Secrets of Y chromosome exposed

The bad news, men, is that the chromosome that lends you your gender is largely irrelevant.

But that’s also good news, University of Hawaii medical researchers have found. That’s because only two genes of the Y chromosome are necessary for many otherwise infertile men to father children.

"Does this mean that the Y chromosome (or most of it) is no longer needed?" Monika Ward, an associate professor at the Institute for Biogenesis Research, said in a statement Thursday. "Yes, given our current technological advances in assisted reproductive technologies."

While women have two X chromosomes, normal men have an X and a Y. But about 1 percent of men have a condition called azoospermia, or zero sperm count. The condition accounts for up to 1 in 5 cases of infertility, urologists estimate.

But Ward and colleagues, in studies in mice, showed that artificial insemination can occur using only two genes from the Y chromosome. The technique is not yet directly applicable to humans, Ward said. She emphasized that the Y chromosome remains important for normal, unassisted fertilization and other aspects of reproduction.

"Most of the mouse Y chromosome genes are necessary for normal fertilization," Ward said. "However, when it comes to assisted reproduction, our mouse study proves that the Y chromosome contribution can be brought to a bare minimum. It may be possible to eliminate the mouse Y chromosome altogether if appropriate replacements are made for those two genes."

The results of the study were published online Thursday in the journal Science. The co-authors are Yasu­hiro Yama­uchi, Jonathan Riel and Zoia Stoy­tcheva, all of the John A. Burns School of Medicine.

For this study, Ward and colleagues used male mice with only two Y genes, Sry and Eif2s3y. These mice were considered infertile because the germ cells that should have developed into sperm did not.

But researchers were able to find a few usable cells. Yama­uchi harvested the immature cells, called "spermatids," and used a technique called "round spermatid injection" to fertilize mouse eggs in the lab. When the developed embryos were transferred to surrogate mothers, live babies resulted.

"We’re not trying to eliminate Y chromosomes with our work — or men, for that matter," Ward told website LiveScience. "We’re just trying to understand how much of the Y chromosome is needed, and for what."