CHANGES IN THE EXPRESSION OF NOVEL CDK5 ACTIVATOR MESSENGER-RNA (P39(NCK5AI) MESSENGER-RNA) DURING RAT-BRAIN DEVELOPMENT

We previously reported that a neuron-specific Cdk5 activator, p35(nck5 a), was most prominent in the newborn rat brain. In the adult brain, t he expression decreased in most regions except hippocampus and primary olfactory cortex. A novel neuron-specific Cdk5 activator, p39(nck5ai) , has been recently cloned. To clarify whether two activators were dif ferentially distributed throughout brain development, in this study, w e examined the spatial and temporal expression of p39(nck5ai) in the d evelopment rat brain. Northern blot analysis showed that p39(nck5ai) e xpression was low in 15-day old fetuses and newborn, and was most prom inent in the 1-3 week-old rat brains. In the adult rat brain, expressi on declined to the same level as in newborn rat brain. In situ hybridi zation showed that p39(nck5ai) mRNA was weakly expressed in all neuron s of all regions in the newborn rat brain and the transcriptional leve l was highest in all regions in the 3 week-old rat brain. In the adult , expression was decreased in most neurons except Purkinje and granule cells in the cerebellum which retained high levels. These results sug gest that p35(nck5a) and p39(nck5ai) may have different functional rol es in distinct brain regions during different states of the rat brain development. (C) 1997 Elsevier Science Ireland Ltd.