Cell cycle regulators at the ocular surface.
The ocular surface provides an outstanding model to examine the regulation of the proliferative cell cycle. Cells within the cornea and conjunctiva exhibit a wide range of proliferative abilities ranging from the rapidly proliferating cells in the basal cell layer of the epithelium to the quiescent keratocytes and endothelial cells. In this review, dedicated to Dr David Maurice, we will discuss four families of proteins known to regulate the cell cycle. These families include: (1) the cyclins; (2) the CIP/KIP family of cell cycle inhibitors--consisting of p21, p27, and p57; (3) the INK4 family of cell cycle inhibitors--including p16, p15, p18, and p19; and (4) the retinoblastoma family--consisting of pRb, p107, and p130. Members of all of these families have been localized in various cells in the ocular surface. We will discuss how these proteins are involved in regulating cell proliferation both in normal homeostasis and during wound healing.