Effect of exogenous hormones on the ovulation of primary and secondary oocytes in LT/Sv strain mice

Abstract

LT/Sv strain mice ovulate both primary and secondary oocytes. These are fertilizable and give rise to digynic triploid and normal diploid conceptuses, respectively. A previous study [Kaufman and Speirs, 1987] had indicated that just over 20% of embryos recovered on the 10th day of gestation from spontaneously ovulating females had a triploid chromosome constitution. This value was considerably lower than might have been expected by extrapolation from earlier studies in which LT/Sv mice had been given exogenous gonadotrophins. In the present study, therefore, cytogenetic analysis of fertilized eggs was performed at the first cleavage mitosis in (1) spontaneously ovulating females mated to F1 hybrid males, and (2) superovulated females mated to similar males. Additional females from group (1) were autopsied on the 10th day of gestation, and the ploidy of embryos isolated at this stage of gestation was determined. Exposure to exogenous gonadotrophins significantly increased the proportion of eggs that were ovulated as primary oocytes (34.4%), compared to the situation observed following spontaneous ovulation (24.4%). All the triploids encountered in both series were of the digynic type and characteristically (for LT/Sv mice) had an oocyte-derived set with 40 chromosomes present, and a sperm-derived set containing 20 chromosomes. Similar numbers of eggs were recovered from spontaneously ovulating females on the 1st and 10th days of gestation, and the incidence of triploidy observed on the 10th day was 22.1%. The influence of exogenous hormones in increasing the "spontaneous" level of triploidy in LT/Sv and in other strains of mice is briefly reviewed.

The Mos/mitogen-activated protein kinase (MAPK) pathway regulates the size and degradation of the first polar body in maturing mouse oocytes.

“…The (24) raises the possibility that they result from an abnormal meiotic division. A similar situation has been observed in oocytes of LT/Sv mutant female mice that arrest and ovulate at metaphase I or 11 (31,32) and spontaneously undergo parthenogenetic activation (33,34) in the ovary (35). Fertilization of primary oocytes from LT/Sv mutant female mice is possible (36).…”

Spindle assembly checkpoint-related failure perturbs early embryonic divisions and reduces reproductive performance of LT/Sv mice

“…The SAC-related anomaly is certainly not the sole reason for the low reproductive performance of LT/Sv females. It coincides with the MI-arrest of oocytes, the development of ovarian teratomas (Stevens & Varnum 1974), spontaneous parthenogenetic activation of ovulated oocytes (Stevens Speirs & Kaufman 1988, Henery & Kaufman 1993a. As a result 30% of LT/Sv females do not reproduce at all and the remaining ones show a significant decrease in fertility (this study).…”

New insights into triploidy and tetraploidy, from an analysis of model systems for these conditions

“…The maternal age has also been found to be of critical importance in relation to the incidence of primary oocytes ovulated; at 6 weeks of age, up to -50% of the oocytes ovulated spontaneously consisted of primary oocytes whilst significantly lower levels were observed when females were examined at 12, 18, 24 and 30 weeks of age . The incidence of the ovulation of primary oocytes could also be increased following treatment of females with exogenous gonadotrophins (Speirs and Kaufman, 1988) and a similar effect has been observed in both A/He and NMRI/Han strain mice (Takagi and Sasaki, 1976;Bartels et al, 1984).…”