endogenous retroviruses and development

A couple years ago I noted a remarkable piece of evidence for common ancestry, the DNA inserted by viruses into our genomes. In a recent study, biologists show how endogenous retroviruses can influence embryonic development in sheep.

Tom Spencer and his colleagues at Texas A&M University in College Station, US, studied the role of ERVs in pregnancy through lab experiments and on live sheep. They already suspected from the lab work on sheep embryos that endogenous Jaagsiekte sheep retroviruses (enJSRVs) help embryos develop.

In the new work, they proved their suspicions correct by injecting the womb linings of sheep with a drug which blocks activity of the virus. The drug was designed to block the specific “envelope” gene of the virus suspected of aiding pregnancy.

Pregnant sheep given the virus-blockers suffered miscarriages. “When production of the envelope protein was blocked in the early placenta, the growth of the placenta was reduced and its development inhibited,” says Spencer. “The end result was that the sheep suffered recurrent early pregnancy loss.”

Such research could open up another front in the war on HIV.

Spencer says that none of the retroviruses “adopted” by the human genome has any surviving infectious counterpart, suggesting that our adopted viruses have “won” the battle for us and wiped out viruses that were previously infectious.

The tantalising implication, he says, is that in years to come we will be protected from today’s killer viruses, like HIV and the hepatitis viruses, by endogenous versions which have taken up residence in our own DNA.