Establishment and maintenance of a regionalized glycoprotein distribution during early mouse development

The regionalization of the cell membranes of the mouse embryo into apical and basolateral zones has been studied using antibodies to a pair of glycoproteins expressed during the two-cell to early blastocyst stage. These antigens are found on the outer, free surface and in the underlying cortical cytoplasm, but are not detectable at areas of cell contact. In the early blastocyst stage, antigen also appears at the free surfaces of cells bordering the blastocoel. Antigen regionalization is also reestablished after experimental manipulation and appears to be a direct consequence of cell contact. Thus, blastomeres examined 4 hr after dissociation from four- and eight-cell stage embryos express antigen in cortical areas underlying newly exposed surfaces and new sites of contact between embryos in multiple-embryo aggregates lose detectable antigen within 2 to 4 hr of the formation of the contacts. Microfilaments are involved in controlling the regional expression of these glycoproteins. Incubation of embryos from the two-cell stage in medium containing cytochalasin B interferes with antigen targeting, resulting in abnormal expression of the antigens both on the surface and in the cytoplasm of the embryos. Cytochalasin B treatment of later stage embryos results in an uneven distribution of the antigen in cortical cytoplasm and prevents the complete removal of antigen from new sites of cell contact in multiple-embryo aggregates. The presence of nocodozole, which inhibits the polymerization of microtubules, had no detectable effect on the expression of the antigens. Interference with the glycosylation of these proteins, by incubation of embryos in the presence of tunicamycin, did not alter the regionalized pattern of expression.