Eggs made from male mouse cells produced living pups

Researchers at Kyushu University in Japan took tail cells from an adult male mouse, reprogrammed them into stem cells, picked out cells that had spontaneously lost their Y chromosome, then used a drug, reversine, to get them to duplicate the remaining X.

The corrected cells, now carrying two X chromosomes, were coaxed to differentiate into mature, functional oocytes in culture. Fertilized with ordinary sperm, the resulting embryos were implanted into surrogate mice and produced live, healthy pups, which went on to reproduce normally themselves.

The technique depended on a chance chromosomal error that the team learned to select for and correct, not a method that reliably converts any male cell into an egg on demand, and the efficiency of producing viable pups this way was low. It demonstrated that a male mammal's cells can be turned into eggs, a result relevant to future same-sex reproduction research in mammals, far from any human application.

A male cell, rebuilt into a working egg.