ABSTRACT
The D-type cyclins form complexes with the cyclin dependent (CD) kinases CDK4 and CDK6 and promote the G1-S phase transition of the cell cycle by antagonizing the retinoblastoma suppresser protein pRB. In the developing nervous system D-type cyclins show spatially and temporally dynamic patterns of expression. We demonstrated that cyclin D1 was transiently expressed in differentiating spinal cord ventral interneurons while cyclin D3 protein was expressed in differentiating motor neurons and dorsal interneurons. This expression of cyclin D3 in neurons of the mantle zone was extended to all regions of the spinal cord at E15.5. The results suggest that cyclin D1 and D3 have specific functions in differentiating neurons. Similarly, in the developing midbrain-hindbrain region the D-type cyclins were expressed in different subsets of cells. Our results argue in favor of different functions for D-type cyclins during proliferation and differentiation of neural progenitors.