Thanks to genetic modification, laboratory mice can produce offspring composed entirely of females or males.
The ability to produce animals of the desired sex has the potential to revolutionise science and farming. Poultry farmers can produce chicks that will produce eggs in the future and breeders can produce calves that will grow into dairy cows without having to deal with an excess of male animals, which are usually sent straight to slaughter. Many laboratory studies relating to biology and medicine also need animals of a strictly defined sex.
Such a possibility may be created by new work by James Turner and his colleagues at Francis Crick University in London, whose paper has been published in the recent issue of Nature Communications. The researchers used CRISPR gene-modification technology to produce lines of laboratory mice that produce offspring of exactly the same sex.
CRISPR uses a nuclease protein capable of cutting DNA in a strictly defined location, as well as a 'guide' RNA that tells the enzyme the place where it will make the cut. This allows a wide range of precise manipulations of the genome, opening up enormous prospects in biology, medicine and industry. Well, British scientists have used the CRISPR system to destroy embryos of one sex in the earliest stages of development, leaving the other intact.
The target gene for the enzyme was topoisomerase 1 (TOP 1), whose function is vital for cell division, so disruption to it rapidly kills the developing embryo. For this purpose, the components of the CRISPR system were split across the genomes of the parents: the nuclease gene was put into one and the gene encoding the guide RNA into the other. For example, the guide RNA gene was put into the DNA of the female and the nuclease gene into the "male" Y chromosome of the father.
Individually they had no effect on the organism, but when combined in the embryo of the future male, they took effect and destroyed it when it was no bigger than a few cells. In this case, the embryos that did not receive a Y-chromosome developed normally, and soon the female brought a litter consisting entirely of females. Similarly, (just placing the gene CRISPR in the reverse order) and managed to get a female, bringing exclusively males.
According to scientists, litters from such GM females were even more numerous than it was possible to expect. Instead of about half the normal number, they produced only 30-40 per cent fewer young. This was most likely because the death of some of the embryos at the earliest stages freed up the resources of the mother's body to develop additional embryos of the 'right' sex.
Given that all animals carry the TOP 1 gene, this method could theoretically be used to produce lines that produce offspring of the correct sex. The authors believe that in the near future it will find application in laboratory research. There are, however, some doubts about farming - above all, ethical issues and the wariness with which many consumers view GM products.
