Genetic influences on mouse sperm capacitation in vivo and in vitro

Intial in vivo studies were performed to observe the proportion of eggs fertillized at specific intervals after natural mating and ovulation in our research mouse colony. Proestrous females of the C57BL/10Wt, SJL/Wt inbred strains and the F₁ hybrid cross (B10 × SJL or reciprocals) were paired in the after-noon with males of their respective strain and examined for vaginal plugs at the midpoint of the dark period (2400 hours). Oviducts were periodically collected from mated females, and ovulation was first observed at 4, 5.2, and 3 hours after 2400 hours in the B10, SJL, and F₁ hyrid, respectively. The clutch of eggs from each ovulating female, was placed in culture, and cleavage oviduct lavage verifying female mating was placed in culture, and cleavage was used as the criterion for fertilizaition. Fifty percent of the eggs were fertilized 2.2, 5.0, and 2.5 hours after ovulation in B10, SJL, and F₁ hybrid females, respectively. Because twice the legth of time was required to fertilize a similar proportion of eggs from the SJL strain as the F₁ hybrid, these two strains were used for determining their rate of fertilization under more fully controlled conditions in vitro. Forty-nine percent of F₁ hybrid eggs were fertilized after 4 hours incubation with SJL epididymal sperm, whereas 53% fo SJL and 56% of F₁ hybrid eggs were fertilized after only 2 hours incubation with F₁ hybrid epididymal sperm. Thus, using sperm from these two mouse strains, the amount of time required to fertilize approximately 50% of the eggs within a clutch both in vivo and vitro was very similar. These observations demonstrte teh validity of using this in vitro system for fertilization studies and confirm that the temporal events in sperm capacitation and egg penetration are dependent on the genotype of the sperm. Similarities in fertilization rates at specific times after ovulation or insemination in vitro imply that the initiationof sperm capacitation in vivo occurs near the time of ovulation and several hours after mating. We tentatively suggest that follicular fluid may be required for completion of mouse sperm capacitaiton in vivo.