In vitro development of ovarian follicles

Tissue banking of ovarian material is being increasingly offered to a variety of patients as a means of fertility preservation. This tissue comprises thin cortical surface biopsies that contain predominantly primordial follicles, and currently the only option to restore fertility is by transplantation. However, this is not a viable option for all patients. The potential of this tissue could be realized by the development of in vitro systems to support complete growth from the early primordial stages through to maturity. This technology would have many therapeutic applications including the production of competent oocytes for assisted reproduction technologies, determination of toxicological effects on germ cell development, assessment of cryopreserved ovarian tissue before transplantation for fertility preservation as well as providing an experimental model to address basic scientific questions concerning human oocyte development. Complete oocyte development in vitro from the primordial stage has been achieved in mice, but the larger size and longer growth period of human follicles has made the interspecies translation of these techniques difficult. Recently progress has been made in defining conditions that support different stages of follicle development in vitro that make a complete in vitro system from primordial to maturation a possible reality. This article deals with our current understanding of in vitro development.