Oocyte Fate Research Articles

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 F 1 hybrids (C57BL/6J × NMRI/Han), (NMRI/Han × C57BL/6J) as well as in NMRI/Han ↔ 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.

Field experiments on sexuality in the freshwater sponge Spongilla lacustris. The control of oocyte production and the fate of unfertilized oocytes.

AbstractGemmulated, female sponge was collected from nature on 10 November 1971 and then stored in the laboratory at 3°C in the dark. Pieces of this sponge were set out in the pond of origin on 29 May, 6 July, 10 August, and 14 September 1972 and on 16 May 1973. Oocyte production was observed in all sponges developing from the hatched gemmules about one week after implantation. The production of young oocytes ceased three or four weeks following implantation except in the sponges implanted on 14 September 1972, which continued to produce oocytes up to 6 November. This extended period of oocyte production was associated with and may be due to low water temperatures.The study shows that oocyte production does not require an environmental stimulus specific to a particular time of year, for oocytes differentiated under conditions of increasing as well as decreasing water temperatures and day lengths. The control of oocyte production is probably endogenous and associated with gemmule hatching. The possible nature and the adaptive significance of this control mechanism are discussed.Oocytes produced in sponges implanted after the normal sexual period in the pond were not fertilized. Such oocytes go through the normal growth sequence up to the end of the “grand accroissement” phase. Then they degenerate, ultimately releasing their stored yolk bodies into the mesenchyme.All evidence indicates that this population of the species is dioecious.