Quantitative expression of antiapoptotic and proapoptotic genes in sheep ovarian follicles grown in vivo or cultured in vitro.

To test the hypothesis that the poor development of the oocytes in cultured ovarian follicles of mammals is due to aberrant expression of developmentally important genes, quantitative expression patterns of Bcl2 (B-cell leukemia/lymphoma 2; antiapoptotic) and Bax (Bcl2-associated X protein; proapoptotic) genes in preantral, early antral, antral, large antral follicles, and cumulus-oocyte complexes (COCs) grown in vivo or cultured in vitro were studied. The level and pattern of expression of Bcl2 in the cumulus cells isolated from different development stages of in vivo- and in vitro-grown ovarian follicles were similar suggesting that in vitro culture did not alter the expression of this antiapoptotic gene in the cumulus cells. However, between the in vivo- and in vitro-grown ovarian follicles (1) Bcl2 expression levels in the oocytes from antral follicles (2.21 ± 0.14 vs. 0.87 ± 0.19), large antral follicles (0 ± 0.35 vs. 1.56 ± 0.13), and COCs (0.45 ± 0.31 vs. 2.69 ± 0.15), Bax expression levels in the (2) cumulus cells from early antral (2.09 ± 0.11 vs. 0.98 ± 0.13) and large antral follicle (0.63 ± 0.44 vs. 0 ± 0.21), and (3) oocytes from antral follicles (1.65 ± 0.20 vs. 0.97 ± 0.15), large antral follicles (0.93 ± 0.18 vs. 2.08 ± 0.11), and COCs (1.03 ± 0.17 vs. 2.09 ± 0.11) were significantly different (P ≤ 0.05). Similarly, Bcl2 to Bax ratios were also significantly different between some but not all stages of in vivo and in vitro development. From the present results, it is concluded that imbalance in the expression of proapoptotic and antiapoptotic genes may be an important cause for the compromised development potential of the oocytes in cultured ovarian follicles of sheep.