Control of meiosis by somatic cells in mice: inheritance of the meiosis I error 'diploidy' and nonexpression in sensitive NMRI/Han oocytes ovulated from chimeras.

NMRI mouse and Djungarian hamster females ovulate diploid and/or hyperploid oocytes with increased frequencies after gonadotrophin stimulation, suggesting that somatic cells are involved in the failures of endocrine control resulting in aneuploidy. To study the inheritance of gonadotrophin-induced aneuploidy as well as the fate of sensitive oocytes in a resistant somatic environment and vice versa, we analysed the frequency of diploid oocytes in NMRI/Han, C57BL/6J and their F1 hybrids (C57BL/6J X NMRI/Han), (NMRI/Han X C57BL/6J) as well as in NMRI/Han in equilibrium C57BL/6J chimeric females after gonadotrophin injections. Ovulated oocytes were analysed in all females for the appearance of diploidy, characterized as premature arrest of development at metaphase I. Our data suggest that the trait of induced diploidy is genetically determined and can be transmitted either maternally or paternally. A maternal effect modulated the expression of that trait. Several mechanisms acting on the feed-back control ovary-hypothalamus/pituitary, within the ovary or even within a chimeric follicle, may be responsible that 'sensitive' oocytes ovulated from chimeras are all normal haploid. These data suggest that not only oocyte maturation but also chromosome disjunction during meiosis I is controlled by somatic cells.