Alterations in ovarian function of mice with reduced amounts of KIT receptor

The KIT receptor, present on oocyte and theca cells in ovarian follicles, a nd its ligand, KIT LIGAND, produced by granulosa cells, are encoded at the Kit gene and the Mgf gene, respectively. Both Kit and Mgf mutations affect oogenesis and folliculogenesis. In this study, the ovarian function of hete rozygous mice with a mutation Kit(W-laCZ) was examined. Firstly, the amount s of KIT and KIT LIGAND proteins in the ovaries of mice at different ages w ere determined. Secondly, in vivo and in vitro folliculogenesis of wild typ e and heterozygous mice were compared. Western blotting showed that the amo unts of both KIT and KIT LIGAND proteins were decreased in mutant mice. Ova rian follicle populations were counted and more type 5a follicles and fewer type 5b (preantral follicles) were present in ovaries from Kit(W-lacZ/+) o varies. Furthermore, the relationships between oocyte size and follicle siz e differed between wild type and heterozygous mice. This finding may be a c onsequence of altered proliferation of granulosa cells or of altered oocyte growth in mutant mice. Other features of folliculogenesis, such as initiat ion of follicular growth, total follicle population and follicular atresia, were not affected by the mutation. Analysis of in vitro folliculogenesis d id not reveal other differences between wild type and mutant mice. It is co ncluded that the Kit(W-lacZ) mutation affects the expression of KIT and KIT LIGAND proteins, resulting in alterations in granulosa cell proliferation and/or oocyte growth in preantral follicles.