Origin of new granulosa cells from OSC during the prime reproductive period in adult human ovaries. A) Panoramic view of ovarian surface and adjacent cortex. Dashed line indicates interface between TA and stroma of the ovarian cortex. osc and black arrow - ovarian stem cells; taf and black arrowhead - TA flap; white arrowhead - a lack of OSC above the TA; white arrow -bilaminar epithelial cord. B) Detail from (A) shows association of CK+ (brown color) fibroblasts (+fb,) with the TA flap surface (arrowhead), transition from mesenchymal to epithelial morphology (fb/se), and ovarian stem cells (osc, arched arrow). C) A parallel section to (B) showing numerous DR+ MDC (asterisks) in the TA flap. Note DR expression also in early OSC (arrow). D) Detail from (A) shows CK+ epithelial cord consisting of two layers of epithelial cells and lying between the ovarian cortex (ovc) and TA (ta). Note diminution of CK immunoexpression in TA fibroblasts (+/-fb). E) Epithelial cords (black arrows) fragmenting into granulosa cell nests (arrowheads in the upper ovarian cortex (uc). White arrow CK+ OSC associated with the TA with flap. F) Lower ovarian cortex (lc) with primordial follicles. Arrow indicates distance from the ovarian surface, dashed box indicates follicle shown in the inset. F29 indicates female age in years. Bar in (D), for (B-D). Panels A, B, D-F adapted from , © Antonin Bukovsky; panel C from , © Wiley-Liss, Inc. with permission.