Distribution of spectrin and lectin-binding materials in surface lamina of RPE cells

Explants of embryonic chick retinal pigmented epithelium (RPE) form colonies in primary cultures in which the cells occupying the center of the colony are cuboidal, pigmented, and resemble closely the differentiated RPE cells found in vivo, while those towards the periphery gradually become less differentiated, flatter, nonpigmented, and motile. In the present article we describe the distribution of alpha-spectrin in cells in different parts of the RPE colony and compare it with that of the surface lamina components that bind the lectins, concanavalin A (Con A) and wheat germ agglutinin (WGA). Spectrin is present predominantly in the cell cortex in both differentiated and undifferentiated cells and seems to be accumulated especially heavily in the differentiated RPE cells in the colony center that have acquired the in vivo morphology. The distribution of lectin-binding materials in the surface lamina of the RPE cells is similar but not identical to that of alpha-spectrin. This is particularly evident in the flatter RPE cells along the edge of the colony in which surface lamina components visualized by fluorescein isothiocyanate (FITC)-WGA are distributed in the punctate pattern that is distinctly different from the reticular pattern in which alpha-spectrin is distributed. Also, in cells of the intermediate and central zones, strong staining along the edge of the cells was seen with antibodies to alpha-spectrin but not with FITC-WGA. Thus, a codistribution similar to that reported for the spectrin-like proteins and WGA-binding material in mesenchymally derived cells is not found in RPE cells.