Histological study of germ cells development and apoptosis in mongolian sheep fetal ovaries

Mammalian germ cells proliferate by mitosis and begin meiotic development in fetal ovaries. The aim of this study is to demonstrate the germ cell proliferation and apoptosis, and elucidated some of the key developmental events and stages in Mongolian sheep fetal ovaries. Fourty three pairs of sheep fetal ovaries at days 37–99 of gestation were collected from local slaughterhouse. Studies in histological structure of ovaries and germ cell apoptosis were achieved by employing light microscopy and terminal deoxynucleotidyl transferase-mediated nick end labeling (TUNEL). Following fetal gestation age increasing, three key development events were detected: oogonia fleetly proliferated by mitosis and clustered at days 37–55 of gestation in ovarian cortex forming oogonia nest; the formation of ovigerous cords (OC) and disorganization took place at day 51–81, especially at days 63–66 more OC developed, and more germ cells in OC entered meiosis prophase; subsequently, with the OC disappeared, primordial follicles gradually prevailed from day 73 of gestation. Another observation was germ cells apoptosis and the number of apoptotic germ cells showed a peak from day 58 to day 73 (P < 0.05) and germ cells in OC were prone to apoptosis. The study provides evidence about histological feature and germ cells apoptosis in sheep fetal ovaries.