It was already known that genes inherited from ancient retroviruses are essential for placental mammals, a finding that scientists contributed Laboratory of Physiology and Pathology Endogenous Retrovirus Molecular and Infectious (CNRS / Université ParisSud, France). Now, these scientists have revealed a new chapter in this story: these viral genes may also be responsible for the increased muscle mass of men. Their findings are published in PLoS Genetics.
The particular feature of retroviruses explains CNRS in a note, is that they have an enzyme that allows transcription of their RNA genome to a molecule “complementary” DNA is capable of integrating into the DNA of the host cell.The AIDS virus (HIV) is the retrovirus known example.
Retroviruses have surface proteins which are capable of mediating fusing its envelope with the membrane of a target cell. Once released inside the cell, the genetic material is integrated into host chromosomes. In the rare cases where the infected cell is involved in reproduction, the viral genes can be transmitted to the progeny.Therefore almost eight percent of the mammalian genome is composed of traces of retrovirus, or endogenous retroviruses.
Most of them are inactive, but some are still able to produce proteins: this is the case of sincitinas, proteins that are present in all mammals and are encoded by genes inherited from retroviruses “captured” by their ancestors.
a little over five years ago, and thanks to the inactivation of these genes in mice, the team led by Thierry Heidmann sincitinas showed that contribute to the formation of the placenta. Because of its ancestral ability to mediate cell-cell fusion, result in the syncytiotrophoblast, a fabric formed by the fusion of a large number of embryo-derived cells in fetomaternal interface.
The syncytiotrophoblast is a part of the placenta, which allows the implantation in the uterus and then constitutes the interface between the mother’s bloodstream and the embryo, where exchanges of gases and nutrients needed for the development of the latter occurring.
Using the same mice, the team has revealed a “collateral” and unexpected effect of these proteins: endow men more muscle mass than women. Like the syncytiotrophoblast, muscle mass develops from stem cells fused. In male mice genetically modified, these fibers were 20 percent smaller and 20 percent showed less cores than in normal men;They were therefore similar to those observed in females and total muscle mass.
other mammals
It therefore appears that inactivation of sincitinas leads to a deficit of mergers during muscle growth, but only in males.
The scientists observed the same phenomenon in the case of muscle regenerated after injury: sincitinas incapable of producing male mice experienced less effective than the other males, but comparable to that observed in females regeneration. Furthermore, the regenerated muscle fibers produced syncytin; once again, only in males.
If this discovery is confirmed in other mammals, could explain the muscular dimorphism observed between males and females, a difference that is not seen consistently in the egg-laying animals.
By culturing muscle stem from different mammalian species (mouse, sheep, dog, human) cells, scientists have advanced part of the way: they have shown that, in fact, sincitinas contribute to the formation of muscle fibers in all species analyzed. Now it is necessary to show whether in these species, the action of sincitinas is also specific to males.
In the study involving experts in muscles: the teams led by Julie Dumonceaux at the Center for Research in Myology (CNRS / UPMC / Inserm) and Laurent Tiret at the National Veterinary School of Alfort and Mondor Institute of Biomedical Research (Inserm / UPEC).
