Fig. 5. Expression of cdkis in the postnatal cerebellar cortex. Bar chart showing times of expression of the various cdkis with respect to the time of generation of the internal granular layer (IGL) in the cerebellar cortex. Two simple schematics outline the formation of the IGL by the migration of cells from the external granular layer (EGL) through the underlying cells. By the end of the second postnatal week the mature structure of the cerebellar cortex is apparent. Except for Kip2, all of the cdkis have been detected in the postnatal cerebellar cortex. Amongst these, Ink4a and Cip1are progressively restricted to Purkinje cells, whereas Ink4d and Kip1 are detected in both Purkinje and granule cells at most ages. The identity of the cells that express the remaining inhibitors Ink4b and Ink4c are unknown. ML, molecular layer; PC, Purkinje cell layer. Information was adapted from data obtained by Zindy et al. (42) , Watanabe et al. (45) , and Miyazawa et al. (46) .