There is no neo-oogenesis in the adult mammalian ovary.

In 2004 and 2005, Johnson et al. published two very provocative studies (1, 2), in which they claimed that in the adult mouse ovary, neo-oogenesis takes place and originates either from the ovarian surface epithelium (OSE) (1) or from the bone marrow (BM) via circulating blood cells (2). These studies were provocative since they challenged the long-held view that mammals are born with a finite number of eggs that declines with ageing. Consequently, an intensive discussion has developed among experts in the field, some of whom are proponents of neo-oogenesis, while others are opponents (Table 1). Neo-oogenesis is a very complex issue that has led to many questions. The aim of our lecture is to explain why we believe that spontaneous neo-oogenesis does not take place in the adult ovary by addressing three of these questions.