THE REGULATION OF THE EXPRESSION, PHOSPHORYLATION, AND PROTEIN ASSOCIATIONS OF PP125(FAK) DURING RAT BRAIN DEVELOPMENT

We have studied both the expression and the interactions of focal adhe sion kinase (FAK) during brain development. We have discovered that du ring different periods of development, FAK apparently has different pr operties. During the early stage of neurogenesis, FAK is phosphorylate d, shows multiple isoforms, and interacts with the proto-oncogenes, sr c, fyn, and lyn. At this stage, FAK also interacts with both the N- an d c-terminal SH2 domains of GAP, a negative regulator of the ras pathw ay. During later embryonic development, none of these protein interact ions are apparent even though FAK is still predominantly phosphorylate d. By adulthood FAK is largely unphosphorylated and migrates as a sing le protein species on SDS-PAGE. We discuss these results in terms of t he dynamic cell movements that occur during embryonic brain developmen t.