Differentiation and migration of endoderm in the rat and mouse at implantation

Abstract

The initial differentiation of endoderm at the time of onset of implantation, and the subsequent rapid differentiation of visceral and parietal endoderm were studied in the rat and mouse. Transmission electron microscopy illustrates the reorientation and loosening of embryonic cell mass cells during implantation, as well as cytological evidence that endoderm cells have differentiated. Using scanning electron microscopy, parietal endoderm consists of individual stellate cells with numerous peripheral branching filopodia. As these cells migrate abembryonically, the rest of the embryonic cell mass becomes recompacted. The visceral endoderm proliferates and forms a columnar epithelium which has the cytological characteristic of an absorptive epithelium and is able to ingest exogenous proteins. Thus, by 24 hours after implantation, the two endodermal derivatives have assumed widely diverse shapes and different types of associations and rates of replication, and are probably performing different functions.

Localization of fibronectin, laminin-entactin, and entactin in Reichert's membrane by immunoelectron microscopy.

“…The distribution of fibronectin so revealed is inconsistent with it being a major structural component of the whole basement membrane. We canot rule out the possibility that parietal endoderm cells transiently synthesize and lay down fibronectin when they first migrate out over the trophectoderm (Enders et al, 1978). This might generate a fibronectin-rich 'screed' over which the later RM is deposited, and could account for the more fibrillar morphology of the outer trophoblast layer in conventional electron microscopy.…”

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

“…With the exception of the DVE, which is morphologically distinct from the EVE, the EVE is characterized by its flat squamous cells, largely without microvilli or apical vacuoles. TVE is cuboidal containing some microvilli and vacuoles, and XVE is columnar with many microvilli and apical vacuoles (Bonnevie, 1950;Enders et al, 1978;Hogan and Tilly, 1981;Solter et al, 1970).…”

Imprinted X-inactivation in extra-embryonic endoderm cell lines from mouse blastocysts

“…1A). By E5.0, the PrE is segregating into two subpopulations of extra-embryonic endoderm: visceral endoderm (VE) and parietal endoderm (PE) (Enders et al, 1978). PE cells grow with minimal cell-cell contact as they scatter on the inner surface of the giant cell layer (Fig.…”