Abstract:
In an attempt to identify factor(s) that influence in vitro development of preantral follicles (PFs) in sheep, small (40–60 μm in diameter) and large (61–100 μm in diameter) PFs were cultured for 6 days in tissue culture medium (TCM 199) supplemented with transforming growth factor-α (TGF-α), insulin-like growth factor-II (IGF-II), epidermal growth factor (EGF) or follicle stimulating hormone (FSH). Increase in follicle diameter, oocyte diameter, induction of new DNA synthesis in the follicular cells and increase in number of follicular cells per follicle were measured as the indicators of development. Only EGF supplemented medium increased the follicle diameter, number of follicular cells and also induced intense DNA synthesis in both small and large PFs. TGF-α, IGF-II and FSH on the other hand were able to stimulate intense DNA synthesis only in large PFs. None of the supplemented media caused an increase in oocyte diameter. It is proposed that EGF stimulates the development of preantral follicles of sheep up to 100 μm in diameter.