Effect on embryo survival of short-term exposure to the uterine environment of two selected lines of mice.

Two genetic lines of mice (Mus musculus), one selected for high embryo survival (Line E) and the other for small litter size (Line CN-), were used as models to study preimplantation embryo survival. The two lines displayed similar ovulation rates, but significantly lower embryo survival to implantation was observed in Line CN- females (P less than 0.01). The effect of the uterine environment on embryo survival was examined by incubating embryos in pseudopregnant host females for 26 hours beginning at 1500 hours on day 2 (day of copulatory plug = day 0). Embryos were then removed from the host and transferred to recipient uteri of the same genetic line as the embryos for development to term. Survival of embryos was significantly greater after exposure to Line E hosts (P less than 0.01). Survival of Line E embryos was reduced from 71% in Line E hosts to 28% in Line CN- hosts. Survival of Line CN- embryos increased from 17% in Line CN- hosts to 70% in Line E hosts. Embryos also were cultured in vitro in uterine flushings collected from each line. More Line E embryos developed to the blastocyst stage than did Line CN- embryos (P less than 0.01). Development of Line CN- (P less than 0.01) embryos, but not Line E embryos, was affected by the line from which uterine flushings were collected. These lines of mice provide a useful model for the study of the physiological basis for differences in embryo survival due to genetic selection.