http://www.ncbi.nlm.nih.gov/pubmed/9619102
Placental endogenous retrovirus (ERV): structural, functional, and evolutionary significance.
Harris JR.
SourceInstitute of Zoology, University of Mainz, Germany.
harris@uzomai.biologie.uni-mainz.de
Abstract
That endogenous retrovirus (ERV) is present within the placenta of humans and other mammals has been known for the past 25 years, but the significance of this observation is still not fully understood. Much molecular biological data have emerged in recent years to support the earlier electron microscopic data on the presence of placental ERV. The evidence for ERV in animal and human placental tissue is presented, then integrated with data on the presence of ERV in a range of other tissues, in particular teratocarcinoma cells. Placental invasiveness and maternal immunosuppression are then discussed in relation to metalloproteinase secretion, the immunosuppressive potential of retroviruses, and placental growth factors, while the evidence for a functional link between placental protooncogenes and trophoblast malignancy is reviewed. Finally, placental development, structure, and life span are discussed within an evolutionary context. The hypothesis that one or more ancient trophoblastic ERVs could have played a role in the evolution and divergence of all placental mammals is evaluated
One of the fascinations of retroviral research is the light is casts on evolutionary processes,. Because it is now being accepted that mutation does not occur "randomly" but could be much more to do with retroviral infection and modification of the genome. Hence the development of the placenta following retroviral infection.
If we have introduced large amounts of foreign DNA into humans inthe last 100 years we could be looking at some real changes to come!.