Retroviruses are stealthy invaders. They’re coated with molecules that enable them to fuse with the membrane that surrounds a cell, smuggling in their genetic payload in the form of viral RNA [a chemical similar to DNA, which contains the virus’ genes]. Once inside, this RNA is converted into DNA and jumps inside the host cell’s genome, lying low until the time is right to make new viruses and break out again. Over millions of years, mammalian cells have managed to tame these viral invaders, stealing their cell-fusing genes – known as syncytins – for more useful purposes. As well as playing a role in making large fused cells in the placenta, scientists have discovered that syncytins also help to fuse together cells to form long fibres in healthy mouse muscles (left). The muscle cells on the right are lacking one of the syncytin genes and can’t form fibres, making much weedier muscles.
Written by Kat Arney
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