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Results for “germ layer specification”

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At least 19 recordsLinked to original sources
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↗
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↗
PubMed1990

Analysis of the ftz upstream element: germ layer-specific enhancers are independently autoregulated.

The Drosophila fushi tarazu (ftz) upstream element is an enhancer-like element that is required for the correct expression of ftz in developing embryos and that directs transcription from a minimal promoter in a ftz-like seven-striped pattern. Using a deletion analysis, we have identified several independent cis-regulatory elements in the upstream element. A distal enhancer directs fusion gene expression in seven stripes primarily in the mesoderm. A more complex proximal enhancer contains a mesodermally active element and a second element with which it interacts to generate seven stripes in the ectoderm. Striped expression directed by each enhancer is ftz-dependent, and each contains binding sites for purified ftz homeo domain. We suggest that ftz protein acts in combination with germ layer-restricted transcription factors directly and positively to regulate the transcription of its own gene.

Animals↗
PubMed1991

A retinoic acid receptor expressed in the early development of Xenopus laevis.

We have isolated cDNAs coding for a putative retinoic acid receptor (RAR) of the gamma-type from a Xenopus laevis neurula cDNA library. By transient cotransfection of COS cells with an expression vector and a reporter plasmid, this cDNA is shown to direct the synthesis of a retinoic acid-dependent transcription factor. In embryos of X. laevis, transcription of the corresponding gene is greatly enhanced during gastrulation and early neurulation. Two distinct areas with high abundance of RAR gamma mRNA are located at the anterior and at the posterior end of the neurula. The two maxima have emerged by the end of gastrulation and they become more pronounced during neurulation. At tailbud and early tadpole stages, the RAR transcripts are found mainly in the head mesenchyme and in the tailbud. The expression of this RAR is region-specific but not germ-layer-specific. The strong and stage-specific activation of zygotic transcription of this RAR gene, and the specific localization of the mRNA are consistent with the temporal and spatial pattern of retinoic acid sensitivity of X. laevis embryos. Therefore it is likely that the gene product mediates the effects of endogenous and of exogenous retinoic acid on early embryogenesis of Xenopus. The significance of these findings for the specification of the anteroposterior axis is discussed.

Amino Acid Sequence↗
PubMed1989

Embryonic cellular organization: differential restriction of fates as revealed by cell aggregates and lineage markers.

Cleavage-stage Lytechinus variegatus embryos were dissociated and the cells were aggregated in an experimental system designed to address questions of embryonic organizational capability. Using monoclonal antibodies against stage- and structure-specific antigens, it was determined that germ-layer specific molecules were expressed in the expected locations in aggregates and that the germ layers differentiated in the normal temporal sequence, but the dorsoventral axis of the embryo was not reestablished properly. In other experiments individual rhodamine-labeled blastomeres were incorporated into unlabeled aggregates. Micromeres localized and differentiated normally. Mesomeres, however, which in normal embryos form only ectoderm, were found to change their specified fate and participate in gut formation. The sequence of aggregate organization revealed other properties of the embryo. Ectodermal and endodermal epithelia formed via two temporally distinct epithelialization events. Ectoderm separated from a mass of interior cells at about 12 hrs, and endoderm compacted from the interior cells at about 20 hr. A lathrytic agent that prevents gut formation in normal embryos also prevented gut formation in aggregates; however, it did not affect formation of the ectoderm. Hence, formation of the triploblastic structure in aggregates appears to be dependent upon developmentally regulated, distinct cell adhesion events.

Animals↗
PubMed1992

Retinoic acid prevents accumulation of a mesoderm-specific mRNA in the amphibian embryo.

Our greatest progress in understanding mechanisms of germ layer specification in vertebrates has come from studies of mesoderm induction in amphibian embryos. A key early observation was that transcriptional activation of the muscle actin gene and accumulation of its mRNA can be used as molecular markers of mesoderm induction. Recent studies of putative amphibian morphogens have shown that exposure to all-trans retinoic acid (RA) can perturb both neural and mesodermal patterning in the Xenopus embryo, and that RA can, under certain conditions, induce the synthesis of mRNA for a gene whose product is able to influence the patterning of the embryo. To characterize further the mechanism of mesoderm induction, the effect of RA exposure on the transcriptional properties of the muscle actin gene has been investigated. Interestingly, prior exposure of embryos to RA appears to inhibit accumulation, rather than initial activation, of the mesoderm-specific muscle actin transcript. This effect is concentration-dependent and is not observed with the ubiquitously expressed genes for cytoskeletal actin and translation elongation factor 1 alpha, nor with a neural-specific beta-tubulin gene. Thus, the molecular mechanism of mesoderm induction may include, in addition to transcriptional activation of specific genes, processes involved in maintenance of mRNA accumulation for those gene products.

Actins↗
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↗
PubMed1990

Regulation of the segmentation gene fushi tarazu has been functionally conserved in Drosophila.

An evolutionary approach was applied to identify elements involved in the regulation of the segmentation gene fushi tarazu (ftz) by comparing the Drosophila melanogaster ftz gene with its Drosophila hydei homologue. The overall organization of the ftz gene is very similar in both species. Surprisingly, ftz proved to be inverted in the ANT-C of D. hydei with respect to D. melanogaster. Strong homologies extend over the entire 6 kb of the ftz upstream region with the best match in the 'upstream element'. We identified several highly conserved boxes embedded in unrelated sequences that correspond extremely well to two germ layer specific enhancers in the upstream element. Transformation experiments revealed that D. hydei ftz gene products can restore D. melanogaster ftz function and, furthermore, that trans-acting factors from D. melanogaster recognize and control D. hydei ftz regulatory elements. These findings indicate a conservation of the entire regulatory network among segmentation genes for several millions of years during the evolution of Drosophila.

Animals↗
PubMed2025

Foxh1 is a locus-specific PRC2 recruiter governing germ layer silencing.

Polycomb Repressive Complex 2 (PRC2) establishes H3K27me3 marks to shape spatiotemporal gene expression during embryogenesis. While its dysregulation is linked to developmental disorders, cancer, and aging, the mechanisms guiding PRC2 to specific genomic loci remain a subject of ongoing debate. A prevailing model proposes that PRC2 recruitment occurs via its intrinsic affinity for chromatin rather than through sequence-specific transcription factors. Here, we provide evidence that the maternally deposited pioneer transcription factor Foxh1 plays a critical role in directing PRC2 to specific genomic loci during zygotic genome activation in Xenopus. Foxh1 is a critical transcription factor mediating Nodal signaling, but it also plays an earlier role by pre-binding enhancers prior to signaling activation. This pre-binding is essential for forming enhanceosome complexes that trigger mesendodermal gene expression and drive gastrulation, in cooperation with other maternal transcription factors. Using maternal Foxh1-null embryos, we demonstrate that Foxh1 directly recruits Ezh2, the catalytic subunit of PRC2, to Foxh1-bound loci. Loss of Foxh1 impairs Ezh2 recruitment, leading to a global reduction in H3K27me3. These findings support a dual-function model in which Foxh1 not only activates endodermal gene expression in endoderm, but also recruits PRC2 to silence the same genes in ectoderm. This dual activity of Foxh1 allows the spatially coordinated epigenetic states of the endodermal gene regulatory program during early embryogenesis.

CRISPR/Cas9↗
PubMed2025

Enhancer remodeling by OTX2 directs specification and patterning of mammalian definitive endoderm.

The molecular mechanisms that drive essential patterning events in the mammalian embryo remain poorly understood. Analysis of transcription factor expression kinetics at peri-gastrulation stages of development suggest Otx2 as a candidate regulator of the definitive endoderm, the precursor of all gut-derived organs. Accordingly, timed OTX2 depletion in gastruloids or during directed differentiation results in abnormal definitive endoderm specification in mouse and human, characterized by altered expression of components and transcriptional targets of the canonical WNT signaling pathway, perturbed adhesion and migration programs, and de-repression of regulators of other lineages. These defects cumulate in impaired foregut formation. Mechanistically, OTX2 is required to activate a subset of endoderm-specific enhancers and to suppress select enhancers of other lineages, allowing timely exit from the primitive streak and correct specification of anterior endoderm. Our results establish OTX2 as an early gut regulator and suggest molecular principles underlying spatiotemporal cell identity conserved across germ layers and species.

Otx Transcription Factors↗
PubMed1989

An avian muscle factor related to MyoD1 activates muscle-specific promoters in nonmuscle cells of different germ-layer origin and in BrdU-treated myoblasts.

We isolated the cDNA encoding a myogenic factor expressed in embryonic chick breast muscle by virtue of its weak hybridization to the mouse MyoD1 clone. Nucleotide sequence analysis and amino acid comparison define this clone, CMD1, as encoding a protein similar to mouse MyoD1. CMD1 encodes a polypeptide smaller than MyoD1, 298 versus 318 amino acids, respectively, and is 80% concordant by amino acid sequence overall. The basic and myc domains required for myogenic conversion of mouse 10T1/2 'fibroblasts' to myoblasts with MyoD1 are completely conserved in CMD1. CMD1 is just as efficient as the mouse homolog in myogenic conversion of 10T1/2 cells and coactivates the endogenous mouse MyoD1 gene in the process. The efficiency of myoblast conversion depends on the levels of CMD1 expression and suggests that the cellular concentration of CMD1 plays a role in the onset of myogenesis. Transient expression of CMD1 in a variety of nonmuscle cells from different germ-layer origins activates both cotransfected muscle-specific promoters and, in some cases, endogenous muscle-specific genes. 5-Bromodeoxyuridine (BrdU) treatment of chicken and mouse myoblasts reduces the expression of CMD1 and MyoD1, respectively, and may explain how this thymidine analog inhibits myogenesis and the activity of transfected muscle-specific promoters in BrdU-treated myoblasts. Transient expression of CMD1 in BrdU-treated myoblasts reactivates cotransfected muscle-specific promoters. CMD1 activates muscle-specific promoters in cotransfections regardless of cell type, whereas 'housekeeping' or constitutive promoters can be activated moderately, unaffected, or repressed, depending on the promoter and cell background. The rate and degree of myogenic conversion may be more restricted by cell phenotype than by germ-layer origin.

Amino Acid Sequence↗
PubMed1986

Epidermolysis bullosa acquisita antigen, a major cutaneous basement membrane component, is synthesized by human dermal fibroblasts and other cutaneous tissues.

The epidermolysis bullosa acquisita (EBA) antigen is identified as 2 chains: a 290,000-dalton protein and a less prominent 145,000-dalton protein. The 290,000-dalton chain is synthesized by human keratinocytes in culture. In this study, we show that the 290,000-dalton chain is synthesized by human skin fibroblasts and cutaneous human tumors. In contrast, HT1080 cells, a human sarcoma cell line known to produce matrix molecules (such as laminin and type IV collagen), does not synthesize the EBA antigen. Further, the EBA antigen is absent from serum and blood components, placenta, amnion, lung, and the EHS tumor, a murine sarcoma that produces large amounts of laminin, type IV collagen, nidogen, entactin, and basement membrane proteoglycan but is present in cutaneous tumors of adnexal and epithelial origin. These data suggest that while the EBA antigen is synthesized by both human skin keratinocytes and fibroblasts and is therefore not specific for a primordial germ layer, it does appear to be specific for tissue containing a stratified squamous epithelium.

Antigens↗
PubMed1991

Immunohistochemical localization of TGF beta 1, TGF beta 2, and TGF beta 3 in the mouse embryo: expression patterns suggest multiple roles during embryonic development.

Isoform-specific antibodies to TGF beta 1, TGF beta 2, and TGF beta 3 proteins were generated and have been used to examine the expression of these factors in the developing mouse embryo from 12.5-18.5 d post coitum (d.p.c.). These studies demonstrate the initial characterization of both TGF beta 2 and beta 3 in mammalian embryogenesis and are compared with TGF beta 1. Expression of one or all three TGF beta proteins was observed in many tissues, e.g., cartilage, bone, teeth, muscle, heart, blood vessels, lung, kidney, gut, liver, eye, ear, skin, and nervous tissue. Furthermore, all three TGF beta proteins demonstrated discrete cell-specific patterns of expression at various stages of development and the wide variety of tissues expressing TGF beta proteins represent all three primary embryonic germ layers. For example, specific localization of TGF beta 1 was observed in the lens fibers of the eye (ectoderm), TGF beta 2 in the cortex of the adrenal gland (mesoderm), and TGF beta 3 in the cochlear epithelium of the inner ear (endoderm). Compared to the expression of TGF beta mRNA transcripts in a given embryonic tissue, TGF beta proteins were frequently colocalized within the same cell type as the mRNA, but in some cases were observed to localize to different cells than the mRNA, thereby indicating that a complex pattern of transcription, translation, and secretion for TGF beta s 1-3 exists in the mouse embryo. This also indicates that TGF beta 1, beta 2, and beta 3 act through both paracrine and autocrine mechanisms during mammalian embryogenesis.

Animals↗
PubMed1989

SPARC: a Ca2+-binding extracellular protein associated with endothelial cell injury and proliferation.

SPARC (Secreted Protein that is Acidic and Rich in Cysteine) is a Ca2+-binding, stress-related protein released in vitro by both malignant and normal cells derived from all primordial germ layers. It is specifically elevated in endothelial cells as a result of "culture shock" (characterized by high levels of proliferation and migration) and exhibits density-dependent secretion. Exposure of bovine aortic endothelial cells to endotoxin results in a 70-100% increase in secreted protein, with a three-fold increase in SPARC. Immunofluorescence histochemistry on mouse tissues revealed (a) a preferential association of SPARC with highly proliferative cells (e.g., gut epithelia, mammary gland, and epidermis), (b) a cell surface or stromal location in thymus, lung, and salivary gland, (c) staining of epididymidal epithelium and testicular cells, and (d) an association with somites of 14 d mouse embryos. We envision SPARC as an extracellular modulator of Ca2+ and other cation-sensitive proteins/proteinases, that facilitates cellular proliferation in response to injury and to developmental signals.

Animals↗
PubMed1985

Normal fates and states of specification of different regions in the axolotl gastrula.

A fate map was constructed for four regions of the early gastrula of Ambystoma mexicanum using orthotopic grafts from donors labelled with FLDx (fluoresceinated-lysinated-dextran). The region around the animal pole gave rise to epidermis only and did not include prospective neural plate. The dorsal marginal zone contributed to cephalic endoderm and to the whole length of the axial mesoderm (notochord and somites), the lateral marginal zone to lateroventral and somitic mesoderm, and the ventral marginal zone to lateroventral mesoderm. It was found that the dorsal marginal zone contributed relatively more to the anterior regions of the mesodermal mantle and the ventral marginal zone more to its posterior parts. The same regions of the gastrula and also vegetal yolky tissue were cultured as explants and labelled with tritiated mannose. Their glycoprotein synthesis pattern was compared to those of the neurula tissues to which they contribute in vivo. Animal pole explants synthesized large amounts of the epidermis-specific marker epimucin. Dorsal marginal zone explants did not synthesize epimucin but did make amounts of S2 and S6 indicative of mesoderm, as well as the notochord-specific markers S2.2 and S3.2. Lateral marginal zone explants showed the same pattern as the dorsal marginal zone including the two notochord-specific markers, although they do not contribute to notochord in vivo. Ventral marginal zone explants were more variable in their behaviour. Yolky tissue from the vegetal hemisphere of the gastrula or the archenteron floor of the neurula synthesized mainly polydisperse material of high molecular weight rather than discrete glycoproteins. The results indicate that at the early gastrula stage states of specification exist which correspond to the three germ layers, ecto-, meso- and endoderm. The ectodermal specification of animal pole explants is quite robust and cannot easily be changed by variation of the culture conditions. However treatment with a concentrated pellet of vegetalizing factor does induce a change to mesodermal specification, which is clearly detectable in the pattern of glycoprotein synthesis. Similar inductive interactions between different regions of the early embryo are thought to occur during normal development.

Ambystoma mexicanum↗