Dynamic changes in meiotic progression and improvement of developmental competence of pig oocytes in vitro by follicle-stimulating hormone and cycloheximide

Abstract

The effects of FSH, LH, and epidermal growth factor (EGF) on the dynamics of nuclear maturation and subsequent embryo development were examined in pig oocytes cultured either conventionally or after preincubation with cycloheximide (CHX). In conventional culture, FSH or EGF significantly increased the rate of attainment of metaphase II (MII) for both gilt (50.0% ± 4.2% and 54.8% ± 4.3%, respectively; control, 5.8% ± 1.8%; P < 0.001) and sow (87.6% ± 3.4% and 78.8% ± 3.9%, respectively; control, 7.8% ± 2.5%; P < 0.001) oocytes. Gilt oocytes treated with both FSH and EGF showed an additive response (93.7% ± 2.1%). Treatment with LH had no effect. Preincubation with CHX caused the majority (84-100%) of both gilt and sow oocytes to undergo germinal vesicle breakdown. Compared to those treated with LH and/or EGF (both > 80%), fewer FSH-treated oocytes reached metaphase I (43.8% ± 5.3%, P < 0.001) by 14 h and MII (48.4% ± 5.9%, P < 0.001) by 24 h, although the majority (71%) did mature to MII by 36 h after removal of CHX. After in vitro fertilization, higher proportions of both CHX-pretreated and untreated, FSH-exposed oocytes cleaved (71.3% ± 2.9% and 75.3% ± 3.1%, respectively) compared with those not treated with FSH (37.7% ± 3.0% and 43.0% ± 2.9%, respectively; P < 0.001). Pretreatment with CHX significantly increased blastocyst yield for both FSH-treated (32.8% ± 2.0% and 10.3% ± 1.5%, respectively; P < 0.001) and untreated (16.7% ± 1.5% and 9.4% ± 1.2%, respectively; P < 0.001) oocytes. Polyspermy rates were unaffected. In conclusion, pig oocytes meiotically arrested by CHX before maturation retain and improve their developmental competence. FSH stimulates nuclear maturation but slows meiotic progression.