In particular, a class of endogenous retroviruses, known as endogenous retroviruses related to Jaagsiekte sheep retrovirus or enJSRVs, are critical during the early phase of pregnancy when the placenta begins to develop.
Retroviruses, such as human immunodeficiency virus or HIV, are one class of viruses. They are best known for their ability to cause diseases, said Dr. Thomas Spencer, a reproductive biologist with the Texas Agricultural Experiment Station and Texas A&M University.
Findings published Sept. 11 in the Proceedings of the National Academy of Sciences demonstrate enJSRVs are essential for the development of the placenta in sheep.
Retroviruses are unique for their ability to permanently insert their genetic material into the DNA of host cells, he said. During evolution of mammals, some retroviruses infected the germline (cells of the ovary and testis that have genetic material that are passed to their offspring) of the host, which is then inherited by their children. These retroviruses, known as endogenous retroviruses, are present in the genome of all mammals, including humans. Consequently, endogenous retroviruses can be considered remnants of ancient retroviral infections, Spencer said.
Many scientists believed these endogenous retroviruses were junk DNA, he said.
"Indeed, these endogenous retroviruses are usually harmless and generally contain mutations that prevent them from producing infectious retroviruses," he said.
However, several endogenous retroviruses appear to provide protection from infection and are involved in reproduction. For instance, the exogenous Jaagsiekte Sheep Retrovirus or JSRV causes lung tumors in sheep and led to the death of Dolly, the world's firs
Source:Texas A&M University - Agricultural Communications