Release 10.1

Koala genome invaded by a new retrovirus

Endogenous retroviruses are vestiges of ancestral viral infection that have been incorporated long time ago into a host's genome. Surprisingly, 8% of the human genome is composed of such "fossil" viruses (1). The most recent endogenization event is a porcine virus that entered its host approximately 5,000 years ago.

Recently a new endogenous retrovirus was identified in Australia koala populations.

Koalas were largely exterminated on mainland southern Australia in the late nineteenth century. Populations were established on a small number of islands in the early 1900s and have remained isolated since 1920s. These populations have since been used to restock the mainland.

The new Koala retrovirus (KoRV) has only been found in mainland populations, suggesting that this virus entered koala species in the last 100 years (2). This retrovirus is both endogenous and fully functional, meaning that it spreads both by contact and by heredity, and is still in the process of invading the koala genome. KoRV is very similar to Gibbon Ape Leukemia Virus (GALV), and these two retroviruses are thought to have diverged very recently. This suggests a scenario in which a monkey retrovirus has crossed species to enter newly established koala population and has started to colonize koala genome.

The KoRV is unique in that we are observing the initial entry of a new family of endogenous retrovirus into a wild host genome. The dynamic interaction between this virus and its new host provides a unique opportunity to study the process of endogenization and its impact on species development and evolution.

Related entries:

• Q9TTC2 (GAG_KORV)
• Q9TTC1 (POL_KORV)
• Q9TTC0 (ENV_KORV)

References:

1. Griffiths D.J.
   Endogenous retroviruses in the human genome sequence
   Genome Biology 2:reviews1017.1-1017.5 (2001).
2. Tarlinton R.E., Meers J., Young P.R.
   Retroviral invasion of the koala genome
   Nature 442:79-81 (2006)