The Cyclin-Dependent Kinase Inhibitor p57Kip2 Regulates Cell Cycle Exit, Differentiation, and Migration of Embryonic Cerebral Cortical Precursors

Abstract

Mounting evidence indicates cyclin-dependent kinase (CDK) inhibitors (CKIs) of the Cip/Kip family, including p57^Kip2 and p27^Kip1, control not only cell cycle exit but also corticogenesis. Nevertheless, distinct activities of p57^Kip2 remain poorly defined. Using in vivo and culture approaches, we show p57^Kip2 overexpression at E14.5–15.5 elicits precursor cell cycle exit, promotes transition from proliferation to neuronal differentiation, and enhances process outgrowth, while opposite effects occur in p57^Kip2-deficient precursors. Studies at later ages indicate p57^Kip2 overexpression also induces precocious glial differentiation, suggesting stage-dependent effects. In embryonic cortex, p57^Kip2 overexpression advances cell radial migration and alters postnatal laminar positioning. While both CKIs induce differentiation, p57^Kip2 was twice as effective as p27^Kip1 in inducing neuronal differentiation and was not permissive to astrogliogenic effects of ciliary neurotrophic factor, suggesting that the CKIs differentially modulate cell fate decisions. At molecular levels, although highly conserved N-terminal regions of both CKIs elicit cycle withdrawal and differentiation, the C-terminal region of p57^Kip2 alone inhibits in vivo migration. Furthermore, p57^Kip2 effects on neurogenesis and gliogenesis require the N-terminal cyclin/CDK binding/inhibitory domains, while previous p27^Kip1 studies report cell cycle-independent functions. These observations suggest p57^Kip2 coordinates multiple stages of corticogenesis and exhibits distinct and common activities compared with related family member p27^Kip1.