FOCAL ADHESION KINASE IN RAT CENTRAL-NERVOUS-SYSTEM

Focal adhesion kinase (pp(125FAK), FAK) is a 125 kDa non-receptor tyro sine kinase enriched in focal adhesions of various cell types, where i t is thought to transduce signals triggered by contact with the extrac ellular matrix. We have studied the expression and localization of FAK in rat CNS. Immunoblotting, immunohistochemistry and in situ hybridiz ation revealed the presence of FAK in all regions of the adult brain a nd demonstrated its enrichment in specific neuronal populations of the cerebral and cerebellar cortex, as well as in the hippocampus. During development, FAK protein levels were highest around birth in cerebral cortex and caudate putamen and decreased in the adult. In situ hybrid ization revealed enrichment of FAK mRNA in the ventricular germinative and external layers during the last period of embryonic growth. In pr imary cultures FAK immunoreactivity was localized in focal adhesions i n astrocytes, whereas in developing neurons the highest levels were fo und in growth cones and perikarya. In the growth cone, FAK immunoreact ivity colocalized with actin filaments. In mature neurons FAK appeared to be distributed in the whole cytoplasm, with no enrichment in any c ellular compartment. Our results demonstrate the presence of high leve ls of FAK in rat CNS, maximal during development but persistent in the adult. Its enrichment in growth cones suggests that it may play a rol e in neurite outgrowth, as well as in plasticity in the adult.