Differential expression of D type cyclins during neuronal maturation.

The multiple cyclins play essential roles in eucaryotic cell cycle. We previously reported that the expression of a D type G1 cyclin (p36cyclinD1) in neurons was increased at the onset of brain maturation. During neuronal differentiation of PC12h cells induced by nerve growth factor (NGF), expression of p36cyclinD1 and p46cyclinX was enhanced concomitant with neuronal maturation. In contrast, p34cyclinD2, which was highly expressed in undifferentiated cells, decreased as the cells matured. In situ hybridization and Western blot analyses demonstrated that embryonic rat brain strongly expressed cyclin D2 gene, but its expression was dramatically repressed in matured brain. These data suggest differential roles of the D type cyclins in the process of neuronal differentiation and/or function.