IDENTIFICATION OF CELLS EXPRESSING A D-TYPE G1 CYCLIN IN MATURED BRAIN - IMPLICATION FOR ITS ROLE IN NEURONAL FUNCTION

The multiple cyclins and their catalytic subunit, cdc2-related kinase, play essential roles in the eucaryotic cell cycle. To examine their p otential roles in highly differentiated nervous system, we determined their activity and localization in rat brain. p13suc1 associated histo ne H-1 kinase activity was dramatically increased at the onset of brai n maturation. The increased kinase activity was coprecipitated with cy clin D1, a type of G1 cyclin, which also increased with brain maturati on. Immunohistochemical analysis demonstrated that anti-cyclin D1-like immunoreactivity was exclusively localized to neurons. From these fin dings, it is suggested that a type of cdc2-related kinase regulated by cyclin D1 might function in neurons independent of cell cycle progres sion.