The expression of Cdk5, p35, p39, and Cdk5 kinase activity in developing, adult, and aged rat brains

The expression of cyclin-dependent kinase 5 (Cdk5) and its regulatory subun its, p35 and p39, was investigated in rat brain from embryonic day 12 (E12) to postnatal 18 months (18M). The Cdk5 protein levels increased from E12 t o postnatal day 7 (P7) and remained at this level until 18M. The Cdk5 kinas e activity and the levels of both p35 mRNA and protein were low at E12, bec ame prominent at E18-P14 but then decreased in the adult and aged rat brain s of 3M to 18M. In comparison, the expression pattern of p39 appeared to ha ve an inverse relationship to that of Cdk5 and p35. In regional distributio n studies, p35 protein levels and Cdk5 kinase activity were significantly h igher in the cerebral cortex and hippocampus, bur lower in the cerebellum a nd striatum. These results suggested that Cdk5, p35 and p39 might have regi on-specific and developmental stage-specific functions in rat brain.