Developmental changes of cyclin dependent kinase 5 subcellular localization in the rat cerebellum

Cyclin dependent kinase 5 (Cdk5) phosphorylates tau protein, a microtubule-associated protein, at pathological sites in vitro as well as in Alzheimer's disease brain. The enzyme is therefore regarded as an important candidate responsible for the progression of Alzheimer's disease. We and others have suggested that the enzyme has physiological roles in brain development and maturation. In this study, we investigated the exact distribution and developmental changes of the enzyme in cerebellum by immunohistochemistry and non-radioactive in situ hybridization. Immunohistochemistry demonstrated that Cdk5 was consistently expressed in the cerebellum at all developing stages. However, the subcellular localization of Cdk5 dramatically changed during maturation of the cerebellum. In the early neonatal stage, Cdk5 was strongly expressed in the cell bodies of neurones. With neuronal maturation Cdk5 immunoreactivity changed its subcellular localization from the cell body to axon. In terminally differentiated neurons, the immunoreactivity was only detected in the axon. These results suggest that subcellular localization of Cdk5 is strictly regulated and may play an important role in neuronal maturation.