CDK5 EXPRESSION AND ASSOCIATION WITH P35(NCK5A) IN EARLY STAGES OF RAT CEREBELLUM NEUROGENESIS - TYROSINE DEPHOSPHORYLATION AND ACTIVATION IN POSTMITOTIC NEURONS

We have examined the expression of cyclin dependent kinase (cdk) 5 pro tein kinase and p35(nck5a). its activator subunit, during postnatal ne urogenesis in rat cerebellum, using mono-specific antibodies. Both cdk 5 and p35(nck5a) are present and associated in proliferative stapes, a lthough cdk5-p35 kinase activity is barely detectable. Cdk5-p35 activi ty, but not the expression of either subunit, increases up to B-fold d uring neuronal differentiation. Since we observe that cdk5 is phosphor ylated on tyrosine in proliferative, bur not in post-mitotic stages, w e suggest that post-translational regulatory mechanisms control cdk5-p 35 protein kinase activity during neurogenesis.