Endogenous retrovirus

Endogenous retroviruses ( ERVs ) are retroviruses that through a full replication cycle, but are inherited from generation to generation as a provirus in the genome of the host. It is believed that they originated many generations ago by infection of germ line cells of humans and other vertebrates.

Retroviruses are viruses that rewrite using the viral enzyme reverse transcriptase their RNA genome into DNA to integrate into the genome of its host cell can. Most retroviruses can only infect some somatic cell types. If it is possible some of infecting germ cells and thus are passed on to subsequent generations, they become endogenous retroviruses, which can remain for long periods in the genome of their host species. Stick with it sometimes only a short time (a few hundred generations) infectious because accumulate in replication by the host mutations that lead to creeping virus inactivation. Others remain active and can continue to produce exogenous virus particles. Under certain conditions, a remobilization of endogenous retroviruses take place, which then perform a transposition. These mobile elements where sometimes only the LTR regions still present (preserved ) are then referred to as LTR - retrotransposons.

As part of the Human Genome Project, several thousand ERVs in the human genome were found, the first in 24 different " families " are divided and account for approximately 8 % of the human genome. More recent evidence suggests that there are already 31 different groups, each caused by a single integration event.

By 2007, it was assumed that only the simple, but the complex retroviruses can not become endogenous retroviruses ( with the exception of the spumaviruses ). 2007 Then, the first endogenous retrovirus derived from a lentivirus, and thus a complex retrovirus described: The rabbit endogenous lentivirus type K ( Relik ). The only retrovirus genus, from the date no endogenous retroviruses have been described, thus the delta retroviruses.

History

ERVs were discovered in the late 1960s. Three different types of endogenous retroviruses have been described about the same time: the avian leukosis virus ( ALV) in the domestic fowl ( Gallus gallus) and the Murine leukemia virus ( MLV ) and the mouse mammary tumor virus ( MMTV ) in the house mouse (Mus musculus).

Human endogenous retroviruses

Human endogenous retroviruses ( HERV ) come in large numbers in the human genome. Since they were part of the genome is already very long ago, numerous mutations of all kinds have in their sequence accumulated, including point mutations, deletions, insertions other retro elements, recombinations and mini - and microsatellite expansion. The retroviral sequences are therefore already changed a lot and often hard to find. Some HERVs are suspected to be involved in the development of some autoimmune diseases, particularly multiple sclerosis.

Endogenous retroviruses in pigs

PERVs ( porcine endogenous retroviruses ), the endogenous retrovirus of pigs. They are the focus of research because pigs as organ donors for xenotransplantation come into consideration, and represent the PERVs this a security risk.