p27(Xic1), 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 kn own function of inhibiting cell division, induces Muller glia from retinobl asts. 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-d ependent kinases. Cotransfections with dominant-negative and constitutively active Delta and Notch constructs indicate that the gliogenic effects of p 27(Xic1) work within the context of an active Notch pathway. The gradual in crease of p27(Xic1) in the developing retina thus not only limits the numbe r of retinal cells but also increasingly favors the fate of the last cell t ype to be born in the retina, the Muller glia.