Wired: Most viral infections are as fleeting as a cold, but two things made the ancient ones unusual... by Sarah Zhang
'One, these viruses had the special ability to copy themselves into the DNA of their hosts. And two, they sometimes got lucky enough to copy themselves into an egg that became fertilized and grew into a full-fledged adult. So that viral DNA got passed down from generation to human generation as so-called endogenous retroviruses.
'But there’s no need for alarm about the DNA of viral origin teeming inside your cells. Some of it may even make you you. As a growing fetus, you co-opted a gene from an ancient virus to form the placenta that kept you nourished in the womb. And in recent years, scientists poring over gigabytes of genetic sequencing data have seen other tantalizing hints of endogenous retroviruses turning useful. A new paper out today in Science suggests humans have also co-opted the remnants of ancient viruses to direct the immune system against other pathogens. Ah, the irony. “The tables have been turned,” says Nels Elde, a biologist at the University of Utah and coauthor of the study. “We’ve claimed those elements to fight off modern viruses.”
'The question now is whether the role of endogenous retroviruses in the immune system is similarly widespread among animals. “Do they contribute on a major scale or are there just a few small cases? The questions is whether it opens new vistas,” says Jonathan Stoye, a retrovirologist at the Francis Crick Institute. With technology like next-generation DNA sequencing and CRISPR-Cas9, there’s no better time to look for those vistas than now.'
"Regulatory evolution of innate immunity through co-option of endogenous retroviruses" by Edward B. Chuong, Nels C. Elde, and Cédric Feschotte here