Expression of Ol-KIP, a cyclin-dependent kinase inhibitor, in embryonic and adult medaka (Oryzias latipes) central nervous system

From an expression screen in a fish model, the medaka, we have isolated Ol- KIP (Oryzias latipes-kinase inhibitor protein), a new member of the KIP sub family of cyclin-dependent kinase (Cdk) inhibitors. We have analysed its ex pression in the developing and adult brain by in situ hybridization and by double labeling with Ol-KIP mRNA and proliferating cell nuclear antigen (PC NA) antibodies. Ol-KIP presents a complex expression pattern in several are as of the embryonic central nervous system, most often in close vicinity to proliferative neuroepithelia. We studied in great detail its expression in the optic tectum; Ol-KIP is expressed in a ring-shaped domain lying exactl y between the proliferative and the postmitotic zones of this structure and is, therefore, potentially involved in cell cycle exit. In the adult CNS, Ol-KIP expression persists in numerous nuclei, both close and distant from proliferative ventricular areas. So, Ol-KIP expression is in part compatibl e with a sustained "stop signal" role for proliferation, but its expression in postmitotic zones suggests that KIP proteins may have late neuronal fun ction(s), in addition to inhibiting Cdks. This first detailed study of the expression profile of a KIP gene in a nonmammalian vertebrate, thus, opens perspectives for analysing the role of these regulators in brain developmen t and function. (C) 2001 Wiley-Liss, Inc.