QUANTITATIVE-EVALUATION OF THE CELL CYCLE-RELATED RETINOBLASTOMA PROTEIN AND LOCALIZATION OF THY-1 DIFFERENTIATION PROTEIN AND MACROPHAGES DURING FOLLICULAR DEVELOPMENT AND ATRESIA, AND IN HUMAN CORPORA LUTEA

Ovarian follicular development is dependent on growth and differentiat ion of the oocyte, as well as the granulosa and theca cell layers. The majority of primary follicles in the adult human ovary are not growin g, and most antral follicles undergo atresia. The mechanisms regulatin g follicular growth and differentiation are poorly understood. Express ion of key regulatory proteins in cells of certain follicles may be in volved. We have studied the distribution of retinoblastoma protein (pR b), a key cell cycle regulator, in human follicles and CL by quantitat ive immunohistochemistry. Recent studies suggest that high nuclear con centrations of pRb are associated with the arrest of cell proliferatio n and the beginning of differentiation; during advanced differentiatio n of cells pRb is markedly depleted or absent. We also studied follicu lar distribution of Thy-1 differentiation protein, a morphoregulatory molecule associated with cell differentiation, and the presence of mac rophages. Macrophages have been shown to stimulate steroidogenesis in granulosa cells in vitro, and they are required for release of Thy-1 d ifferentiation protein from vascular pericytes among granulosa cells i n vivo. Our results indicate that oocytes in resting follicles exhibit pRb in the nucleoli. During initiation of follicular growth, the pRb expression first extends over the oocyte nuclei and then diminishes fr om both nuclei and nucleoli in preantral follicles. When the oocytes r each maximum size in small antral follicles, the pRb expression is ree stablished in oocyte nucleoli. In differentiating granulosa and theca cell layers of preantral and small antral follicles, pRb expression is high, but it is low in growing large antral follicles. During CL deve lopment and regression, pRb expression in the nuclei of granulosa lute in cells first increases and then decreases. Follicular development is accompanied by the presence of Thy-1 differentiation protein and macr ophages under the follicular basement membrane. In growing large antra l follicles, during the mid-follicular phase, larger macrophages exhib it physical contacts with granulosa cells through the follicular basem ent membrane, and, during the late follicular phase, small dendritic m acrophages can be detected among granulosa cells, but not within the f ollicular antrum. Large antral follicles undergoing atresia exhibit st rong pRb expression in granulosa cells. This is accompanied by a lack of Thy-1 differentiation protein among granulosa cells and the occurre nce of large phagocytic macrophages in the follicular antrum. This is the first report of pRb expression in the human ovary. Our data show t hat enhanced pRb expression accompanies Initiation of oocyte growth an d differentiation of granulosa and theca cells, and that low levels of pRb accompany advanced differentiation of these cells. Differentiatio n of preantral and antral follicles is accompanied by release of Thy-1 differentiation protein from vascular pericytes and association of ma crophages with differentiating cells.