Posted by RJG on September 29th, 2013 • Where are the canine retroviruses?
The mysterious absence of canine retrovirusesIt is striking that no exogenous retroviruses have been identified in domestic dogs (Canis familiaris), or any canine species for that matter. Historically, research on mammalian viruses has tended to focus on domesticated species (or else on species that are vectors or reservoirs for human viruses). A precondition of discovering a new mammal virus is locating and sampling an infected animal, and viruses that cause chronic, lifelong infections, such as retroviruses, are often more easy to locate than those that cause transient infections. Accordingly, exogenous retroviruses have been identified in many livestock or companion animals, including cows, horses, sheep, goats and cats, but not dogs.
Oocyan (blue eggshell color) is caused by an ERV insertion upstream of the SLCO1B3 gene in chickens.
Parallel ERV-mediated evolution of blue egg color in chickensThe delightful word 'oocyan' refers to the trait of blue-green eggshell color that occurs in native chickens of Chile (Mapuche fowl) and some of their descendants in North America and Europe, as well as certain Asian chicken breeds (e.g. Dongxiang, Lushi).
Oocyan is an autosomal dominant trait, and recent papers in PLoS Genetics and PLoS ONE have established that it's occurrence in chickens from different geographical regions is due to an endogenous retrovirus (ERV) insertion upstream of the SLCO1B3 gene [1, 2].
Remarkably, the ERV insertions responsible for oocyan appear to represent separate integration events in Chinese versus American/European chicken breeds - thus it appears that the oocyan phenotype has evolved on two separate occasions, via the same ERV-mediated mechanism, in distinct populations of chickens.
Endogenous retroviruses in aquatic mammal genomesThe first aquatic mammal ERV sequence was described in 1996, recovered from the genome of a 'hook-nosed sea pig' (Halichoerus grypus) by Tristem .
In 2005, I reported the first cetacean ERV sequence - this betaretroviral ERV sequence fragment spanned the protease (PR) and reverse transcriptase (RT) genes, and was recovered from the Risso's dolphin genome .
The sequence of a complete ERV provirus from a cetacean was described shortly afterwards - this time an endogenous gammaretrovirus, identified in the killer whale (Orcinus orca) genome . Recently, another gammaretroviral provirus sequence was recovered from the bottlenose dolphin (Tursiops truncatus), along with several other ERV PR-RT sequence fragments from cetacean genomes . This most recent set of cetacean ERV sequences has been incorporated into our online retroviral reference sequence library.
Visitors arriving at the gates of the New York Zoological Park in 1911
The extraordinary evolutionary history of the REVsTheir story unites mammals from Madagascar with birds from South East Asia, and links the distant evolutionary past to a more recent history of environmental and technological change.
The reticuloendotheliosis viruses (REVs) are retroviruses that were identified in the 1950s as the agents of virulent disease in gamebirds and waterfowl. Remarkably, DNA sequences derived from REVs are present in the genomes of two other, unrelated viruses - gallid herpesvirus-2 (GHV-2), the cause of Marek's disease, and fowlpox virus (FWPV), the cause of fowlpox.
In a study published today in PLoS Biology , we shed new light on the origin and evolution of REVs, accounting for their unusual distribution in nature.