Retroviruses are viruses made up of RNA genetic material. Endogenous retroviruses (ERV) are those sequences derived from retroviral infections introduced into the germinal line cells that, being incorporated in the genome, are transmitted from generation to generation. According to a number of investigations, the expression of ERV can benefit the host if it is controlled; it can help, for example, in the protection of the embryo. However, given its pathogenic nature, ERV also tends to be linked to cancer, schizophrenia and autoimmune diseases.
In any case, our knowledge about ERV is still scant. They have been detected in all mammals and in many vertebrates, but genic research in this regard has only been carried out on primates and rodents. Biologist Mr Koldo García has made a step forward in the field on studying ERV in cows and horses. He undertook the first genomic analysis of ERVs of two species respectively belonging to families of ruminants and equidae. His PhD thesis, presented at the University of the Basque Country (UPV/EHU), is entitled Erretrobirus endogenoen detekzioa eta karakterizazioa behietan eta beste hainbat mamaliotan (Detection and characterisation of endogenous retroviruses in cattle and a number of other mammals).
BoERV1, the most abundant amongst cattle
Mr García made use of computer tools in order to detect ERV. Concretely, he used three methods: the first based on the BLAST algorithm, and the other two on LTR_STRUC and Retrotector© programmes. As a result, a total of 35 families of ERV (cows and horses), hitherto not appearing in the literature, were detected; in concrete, 24 possible families of ERV in cattle, 20 of which had not been described experimentally. Amongst the latter, Mr García highlighted the BoERV1 family, being the most abundant amongst those found. As shown in the thesis, it may be the case that this is a family of ERV specific to ruminants. With regard to horses, 15 possible families were detected, none of them described to date.
The researcher also studied how ERV proliferates in both species and concluded that re-infection is the most common method in both cases. In general, ERV proliferates in two main ways: by transposition (occurring in the germinal line cell itself) or by re-infection (the ERV exit their cells and infect another germinal line cell). The PhD thesis shows that re-infection is very common, as the same manner of proliferation is the most common in many other animals. In concrete, Mr García brought together data on humans, chimpanzees, mice, rats and dogs for his research, in order to compare them with that of cows and horses; and he thus showed that, excepting rats, all these animals use re-infection more than transposition.
Expression in cattle tissue
Mr García undertook a more in-depth investigation in the case of cattle, focusing also on the genes surrounding the ERV; in other words, within the genomic context. As shown in the thesis, many of the genes close to the ERV are linked to protecting themselves against viruses and with histones (proteins which participate in the compacting and regulation of DNA). According to the researcher, this could be due to the genes being active when the retroviruses are introduced, or to the fact that they have characteristics recognisable by them.
Apart from detecting ERVs, the thesis demonstrates their expression in bovine tissue for the first time. It involves, moreover, a controlled expression and, therefore, valuable for the protection of the host. As shown in the thesis, this expression occurs mainly in the endocrine glands and in embryos, and so could be linked to the protection of the embryo.
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