2016-04-11 21:57:48
Truly amazing facts have been discovered about the genes that turn half the population into males.
If someone still doubts that genes exert a determining influence on who we are, they only have to take a look at those that determine a very important human condition: sex. Whether we are men or women is, without a doubt, a matter of genes, and not a personal choice, as it is if we decide to be engineers or architects, as long as the economic situation of our families allows it.
As almost everyone educated knows, in mammals the male sex is determined by the inheritance of one X chromosome from the mother and one Y chromosome from the father, and the female sex is determined by the inheritance of one X chromosome from each parent. . This discovery allowed the study of which genes of these two chromosomes are those that determine the development of organs as important for males as the testicles or the penis, and as important for females as the ovaries and the uterus. Today, thanks to the techniques of molecular biology, truly amazing facts have been discovered about the genes that turn half the population into males.
Recently, a group of researchers from the Universities of Hawaii and Marseille have published that of all the genes contained in the Y chromosome, only two are necessary for the development of fertile males, although this fertility is only possible through assisted reproduction. These genes are called Sry and Eif2s3y.
The Sry gene produces a transcription factor, that is, a protein that can activate the functioning of some other genes. One of the most important genes induced by Sry is the gene called Sox9, which is another transcription factor. The functioning of this last gene is necessary for the development of the seminiferous tubules in the testicles, without which the production of sperm and testosterone – the male sex hormone – is impossible. On the other hand, the Eif2s3y gene produces a protein necessary for the proliferation of spermatogonia, which are the precursor cells of spermatozoa. Obviously, without the correct functioning of this gene, spermatozoa cannot develop, and what self-respecting male would be that one who cannot generate spermatozoa no matter how many testicles he has?
Males without Y
Interestingly, the Sry and Eif2s3y genes have “colleagues” on other chromosomes that could theoretically replace their function if it fails. The same previous research group wonders for this reason if this could be a reality or is it only in theory. To verify this, they carry out a series of interesting experiments with laboratory mice, the results of which are published in the journal Science.
To begin with, the researchers generate mice without a Y chromosome that have been genetically modified so that they have only one X chromosome. This single X chromosome has also been manipulated and has the Sox9 gene turned on (which, let’s remember, is induced by Sry) and also has the Eif2s3y gene activated. The rest of the genes on the Y chromosome have been deleted, but the genes on the only X chromosome that these animals have function normally, with the addition of the two mentioned. What is the sex of these animals?
The researchers find that these animals are male. As we have said, these males do not have the Sry gene (they only have the Sox9 gene), so the only Y chromosome gene involved in their masculinity is Eif2s3y, which, in this case, has been inserted into the X chromosome. .
As if the above weren’t impressive enough to show that just two genes turn otherwise (supposedly) females into males, the researchers run another experiment with even more impressive results. It turns out that the Eif2s3y gene on the Y chromosome has a “colleague” very similar to it on the X chromosome, which is called Eif2s3x. Could this gene, if artificially activated, replace Eif2s3y?
To test this, the researchers generate a new strain of mouse that has a single X chromosome to which the Sry gene has been inserted and to which the Eif2s3x gene has been activated. These mice are also male. His testicles are small, but they exist, an unequivocal sign of his sex. In addition, these mice are capable of generating functional sperm that allow them to reproduce through assisted reproduction (in vitro fertilization).
In the two experiments above, at least one gene on the Y chromosome is involved in the masculinity of the mice. The researchers therefore wonder if they could remove all the genes on the Y chromosome completely from the genome and still generate males.
To find out, they generate transgenic mice that carry the Sox9 and Eif2s3x genes activated on the X chromosome, but completely lack the Y chromosome. These mice, therefore, carry two genes that are not specific to the Y chromosome, but that could replace the previous ones. originals of that chromosome.
All of the mice generated in this way were male, although the majority (35 of 48) had testis defects and were not capable of generating sperm. The rest of the animals could generate them in a way comparable to that of the previous mice that had the Sry gene and the Eif2s3x gene activated.
These studies indicate that the Eif2s3y gene is likely derived from its X-chromosome partner, Eif2s3x, and that this gene was critical to the generation of sperm throughout evolution. Furthermore, at least in the case of the mouse, the results indicate that the Y chromosome is not strictly necessary for male fertility if assisted reproduction can be used. Who would have suspected, right?
Referencia: Yasuhiro Yamauchi et al. (2016). Two genes substitute for the mouse Y chromosome for spermatogenesis and reproduction. Science. 29 JANUARY 2016 • VOL 351 ISSUE 6272, pp. 514.
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