Males Without the Y Chromosome Can Still Father Offspring in Mice

It turns out that male mice without Y chromosomes can still father other mice. Scientists have discovered the live mouse progeny can be created by these mice with assisted reproduction.

Two years ago, researchers demonstrated that only two genes of the Y chromosome were needed for male mice to sire offspring with assisted fertilization. Now, the same researchers have taken it a step further and have shown that males completely devoid of the Y chromosome can also reproduce.

In this latest study, the researchers described how they generated the "No Y" males and defined the ability of these males to produce gametes and sire offspring.

In this case, the researchers first replaced the Y chromosome gene Sry with its homologue and direct target encoded on chromosome 11, Sox9. In a normal situation, Sry activates Sox9 and this initiates a cascade of molecular events that ultimately allow an XY fetus to develop into a male. The resrearchers used transgenic technology to activate Sox9 in the absence of Sry.

Then, the researchers replaced the second essential Y chromosome gene, Eif2s3y, with its X chromosome encoded homologue, Eif2s3x. The researchers speculated that these two genes may play similar roles.

The males that had these replaced genes developed testes populated by male germ cells. Round spermatids were harvested and then used to successfully fertilize oocytes. These mice created from the "No Y" males were healthy and lived for a normal life span

The findings provide important new insights into the Y chromosome gene function and evolution.

The findings are published in the journal Science.

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