EFFECT OF MITOCHONDRIAL-DNA (MTDNA) TYPE ON PREGNANCY RATE AFTER EMBRYO-TRANSFER IN RATS

Because the mtDNA is maternally inherited, embryos resulting from matings or artificial inseminations have the same type of mtDNA as that of the mother. However, when embryos are transferred the mtDNA of the embryos may be different to that of the recipient and this may interfere with maternal recognition and the establishment of pregnancy. This study was done to determine whether differences in the mtDNA between embryos and recipients would influence the survival to term of transferred embryos. A total of 1,220 rat embryos were recovered from non-superovulated donors of known mtDNA type. The number and distribution of developmental stages of embryos collected from 51 rats of mtDNA type A (n = 595) were not different (P > 0.05) from those collected from 50 rats of mtDNA type B (n = 625). The overall pregnancy rate after transfer of embryos to pseudopregnant rats was 54% (26/48). The pregnancy rate was not affected (P > 0.05) by the type of mtDNA of the recipient or of the embryo, and the interaction between mtDNA type of embryos and recipients was also not significant (P > 0.05). Embryonic survival to birth was low (78/622, 12.5%) but was not affected (P > 0.05) by the type of mtDNA of the recipient (A = 28/250; B = 50/372) or of the embryo (A = 41/306; B =37/316). Survival of pups to weaning was affected by the type of mtDNA of the embryo (P < 0.01) but not by the type of mtDNA of the recipient (P > 0.05) and the interaction between mtDNA type of embryos and recipients was also not significant (P > 0.05). More pups (P < 0.005) derived from donor rats of mtDNA type A (34/41)survived to weaning age than pups from donor rats of mtDNA type B (18/37). These results indicate that differences in the type of mtDNA between embryos and recipients do not interfere with establishment of pregnancy in pseudopregnant recipients.