Washington, Jan 30 : The DNA that originated from ancient viral infections are essential for a healthy pregnancy, says a new study. Retrovirus infections represent the most intimate host-pathogen relationship.
The virus inserts a copy of its genome into the DNA of the host cell, resulting in an irreversible, stable and sometimes lifelong infection.
If a sperm or egg cell is infected, the virus DNA can be passed down generations, permanently fixed in the germ line. As a result, an Endogenous RetroVirus (ERV) can exist for millions of years.
"Over the course of evolution, retroviruses have invaded the germ-line of our ancestors on numerous occasions. Now, human ERVs (HERVs) make up around 8% of our genome," said Dr David Griffiths from the Moredun Research Institute and Cecile Voisset from the Faculte de Medecine et des Sciences de la Sante in France.
Although there are no viruses similar to these ancient pathogens currently infecting humans, there are some related viruses in animals.
For a retrovirus to become part of the host genome it is usually inactivated by mutation or silencing so it does not express any proteins.
"Recent work has provided some tantalizing evidence supporting the roles of HERVs in normal physiology and also in disease, they can be seen as bona fide human genes," Griffiths said.
The study is published in Microbiology Today.