MG132 treatment during oocyte maturation improves embryonic development after somatic cell nuclear transfer and alters oocyte and embryo transcript abundance in pigs.

The objective of this study was to examine the effect of treating pig oocytes during in vitro maturation (IVM) with a proteasome inhibitor, MG132, on oocyte maturation and embryonic development. In one series of experiments, oocytes from medium-sized follicles (3-8 mm in diameter) were untreated (MCO) or treated with MG132 during 0-22 hr (M0-22) or 30-42 hr (M30-42) of IVM. There was no significant effect of MG132 on nuclear maturation or cytoplasmic maturation (as assessed by intracellular amounts of glutathione and p34cdc2 kinase activity). Blastocyst formation after parthenogenetic activation (PA) and somatic cell nuclear transfer (SCNT), however, was increased for M30-42 (65.2% and 27.7% for PA and SCNT, respectively) compared to MCO (42.6% and 13.6%, respectively) and M0-22 (45.3% and 19.5%, respectively; P<0.05). Expression of PCNA and ERK2 was increased in M30-42 for IVM oocytes while transcript abundance for POUF51, DNMT1, FGFR2, and PCNA was increased in M30-42 for 4-cell SCNT embryos. When oocytes derived from small follicles (<3 mm in diameter) were untreated (SCO) or treated with MG132 during 0-22 hr (S0-22), 30-42 hr (S30-42) of IVM, or 0-22 and 30-42 hr of IVM (S0-22/30-42), expression of POU5F1, DNMT1, FGFR2, and PCNA and blastocyst formation were increased for SCNT embryos derived from S30 to 42 (16.5%) and S0-22/30-42 oocytes (20.8%) as compared to embryos from SCO (8.7%) or S0-22 oocytes (8.8%; P<0.05). Results demonstrate that treatment of oocytes with MG132 during the later stage of IVM improves embryonic development and alters gene expression in pigs.