VIABILITY, DEVELOPMENT AND INCIDENCE OF CHROMOSOME-ANOMALIES OF PREIMPLANTATION EMBRYOS FROM XO MICE

We examined the viability and developmental status of XO embryos at pr eimplantation stage (day 3 of gestation) by assessing blastocyst forma tion and counting cell number using our XO mouse colony. We also exami ned the incidence of chromosome anomalies. Embryos from XO mice (XY, X X and XO) developed more slowly (in cell numbers and blastocoele forma tion) than those from XX mice (XY and XX). XO embryos also tended to d evelop more slowly than XX embryos in the XO group. Although litter si ze at the preimplantation stage of gestation was almost twice as large (12.7) as those at mid-gestation (7.6) and near-term (7.2) in this co lony, the adjusted XY:XX:XO ratio (2.8:2.0:1.0) did not differ greatly . This indicates that almost half of the embryos must have been elimin ated during the first half of gestation in the XO group, probably rega rdless of sex chromosome complements. Thus, we consider that maternal XO sex chromosome constitution is disadvantageous for the intrauterine development of the embryo during the early period of gestation. This may be related to precocious aging of XO mice. Further, we confirmed t hat a high incidence of abnormal karyotypes occurs in embryos from our XO mouse colony.