Viability of Frozen-Thawed Mouse Embryos is Affected by Genotype

Abstract

Embryos from mice of 5 different genotypes were evaluated for their ability to survive cryopreservation as measured by post-thaw in vitro development. In Study 1, ovulation was induced with a standardized pregnant mares'' serum gonadotropin (PMSG)/human chorionic gonadotropin (hCG) regimen, after which females were mated with males of the same genotype to produce incrossed embryos. Four- to 8-cell embryos were frozen in 1.5 M dimethyl sulfoxide (DMSO) at a rate of 0.5.degree. C/min to -80.degree. C and stored in liquid N. Following thawing at room temperature, embryos were cultured and development was evaluated 24 h later. The mean (.+-. Standard error of the mean) number of 4- to 8-cell embryos/pregnant female by stock/stain were: N:NIH(S), 6.8 .+-. 0.8; N:NIH(S)-B, 5.8 .+-. 0.5; N:GP(S), 6.5 .+-. 0.6; C57BL/6N, 9.7 .+-. 1.0; C3H/HeN MTV-, 9.5 .+-. 0.9 (P < 0.05). Post-thaw in vito development was related to genetic background; the proportion of embryos culturing after thawing was: N:NIH(S), 49%; N:NIH(S)-B, 61%; N:GP(S), 66%; C57BL/6N, 75% C3H/HeN MTV-, 56% (P < 0.05). Study 2 was conducted to evaluate the influence of mating various females to males of a genotype known to have a lower post-thaw embryo survival rate. N:NIH(S)-B, N:GP(S), C57BL/6N, and C3H/HeN MTV- female mice were mated with N:NIH(S) males to produce hybrid embryos. Post-thaw embryo survival was reduced (P < 0.05) in 3 of the 4 hybrid groups. Fresh incrossed and hybrid embryos from each study were cultured for 24 h and yielded culture rates ranging from 95% to 99% (P > 0.05) among all groups. Apparently, the proportion of incrossed embryos surviving cryopresevation varies significantly among mouse stocks and strains. Embryo viability postfreezing can be affected by mating an incrossed male to a genotypically different female, suggesting a genetic influence of the male on the ability of embryos to survive cryopreservation. Evidently, the efficiency of a mouse embryo banking program is significantly influenced by and markedly dependent upon genotype within the species.