Effect of maternal age on the incidence of digynic triploidy in LT/SV strain mice: Implications for the ovulation of primary and secondary oocytes in this strain

Abstract

LT/Sv strain mice ovulate both primary and secondary oocytes, which are fertilisable, giving rise to digynic triploid and normal diploid fertilised conceptuses, respectively. Since the proportion of primary and secondary oocytes ovulated in our earlier studies varied widely among females, we investigated whether the proportion of primary oocytes ovulated in LT/Sv strain mice was influenced by maternal age. Females 6, 12, 18, 24, and 30 weeks old were mated with F1 hybrid males. The females were autopsied on the 10th day of gestation, and the intact conceptuses or extraembryonic membranes analysed cytogenetically. Since no selective loss of the triploids occurs up to the 10th day of gestation, analysis at this time also provides indirect information on the proportion of primary and secondary oocytes ovulated. We observed 1) that the overall incidence of triploidy decreased from 55% in the 6-week-old females to 6% in the 30-week-old group; 2) that the number of females from which both triploid and diploid embryos were recovered decreased with increased maternal age; 3) that a substantial decrease in the proportion of triploid embryos was observed in those females in which both triploid and diploid embryos were recovered, in relation to increased maternal age; 4) that there was no overall decrease in the total number of implants with increasing age; and 5) that there was no increase in the incidence of resorptions with increasing maternal age. We believe that no comparable relationship between the ovulation of primary and secondary oocytes and maternal age has previously been reported.