Natural history of the mammalian oocyte.

Combining cryopreservation of immature oocytes with in-vitro growth/maturation techniques is the ambition of many IVF clinics. Whilst these techniques have been demonstrated in rodents their application to humans and domestic species has been slow. There are many technical reasons for the lack of progress in these species, but the major problem is that we have very little knowledge of how the oocyte acquires developmental competence during its growth within the follicle. The life history of the mammalian oocyte involves a complex series of co-ordinated developmental processes that in the human take place over several months. This review will consider: (i) growth and development of the oocyte; (ii) the newly regenerated debate on the existence of germ-line stem cells in the mammalian ovary; and (iii) strategies for producing oocytes in vitro.