Effects of Kit Ligand and anti-Kit antibody on growth of cultured mouse preantral follicles

Paracrine regulations between the oocyte and granulosa cells are likely to be key regulators of early folliculogenesis. Evidence obtained from genetic mutants as well as in vivo experiments suggest that Kit and Kit Ligand (KL ) may regulate early follicular morphogenesis and function. In this study, we used in vitro culture of intact mouse follicles to confirm and extend th ese findings. Two concentrations of Kit Ligand (20 and 50 ng/ml) or an anti body blocking the Kit-Kit Ligand interactions (SC1494) were added to preant ral follicles grown individually for 12 days and which were finally trigger ed to ovulate. Effects on follicle and oocyte survival, granulosa cell func tion tantrum formation, cell numbers, steroidogenesis), and oocyte function (growth, survival, nuclear and/or cytoplasmic maturation) were then analyz ed. In optimal culture conditions (presence of 5% fetal calf serum), 50 ng/ ml of KL significantly improved cytoplasmic maturation of the oocyte and in creased follicular testosterone output, but other parameters were not alter ed. In serum-free culture conditions, KL was mitogenic for granulosa cells at 50 ng/ml, but could not induce antrum formation and no differences were observed between control and treated groups for steroidogenesis or oocyte g rowth. Blockade of Kit-Kit Ligand interactions by addition of a blocking an tibody decreased oocyte survival 6-9 days after addition of the antibody, b ut did not upset granulosa cell proliferation. Antrum formation was, howeve r, strongly inhibited. In addition, the blocking antibody markedly reduced aromatase activity of granulosa cells. We conclude that Kit/KL interactions are important for antrum formation and follicular steroidogenesis and regu late survival and cytoplasmic maturation of the oocyte. (C) 2000 Wiley-Liss , Inc.