Differentiation of the inner cell mass of the baboon blastocyst

Abstract

During the blastocyst stage of development in the baboon, the inner cell mass changes from an irregular accumulation of cells within the cavity of the blastocyst to a disk at one side of the blastocyst and finally to a spherical mass of epiblast cells exhibiting a distinct polarity. The cells that will become the primitive endoderm are first seen as flattened but undifferentiated cells on the cavity side of the disk-shaped inner cell mass. After endoderm cells develop their typical cytological characteristics, they extend well beyond the inner cell mass to form parietal endoderm. A basal lamina develops associated with the epiblast cells and mural trophoblast, but not with either parietal or visceral endoderm. Cytological differentiation of inner cell mass cells includes increased numbers of polyribosomes and a change in mitochondria from long, convoluted structures to short, more typical shapes. Evidence that epiblast is polarized is seen by the late zonal blastocyst stage. Apical junctional complexes develop within the center of the epiblast. These junctions presage the development of the potential amniotic cavity. Large vacuoles containing cell debris, some of which contain nuclear fragments, are present at all stages. Extensive cell death occurs during growth of the blastocyst, but the pattern appears to be random and products of cell death are readily phagocytized by adjacent cells.

The hypoblast (visceral endoderm): an evo-devo perspective

“…This model is consistent with reports that the AVE arises partly from de novo gene expression in new cells and partly by early cells (Torres-Padilla et al, 2007). As in birds, there are differences in this topology and sequence of events among different mammals, including the rabbit (Viebahn et al, 1995), primates (Enders et al, 1990;Enders et al, 1986), pig (Hassoun et al, 2009) and monotremes (Kress and Selwood, 2006;Selwood and Johnson, 2006).…”

“…These include the observations of Enders and colleagues in a number of different mammalian species (Enders et al, 1990;Enders et al, 1986;King and Enders, 1970), explant studies in rat Svajger and Levak-Svajger, 1974), transplantation experiments by Gardner and colleagues in the mouse (Gardner, 1982;Gardner, 1984;Gardner, 1985;Gardner and Papaioannou, 1975;Gardner and Rossant, 1979), and eventually the clonal analyses of VE cells (Lawson et al, 1986;Lawson and Pedersen, 1987) and other important observations (Kadokawa et al, 1987;Lamers et al, 1987; for reviews, see Rivera-Perez et al, 2003;Rossant and Tam, 2009). …”

Human embryonic stem cells: prospects for development

“…Structural studies of early postimplantation development in the baboon (Enders et al, 1990) and human (Hamilton and Mossman, 1972;Luckett, 1978) show that they closely resemble that in the rhesus macaque monkey. The human embryo undergoes interstitial implantation (it becomes entirely surrounded by endometrial tissue).…”

Regulation of human embryonic stem cell differentiation by BMP-2 and its antagonist noggin

“…This cell was known classically in the human embryology literature as a mesoblast, but on comparative anatomical grounds Luckett (Luckett, 1978) argued that these cells were more likely to represent extra-embryonic endoderm. Several further morphological studies of the primate embryo have documented the development of cells resembling parietal endoderm and visceral endoderm from flattened cells formed below the epiblast (Enders et al, 1990;Enders and Schlafke, 1981;Enders et al, 1986). Although detailed studies of marker expression in these cells in the primate embryo have not been carried out, the properties of the BMP-induced cell are consistent with their identification as extra-embryonic endoderm.…”