Y-chromosome loss didn’t make Japanese mice female

(ORDO NEWS) — In mammals, the main difference between a male and a female lies in the set of their sex chromosomes: the female has two X chromosomes, the male has XY.

The “male” chromosome plays a key role in the development of male genitalia. However, in male Japanese rodents, testes are present; nevertheless, the Y chromosome is not observed in the genomes.

The male from the female in mammals is determined by the set of sex chromosomes. The female has two X chromosomes, while the male has one X and one Y chromosome.

The latter contains the genes necessary for the proper development of the male reproductive system. In the absence of it, a person is born with Shereshevsky-Turner syndrome and develops according to the female type.

However, the absence of the Y chromosome does not lead to developmental disorders in all mammals. In some species of rodents, in particular the Ryukian mouse ( Tokudaia osimensis ), endemic to the tiny island of Oshima off the coast of Japan, both the male and the female have 25 chromosomes in the genome, so the development of the testes in them is triggered in a different way.

Now a group of Japanese researchers led by Asato Kuroiwa ( Asato Kuroiwa ) from the University of Hokkaido managed to find out how mouse embryos “understand” whether they become males or females.

After collecting tissue samples from six animals, three males and three females, the scientists studied the genome of each individual and, finally, identified a double DNA segment on the third chromosome in all three males.

It was located near the Sox9 gene , which in other mammals is involved in the development of the testes. Normally, Sox9 needs a special protein produced by the Y chromosome to start up, but in Ryukian mice, duplicated DNA was able to replace it.

To test this hypothesis, scientists artificially duplicated this region of the genome in the third chromosome of embryos of female laboratory mice, and they earned a gene responsible for the development of the testes.

Y chromosome loss didnt make Japanese mice female 2
The eastern mole vole is another species of rodents whose males do not have a Y-chromosome

Thus, for the first time, scientists discovered in mammals a mechanism for determining sex that does not depend on the sex chromosomes.

In the future, the authors of the work plan to study the exact mechanisms of the influence of the doubled DNA segment on the functioning of Sox9 and clarify the principle by which sex is determined in other rodent species whose genome lacks a Y chromosome.


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