#Human #genome not entirely human

A new discovery reported in the PNAS (http://1.usa.gov/1TzvENa)
suggests that human DNA is less human than previously thought. By
examining >2500 sequenced genomes, scientists discovered 19
previously unidentified Human Endogenous Retrovirus (HERV)
insertions. In fact it is suggested that about 8% of what we believe is
human DNA was actually handed down from viruses over generations.
One stretch of DNA found in 50 out of 2500 sequenced genomes,
contains the genetic recipe for an intact provirus. Whether the provirus
can replicate or not is not known yet but related studies of ancient
virus DNA in human sequences suggests that it can impact humans.

The provirus was found on the X chromosome has been dubbed Xq21
and it's only the second intact provirus found in human genome. The
provirus seems capable of making infectious virus and it could be
remnant of a viral epidemic that took place long ago.
In certain instances the HERV sequences are used by the human
body to serve a useful purpose. One example is the role of HERV-W
syncytin-1 in maintaining human pregnancy. Syncytin was found to be
part of the trophoblast cells that surround fetal cells during pregnancy.
This layer of cells around the developing fetus protects it from toxins in
the mother's blood. The finding provides important information for
understanding how retroviruses and humans have evolved together.
The results from the current study provide a basis for future studies of
HERV evolution and its implication for disease.

http://bit.ly/1TzvBRw