Abstract

Avian embryonic corneal epithelia are two cell layers thick. If isolated without (-) basal lamina, the basal cells have unorganized actin and project cytoplasmic protrusions termed blebs. The actin-based cytoskeleton at the cell-extracellular matrix junction (termed the actin cortical mat) is disrupted. These epithelia respond to soluble extracellular matrix molecules by reorganizing the actin cortical mat. Sheets of epithelia were isolated + or -basal lamina. Epithelia isolated -basal lamina were cultured +/- laminin-1 and/or +/- cytochalasin D (CD). The intracellular localization of zyxin, vinculin, paxillin, focal adhesion kinase, and tensin was determined using indirect immunohistochemistry. Protein levels were determined by Western blot analysis. Zyxin and vinculin were concentrated in two areas of the tissue. The interface between the upper cell layer (periderm) and the basal cells. The second area of concentration was at the inferior 1-4 microns of the basal cells in an area with multiple actin bundles termed the actin cortical mat. The actin bundles align toward zyxin and vinculin that were located near basal lateral membranes. Zyxin was displaced from the basal compartment of blebbing basal cells. In contrast tensin, vinculin and focal adhesion kinase were found diffusely throughout the blebs. Zyxin and vinculin redistributed to the basal-lateral membranes as actin bundles reorganized in laminin-stimulated epithelia. In contrast to the altered protein distribution, extractable protein levels were similar in blebbing and laminin-stimulated epithelia. Zyxin, vinculin, and other associated proteins were disrupted in the CD-treated tissues and do not colocalize with each other or CD-induced actin aggregates. The intracellular localization of zyxin and vinculin were concentrated in distinct areas along the inferior basolateral membranes of basal cells termed the cell-extracellular matrix attachment complex (CMAX). The distribution of CMAX proteins was dependent upon actin bundle organization.