Kit ligand and insulin-like growth factor I affect the in vitro development of ovine preantral follicles

We investigated the effect of KL and IGF-I, alone or in combination, on the in vitro survival, growth and antrum formation of sheep preantral follicles, and subsequent oocyte developmental competence. Preantral follicles ∼200 μm were isolated and cultured for 18 days in basic medium (control) added or not by KL, IGF-I or both. Every six days follicular survival, growth and antrum formation was evaluated. At the end of the culture period, the oocytes underwent in vitro maturation (IVM) and their viability and chromatin configuration were assessed. To evaluate oocyte quality and its developmental competence, parthenogenetic activation and in vitro fertilization (IVF) of the oocytes recovered from in vitro grown preantral follicles were performed. Medium supplementation with KL improved follicular integrity and antrum formation. IGF-I promoted the increase in follicular diameter at the end of the in vitro culture when compared to control, but not differently from KL. Follicles cultured in the presence of KL presented the highest percentages of meiosis resumption (92.3%). Therefore, these oocytes were submitted to parthenogenetic activation and IVF resulting in a percentage of 35.6% of parthenotes and 23.1% of 2- or 4-cells embryos. Medium supplementation with KL results in increased rates of antrum formation, as well as in meiosis resumption, resulting in the production of embryos using parthenogenetic activation or IVF.