In vitro follicle growth: Achievements in mammalian species

The exact mechanisms regulating in vivo folliculogenesis in mammalians have only been partly unravelled. Some processes, such as the initiation of gro wth of primordial follicles are still poorly understood. This increases the difficulty to culture follicles in vitro as the primordial follicles will be the ultimate starting material for culture. There are important species differences in regulation and timing of maturat ion, which makes it difficult to transpose techniques. Only in the mouse model, live pups were born when primordial or early prean tral follicles were cultured entirely in vitro. Although no systems are as yet permitting complete in vitro culture of early follicle stages in large animals or humans, parts of folliculogenesis have been successfully reprodu ced in vitro. This review summarizes achievements of the last years in foll icle culturing starting off at several stages of development. Future applications of in vitro follicle culture include fertility preserva tion for humans, preservation of rare animal species and creation of oocyte banks for research.