Made Simple: Selecting The Sex Of Offspring

A research group in Japan has identified a chemical that affects sperm bearing the Y chromosome differently from those bearing the X chromosome.

AsianScientist (Aug. 27, 2019) – Scientists in Japan have developed a simple, reversible chemical treatment to segregate sperm based on the sex-determining chromosomes each sperm carries. The findings are published in the journal PLOS Biology.

Most cells from male mammals contain both an X and a Y chromosome, but during sperm development, the X and Y chromosomes are segregated into different cells so that an individual sperm will carry either one or the other. An X chromosome gives rise to daughters and a Y chromosome to sons.

Unlike the Y chromosome, which carries very few genes, the X chromosome carries many, some of which remain active in the maturing sperm. This difference in gene expression between X- and Y-bearing sperm provides a theoretical basis for distinguishing the two.

In the present study, researchers led by Professor Masayuki Shimada and colleagues at Hiroshima University, Japan, found that almost 500 genes are active only in X-bearing sperm, of which 18 genes encoded receptors. The team focused on a pair of receptors called toll-like receptor 7 and 8, and discovered that a chemical that bound to the receptors slowed sperm motility without impairing either sperm fertilization ability or viability. They showed the effect was due to impaired energy production within the sperm and could be reversed by removal of the chemical from the medium.

Treatment of mouse sperm with this X-retarding chemical, followed by in vitro fertilization with the fastest swimmers, led to litters that were 90 percent male. When the slower swimmers were used instead, the litters were 81 percent female.

There are other procedures that can be used to separate X and Y sperm, but they are cumbersome, expensive and risk damaging the DNA of the sperm. The procedure developed by these authors has the potential to simplify sex selection for either in vitro fertilization—in which sperm and egg fuse in a lab dish—or artificial insemination, in which sperm are implanted into the female reproductive tract. Such techniques are widely used in the agricultural animal breeding field, as well as in human assisted reproduction.

“The differential expression of receptor genes by the two sex chromosomes provides the basis for a novel and potentially highly useful method for separating X and Y sperm. We have already succeeded in selectively producing males or females in cattle and pig with our technique,” Shimada said. “Nonetheless, the use of this method in human reproductive technology is speculative at the moment, and involves significant ethical issues unaffected by the utility of this new technique.”

The article can be found at: Umehara et al. (2019) Activation of Toll-like Receptor 7/8 Encoded by the X Chromosome Alters Sperm Motility and Provides a Novel Simple Technology for Sexing Sperm.


Source: PLOS; Photo: Shutterstock.
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