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At least 19 recordsLinked to original sources
PubMed1985

Effect of concanavalin A and vegetalizing factor on the outer and inner ectoderm layers of early gastrulae of Xenopus laevis after treatment with cytochalasin B.

Neural (archencephalic) structures have been evoked in the competent ectoderm (consisting of both ectodermal layers) of Xenopus laevis by treatment with Concanavalin A (Con A), which probably acts on the plasma membrane. The size of the neural structures is increased when the ectoderm is incubated in Cytochalasin B prior to the Con A treatment. The results indicate that Cytochalasin B could have an influence on the binding of Con A to receptors on the plasma membrane. On the other hand, Cytochalasin B seems to have an inhibitory effect on the action of the vegetalizing factor, which could be correlated with the decline of endocytotic processes and internalization. In further series, it could be shown that the isolated superficial ectoderm, in contrast to the inner ectoderm layer, does not react to Con A treatment with the differentiation of neural structures. Studies with FITC-Con A indicate that the marker binds less to the outer ectoderm than to the inner ectoderm layer. However, by xenoplastic combinations of the outer ectoderm layer of X. laevis as reacting tissue and chordamesoderm of Triturus vulgaris as inducer, it could be demonstrated that the superficial layer, which is normogenesis does not come into contact with the inducing chordamesoderm but forms the ependymal part of the brain only, is also able to form archencephalic brain structures under in vitro conditions.

Animals↗
PubMed1985

Information transfer during embryonic induction in amphibians.

Neural induction and differentiation has been studied using Concanavalin A, cyclic AMP, tunicamycin and calcium ionophore A 23187. Competent ectoderm of Xenopus laevis treated with Concanavalin A differentiates into neural (archencephalic) structures. Binding studies with gold-labelled ConA indicate that the superficial ectodermal layer contains fewer ConA-sensitive sites (alpha-D-mannoside and alpha-D-glucoside residues of glycoproteins) than the inner ectodermal layer. The small number of ConA-sensitive sites can be correlated with the fact that the isolated superficial ectoderm layer, in contrast to the inner layer, does not differentiate into neural structures. The gold-ConA particles bound to inner ectoderm are quickly (within 30 minutes) internalized, presumably by receptor-mediated endocytosis. However, endocytosis is not a prerequisite for neural induction. On the contrary ConA apparently must be bound to the plasma membrane for a certain period to initiate neural induction. The rapid internalization of ConA could explain why neural inductions are evoked only if ectoderm is incubated in ConA-containing medium for longer than 30 minutes. On the other hand cyclic AMP or calcium ionophore A 23187 does not elicit neural inductions. On the contrary calcium ionophore A 23187 apparently inhibits neural and mesodermal differentiation. This effect could be correlated with an increase of intracellular calcium level of the ectodermal target cells, which could influence the permeability of gap junctions resulting in a loss of cell communication, followed by a change of differentiation and pattern formation.

Amphibians↗
PubMed1991

Gastrulation.

At gastrulation, a single layer of cells is converted into an outer ectodermal covering, an inner ectodermal tube, and in triploblastic phyla, a middle mesodermal layer. This morphogenesis is driven by motility and directed by cell interactions, some of which involve adhesion and others that involve information transfer.

Amino Acid Sequence↗
PubMed1987

Cell-type-specific expression of epidermal cytokeratin genes during gastrulation of Xenopus laevis.

Analysis of the spatial pattern of expression of embryo-specific epidermal cytokeratin genes in Xenopus laevis shows earliest activity in the animal pole cells of stage-9 blastulae. These genes are transcribed predominantly in the epithelial or outer ectoderm, to a lesser extent in the sensorial or inner ectoderm, and at low levels if at all in other regions of the embryo. In the early gastrula the entire ectoderm, including preneural and preepidermal regions, expresses cytokeratin mRNAs; accumulation of these mRNAs in preneural cells is terminated after contact is made with involuting chordamesoderm. On the basis of this and earlier work (Sargent et al. 1986) we suggest that the pattern of expression of cytokeratin genes in frog embryogenesis is based on prelocalized components modulated by the inductive influence of involuting chordamesoderm. The cytokeratin proteins are deposited in the form of filamentous networks in both layers of the epidermis. In the epithelial layer, a much denser mesh of filaments is facing the outside of the embryo. This polarity is established at the onset of the polymerization of these filaments. Thus, intraembryonic and intracellular localization of keratin gene expression and protein deposition is established at the onset of activation of these genes.

Animals↗
PubMed1998

BMP1-related metalloproteinases promote the development of ventral mesoderm in early Xenopus embryos.

Bone morphogenetic protein 1 (BMP1) is a metalloproteinase closely related to Drosophila Tolloid (Tld). Tld regulates dorsoventral patterning in early Drosophila embryos by enhancing the activity of Dpp, a member of the TGF-beta family most closely related to BMP2 and BMP4. In Xenopus BMP4 appears to play an essential role in dorsoventral patterning, promoting the development of ventral fates during gastrula stages. To determine if BMP1 has a role in regulating the activity of BMP4, we have isolated cDNAs for Xenopus BMP1 and a novel closely related gene that we have called xolloid (xld). Whereas xbmp1 is uniformly expressed at all stages tested, the initial uniform expression of xld becomes localized to two posterior ectodermal patches flanking the neural plate and later to the inner ectoderm of the developing tailbud. xld is also expressed in dorsal regions of the brain during tailbud stages and is especially abundant in the ventricular layer of the dorsal hindbrain caudal to the otic vesicle. Overexpression of either gene inhibits the development of dorsoanterior structures in whole embryos and ventralizes activin-induced dorsal mesoderm in animal caps. Since ventralization of activin-induced animal caps can be blocked by coinjecting a dominant-inhibitory receptor for BMP2 and BMP4, we suggest a role for BMP1 and Xld in regulating the ventralizing activity of these molecules.

Activins↗
PubMed1988

Concanavalin A induces neural tissue and cartilage in amphibian early gastrula ectoderm.

We have studied in vitro differentiation of explants of the amphibian (Rana temporaria) early gastrula ectoderm after treatment with various concentrations (50-300 micrograms/ml) of 'free' and Sepharose-bound concanavalin A (Con A). The explants were incubated with Con A for 3 h at 20 degrees C; the rolling up of the explants was prevented by using special weights. We have demonstrated that: (1) free Con A has an inducing action on the explants in the concentration range 100-300 micrograms/ml medium; (2) when treated with Con A the explants produce neural tissue (50-70%), cartilage (20-40%) and, rarely, lentoids (5-10%); (3) the frequency of neural and cartilage inductions was similar at various Con A concentrations; (4) alpha-methyl-D-mannoside pyranoside inhibited the Con A effects; (5) Sepharose-bound Con A had no effect on the explants, although it was bound to the cell surface of the ectoderm inner layer. Possible mechanisms of the neutralizing and chondrogenic effects of Con A on ectodermal explants are discussed.

Animals↗
PubMedDate not supplied

[The spatio-temporal distribution of single-stranded breaks in nuclear DNA in sections of clawed toad embryos during gastrulation and neurulation].

Spatial and temporal pattern and quantities of nicks in nuclear DNA during gastrulation and neurulation was studied using nick-translation in sections of Xenopus laevis embryos. Specific changes in the number of nicks in different mesoderm and ectoderm regions were detected during embryogenesis. Dorso-ventral gradient of nuclear labelling was observed in mesoderm and inner ectoderm layer of early and middle gastrula. The gradient was inverted during transition from gastrula to neurula. At the same time dorso-ventral (in mesoderm) and ventro-dorsal (in outer ectoderm layer) gradients of nuclear labelling were increased. The intensity of nuclear labelling in all parts of embryo as a whole was remarkably higher during neurulation as compared with gastrulation. Dorso-ventral gradient of nuclear labelling was observed in mesoderm and ectoderm during neurulation. A connection between the nicks and differentiation status of the cells during early embryogenesis in amphibians is suggested.

Animals↗
PubMed2001

Hindgut visceral mesoderm requires an ectodermal template for normal development in Drosophila.

During Drosophila embryogenesis, the development of the midgut endoderm depends on interactions with the overlying visceral mesoderm. Here we show that the development of the hindgut also depends on cellular interactions, in this case between the inner ectoderm and outer visceral mesoderm. In this section of the gut, the ectoderm is essential for the proper specification and differentiation of the mesoderm, whereas the mesoderm is not required for the normal development of the ectoderm. Wingless and the fibroblast growth factor receptor Heartless act over sequential but interdependent phases of hindgut visceral mesoderm development. Wingless is required to establish the primordium and to enhance Heartless expression. Later, Heartless is required to promote the proper differentiation of the hindgut visceral mesoderm itself.

Animals↗
PubMed1980

Morphology, ultrastructure, and development of the parasitic larva and its surrounding trophamnion of Polypodium hydriforme Ussov (Coelenterata).

The larval stage of Polypodium hydriforme is planuliform and parasitic inside the growing oocytes of acipenserid fishes. The larva has inverted germ layers and a special envelope, the trophamnion, surrounding it within the host oocyte. The trophamnion is a giant unicellular provisory structure derived from the second polar body and performing both protective and digestive functions, clearly a result of adaptation to parasitism. The trophamnion displays microvilli on its inner surface, and irregular protrusions anchoring it to the yolk on its outer surface. Its cytoplasm contains long nuclear fragments, ribosomes, mitochondria, microtubules, microfilaments, prominent Golgi bodies, primary lysosomes, and secondary lysosomes with partially digested inclusions. The cells of the larva proper are poorly differentiated. No muscular, glandular, neural, interstitial, or nematocyst-forming cells have been found. The entodermal (outer layer) cells bear flagella and contain rough endoplasmic reticulum; the ectodermal (inner layer) cells lack cilia and contain an apical layer of acid mucopolysaccharid granules. The cells of both layers contain mitochondria, microtubules, and Golgi bodies; their nuclei display large nucleoli with nucleolonema-like structure, decondensed chromatin, and some perichromatin granules. At their apical rims, the ectodermal cells from septate junctions; laterally, the cells of both layers form simple contacts and occasional interdigitations. The lateral surfaces of entodermal cells are strengthened by microtubules.

Animals↗
PubMed1995

Signals for death and survival: a two-step mechanism for cavitation in the vertebrate embryo.

Conversion of a solid primordium to a hollow tube of cells is a morphogenetic process used frequently during vertebrate embryogenesis. In the early mouse embryo, this process of cavitation transforms the solid embryonic ectoderm into a columnar epithelium surrounding a cavity. Using both established cell lines and normal embryos, we provide evidence that cavitation in the early mouse embryo is the result of the interplay of two signals, one from an outer layer of endoderm cells that acts over short distances to create a cavity by inducing apoptosis of the inner ectodermal cells, and the other a rescue signal mediated by contact with the basement membrane that is required for the survival of the columnar cells that line the cavity. This simple model provides a paradigm for investigating tube morphogenesis in diverse developmental settings.

Amnion↗
PubMed1990

Effects of relaxation of mechanical tensions upon the early morphogenesis of Xenopus laevis embryos.

In Xenopus laevis embryos at the early gastrula stage, circumferential tensions of embryonic ectoderm were relaxed by making sagittal or transversal slits in the ventral parts of embryos and inserting into surgical cuts the sectors of homologous tissue from same-stage embryos. Changes in tensile patterns were controlled by measuring cell surface angles. Immediate decreases in surface cell wall tension as related to transversal wall tension were registered. Within minutes of the operation, the lobopodial activity of the inner ectodermal surface increased. The subsequent gastrulation movements were disturbed, germ layers partially mixed and archenteron reduced. The areas of extensive cell columnarization in the ectoderm of operated embryos were less regularly arranged and were extended much more ventrally than in intact embryos. Ventro-dorsal migration and latero-medial intercalation of mesodermal cells also were suppressed. As the operated embryos developed, we observed increases in the total amount of neural tissue, associated sometimes with duplication and even triplication of neural tubes, duplication of otic vesicles, partial fusion of axial rudiments, suppression of mesodermal segmentation and branching or bending of notochord. In the gravest cases the antero-posterior embryo polarity was disturbed. In some cases we observed the formation of axial rudiments in ventral implants. The role of tensions in determining the patterns of morphogenetic cell movements and in establishing the morphological order of normal development is discussed.

Age Factors↗
PubMed2005

Midgut epithelium formation in Thermobia domestica (Packard) (Insecta, Zygentoma).

The origin of midgut epithelium may begin either from yolk cells (energids), tips of stomo- and proctodaeum (ectoderm), inner layer (endoderm) or from both kinds of the above mentioned cells. The origin of the midgut epithelium in wingless insects (Apterygota) has still not been determined. In Thermobia domestica the formation of midgut is much delayed, and it completes in the post-embryonic stage, while the stomo- and the proctodaeum are well-developed in the embryonic period. The energids, which remain inside the yolk, start to migrate to its periphery, where they arrange singly close to cell membrane. The yolk mass with the energids at the 14th day of embryogenesis are referred to as the primary midgut. During the first instar larval stage more and more energids migrate to the yolk periphery and the cell membrane starts to form numerous foldings surrounding the groups of energids, which in turn lead to formation of isolated regenerative cell groups. Eventually the cell membrane invaginations reach the center of the yolk mass. Large cells of the primary epithelium, surrounding the newly formed midgut lumen are formed. The cells of the primary epithelium are filled with yolk and are equipped with microvilli pointing to the midgut lumen. As the yolk is being digested, the process of the primary epithelium cells degeneration begins. The cells are getting shorter and start to degenerate. The definitive midgut epithelium is formed from proliferating regenerative cells. It consists of regularly spaced regenerative cell groups as well as the epithelial cells. The ultrastructure of both these cell groups has been described.

Animals↗
PubMed1988

Accumulation and decay of DG42 gene products follow a gradient pattern during Xenopus embryogenesis.

The DG42 gene is expressed during a short window during embryogenesis of Xenopus laevis. The mRNA for this gene can be first detected just after midblastula, peaks at late gastrula, and decays by the end of neurulation. The sequence of the DG42 cDNA and genomic DNA predicts a 70,000-Da protein that is not related to any other known protein. Antibodies prepared against portions of the DG42 open reading frame that had been expressed in bacteria detected a 70,000-Da protein in the embryo with a temporal course of appearance and decay that follows that of the RNA by several hours. Localization of the mRNA in dissected embryos and immunohistochemical detection of the protein showed that DG42 expression moves as a wave or gradient through the embryo. The RNA is first detected in the animal region of the blastula, and by early gastrula is found everywhere except in the outer layer of the dorsal blastopore lip. By midgastrula DG42 protein is present in the inner ectodermal layer and the endoderm; it disappears from dorsal ectoderm as the neural plate is induced and later decays in a dorsoventral direction. The last remnants of DG42 protein are seen in ventral regions of the gut at the tailbud stage.

Animals↗
PubMed1983

Effects of inducers on inner and outer gastrula ectoderm layers of Xenopus laevis.

Gastrula ectoderm, isolated from Xenopus laevis, was cultured in Holtfreter solution or modified Leibovitz medium (L-15) by the sandwich-method with or without inducer. The ectoderm (SD cell layers) consisted of two cell sheets, representing a superficial (S) and a deep (D) layer. In the L-15 medium rather than in Holtfreter solution, the two cell layers separate out into distinct cell masses. This difference in cell affinity under certain experimental conditions could indicate that the deep layer contains endodermal cells. However, an endodermal character of the deep layer can be ruled out by induction experiments with vegetalizing factor or dorsal blastopore lip as inducers. Under the influence of vegetalizing factor the outer as well as the inner ectoderm layer differentiated into mesodermal derivatives such as notochord and somites. The results of the experiments with dorsal blastopore lip as inducer indicate that both inner and outer ectoderm layers are responsive to the neural stimulus. The lower neural competence of the outer ectoderm layer observed by several authors in normogenesis is discussed with regard to the hypothesis about short distance diffusion of the neutralizing factor and/or close cell-to-cell contact between inducing tissue and ectodermal target cells.

Animals↗
PubMed1983

A study of the properties, morphogenetic potencies and prospective fate of outer and inner layers of ectodermal and chordamesodermal regions during gastrulation, in various Anuran amphibians.

In both the ectodermal and the chordamesodermal regions of Anuran embryos, the outer layer of cells possesses epithelial properties and has the same restricted morphogenetic potencies. It is thus interchangeable between the regions, capable of epiboly and, when underlain by notochord material, of the formation of bottle-shaped cells as at the blastoporal groove, and invagination. When taken from the chordamesoderm region, this outer layer has no inducing effect on the ectoderm of the early gastrula. In normal development the outer layer of the neural plate takes an active part in forming the neural tube cavity. It gives rise to the neuroepithelial roof of the diencephalon and medulla oblongata and, when underlain by neuroblasts that develop from the inner cell layers, to ependymal cells of the brain wall. The outer layer of the notochord material is included in the epithelial layer underlying the roof of the gastrocoel - the hypochordal plate. The inner layers of these regions consist of loosely arranged cells and normally have no epithelial properties although, when taken from the ectoderm region, they may acquire such properties upon long-term contact with the environment. However they have wide morphogenetic potencies; the differences in these potencies between cells taken from the various presumptive regions being less than the differences between outer and inner cell layers in each region. Maps are provided which show the arrangement of presumptive rudiments in the ectoderm and chordamesoderm on sagittal sections through Bombina bombina embryos in early and late gastrulation.

Animals↗
PubMed2004

Expression of mouse Foxi class genes in early craniofacial development.

Recent models of craniofacial development suggest the existence of a common pan-placodal domain lying next to the neural plate, from which all sensory placodes will arise. In support of this idea, several genes are expressed in the surface ectoderm of the head adjacent to the neural plate, before the appearance of genes in specific cranial placodes. In this study, we examine the expression patterns of the mouse Foxi class genes from embryonic day 6.5 to 10.5. Foxi2 is expressed throughout the cranial ectoderm adjacent to the neural plate from the 4-somite stage, later becoming excluded from the otic placode. Foxi3 is expressed in a broad region of the pan-placodal ectoderm adjacent to the neural plate from embryonic day (E) 6.75 to the first somite stage. Its expression becomes restricted to the ectoderm and the endoderm of the branchial pouches at E10.5. Foxi1 expression is first detected in the endolymphatic duct in the otic vesicle at E10.5. These results suggest that the mouse Foxi class genes may play important roles, both during cranial placode specification and in later development of individual cranial sensory structures and other organs derived from the cranial ectoderm.

Animals↗