Germ stem cells in the mammalian adult ovary: considerations by a fan of the primordial germ cells.
At or early after birth, mammalian ovaries are filled with primordial follicles each composed by an oocyte blocked at the end of prophase I surrounded by a single layer of granulosa cells. The doctrine that female mammals are born with a finite number of oocytes fated to be exhausted with the age has been challenged by recent results claiming that new oocytes can be continuously formed in the post-natal mouse ovary. In my view, this notion, termed neo-oogenesis, is strictly linked to the process of the germline specification which presents unique features. Therefore, in the present paper, I am going to discuss two aspects of neo-oogenesis related to this process: first, evidence showing that adult mammalian ovary contains cells able to undergo germline specification and produce new oocytes; and second, the possible origin of such cells. In conclusion, I favour the possibility that a small number of primordial germ cells (PGCs)/oogonia or of PGC-derived undifferentiated cells with stem cell characteristics could remain in the post-natal ovary and under certain conditions may resume mitosis, enter meiosis and give rise to oocytes.
De Felici
Massimo
M
Department of Public Health and Cell Biology, Section of Histology and Embryology, University of Rome Tor Vergata, Via Montpellier 1, Rome 00173, Italy. defelici@uniroma2.it
D053687:Adult Stem Cells / Q000502:physiology*; D000367:Age Factors; D000818:Animals; D019070:Cell Lineage; D005260:Female; D006801:Humans; D008540:Meiosis; D008938:Mitosis; D009865:Oocytes / Q000502:physiology*; D009866:Oogenesis; D006080:Ovarian Follicle / Q000166:cytology / Q000502:physiology*; D010053:Ovary / Q000166:cytology / Q000502:physiology*