The focal adhesions of chick retinal pigmented epithelial cells

Retinal pigmented epithelial (RPE) cells obtained from the eyes of chick embryos from colonies in vitro in which cells at the periphery of the colony express an undifferentiated, well-spread morphology and develop extremely large areas of cell-substratum adhesion. These adhesions can be classified as focal on the basis of the following: (a) their black surface reflection interference image, the contrast of which is not affected by changes in either the wavelength of the incident light or the refractive index of the immersion medium; (b) their association with the termini of actin-containing microfilament bundles; and (c) their ability to be labelled with antiserum against vinculin, a protein specific for adhesions of the focal type. The focal adhesions of RPE cells comprise laterally associated individual focal contacts, the mechanism by which this association is achieved and maintained is yet unknown. Because of the unusually large size and excellent microscopical definition of their focal adhesions, I used RPE cells to investigate the role of other actin-associated proteins in adhesion complexes. One of these, nonerythroid spectrin (fodrin), a protein suggested to play a role in anchoring actin filaments to the plasma membrane, was neither concentrated in nor excluded from the focal adhesions of RPE cells. Thus, at least in this cell type, spectrin seems unlikely to serve as a link between the major actin-containing microfilament bundles and the plasma membrane in the regions of cell-to-substratum contacts.