Stem Cells from Oocytes and Oocytes from Stem Cells
Pp. 156-166 (11)
Fulvio Gandolfi, Georgia Pennarossa, Arianna Vanelli, Mahbubur M. Rahman and Tiziana A.L. Brevini
Full oocyte competence is the indispensable requisite for embryonic development and, at present, no
ways are known to restore competence if, for any reason, it has been even slightly compromised. The same is not
true for sperm cells that can initiate and sustain development even if severely abnormal or damaged as long as the
DNA is intact. This points clearly to the uneven burden carried by the two gametes and indicates clearly the
essential role of the oocyte. Parthenogenesis is the obvious consequence of such disparity with a number of lower
species capable of giving birth to new individuals without any paternal contribution. Mammals are an exception
to the rule due to epigenetic mechanisms limiting the parthenotes developmental potential. However, the
blastocyst stage is easily reached and parthenogenetic stem cells can be generated whose differentiation potential
seems to be much wider than that of whole parthenotes. Switching perspective, we move from stem cells
originated from oocytes to oocytes originated from stem cells. Since embryonic stem cells can colonize the germ
cell lines when chimeras are generated, it was not so surprising that oocytes can be obtained from stem cells.
Although there is still a long way to go before full competence is reached it clearly opens the way to the
hypothesis of having an unlimited source of oocytes. Finally, a recent and highly controversial set of results
suggests that oocytes are not in such a limited supply as it is generally believed but post-natal oogenesis takes
place at a surprisingly high rate.
Laboratory of Biomedical Embryology, UniStem-Centre for Stem Cell Research, Università degli Studi di Milano, Milano, Italy.