germ layers: the ectoderm, mesoderm and endoderm. The analysis of gene expression patterns during gastrulation has been central to the identification of genes involved in germ layer formation. However, many proteins are regulated on a translational or post-translational level and are thus undetectable by gene expression analysis. Therefore, we developed a 2D-gel-based comparative proteomic approach to target proteins involved in germ layer morphogenesis during zebrafish gastrulation. Proteomes of ectodermal and mesendodermal progenitor cells were compared and 35 significantly regulated proteins were identified by mass spectrometry, including several proteins with predicted functions in cytoskeletal organization. A comparison of our proteomic results with data obtained in an accompanying microarray-based gene expression analysis revealed no significant overlap, confirming the complementary nature of proteomics and transcriptomics. The regulation of ezrin2, which was identified based on a reduction in spot intensity in mesendodermal cells, was independently validated. Furthermore, we show that ezrin2 is activated by phosphorylation in mesendodermal cells and is required for proper germ layer morphogenesis. We demonstrate the feasibility of proteomics in zebrafish, concluding that proteomics is a valuable tool for analysis of early development.

Animals↗

PubMed1992

Establishment and organization of germ layers in the gastrulating mouse embryo.

By following the distribution of wheat germ agglutinin-gold-labelled cells in primitive streak stage embryos, we obtained direct evidence for a continuous recruitment of the embryonic ectoderm cells to the definitive endoderm and to the embryonic and extraembryonic mesoderm during gastrulation. The majority of the definitive endodermal cells ingressed through the anterior end of the primitive streak and were incorporated initially into the midline endoderm at the archenteron, but a small population of endodermal cells may be recruited by direct delamination from the embryonic ectoderm. The pre-existing visceral embryonic endoderm was progressively replaced, but not totally, by the newly recruited population which colonized the embryonic foregut and the notochord. The developmental fate of the recruited endoderm and that of cells in the embryonic ectoderm and the mesoderm of late primitive streak stage embryos indicate that concomitant with the establishment of the germ layers, an orderly allocation of prospective fetal tissues to specific parts of the body occurs simultaneously in all three germ layers.

Animals↗

PubMed2000

Some new thoughts on evolution: the role of the germ layers.

At an early stage of embryonic development, the animal body divides itself into the three germ layers - the ectoderm, mesoderm and entoderm. It is proposed that this division repeats a fundamental functional differentiation of cells in phylogeny. The tasks of life have been divided into three groups, each germ layer specializing in one of them. The task of the entoderm is metabolism and homeostasis, that of the mesoderm is the structural organization of the body, that of the ectoderm interactions with the environment. In effect, the entoderm is the chemist of the body, the mesoderm its architect and engineer, the ectoderm deals with its external affairs. It is proposed that cognitive and reasoning faculties are inherent in every germ layer and when they separate, they all take an equal share. Each performs its complex and multitudinous tasks by virtue of its faculty of conceptual thought, except that the entoderm and mesoderm began to develop that faculty millions of years before the ectoderm.

Animals↗

PubMed1987

Cell fate, morphogenetic movement and population kinetics of embryonic endoderm at the time of germ layer formation in the mouse.

The fate of the embryonic endoderm (generally called visceral embryonic endoderm) of prestreak and early primitive streak stages of the mouse embryo was studied in vitro by microinjecting horseradish peroxidase into single axial endoderm cells of 6.7-day-old embryos and tracing the labelled descendants either through gastrulation (1 day of culture) or to early somite stages (2 days of culture). Descendants of endoderm cells from the anterior half of the axis were found at the extreme cranial end of the embryo after 1 day and in the visceral yolk sac endoderm after 2 days, i.e. they were displaced anteriorly and anterolaterally. Descendants of cells originating over and near the anterior end of the early primitive streak, i.e. posterior to the distal tip of the egg cylinder, were found after 1 day over the entire embryonic axis and after 2 days in the embryonic endoderm at the anterior intestinal portal, in the foregut, along the trunk and postnodally, as well as anteriorly and posteriorly in the visceral yolk sac. Endoderm covering the posterior half of the early primitive streak contributed to postnodal endoderm after 1 day (at the late streak stage) and mainly to posterior visceral yolk sac endoderm after 2 days. Clonal descendants of axial endoderm were located after 2 days either over the embryo or in the yolk sac; the few exceptions spanned the caudal end of the embryo and the posterior yolk sac. The clonal analysis also showed that the endoderm layer along the posterior half of the axis of prestreak- and early-streak-stage embryos is heterogeneous in its germ layer fate. Whereas the germ layer location of descendants from anterior sites did not differ after 1 day from that expected from the initial controls (approx. 90% exclusively in endoderm), only 62% of the successfully injected posterior sites resulted in labelled cells exclusively in endoderm; the remainder contributed partially or entirely to ectoderm and mesoderm. This loss from the endoderm layer was compensated by posterior-derived cells that remained in endoderm having more surviving descendants (8.4 h population doubling time) than did anterior-derived cells (10.5 h population doubling time). There was no indication of cell death at the prestreak and early streak stages; at least 93% of the cells were proliferating and more than half of the total axial population were in, or had completed, a third cell cycle after 22 h culture.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1995

Allocation of epiblast cells to germ layer derivatives during mouse gastrulation as studied with a retroviral vector.

The embryonic ectoderm, or epiblast, is the source of the three primary germ layers that form during gastrulation in the mouse embryo. Previous studies have investigated the fate of epiblast cells in early gastrulation stages using clonal analysis of cell lineage and in late gastrulation stages using transplantation of labeled grafts. In this study, we studied the fate of late gastrulation stage epiblast using a clonal analysis based on a retroviral vector encoding the Escherichia coli lacZ gene. We found that by reducing the volume of viral suspension injected into each embryo, it was possible to achieve single infectious events. Our analysis of 20 embryos singly infected at the late streak stage and 21 at the head fold stage revealed clonal descendants in only a single germ layer in each embryo. These results indicate that allocation of epiblast progenitors to a single germ layer fate has occurred by late gastrulation in mouse embryos.

Animals↗

PubMed1992

Embryonal germ-layer antigens: target for autoimmunity.

Histopathological analysis of some systemic autoimmune diseases and syndromes led us to the conclusion that the common feature of the organs involved might be their embryonal origin. We suggest that organs derived from the same germ layer express common germ-layer-specific antigens. Such antigens could serve as target antigens for the autoimmune response.

Autoantibodies↗