Development of mouse ovarian follicles from primary to preovulatory stages in vitro.

An in-vitro culture system was developed in which primary mouse follicles from 12-16-day-old mice grew to the preovulatory stage. The important determinants of growth in culture were the inclusion of stroma with the primary follicles, the age of the mouse, the presence of FSH and LH, the use of culture dishes with a hydrophobic membrane and the use of post-menopausal human serum to supply growth factors. During culture the pieces of ovarian tissue containing the primary follicles coalesced to form characteristic spherical clusters. The cultured follicles appeared to be normal as determined by the appearance and organization of the granulosa cells, the appearance of the antrum and the accompanying steroidogenesis, but the ova had not resumed meiosis. The results show that the growth of mouse follicles starting from the primary stage is critically dependent on adequate concentrations of FSH.