Fig. 6. Ki67, Cdc6, Cdt1, Mcm2 and Geminin protein expression in human ovary (original magnification x120). The schematic drawing of adult ovary (cross section; top left) shows that the predominant follicles are primordial follicles (white arrow) composed of primary oocytes arrested in the prophase of MI and surrounded by flattened follicular cells (black thin arrow). Primordial follicles mature into Graafian follicles following a period of follicular growth. Follicular growth involves proliferation of follicular cells and increase in size of oocytes to form primary follicles (white arrowhead). Primary oocytes do not express Ki67 contrasting with expression in follicular cells of primary follicles. Virtually all primary oocytes express Cdt1 and Mcm2 proteins. Geminin is found in a proportion of proliferating follicular cells, but is not expressed in primary oocytes. Cdc6 is detected in proliferating follicular cells of primary and secondary follicles (inset; arrowhead) but not in primary oocytes.