LOCALIZATION OF FOCAL ADHESION KINASE IN DIFFERENTIATING SCHWANN CELLNEURON CULTURES/

Previous studies have shown that Schwann cells (SCs) differentiate int o myelin-forming or ensheathing cells only under conditions which allo w the deposition of basal lamina and extracellular collagen [Bunge (19 93) Peripheral Neuropathy, pp. 299-316]. SC adhesion to basal lamina i s mediated by pi integrins and function blocking antibodies to pi inte grins inhibit myelination [Fernandez-Valle et al. (1993) Development 1 19:867-880]. Recently, focal adhesion kinase (FAK), a cytoplasmic non- receptor tyrosine kinase, was found to mediate pi integrin-dependent s ignalling in a variety of cultured cell types adhering to ECM componen ts such as fibronectin [reviewed in Schwartz et al. (1995) Ann. Rev. C ell Biol. 11:549-599; Ilic et al. (1997) J. Cell Sci. 110:401-407]. In the present study, we have determined more precisely the respective t ime courses of ECM deposition and myelination. In addition, we have st udied by immunocytochemistry, immuno-gold labelling, and electron micr oscopy the expression and subcellular localization of FAK in nondiffer entiating SCs and in SCs differentiating into myelinating cells. We sh ow that the development of basal lamina and extracellular collagen fib rils precedes by 3 days the appearance of the first myelin sheaths. FA K was detected by immunocytochemistry or immune-gold labelling only in SCs differentiating in the presence of ascorbic acid. Localization of FAK to the abaxonal plasma membrane was dependent upon ECM deposition . Cytochalasin D did not prevent or disrupt localization of FAK to the plasma membrane. These data support the possibility that FAK acts as an intermediate in the pathway by. which basal lamina regulates SC dif ferentiation. Microsc. Res. Tech. 41:416-430, 1998. (C) 1998 Wiley-Lis s, Inc.