In Vitro Development of Caprine Preantral Follicles Is Improved with Insulin-Like Growth Factor-I (IGF-I).

Abstract

In vitro culture of preantral follicles is a powerful technique to study the basic mechanisms of folliculogenesis and also represents a promising approach to obtain viable embryos in vitro. Currently, the rates of embryo production from preantral follicles cultured in vitro are very low. Efforts are still required to improve this technique and make it a potential tool for in vitro embryo production. The control of folliculogenesis involves a complex interaction among endocrine, paracrine, and autocrine factors. The involvement of IGF-I in preantral and antral follicles has been elegantly evidenced by studies with IGF-I gene knockout mice. Although the importance of IGF-I on folliculogenesis of several species is well known, the effect of this growth factor on the in vitro culture of isolated caprine preantral follicles has not been studied. Thus, this study was developed to evaluate the effects of IGF-I on follicle survival, antral cavity formation, and in vitro growth and maturation of caprine oocytes. Preantral follicles were individually cultured for 18 days with α-MEM associated or not to IGF-I (50 or 100 ng/ml) in three treatments: 1) alpha-MEM; 2) alpha-MEM + IGF-I 50, and 3) alpha-MEM + IGF-I 100. At the end of the culture period, the oocytes underwent in vitro maturation (IVM). Results showed a higher (P<0.05) percentage of normal follicles on days 6, 12, and 18 of culture in IGF-I 50 (97%, 92%, 67%) and IGF-I 100 (100%, 90%, 80%) groups versus the control (90%, 64%, 36%). In addition, the rate of antrum formation at 6, 12, and 18 days of culture was significantly higher (P<0.05) in IGF-I groups (IGF-I 50: 72%, 90%, 92% and IGF-I 100: 69%, 85%, 85%) versus the control group (41%, 59%, 69%). After 18 days of culture, the percentages of grown oocytes acceptable for IVM were significantly higher (P<0.05) in follicles cultured in the presence of IGF-I (82% vs. 49%). Furthermore, follicles cultured in the presence of IGF-I 50 and IGF-I 100 had higher (P<0.05) meiotic resumption rates (63% and 66%, respectively) when compared to the control group (11%). Results of the present study demonstrated, for the first time, that the addition of IGF-I in the culture medium was beneficial to the in vitro development of caprine preantral follicles and the production of oocytes capable of resuming meiosis. (poster)