Mitochondrial membrane potential in 2-cell stage embryos correlates with the success of preimplantation development.

Hormonal stimulation in superovulation induces female mice to ovulate more oocytes than spontaneous ovulation. Because the superovulated oocytes contain a number of oocytes that normally regress before spontaneous ovulation or immature oocytes, the development of some embryos that derive from these oocytes by IVF is prevented. Therefore, the quality of superovulated oocytes should differ from that of spontaneously ovulated oocytes. In this study, we evaluated the quality of superovulated oocytes, by examining 1- and 2-cell stage embryos, in which the development mainly depends on the maternal mRNA, proteins, and mitochondria that are contained in the oocytes, and we then measured the mitochondrial membrane potential (ΔΨm) of the 1- and 2-cell stage, in vivo-fertilized, and IVF embryos. The ΔΨm of 1-cell stage IVF embryos was lower than that of in vivo-fertilized embryos; however, there was no difference between IVF embryos. During the developmental process from 1- to 2-cell stage, the ΔΨm of in vivo-fertilized embryos was highly upregulated, whereas a number of IVF embryos remained unchanged. As a result, 2-cell stage embryos were divided into two groups: high- and low- ΔΨm 2-cell stage IVF embryos. The development of low-ΔΨm 2-cell stage IVF embryos tended to be arrested after the 2-cell stage. These results indicated that the upregulation of ΔΨm during the 1- to 2-cell stage was important in the development of early preimplantation embryos; there were some defects in the mitochondria of superovulated oocytes, which prevented their development.