Direct Impact

Scientists from the University of Nevada School of Medicine's Department of Physiology and Cell Biology have managed to glean new insight into the reproductive mechanics of the male sex chromosome. These new discoveries may have a direct impact on the medical community's understanding of male infertility and contraception. The researchers' findings have been published in Nature Genetics.

The study revealed that the X chromosome in early sperm cells encode many small ribonucleic acids known as microRNAs, even though most of the genes along the X chromosomes are held in check. This never before observed encoding of so many microRNAs have led researchers to conclude that these small ribonucleic acids perform an integral role in inactivating chromosomes and in the formation of sperm.

Wei Yan, M.D., Ph.D., the lead investigator of the study and associate professor of physiology and cell biology at the School of Medicine commented that it has long been known that the sex chromosomes within the male germ cells are suppressed, and this is known as meiotic sex chromosome inactivation. But Yan was surprised to see the large number of microRNAs so highly expressed within the cells.

Silencing Effects

Yan worked together with Dr. John McCarrey, a professor of molecular biology and reproductive biology at the University of Texas, in San Antonio. Yan's research team followed up the original surprise finding by investigating all the X-linked microRNAs that are currently known. The data generated by the team proved that the microRNAs derived from the X chromosome did escape the silencing effects and manage expression.

Yan explained that the findings of his team give another avenue for understanding the role of small RNA's in managing sperm production. Today, one in every nine couples within their reproductive years experience infertility worldwide. "On the other hand, the number of unintended pregnancy is increasing yearly. Since these small RNAs are involved in the control of sperm formation, they can be causative factors in male infertility and also can be used as non-hormonal male contraceptive targets," said Yan.

Yan's research centers in the main on sperm and egg production in mammals and his work is funded by the National Institutes of Health. Main co-authors Rui Song, a third year graduate student, and Seungil Ro, Ph.D., an assistant professor of physiology and cell biology were assisted by contributing authors Jason D. Michaels, a third year medical student, and Chanjae Park, Ph.D., a post-doctoral researcher.


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