Characterization of focal adhesion assembly in XR1 glial cells

In the present communication, we have characterized focal adhesions in cultured glial cells derived from the Xenopus retina. Using antibodies directed against focal adhesion proteins we found that beta1 integrin immunoreactivity colocalized with talin, vinculin, and phosphotyrosine immunoreactivities in glial cells from primary cultures of Xenopus retina, as well as in the XR1 glial cell line, an immortal cell line derived from Xenopus retinal neuroepithelium. beta1 integrin immunoreactivity also colocalized with the termini of rhodamine phalloidin-labeled filamentous-actin at focal adhesions. The regulation of focal adhesion assembly was examined in XR1 glial cells using inhibitors against actin polymerization (cytochalasins) or tyrosine kinase activity (genistein). Compared to control cultures, those treated with the inhibitors exhibited a dose-dependent decrease in the proportion of cells displaying focal adhesions. Treatment with cytochalasin B also resulted in a dose-dependent decrease in cell area. Mature focal adhesions in XR1 cells with a flattened, spread morphology also were disrupted by the presence of these inhibitors. These results provide strong evidence that an intact actin cytoskeleton and tyrosine kinase activity regulate focal adhesion assembly and also play important roles in the maintenance of the integrity of focal adhesions in glial cells.