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Can Y Chromosome Be Even Shorter?

–Study Says 2 Y Genes Can Replace the Entire Y Chromosome in Assisted Mice Reproduction

In human’s long evolution history, the Y chromosome keeps losing approximately 4.6 genes in every 1 million years. However, the shortening Y chromosome seems not to worry about this situation. Today, a group of U.S. scientists noted that only 2 Y genes are needed in assisted reproduction. Will this be the bottom line for the Y chromosome?

The function and evolution of the Y chromosome has long been a hot spot for scientific research and there has been debates on whether the Y chromosome will degenerate or disappear. Recently, Monika Ward, associate professor from Institute for Biogenesis Research at University of Hawaii found that the entire Y chromosome can be replaced with two genes Sry and Eif2s3y and they can assist mice to generate sperm cells that can impregnate oocytes. and foster offspring. These new findings was published on recent Science.

 “Our experimental results revealed that only two genes from the Y chromosome can facilitate the development of sperm cells and initiate the first step in meiosis. Some cells also have the capability of completing the whole process and function during fertilization process. Monika noted:” This also proved that with the help of assisted reproduction technology, only a very small portion of genes from the Y chromosome is needed to foster offspring.”

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The genesis of sperm cells. In this study, the researchers injected the round spermatids—the precursor for sperm cells—into oocytes. *Image source: repropedia.org

For mammals including mice and human being, Sry is the testis determinant factor, which can direct the gonad of fetus to male while Eif2s3y is the spermatogonial proliferation factor, which can guide the genesis of sperm. The researchers constructed mice with only Sry and Eif2s3y from the Y chromosome and injected the sperm cells into oocytes, however, they only achieved very low fertilization rate. “One of the challenges during the process of building parents was the low breeding efficiency. Mice with the only two genes on the Y chromosome were not commonly seen, however we still got some qualified male mice. Excitingly, some of the cells in the mice’s testis seemed to resemble sperm cells.” Monika explained:“ Since these cells were too rare, it was also difficult to find them. When we obtained these sperm cells, we would use round spermatid injection (ROSI) technology to inject them into oocytes. We could obtain live offspring when the developed embryos were transferred to the fallopian tube of the female surrogate mice.”

 “The offspring fostered with this technology are all normal and healthy. Some offspring can live as long as two years and they don’t get sick or show any differences from regularly cultivated mice.” Monika said:” However, we didn’t perform molecular genetics analysis on these mice and we can’t completely exclude the possibility of the difference that might exist.”

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This is a mature daughter of the male with two Y genes obtained by ROSI. It is healthy and fertile, and the above image shows her with her own litter.  *Image source: Monika Ward.

 “Our study is a fundamental research based on mice, aiming to investigate different functions of various genes from the Y chromosome with the help of assisted reproduction technology. Hence, the results can’t directly be used for research on human reproduction.” Monika emphasized. For the following research, Monika and her group have two potential research directions. “We will study the influence of adding several more Y chromosome genes,” adds Monika:” Moreover, we’ll try to take out the entire Y chromosome to see whether we can foster offspring by assisted reproduction technology.”

Source:Eurekalert!

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