By Chloe Mitchell, ASAP/ASAS Intern
February 18, 2016 – A recent article in Science highlights new research from reproductive biologists at the University of Hawaii, Honolulu, who have produced male mice lacking a Y chromosome. Monika Ward and colleagues developed the engineered males from mice with a single X chromosome via genetic manipulation on the X chromosome and another chromosome. This led to the creation of male mice capable of immature sperm production.
These results may initially appear to suggest that the Y chromosome is becoming obsolete in regard to reproduction. However, there are conflicting opinions in the scientific community as to what this research means for the Y chromosome. La Trobe University reproductive biologist Jennifer Marshall Graves (Melbourne, Australia) says the work is “a lovely example of how you can lose even a really important gene [and still maintain function].” Read more in an article in ScienceNews.
Ward maintains that the results cannot be interpreted as the end of the Y chromosome, as engineered males could only produce offspring when assisted: the immature sperm was injected into ova, producing viable offspring.
Previous studies by Ward and colleagues have shown that there are two Y chromosome genes vital to male development in the mouse: Sry and Eif2s3y. Sry is the sex-determining gene, which turns on Sox9, responsible for initiating male development in the early mouse embryo. Turning on Sox9 in a female embryo will result in male development, but no sperm production. The Eif2s3y gene on the Y chromosome is the gene responsible for initiating sperm production. Therefore, mice without the Y chromosome will be missing this gene. The researchers substituted an analogous transgene Eif2s3x from the X chromosome, however where one copy of the Y version is sufficient for sperm production, the X version requires at least five or more copies for viable sperm.
More about the research can be found in this University of Hawaii news release.
About the photo: Three male mice lacking any Y chromosome genes produced by round spermatid injection (ROSI). The males shown on the left and right are 2 years and 1 month old, and the male in the center is 1 year and 10 months old. Photo courtesy of Yasuhiro Yamauchi.