Photo/Illutration(The Asahi Shimbun)

A Japanese research team said it manipulated DNA so it could decide the sexes of mice and cows before birth.

The team at Hiroshima University reported developing a method to select the sex of mammals before birth and demonstrated their results from experiments with mice and cows.

Using the differences of sperm’s sex chromosomes, the team achieved a high success rate in selecting sexes, without following the time-consuming process with sophisticated equipment. The team said that technically, the method can be applied to humans. The research result was published on Aug. 14 in the online edition of the U.S. journal PLOS Biology.

A mammal's sex is determined by two sex chromosomes, X and Y. Females have two X chromosomes, and males have one X and one Y.

All female eggs are X chromosomes, but there are two kinds of sperm: X-sperm bearing the X chromosome and Y-sperm bearing the Y chromosome.

If X-sperm is fertilized, a mammal becomes female, and if Y-sperm is fertilized, it becomes male.

Until now, it had been assumed that the numbers of X-sperm and Y-sperm were equal, and that there were no differences between them in their functionality.

The team focused on the process of how X-sperm and Y-sperm are produced from cells which sperms originate.

It thoroughly researched the genes and discovered receptors only carried in X-sperm. The receptors are in the sperm’s tail, and the sperm’s movement slows when the receptors are being stimulated.

In the experiment, the team placed sperm from mice and a drug that binds to the receptors in a test tube. About an hour later, only the X-sperm stopped moving and precipitated. The team confirmed that it started to move again after the drug was rinsed off it.

The team separated Y-sperm, which rose to the upper part of the test tube from the precipitated X-sperm, which was later cleaned.

Then, they were separately fertilized in vitro. The team was eventually able to select sexes of more than 80 percent of their mice. The success rate was 90 percent in cows.

The method of judging differences in the amount of X and Y chromosomes has been previously used to select the sex of cows.

However, it required expensive equipment, and the sperms had to be exposed to a laser one at a time when they were being evaluated. This was time-consuming and risked degrading the quality of the cows' sperm.

“There is a possibility that even private companies and livestock farmers can select sexes of animals in the future,” said Masayuki Shimada, a member of the research team and a professor of Hiroshima University specializing in reproductive biology, commenting on the team's findings.

The receptors the team discovered are present in the X chromosome in almost all mammals. Since humans also have them, the team believes it is also technically possible to select the sexes of human offspring.

“The receptors we discovered can also recognize viruses. This is meaningful for basic research, including the relation between sex determination and infection,” Shimada said.

However, he also added that discussions involving ethics will be needed to apply it to human sex selection.

A method already exists to examine fertilized eggs to select sexes, but the Japan Society of Obstetrics and Gynecology has not approved it for this purpose.

The paper can be read: https://doi.org/10.1371/journal.pbio.3000398