Effects of Ooplasmic Transfer on Rabbit Oocyte Fertilization and Early Embryonic Development

In order to evaluate the effects of ooplasm on oocyte fertilization and early embryonic development and to study themitochondrial DNA (mtDNA) heterogeneity of early embryos, microinjection was first performed to transfer a smallamount (5 to 7%) of donor ooplasm into recipient oocytes, then the eggs were fertilized with rabbit sperm throughintracytoplasmic sperm injection (ICSI). In group 1 (homogeneous ooplasmic transfer), both the donor and recipient rabbitoocytes were at metaphase II (MII). In group 2 (heterogeneous ooplasmic transfer), the donor was mouse MII oocyte andthe recipient was rabbit MII oocyte. In the control group, only ICSI was done on rabbit oocyte without ooplasmic transfer.No significant difference (P>0.05) was observed in blastocyst development rates between group 1 (13.0%, 3/23) and thecontrol group (16.7%, 4/24), but significant difference (P<0.05) was examined in blastocyst development rate betweengroup 2 (0, 0/27) and the control group. Blastomeres cleaved unequally and embryonic fragments increased after ooplasmictransfer and ICSI. In early embryos, in group 2, donor mouse mtDNA was detected in 2-cell embryos (3/3), 4-cell embryos(3/4), 8-cell embryos (4/4), and morulae (2/2). The mtDNA fingerprinting analysis showed that mouse mtDNA detected inheterogeneous embryos of different developmental stages had exactly the same sequence as that of the donor mousemtDNA, thus indicating that homogenous ooplasmic transfer had no significant influence on rabbit oocyte fertilizationand early embryonic development, and that heterogeneous ooplasmic transfer did cause notable reduction in blastocystdevelopment rate. Heterogeneous mtDNA sequence in early embryos did not mutate. Compared with the control group,the embryonic quality declined after ooplasmic transfer operation in the present experiment.