p27Xic1, a cdk inhibitor, promotes the determination of glial cells in Xenopus retina

p27(Xic1), a member of the Cip/Kip family of Cdk inhibitors, besides its known function of inhibiting cell division, induces Muller glia from retinoblasts. This novel gliogenic function of p27(Xic1) is mediated by part of the N-terminal domain near but distinct from the region that inhibits cyclin-dependent kinases. Cotransfections with dominant-negative and constitutively active Delta and Notch constructs indicate that the gliogenic effects of p27(Xic1) work within the context of an active Notch pathway. The gradual increase of p27(Xic1) in the developing retina thus not only limits the number of retinal cells but also increasingly favors the fate of the last cell type to be born in the retina, the Muller glia.