Young mice from two fathers and a surrogate mother
In 2018, a team of Chinese researchers managed to obtain baby mice from same-sex parents. But if the rodents conceived from two mothers were viable, the young from two fathers – and a surrogate mother – died forty-eight hours after their birth. A Japanese team has just overcome this obstacle with a completely different approach, producing viable oocytes from only male cells. The experience, published in Nature March 15had been presented a week earlier – ironically on March 8, International Women’s Day – at the Third International Human Genome Editing Summit in London.
Katsuhiko Hayashi (Universities of Kyushu, Fukuoka, and Osaka) and his colleagues drew on a decade of work on gametogenesis, that is, the formation of male (sperm) and female (oocytes) sex cells ). In this case, it is the latter which have been produced from male cells. The Japanese team took advantage of a phenomenon that is generally a handicap when culturing cells in vitro: the spontaneous loss of chromosomes, in particular of the Y present in the male cells, coupled with the X – remember that the female cells have two X chromosomes.
Katsuhiko Hayashi departed from adult cells taken from the tail of male mice (XY), treated to become pluripotent stem cells again, that is to say capable of differentiating into any cell type. In vitro, as they divide, some cells – around 6% – have therefore lost their Y chromosome. The cells in question, known as X0, were then placed in a medium containing reversine, a molecule that disrupts division, which which induced the duplication of the X chromosome. These XX cells could then be cultured together with fetal ovarian cells, constituting a favorable medium for their transformation into oocytes. These could then be fertilized in vitro to produce embryos, which were then implanted in surrogate mothers.
In the end, out of 630 implanted embryos, 7 led to the birth of young mice which, says Katuhiko Hayashi, “seem to grow normally into adulthood”a success rate of 1.1%.
For Jonathan Bayerl and Diana Laird (University of California, San Francisco) who comment on this work in Naturethese “open up new perspectives in reproductive biology and fertility research”. Firstly for fundamental research, by producing lines of mice offering a stable genetic background, a bit like identical twins. “It could also offer a way to rescue endangered species from a single male, provided a carrier female of the same or related species is available to carry the embryos to term.”, they add. Incidentally, Katsuhiko Hayashi is involved in a white rhino conservation programthe problem being in this case that only two females of this species still exist…
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