The cellular distribution and kinase activity of the Cdk family member Pctaire1 in the adult mouse brain and testis suggest functions in differentiation

Pctaire1, a member of the family of cyclin-dependent kinases, has been show n to be particularly abundantly expressed in differentiated tissues such as testis and brain. However, very little is known about the cellular and sub cellular distribution and function of Pctaire1 protein(s), which is the foc us of this study. We show that Pctaire1 encoded two major proteins of M-r s imilar to 62,000 and similar to 68,000, found predominantly in testis and b rain. Within these two tissues, Pctaire1 was most abundant in the cytoplasm of terminally differentiated cells, notably, the pyramidal neurons in brai n and elongated spermatids in testis. Immunoprecipitation experiments furth er showed that a kinase activity toward myelin basic protein was associated with Pctaire1 in the adult testis and brain and that its activity was pote ntially regulated through association with regulatory partner(s). These res ults suggest that Pctaire1 kinase might have an important role in different iated cells such as postmitotic neurons and spermatogenic cells.