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PubMed1995

Homozygosity for the Min allele of Apc results in disruption of mouse development prior to gastrulation.

Mutation of the APC (adenomatous polyposis coli) gene is an early event in colon tumor development in humans. Mice carrying Min (multiple intestinal neoplasia), a mutant allele of Apc, develop intestinal and mammary tumors as adults. To study the role of the Apc gene in development, we have investigated the phenotype of embryos homozygous for ApcMin (Min). Development of the primitive ectoderm fails prior to gastrulation in homozygous Min embryos. By midgestation, the presumed homozygotes consist of a mass of trophoblast giant cells with an additional cluster of much smaller embryonic cells. These results indicate that functional Apc is required for normal growth of inner cell mass derivatives.

Alleles↗

PubMed1990

Microstructural features of dipnoan tooth enamel.

Tooth plates of extant lungfishes were examined by contact microradiography, light microscopy and TEM, to elucidate the nature and origin of the hypermineralized surface layer. TEM indicated that the matrix of this layer consisted of organic filamentous material, and no collagen fibres were seen in the matrix. The matrix appeared to be secreted by oral epithelial cells of the inner fold surrounding the surface of the tooth plate, and deposited in the area between the cell membrane and basal lamina-like structure of these epithelial cells. Therefore, it is suggested that the hypermineralized surface layer of lungfish plates is enamel of ectodermal origin.

Actin Cytoskeleton↗

PubMed1982

Investigation of cell lineage and differentiation in the extraembryonic endoderm of the mouse embryo.

The technique of injecting genetically labelled cells into blastocysts was used in an attempt to determine whether the parietal and visceral endoderm originate from the same or different cell populations in the early embryo. When the developmental potential of 5th day primitive ectoderm and primitive endoderm cells was compared thus, only the latter were found to colonize the extraembryonic endoderm. Furthermore, single primitive endoderm cells yielded unequivocal colonization of both the parietal and the visceral endoderm in a proportion of chimaeras. However, in the majority of primitive endodermal chimaeras, donor cells were detected in the parietal endoderm only, cases of exclusively visceral colonization being rare. Visceral endoderm cells from 6th and 7th day post-implantation embryos also exhibited a striking tendency to contribute exclusively to the parietal endoderm following blastocyst injection. The above findings lend no support to a recent proposal that parietal and visceral endoderm are derived from different populations of inner cell mass cells. Rather, they suggest that the two extraembryonic endoderm layers originate from a common pool of primitive endoderm cells whose direction of differentiation depends on their interactions with non-endodermal cells.

Animals↗

PubMedDate not supplied

Pattern formation of the otic placode and morphogenesis of the otocyst.

The early embryonic development of the inner ear anlage, from the otic placode stage to formation of the otocyst, was documented in CBA/CBA mice by scanning electron microscopy. The otic placode is identified at the eight- to ten-somite stage, as revealed by the surface morphology of the developing ectoderm. The cells in the otic depression are considerably smaller than those of the adjacent ectodermal surface. Rapid invagination of the otic anlage occurs during the ninth gestational day (approximately eight to 20 somites). In most specimens from the tenth gestational day, the otic vesicle has closed toward the ectodermal surface. The surface of the otocyst on the 13th gestational day shows considerable specialization, with regional differences of the surface structure.

Animals↗

PubMed1982

Lineage analysis of inner cell mass and trophectoderm using microsurgically reconstituted mouse blastocysts.

The fate of mouse blastocyst tissues was examined following reconstitution of blastocysts from isolated inner cell mass (ICM) and trophectoderm differing for electrophoretic variants at the glucose phosphate isomerase (GPI-1) locus. A modified microsurgical method was used and a more sensitive enzyme assay allowed finer dissection of developing chimaeric conceptuses. In seven of nine cases, the extraembryonic ectoderm or the later ectoderm of the chorion was entirely of the blastocyst trophectoderm enzyme type, providing the first direct evidence that this tissue can be wholly derived from the trophectoderm. The two exceptions could represent contamination of the ICM with trophectoderm or might indicate some developmental lability of ICM cells. In addition, the results confirm the cell lineages of other tissues of the 7.5- to 9.5-day pc embryo and, for the first time, directly demonstrate the ICM origin of the parietal endoderm.

Animals↗

PubMed1984

Endogenous peroxidase in the visceral endoderm of early mouse embryos.

Endogenous peroxidase activity was demonstrated in early mouse embryos by means of the diaminobenzidine staining reaction. This enzyme was observed in visceral endoderm on the seventh to eighth day of gestation in vivo, but was no longer detected on the ninth day of development. In cell layers developing from blastocysts or isolated inner cell masses cultured for 96-144 h (developmental stage equivalent to 6-7.5-day-old embryos), diaminobenzidine product was also observed in visceral endodermal cells. Most of the endogenous peroxidase was localized inside or close to the numerous apical vacuoles in the endoderm. Ectoderm, mesoderm, ectoplacental cone, and trophoblast cells did not contain endogenous peroxidase.

Animals↗

PubMed1993

Derivation and characterization of putative pluripotential embryonic stem cells from preimplantation rabbit embryos.

We have derived putative embryonic stem (ES) cell lines from preimplantation rabbit embryos and report here their initial characterization. Two principal cell types emerged following serial passage of explanted embryos, and each has subsequently given rise to immortalized cell lines. One cell type has morphology identical to primary outgrowths of trophectoderm, is strictly feeder-cell dependent, and spontaneously forms trophectodermal vesicles at high cell density. The second type appears to represent pluripotent ES cells derived from the inner cell mass as evidenced by 1) ability to grow in an undifferentiated state on feeder layers, 2) maintenance of a predominantly normal karyotype through serial passage (over 1 year), and 3) ability to form embryoid bodies, which form terminally differentiated cell types representative of ectoderm, mesoderm, and endoderm. These ES cells may ultimately be suitable for introduction of germline mutations (via homologous recombination). The rabbit's size, reproductive capability, and well-characterized physiology make it suitable for a wide range of investigations, particularly for development of large animal models of human disease.

Animals↗

PubMed2001

Pluripotent cells (stem cells) and their determination and differentiation in early vertebrate embryogenesis.

Mammalian embryonic stem cells can be obtained from the inner cell mass of blastocysts or from primordial germ cells. These stem cells are pluripotent and can develop into all three germ cell layers of the embryo. Somatic mammalian stem cells, derived from adult or fetal tissues, are more restricted in their developmental potency. Amphibian ectodermal and endodermal cells lose their pluripotency at the early gastrula stage. The dorsal mesoderm of the marginal zone is determined before the mid-blastula transition by factors located after cortical rotation in the marginal zone, without induction by the endoderm. Secreted maternal factors (BMP, FGF and activins), maternal receptors and maternal nuclear factors (beta-catenin, Smad and Fast proteins), which form multiprotein transcriptional complexes, act together to initiate pattern formation. Following mid-blastula transition in Xenopus laevis (Daudin) embryos, secreted nodal-related (Xnr) factors become important for endoderm and mesoderm differentiation to maintain and enhance mesoderm induction. Endoderm can be induced by high concentrations of activin (vegetalizing factor) or nodal-related factors, especially Xnr5 and Xnr6, which depend on Wnt/beta-catenin signaling and on VegT, a vegetal maternal transcription factor. Together, these and other factors regulate the equilibrium between endoderm and mesoderm development. Many genes are activated and/or repressed by more than one signaling pathway and by regulatory loops to refine the tuning of gene expression. The nodal related factors, BMP, activins and Vg1 belong to the TGF-beta superfamily. The homeogenetic neural induction by the neural plate probably reinforces neural induction and differentiation. Medical and ethical problems of future stem cell therapy are briefly discussed.

Animals↗

PubMed2004

Clonogenic analysis reveals reserve stem cells in postnatal mammals. II. Pluripotent epiblastic-like stem cells.

Undifferentiated cells have been identified in the prenatal blastocyst, inner cell mass, and gonadal ridges of rodents and primates, including humans. After isolation these cells express molecular and immunological markers for embryonic cells, capabilities for extended self-renewal, and telomerase activity. When allowed to differentiate, embryonic stem cells express phenotypic markers for tissues of ectodermal, mesodermal, and endodermal origin. When implanted in vivo, undifferentiated noninduced embryonic stem cells formed teratomas. In this report we describe a cell clone isolated from postnatal rat skeletal muscle and derived by repetitive single-cell clonogenic analysis. In the undifferentiated state it consists of very small cells having a high ratio of nucleus to cytoplasm. The clone expresses molecular and immunological markers for embryonic stem cells. It exhibits telomerase activity, which is consistent with its extended capability for self-renewal. When induced to differentiate, it expressed phenotypic markers for tissues of ectodermal, mesodermal, and endodermal origin. The clone was designated as a postnatal pluripotent epiblastic-like stem cell (PPELSC). The undifferentiated clone was transfected with a genomic marker and assayed for alterations in stem cell characteristics. No alterations were noted. The labeled clone, when implanted into heart after injury, incorporated into myocardial tissues undergoing repair. The labeled clone was subjected to directed lineage induction in vitro, resulting in the formation of islet-like structures (ILSs) that secreted insulin in response to a glucose challenge. This study suggests that embryonic-like stem cells are retained within postnatal mammals and have the potential for use in gene therapy and tissue engineering.

Animals↗

PubMed2005

A germ cell origin of embryonic stem cells?

Because embryonic stem (ES) cells are generally derived by the culture of inner cell mass (ICM) cells, they are often assumed to be the equivalent of ICM cells. However, various evidence indicates that ICM cells transition to a different cell type during ES-cell derivation. Historically, ES cells have been believed to most closely resemble pluripotent primitive ectoderm cells derived directly from the ICM. However, differences between ES cells and primitive ectoderm cells have caused developmental biologists to question whether ES cells really have an in vivo equivalent, or whether their properties merely reflect their tissue culture environment. Here, we review recent evidence that the closest in vivo equivalent of an ES cell is an early germ cell.

Animals↗

PubMed2001

Deriving and propagating mouse embryonic stem cell lines for studying genomic imprinting.

Embryonic stem (ES) cells are a cell culture derivative of the blastocyst inner cell mass (ICM), the latter giving rise to the embryo, the amnion, the yolk sac, and the chrorioallantoic portion of the placenta. Blastocyst injection chimera experiments show that ES cells are similar to early-stage ICM cells in that they contribute to the primitive ectoderm and endoderm derivatives (1). However, it is probably not possible to equate these two cell types, as ES cells appear to be produced by the cell culture environment and have no exact counterpart in the blastocyst. Instead, ES cells could be thought of as being ICM cells that, instead of undergoing rapid differentiation as they would in vivo, are abnormally locked into continuing cycles of division in the undifferentiated state by virtue of the action of exogenous factors. Leukemia inhibitory factor, LIF, is one such factor (2,3) and is indispensable for the propagation of mouse ES cells at least when primary embryo fibroblasts (PEFs) are used as feeder layers (4).

Animals↗

PubMed1998

Developmental complexity of early mammalian pluripotent cell populations in vivo and in vitro.

Early mammalian embryogenesis is characterised by the coordinated proliferation, differentiation, migration and apoptosis of a pluripotent cell pool that is able to give rise to extraembryonic lineages and all the cell types of the embryo proper. These cells retain pluripotent differentiation capability, defined in this paper as the ability to form all cell types of the embryo and adult, until differentiation into the three embryonic germ layers at gastrulation. Our understanding of pluripotent cell biology and molecular regulation has been hampered by the difficulties associated with experimental manipulation of these cells in vivo. However, a more detailed understanding of pluripotent cell behaviour is emerging from the application of molecular technologies to early mouse embryogenesis. The construction of mouse mutants by gene targeting, mapping of gene expression in vivo, and modelling of cell decisions in vitro are providing insight into the cellular origin, identity and action of key developmental regulators, and the nature of pluripotent cells themselves. In this review we discuss the properties of early embryonic pluripotent cells in vitro and in vivo, focusing on progression from inner cell mass (ICM) cells in the blastocyst to the onset of gastrulation.

Animals↗

PubMed1976

Investigation of inner cell mass determination by aggregation of isolated rat inner cell masses with mouse morulae.

Inner cell masses (ICMs) dissected from 4 1/2-day rat blastocysts were aggregated with 2 1/2-day mouse morulae. Successful aggregates formed blastocysts in vitro and morphologically normal 5 1/2-day conceptuses in the mouse uterus. Immunofluorescent analysis of these conceptuses revealed that rat cells were only present in the embryonic ectoderm and endoderm and never in the trophectoderm derivatives, although rat trophoblast did develop in the mouse uterus in various control experiments. The single-cell resolution of this technique extends the results obtained from aggregating mouse ICMs with mouse morulae and provides strong evidence that ICM cells, although not overtly differentiated, are determined by the blastocyst stage.

Animals↗

PubMed1989

Distribution of fibronectins and laminin in the early pig embryo.

Fibronectins (FN) and laminin (LN) distributions were studied in the pig embryo by indirect immunofluorescence using antiporcine FN and antimurine LN antibodies. Extracellular FN are first detected in the early blastocyst before endodermal cell migration. They appear between the cells and on the blastocoelic face of the inner cell mass; thus, they are located at the interface of the trophectoderm and extraembryonic endoderm. Mesodermal cells migrate in a tridimensional network of fibrillar FN. These glycoproteins are also in the extraembryonic membranes (chorion and yolk sac wall) contiguous to the FN-rich basement membranes of embryonic ectoderm and endoderm. Extracellular LN appears in the blastocyst when the endoderm is already established as a continuous cellular monolayer, and is located between the trophectoderm and the extraembryonic endoderm, which produces it. Laminin also accumulates at the basal surface of the embryonic ectoderm at the onset of gastrulation. In the extraembryonic membranes, LN appears at the interface of the endoderm and mesoderm and at the interface of the trophectoderm and mesoderm. It is produced and secreted by extraembryonic mesodermal cells. Analysis of the distribution of these glycoproteins suggests that FN allow the migration of endodermal and mesodermal cells by providing them with a suitable substrate. When these cells become immobilized, they synthesize LN, probably to stabilize their interactions with the underlying extracellular material and epithelia.

Animals↗

PubMed1988

Molecular differentiation of the otic vesicle and neural tube in the chick embryo demonstrated by monoclonal antibodies.

Monoclonal antibodies (MAbs) were produced against membrane fractions of the chick neural tube and somite. These MAbs selectively stained the neural tube and neural crest cells; the antigens for some of these MAbs were identified as cell adhesion molecules or glycolipids. Histochemistry of the otic vesicle and its progeny in the chick embryo was performed with these MAbs and other MAbs obtained previously in our laboratory. It was demonstrated that differentiation of the otic placode and vesicle from the ectoderm, and development of the acoustic ganglion from the otic vesicle were accompanied by the appearance and disappearance of various molecules.

Animals↗

PubMed1976

Enveloping layer and periderm of the trout embryo (Salmo trutta fario L.)20U.

The origin of pericarderm and epidermis has been studied in trout embryos from stage 20(2 days after fertilization at 10degrees c) to hatching (stage 410). Between stages 20 and 50, the blastodisc consists of an inner mass of blastomeres covered by a superficial layer of closely packed blastomeres, the peripheral layer. This layer gives rise to both peripheral cells and to cells joining the inner mass of blastomeres. Between stages 50 and 110, junctions differentiate between peripheral cells. This newly formed superficial epithelium the enveloping layer, no longer gives rise to inward migrating cells. From stage 110 on, a basement membrane differentiates beneath a one-cell thick subperipheral layer, which thus becomes the ectodermal basal layer, the prospective epidermal basal layer. From these and ultrastructural observations, it is concluded that 1)the epidermis apparently originates, at least in part from the peripheral cells, between stages 20 and 50; 2) the periderm assumes a protective function over the body of the embryo and also a secretory function over the yolk sac (probably producing the hatching enzymes); 3)the periderm, which is a temporary structure, appears to play the role of an embryonic membrane in teleosts.

Animals↗

PubMed1991

The Msh-like homeobox genes define domains in the developing vertebrate eye.

The mouse Hox-7.1 gene has previously been shown to be related to the Drosophila Msh homeobox-containing gene. Here we report the isolation of a new member of this family which resides at an unlinked chromosomal location and has been designated Hox-8.1. Both Hox-7.1 and Hox-8.1 are expressed in the mouse embryo during the early stages of eye development in a distinct spatial and temporal relationship. Hox-8.1 is expressed in the surface ectoderm and in the optic vesicle before invagination occurs in regions corresponding to the prospective corneal epithelium and neural retina, respectively. Hox-7.1 is expressed after formation of the optic cup, marking the domain that will give rise to the ciliary body. The activity of these genes indicates that the inner layer of the optic cup is differentiated into three distinct compartments before overt cellular differentiation occurs. Our results suggest that these genes are involved in defining the region that gives rise to the inner layer of the optic cup and in patterning this tissue to define the iris, ciliary body and retina.

Amino Acid Sequence↗

PubMed2006

Trophoblast cells exhibit differential responses to laminin isoforms.

Extracellular matrix (ECM) has specific effects on cell behavior that influence many aspects of early development. In the early postimplantation mouse embryo the ECM component laminin promotes polarization and survival of the embryonic ectoderm and formation of Reichert's membrane. In addition, dynamic patterns of laminins 1 and 10/11 expression in the embryo and the uterus correlate with the progression of implantation. In the implanting blastocyst, laminin 1 is strongly expressed in the trophectoderm basement membrane, whereas laminin 10/11 is expressed only in the inner cell mass and polar trophectoderm. In the uterus, laminin 10/11 is strongly expressed in the decidualizing matrix of the stroma. We show here that laminins 1 and 10/11 have distinct effects on trophoblast cell behavior that influence the process of implantation. Laminin 1 promotes random migration and decreases spreading, whereas laminin 10/11 promotes both spreading and persistent migration. When presented as adjacent substrates, cells stop at the boundary and do not enter the region containing laminin 1. Laminin 1 also affects cell-cell adhesion through changes in the localization of vascular endothelial (VE) cadherin. Cultured cells and primary trophoblast explants become single cells or very small groups on laminin 1 and VE-cadherin localization at regions of cell-cell contact decreases dramatically. In contrast, trophoblast cells maintain strong cell-cell contacts on substrates of laminins 10/11, and exhibit strong staining of VE-cadherin in all regions of cell-cell contact. These effects, and the localization of laminin 1 in Reichert's membrane and laminin 10/11 in the surrounding decidual matrix, suggest that these laminin isoforms influence the direction and quality of invasion of trophoblast cells during implantation, and provide epigenetic cues that drive the morphogenesis of the yolk sac placenta.

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