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Monday, December 13, 2010

Mice with two fathers

Scientists led by Richard Behringer of the M.D. Anderson Cancer Center have successfully produced mice that had two male parents. Here’s how they did it.

First, the researchers took cells from a male mouse (Dad #1, or D1) and induced them into becoming pluripotent stem cells. They next grew these D1 cells in culture until some of them spontaneously lost their Y chromosome (which occurs somewhere between 1 and 3% of the time. The geneticists now had their hands on cells containing only a single X chromosome (XO cells) that were female despite having been derived from a male.

In humans, having only one X chromosome (Turner’s syndrome) causes sterility. Not so in mice. The D1-derived female cells were mixed with the normal XX cells in an early stage female embryo. This resulted in a chimeric mouse, with some cells containing the two X chromosomes of the female embryo and others only the one X chromosome of the D1 cells. All the cells developed inside a female body however, meaning that any D1 cells that happened to be in the ovaries could develop into egg cells.

Finally, Dad #2, an ordinary male, was called upon to fertilize the D1 eggs. Genetic testing confirmed that the resulting offspring got their DNA only from D1 and D2, and not from the female host that housed the D1 cells.

To be clear, this technique is not yet possible in humans for a couple of reasons. First, as stated above, women with Turner’s syndrome are sterile. Thus, there wouldn’t be any XO eggs. Second, we haven’t been able to create pluripotent cells from somatic (non-sperm or egg) cells in humans. And of course, even if these problems could be solved there are many ethical questions, not least of which is getting host women to supply the D1 eggs. Remember, these women would have been made into D1 chimeras from an early embryonic stage, a rather objectionable prospect. So don’t expect to see babies born from two fathers any time soon, if ever.

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