Expression of the cyclin-dependent kinase inhibitor p27Kip1 by developing retinal pigment epithelium

The cyclin-dependent kinase (Cdk) inhibitor p27Kip1 contributes to the timing of cell cycle withdrawal during development and, consequently, in organogenesis. Within the retina, this effector protein is up-regulated during the birth of neuronal and glial cells [Dev. Biol. (2000) 299]. However, its expression within the retinal pigment epithelium (RPE), a supporting cell layer that is essential for neural retina development and function, has not previously been reported. We show that p27Kip1 protein expression in the RPE occurs in two phases: an up-regulation during mid-to late embryonic stages and a down-regulation during the subsequent postnatal period. In the early phase of upregulation, an inverse relationship is seen between expression of p27Kip1 and PCNA, an indicator of cycling cells. During both up-and down-regulation, the change in spatial pattern of expression proceeds in a central to peripheral manner, with p27Kip1 up-regulation paralleling retinal maturation. These data suggest that this cell cycle regulator may be an important factor controlling the timing of RPE cell cycle withdrawal. (C) 2003 Elsevier B.V. All rights reserved.