Figure 7

Follicular renewal in adult human ovaries. A) Cytokeratin (CK) positive (brown color) cells of fibroblast type (fb) in tunica albuginea (ta) exhibit mesenchymal-epithelial transition into OSC (osc). Inset shows a transitory stage (fb/e). B) The CK+ epithelial nest (n) inside of the venule (v) in deep ovarian cortex, which extends an arm (a) to catch the oocyte (o, dashed line) from the blood circulation. e = endothelial cell. C) The nest body (n) and closing "gate". A portion of the oocyte (dashed line) still lies outside of the complex, and is expected to move inside (arched arrow). The oocyte contains intraooplasmic CK+ extensions from the nest wall (arrowheads), which contribute to the formation of CK+ paranuclear (Balbiani) body (asterisk). The oocyte nucleus is indicated by a dotted line. D) The occupied "bird's" nest type indicates a half way oocyte-nest assembly. CK indicates cytokeratin staining of primitive granulosa cells and ZP indicates zona pellucida expression in the assembling oocyte. E) Segments of OSC show cytoplasmic PS1 (meiotically expressed carbohydrate) expression. Asymmetric division of OSC gives rise to cells exhibiting nuclear PS1 (+ nuclei vs. - cell daughters) and descending from the OSC into tunica albuginea (ta). F) In tunica albuginea, the putative germ cells increase in size, show a symmetric division (black arrow) and exhibit development of cytoplasmic PS1 immunoexpression when entering (white arrow) the upper ovarian cortex (uc). G) Association of primary follicles (arrowhead) with the cortical epithelial crypt (ec). Dashed boxes indicate unassembled epithelial nests. Inset shows origination of germ-like cells among CK+ cells (CK) in epithelial crypt. Note ZP+ segment (white arrowhead) associated with unstained round cell nucleus (asterisk). H) Migrating germ cells with tadpole shape (dashed line), unstained nucleus (dotted line) and ZP+ staining of the intermediate segment (arrowhead). I) Some medullary vessels (v) show accumulation of ZP+ (dark color) degenerating oocytes with unstained nuclei (arrowheads). Arrow indicates ZP release. Adapted from [11], © Antonin Bukovsky.