Factors Affecting the Efficiency of Embryo Cryopreservation and Rederivation of Rat and Mouse Models

The efficiency of embryo banking for rat and mousemodels of human disease and normal biological pro-cesses depends on the ease of obtaining embryos. Authors report on the effect of genotype on embryo produc-tion and rederivation. In an effort to establish banks of cryopreserved embryos, they provide two databases for com-paring banking efficiency: one that contains the embryo col-lection results from approximately 11,000 rat embryo donors (111 models) and another that contains the embryo collec-tion results from 4,023 mouse embryo donors (57 induced mutant models). The genotype of donor females affected the efficiency of embryo collection in two ways. First, the pro-portion of females yielding embryos varied markedly among genotypes (rats: 16-100%, mean=71%; mice: 24-95%, mean=65%). Second, the mean number of embryos recov-ered from females yielding embryos varied considerably (rats: 4-10.6, mean=7.8; mice 5.3-32.2, mean=13.7). Geno-type also affected the efficiency of rederivation of banked rat and mouse embryos models by embryo transfer. For rats, thawed embryos («=684) from 33 genotypes were transferred into 66 recipient females (pregnancy rate: 76%). The aver-age rate of developing live newborns for individual rat geno-types was 30 % with a range of 10 to 58%. For mice, thawed embryos (n=2,064) from 59 genotypes were transferred into 119 pseudopregnant females (pregnancy rate: 78%). The average rate of development of individual mouse genotypes was 33 % with a range of 11 to 53%. This analysis demon-strates that genotype is an important consideration when planning embryo banking programs