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PubMed1991

Immunohistochemical localization of the carbohydrate antigen 4C9 in the mouse embryo: a reliable marker of mouse primordial germ cells.

Expression of 4C9, a Lex[Gal beta 1----4(Fuc alpha 1----3)GlcNAc] antigen, during mouse embryogenesis was studied by immunohistochemical methods. Distribution of 4C9 was similar to, but not identical with that of SSEA-1 (stage-specific embryonic antigen-1). Notably, 4C9 was detected in some of the inner cell mass cells of late blastocysts, ectoderm cells migrating from the primitive streak to the mesoderm space and primordial germ cells just formed from the migrating cells. Thus, 4C9 was considered to be continuously expressed in the cell lineage starting at the totipotent 8 cell stage and leading to primordial germ cells. While 4C9 gradually decreased from the surface of primordial germ cells after they have settled in the gonad, the antigen remained in cytoplasmic granules for some period in a sex determined manner. In male gonads, cytoplasmic granules positive for 4C9 tended to be polarized to one side of cytoplasm. The 4C9 reactive material completely disappeared from male germ cells by day 16 of gestation. In female gonads, granules scattered throughout the cytoplasm and cell surface were positive for 4C9. On day 16 of gestation the cell surface antigenicity was lost, but some cytoplasmic antigenicity still remained. As above, 4C9 is a reliable marker to study the origin, migration and differentiation of primordial germ cells, and to distinguish male and female germ cells. By immunoelectron microscopy, 4C9 was detected at the plasma membrane, the Golgi apparatus, and dense-cored vesicles in primordial germ cells on 10-11 days of gestation.

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PubMedDate not supplied

[An immunohistochemical study of early embryogenesis in the clawed toad Xenopus laevis by using monoclonal antibodies to intermediate filament proteins].

Distribution of cytokeratin epitopes was studied in X. laevis embryos at stages 10-25 using 5 monoclonal antibodies against proteins of the human and rat keratin filaments. Specific staining was observed in chorda, outer layers of ectoderm and presumptive epidermis (late gastrula), and inner layer of presumptive epidermis. The cells of the stained zone (presumptive epidermis) were compressed while the cells of unstained zone (presumptive neuroectoderm) were extended tangentially.

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PubMed1998

The Notch signalling pathway in hair growth.

The Notch signalling pathway is an important mediator of cell fate selection whose involvement in epidermal appendage formation is now becoming recognised. Hair follicle development and hair formation involve the co-ordinated differentiation of several different cell types in which Notch appears to have a role. We report intricate expression patterns for the Notch-1 receptor and three ligands, Delta-1, Jagged-1 and Jagged-2 in the hair follicle. Notch-1 is expressed in ectodermal-derived cells of the follicle, in the inner cells of the embryonic placode and the follicle bulb, and in the suprabasal cells of the mature outer root sheath. Delta-1 is only expressed during embryonic follicle development and is exclusive to the mesenchymal cells of the pre-papilla located beneath the follicle placode. Expression of Jagged-1 or Jagged-2 overlaps Notch-1 expression at all stages. In mature follicles, Jagged-1 and Jagged-2 are expressed in complementary patterns in the follicle bulb and outer root sheath, Jagged-1 in suprabasal cells and Jagged-2 predominantly in basal cells. In the follicle bulb, Jagged-2 is localised to the inner (basal) bulb cells next to the dermal papilla which do not express Notch-1, whereas Jagged-1 expression in the upper follicle bulb overlaps Notch-1 expression and correlates with bulb cell differentiation into hair shaft cortical and cuticle keratinocytes.

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PubMed1990

Serotonin-immunoreactive neurons in the cnidarian Renilla koellikeri.

The cellular localization of 5-hydroxytryptamine (5-HT) was investigated in the pennatulid anthozoan Renilla koellikeri by means of peroxidase-antiperoxidase-immunohistochemistry with an antiserum against 5-HT-formaldehyde-protein conjugate. In many colonies, strong 5-HT-immunoreactivity was displayed by the cell bodies and beaded processes of relatively small neuronlike elements predominating in the outer ectoderm or scattered in the underlying mesoglea. The immunostained neurons of the mesoglea were generally bipolar and their relatively short processes extended toward myoepithelial cells. In the ectoderm, most immunostained neurons appeared pseudounipolar. These cell bodies were endowed with a small, superficially directed, conical appendage reaching the outer surface of the epithelium. Their neurites emerged from the inner pole of the perikarya and branched toward other immunopositive ectodermal and mesogleal nerve cells, or nematocytes in the tentacles. The networklike distribution of the presumed 5-HT ectodermal neurons varied between the different regions of colonies and along the autozooid column. In the context of earlier observations in cnidarians, these cytological features suggest a sensory as well as a modulatory function for 5-HT in Renilla koellikeri.

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PubMed1980

Development of dentition and dermal skeleton in embryonic Scyliorhinus canicula.

Serial sections ranging from very young embryos to hatched juveniles and whole embryos of Scyliorhinus show that dentition and dermal skeleton belong to two independent secondary developmental fields that differ both developmentally and structurally. The development of the dentition starts very early, with a thickening of the ectoderm in the region of the mouth (stage 04), the invagination of the dental lamina (stage 18), and the formation of the germs of the first generation (stage 20). Tooth replacement movements start only near the end of embryogenesis (stage 35). Scale germs, on the other hand, first begin to form at stage 24. Scales erupt shortly before the animal hatches (stage 43). Only one scale generation is formed during embryogenesis. The forces which erupt the scales may come from fluid pressures in vacuoles of the fibrous layer of the dermis. Those which erupt the teeth probably also result from similar fluid pressures. The crown and upper part of the base of scales and teeth are formed by cells of the inner dental epithelium which are differentiated from the ectoderm. They are also formed by odontoblasts which are derived from the vascular layer of the dermis. However, the basal plates of scales and teeth containing the anchoring fibers are formed by osteoblasts, which are derived from the fibrous layer of the dermis.

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PubMed1976

The fine structure of the embryo during the gastrula stage of Comanthus japonica (Echinodermata: Crinoidea).

The fine structure of the embryo of Comanthus has been described by scanning and transmission electron microscopy at two-hourly intervals throughout the gastrula stage (from the fifth through the fifteenth hours of development). At 5 hr, gastrulation has occurred in the absence of any structure comparable to the echinoid hyaline layer; therefore, at least one important mechanism proposed for echinoid gastrulation cannot occur in this crinoid. At 7 hr, the blastocoelic basal lamina has formed, and all ectodermal and entodermal nuclei contain dense aggregates, which are probably perichromatin fibrils. At 9 hr, the blastocoel contains mesenchyme cells, presumably of entodermal origin. At 11 hr, ciliogenesis has started at the apical surfaces of the ectoderm cells and at the archenteral surfaces of the entoderm cells; many of the newly formed cilia are swollen subterminally. At 13 hr, a conspicuous glycocalyx is beginning to cover the apical ends of the ectoderm cells, and the fertilization membrane is beginning to dissolve from its inner surface. Between 5 and 13 hr, there is a gradual development of a junctional complex associating the apicolateral margins of the ectoderm cells; the zonula adherens part of the complex appears at 5 hr and is well developed by 7 hr, and then the septate junction part of the complex appears at 9 hr and is well developed by 13 hr. At 15 hr, the blastopore has closed, the ectodermal glycocalyx is fully developed, some mesenchyme cells appear to be differentiating into skeleton forming cells, and the fertilization membrane is in the last stages of dissolution.

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PubMed2003

Fgf3 and Fgf8 dependent and independent transcription factors are required for otic placode specification.

The vertebrate inner ear develops from the otic placode, an ectodermal thickening that forms adjacent to the presumptive hindbrain. Previous studies have suggested that competent ectodermal cells respond to signals from adjacent tissues to form the placode. Members of the Fgf family of growth factors and the Dlx family of transcription factors have been implicated in this signal-response pathway. We show that compromising Fgf3 and Fgf8 signaling blocks ear development; only a few scattered otic cells form. Removal of dlx3b, dlx4b and sox9a genes together also blocks ear development, although a few residual cells form an otic epithelium. These cells fail to form if sox9b function is also blocked. Combined loss of Fgf signaling and the three transcription factor genes, dlx3b, dlx4b and sox9a, also completely eliminates all indications of otic cells. Expression of sox9a but not dlx3b, dlx4b or sox9b requires Fgf3 and Fgf8. Our results provide evidence for Fgf3- and Fgf8-dependent and -independent genetic pathways for otic specification and support the notion that Fgf3 and Fgf8 function to induce both the otic placode and the epithelial organization of the otic vesicle.

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PubMed1978

Surface topography of isolated gastrula ectoderm of Triturus vulgaris.

The surface topography of the outer cell layer of the two-layered gastrula ectoderm of Triturus vulgaris resembles that of the other amphibians: the cells are tightly packed and devoid of pseudopodia. The cells of the inner layer are spherical and interconnected with pseudopodia of various lengths. After excision of the ectoderm the peripheral cells of the outer layer elongate perpendicularly to the edge of the explant, while the number of pseudopodia on the inner layer greatly increases. The results show that the curling-up of the explant and formation of a sphere results from locomotor activity of the cells in both layers.

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PubMed1990

Permissiveness to murine leukemia, virus expression during preimplantation and early postimplantation mouse development.

Permissiveness to Moloney Murine Leukemia Virus (MoMuLV) expression was examined during preimplantation and early postimplantation development of the mouse embryo. Blastocysts and 8th, 9th and 10th day postimplantation embryos were infected in vitro with a MoMuLV-based retroviral vector expressing the lacZ gene driven off an internal rat beta-actin promoter. Beta-galactosidase-positive cells were identified in all embryonic tissues including inner cell mass, epiblast, mesoderm, endoderm and definitive ectoderm. In contrast, embryos infected with a MoMuLV-based vector expressing the lacZ gene driven off the viral LTR showed beta-galactosidase-positive cells only in mesoderm and definitive ectoderm. We conclude that permissiveness to transcriptional activity of the LTR is acquired immediately upon differentiation of epiblast during gastrulation of the mouse embryo.

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PubMed2004

Interaction between SPARC and tubulin in Xenopus.

Secreted protein, acidic, rich in cysteine (SPARC) is an ancient calcium-binding glycoprotein associated with the extracellular matrices of invertebrates and vertebrates. We have previously reported an intracellular association of SPARC with the 9+2 microtubule arrays of cilia on the surface ectoderm of Xenopus embryos. During early development in Xenopus, ciliated cell precursors are associated with the inner sensorial layer of the two-layered embryonic skin. The ciliated cell precursors migrate to the overlying surface ectoderm where they undergo ciliogenesis. Whole-mount immunohistochemical data indicate SPARC is associated with the ciliary tuffts until ciliated cells begin to disappear from the surface ectoderm during late tailbud development. We now report an association between SPARC and tubulin in Xenopus embryonic cell lysates by co-immunoprecipitation. Tubulin is not co-immunoprecipitated by anti-SPARC antibodies that show no cross-reactivity to Xenopus SPARC by whole-mount immunocytochemical analysis. An association of SPARC with tubulin has also been observed in pull-down assays with biotinylated SPARC as bait. These data indicate that SPARC may have intracellular and extracellular functions during development in Xenopus.

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PubMed1985

Ultrastructure of the full-term shark yolk sac placenta. II. The smooth, proximal segment.

The smooth, proximal portion of the yolk sac placenta of the sandbar shark, Carcharhinus plumbeus is comprised of: (1) An outermost epithelial ectoderm; (2) an intervening collagenous stroma; and (3) an inner mesothelium. The surface epithelium may be one to three cell layers thick. The surface epithelium comprises two cell types. A cuboidal cell that has a dome-like apical surface covered with microvilli and an ovoid nucleus predominate. These cells contain lipid inclusions, many cytoplasmic filaments, and are joined by desmosomes. The second cell type has a convoluted nucleus and a flattened cell apex with microvilli, cilia, and paddle cilia. Golgi complexes and elements of the endoplasmic reticulum are relatively uncommon in the cytoplasm of both cell types. Microplicae also occur on the surface of some cells. The smooth, proximal portion of the placenta is sparsely vascularized. The innermost cellular elements of the surface epithelium rest on a prominent basal lamina. A collagenous zone separates the epithelial basal lamina from the basal lamina of the mesothelium. The mesothelial cells are squamous with a fusiform nucleus, many pinocytotic pits and vesicles, and a large number of cytoplasmic filaments. The endoplasmic reticulum, except for occasional patches of the rough type, and the Golgi complex are poorly developed. Ultrastructural tracer studies show that this portion of the placenta does not absorb horseradish peroxidase (HRP) and trypan blue.

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PubMed2004

Islet-1 expression in the developing chicken inner ear.

The cell types of the inner ear originate from the otic placode, a thickened layer of ectoderm adjacent to the developing hindbrain. The placode invaginates and forms the otic pit, which pinches off as a small vesicle called the otocyst. Presumptive cochleovestibular neurons delaminate from the anterior ventral part of the otocyst and form the cochleovestibular ganglion of the inner ear. Here we show that the LIM/homeodomain protein islet-1 is expressed in cells of the ventral part of the otic placode and that this ventral expression is maintained at the otic pit and the otocyst stages. Auditory and vestibular neurons originate from this islet-1-positive zone of the otocyst, and these neurons maintain islet-1 expression until adulthood. We also demonstrate that islet-1 becomes up-regulated in the presumptive sensory epithelia of the inner ear in regions that are defined by the expression domains of BMP4. The up-regulation of islet-1 in developing inner ear hair and supporting cells is accompanied by down-regulation of Pax-2 in these cell types. Islet-1 expression in hair and supporting cells persists until early postnatal stages, when the transcriptional regulator is down-regulated in hair cells. Our data is consistent with a role for islet-1 in differentiating inner ear neurons and sensory epithelia cells, perhaps in the specification of cellular subtypes in conjunction with other LIM/homeodomain proteins.

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PubMed1995

Localization of alpha-fetoprotein in developing chick amniotic membrane.

The aim of this work was to investigate the localization of alpha-fetoprotein (AFP) in amniotic membrane (AM). By using the immunoperoxidase technique in several developmental stages, which reflected the changes of structure of the AM germinal layers, AFP was detected earliest in 7-day AM and localized selectively in the ectodermal cell layer. This was the only developmental stage at which AM occurred as a two-layer structure, ectoderm and somatic mesoderm, and was AFP-positive. In the zone of fusion of the AM with the inner wall of the allantoic sac, cystlike cavities were observed which were markedly immunoreactive to AFP. In those membranes where fusion had consolidated and a four-layer structure could be distinguished: ectoderm, somatic mesoderm, splanchnic mesoderm and endoderm, AFP was localized in the ectodermal cells and in the splanchnic mesoderm resulting from the inner wall of the allantoic sac. Both mesodermal layers could be distinguished by means of the AFP immunoreaction since AFP labelled the splanchnic, but not the somatic mesoderm. At later developmental stages, e.g. 18-day, the AM had a three-layer structure and AFP was localized selectively throughout the splanchnic mesoderm. The disappearance of the somatic mesoderm coinciding temporarily with the disappearance of AFP from the ectodermal cells, suggests that the presence of AFP in such cells could depend on some factors related to the somatic mesoderm.

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PubMed1998

A role for neural cell adhesion molecule in the formation of the avian inner ear.

The inner ear forms by a series of folds within an ectodermal placode. Previous work has shown that changes in surrounding tissues play a more prominent role in invagination than changes in the cytoskeleton of the primordium. Interference with the integrity of the extracellular matrix causes abnormalities in the folding process, primarily related to abnormalities in the paraxial mesoderm which lies ventral to the placode. In this study, the role of the neural cell adhesion molecule (N-CAM) was investigated, based on the expression of this component of the plasmalemma at the time the otic placode begins to fold. Microinjection of blocking antibodies to N-CAM into the paraxial mesoderm adjacent to the otic placode resulted in two major classes of defects, detachment of the primordium from the neural tube and interference with formation of the folds. Microinjection of saline, control immunoglobulin, or antibody against cytoplasmic domain had no effect. These defects correlate with the pattern of N-CAM expression at the time of injection, along the neural ectoderm and otic epithelium and the mesenchyme cells ventral to the primordium. It seems likely that N-CAM is playing a role in heterophilic associations rather than through the homophilic binding domain during formation of the otic vesicle.

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PubMed1983

Regeneration by dissociated adult Hydra cells: a histologic study.

Adult Hydra attenuata with vitally stained gastrodermal cells were dissociated into their component cells which were then randomly reaggregated into pellets by low-speed centrifugation. Representative examples of these preparations, which develop into normal adult hydra if left undisturbed, were examined fresh at low magnification and at higher magnification in fixed, stained, and sectioned specimens. The actual pellet stage lasts less than 1 hour because the adult ectodermal and gastrodermal cells rapidly sort themselves into an inner and outer layer and seem to secrete a new mesoglea immediately thereafter. The "embryo" becomes trilaminar and attains a central cavity by extruding a large amount of cellular debris at the end of the first day. At about this same time, new tentacles begin to differentiate from rapidly dividing and undifferentiated interstitial cells. Regulation of tentacle number and position occurs at the end of two days, and the body form is essentially reestablished within 60 hours by further differentiation of the hypostomes and body wall. Complete separation of the preparation into individual polyps does not occur until about 190 hours of development.

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PubMed1999

A two-step mechanism generates the spacing pattern of the ciliated cells in the skin of Xenopus embryos.

The skin of Xenopus embryos contains a population of specialized ciliated cells that are distributed in an evenly spaced pattern. Here we describe two successive steps that govern the differentiation and the generation of the spacing pattern of these ciliated cells. The first step occurs in the inner or sensorial layer of the non-neural ectoderm where a subset of cells are chosen to differentiate into ciliated-cell precursors. This choice is under the control of lateral inhibition mediated by a Suppressor of Hairless-dependent Notch signaling pathway, in which X-Delta-1 is the putative ligand driving the selection process, and a new Enhancer-of-Split-related gene is an epidermal target of Notch signaling. Because nascent ciliated-cell precursors prevent neighboring cells from taking on the same fate, a scattered pattern of these precursors is generated within the deep layer of the non-neural ectoderm. Ciliated-cell precursors then intercalate into the outer layer of cells in the epidermis. We show that the intercalation event acts as a second step to regulate the spacing of the mature ciliated cells. We propose that the differentiation of the ciliated cells is not only regulated by Notch-mediated lateral inhibition, but is also an example where differentiation is coupled to the movement of cells from one cell layer to another.

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PubMed1998

Ectoderm cell--ECM interaction is essential for sea urchin embryo skeletogenesis.

Paracentrotus lividus sea urchin nectin (Pl-nectin) is an extracellular matrix (ECM) protein of the sea urchin embryo on the apical surface of the ectoderm and has been shown to be an adhesive substrate for embryonic cells. A monoclonal antibody (McAb) to Pl-nectin was generated that inhibits the adhesion of blastula cells to Pl-nectin-coated substrates in an in vitro functional assay. To examine for possible in vivo functions of Pl-nectin, Fab fragments (Fabs) of Pl-nectin McAb were added to early blastulae. Ingression of primary mesenchyme cells was not affected by Fabs. As control embryos reached the pluteus stage, treated embryos showed a severe inhibition of skeletal elongation and patterning. When the Fabs were injected directly into the blastocoel, even at higher concentration than was applied externally, skeletogenesis was normal. Therefore, the effect of the antibody on spiculogenesis was indirect. The treatment was partially reversible as embryos eventually seemed to recover and elongate spicules, although with an incorrect patterning. Migration of pigment cells was also affected by the Fabs, since they did not disperse throughout the ectoderm but remained clustered in ectopic areas. In contrast, the development of endoderm structures was not affected. Our results indicate that in the sea urchin embryo the appropriate contact of ectodermal cells with outer ECM components is essential for the correct morphogenesis of inner mesodermal structures.

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PubMed1986

Development of the ectoderm in Xenopus: tissue specification and the role of cell association and division.

When do ectodermal cells become specified to form epidermis, that is, become committed to form epidermis when isolated? Animal pole explants of Xenopus cultured in saline from the 8-cell stage onwards express a specific epidermal antigen, whereas vegetal explants do not. The isolated outer layer of ectoderm formed by stage 7 is almost completely specified, the inner layer is only partially so. When are cell associations and cell divisions necessary for epidermal differentiation? Embryos that were either disaggregated or incubated in cytochalasin B after the midblastula stage do not require cell interactions, Ca2+, or cell divisions for epidermal differentiation to occur. Inhibition of mRNA transcription with actinomycin D shows that the epidermal antigen is certainly transcribed by the late gastrula stage (stage 12).

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