Abstract

Dedifferentiated pigmented epithelial cells exhibit a bipotential phenotype when cultured. The expression of either of two differentiated phenotypes (pigmented or lentoid) is effected by signals in the culture environment which are mediated by the cell surface and its associated cytoskeleton. This paper describes the structural analysis of the circumferential microfilament bundle with the cell membrane of cultured pigment de epithelial cells from chick retina. The techniques of electron microscopy r veal that microfilaments associate both with zonula occludens junctions and with membrane domains that are separate from the specialized junction. At both sites, intermembrane linkages are present which provides structural continuity between cells at their apical surfaces. This ultrastructure contributes to the anchoring of the circumferential bundle to the cell membrane, which in tum provides a structural basis for the generation of tensile force and the characteristic polygonal shape of differentiated cells in the retinal pigmented epithelium.