Expression and herbimycin A-sensitive localization of pp125FAK in retinal growth cones

Proper elongation of Xenopus retinal ganglion cell (RGC) axons in the optic tract during development requires intact functioning of beta 1 integrin and tyrosine kinase (TK) activity. The cytoplasmic TK pp125FAK can directly associate with and become activated by beta 1 integrin in cultured fibroblasts. Here we demonstrate the presence of pp125FAK in the developing retina and in cultured retinal neurities, growth cones and filopodia. We show that pp125FAK immunoprecipitated from neural tissue is phosphorylated, and we compare the pattern of FAK and phosphotyrosine immunolabeling. Finally, we show that the localization of pp125FAK in filopodia depends upon TK activity sensitive to the TK inhibitor herbimycin A. These results indicate a role for pp125FAK in signaling the growth of retinal axons.