Characterization of apoptosis in the developing bovine fetal ovary: association with germ cell loss

Abstract

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] During early bovine fetal development a 170 fold increase in germ cells occurs from d 50 to 110 followed by a rapid decline of germ cells by d 170. To better understand the sudden and rapid decline in germ cell numbers, fetal ovaries were examined for signs of apoptosis. The objectives were as follows: 1) To characterize germ cell numbers during bovine fetal ovarian development as previously described by Erickson (1966; Exp. 1), 2) To determine if apoptosis occurs in the developing bovine fetal ovary (Exp. 2), 3) To determine the type of fetal ovarian cells undergoing apoptosis via activated caspase-3 and Oct-4 protein expression (Exp.3 and 4), and 4) To distinguish germ cells undergoing apoptosis from ovarian somatic cells via Oct-4 (stem cell marker) protein expression (Exp. 4). Comparison of germ cell numbers collected by Erickson (1966) and the current study show a similar pattern of cellular proliferation (peak d 110) followed by a sharp decline (by d 170) in germ cell numbers. There was a correlation of 0.82 between the two studies indicating the germ cell profile was similar between the two studies. Presence of apoptotic cells, via TUNEL (fragmented DNA), was observed from d 90 to 190; but not in d 200 to 260, with a visible decrease in the amount of fragmented DNA at d 170 and d 190 (Exp. 2). The mean numbers of active caspase-3 protein expressing germ cells, per field, were 18.4bc, 50.4a, 13.9ab,3.5c, 6.1bc, and 0.9c for d 60 to 80, 100 to 120, 130 to 150, 170 to 180, 190 to 200, and 240 to 260, respectively (abc[rho] [less than] 0.05; Exp 3). Possible application of Oct-4 as a germ cell marker proved unsuccessful. Expression of the Oct-4 protein was observed in non-germ cells located in and around the surface epithelium (Exp. 4).