DEVELOPMENTAL ALTERATION OF THE EXPRESSION AND KINASE-ACTIVITY OF CYCLIN-DEPENDENT KINASE-5 (CDK5) P35(NCK5A) IN THE RAT RETINA/

Neuronal Cdc2-like kinase has been purified from the bovine brain as a proline-directed serine/threonine kinase. This kinase is a heterodime r of Cdk5 and p35(nck5a) and influences neuronal maturation or sprouti ng in the normal brain. In this study, we showed the expression of Cdk 5/p35(nck5a) kinase in the developing rat retina. The expression of Cd k5 and p35(nck5a) increased between 1 week and 3 weeks after birth. Th ese expression levels were most prominent from 2 weeks to 3 weeks afte r birth and decreased after 4 weeks. The developmental change of Cdk5/ p35(nck5a) kinase activity coincided with those of the expression of p 35(nck5a) and Cdk5. An immunohistochemical study showed that Cdk5 was expressed in the ganglion cells and in some cells in the inner nuclear layer at an early stage. With retinal development, Cdk5 was expressed in the inner plexiform layer also. In the adult, the expression of Cd k5 was restricted to the inner plexiform layer and to some cells in th e inner nuclear layer. These changes of localization in the developing retina were very close to those of B-50/GAP-43. On the other hand, th e expression of p35(nck5a) was restricted to the soma of the neuron in the developing retina. This subcellular localization in the developin g retina agreed with that in the developing rat brain. The expression levels of Cdk5 and p35(nck5a) in retina of rats raised from fetus to 3 weeks after birth in darkness were 36% and 40% respectively, of the b aseline for control rats. Moreover, the kinase activity in rats raised in darkness was lower than that in control rats. These data suggest t hat Cdk5/p35(nck5a) may play a role in neuronal plasticity in the deve loping rat retina.