181 The effects of aging in the oocyte induced by trichostatin A

Abstract

Successful fertilization and embryonic development decreases for an aged oocyte that is not fertilized during the optimal window of time after ovulation. If fertilization of an aged oocyte does occur, the developing embryo is prone to have a delay through meiosis and a decrease in cleavage and blastocyst formation. Trichostatin A (TSA) prohibits the breakdown of the germinal vesicle during meiosis. The objective of this study was to create an in vitro model to study the effects of aging in pig oocytes. Oocytes (n = 1489) were matured with or without TSA (100 ng mL⁻¹) for 24 or 48 h followed by an additional 16 h of maturation without TSA. A portion of the oocytes were evaluated for stage of meiosis (MI and MII) before maturation (n = 95), after the first part of maturation (OMI; 24 or 48 h, n = 363), or after completing maturation (OMII; 16 h, n = 230). The remaining oocytes (n = 801) were fertilized for 6 to 8 h and potential embryos developed. A portion of the embryos were evaluated for fertilization characteristics 12 h after IVF (n = 400). Remaining embryos (n = 401) were evaluated for cleavage by 48 h and blastocyst formation by 144 h, after IVF. Data were analysed using ANOVA and Tukey's test. Oocytes matured without TSA for 64 h had a significantly higher (P < 0.05) percentage of oocytes at the MI stage of meiosis compared with all other treatment groups (16.00 ± 6.80), and oocytes matured without TSA for 40 h had a significantly higher (P < 0.05) percentage of oocytes at the MII stage of meiosis compared with all other treatment groups (14.7 ± 11.30). The results (Table 1) indicate that supplementation of TSA to OMI significantly decreased fertilization penetration rates compared with not supplementing TSA for 24 h. However, the percent of embryos cleaved by 48 h after IVF was significantly higher in oocytes matured for 40 h compared with those matured for 64 h. The percent of embryos reaching the blastocyst stage of development by 144 h after IVF was significantly lower in oocytes matured for 64 h compared with those matured for 40 h without TSA. In conclusion, these results suggest that supplementation of TSA during early maturation delays meiosis and decreases fertilization, and increasing maturation time causes a decrease in early embryonic development. By supplementing TSA during early maturation and increasing the length of maturation by 24 h, we have created an in vitro model to study the effects of aging in pig oocytes.

Table 1.  Fertilization and developmental characteristics of oocytes¹