Paleovirology

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Paleovirology is the study of viruses that existed in the past but are now extinct. In general, viruses cannot leave behind physical fossils[1] Therefore, indirect evidence is used to reconstruct the past. For example, viruses can cause evolution of their hosts, and the signatures of that evolution can be found and interpreted in the present day.[2] Also, viral genetic material that was integrated into another organism has been passed down to our time as a viral fossil.[2] Viral fossil is an informal term for regions of genomes that originate from ancient germline integration of viral genetic material. The scientific term for such regions is endogenous viral element or EVE.[3] EVEs that originate from the integration of retroviruses are known as endogenous retroviruses, or ERVs,[4] and most viral fossils are ERVs. They may be traced to millions of years back, hence the terminology, although strictly speaking, no one has detected a virus in fossils.[5] The most surprising viral fossils originate from non-retroviral DNA and RNA viruses.

Terminology[edit]

Although there is no formal classification system for EVEs, they are categorised according to the taxonomy of their viral origin. Indeed, all known viral genome types and replication strategies, as defined by the Baltimore classification, have been found in the genomic fossil record.[6][7] Acronyms have been designated to describe different types of viral fossil.

EVE: Endogenous viral element

NIRV: Non-retroviral Integrated RNA Virus

ERV: Endogenous retrovirus

HERV: Human Endogenous Retrovirus

Other viral fossils originate from DNA viruses such as hepadnaviruses (a group that includes hepatitis B).[8]

Viral fossils originating from non-retroviral RNA viruses have been termed Non-retroviral Integrated RNA Viruses or NIRVs.[9][10] Unlike other types of viral fossils, NIRV formation requires borrowing the integration machinery that is coded by the host genome or by a co-infecting retrovirus.

Resurrection[edit]

Successful attempts to "resurrect" extinct viruses from the DNA fossils have been reported.[11]

See also[edit]

References[edit]

  1. ^ Laidler J.R., Stedman K.M. "Virus Silicification under Simulated Hot Spring Conditions" "Astrobiology", August 2010, 10(6):569-576.' doi:10.1089/ast.2010.0463
  2. ^ a b Emerman M., Malik H.S. "Paleovirology — Modern Consequences of Ancient Viruses". PLoS Biology, 8(2)2010 doi:10.1371/journal.pbio.1000301
  3. ^ Katzourakis, Aris; Gifford, Robert J. (18 November 2010). "Endogenous Viral Elements in Animal Genomes". PLoS Genetics. 6 (11): e1001191. doi:10.1371/journal.pgen.1001191. PMC 2987831Freely accessible. PMID 21124940. 
  4. ^ Weiss, RA (Oct 3, 2006). "The discovery of endogenous retroviruses.". Retrovirology. 3: 67. doi:10.1186/1742-4690-3-67. PMC 1617120Freely accessible. PMID 17018135. 
  5. ^ Emerman M., Malik H.S. "Paleovirology — Modern Consequences of Ancient Viruses". PLoS Biology, 8(2)2010 doi:10.1371/journal.pbio.1000301
  6. ^ Pakorn Aiewsakun, Aris Katzourakis (2015). "Endogenous viruses: Connecting recent and ancient viral evolution". J.virol. 479-480: 26–37. doi:10.1016/j.virol.2015.02.011. 
  7. ^ Aris Katzourakis, Robert J. Gifford (2010). "Endogenous Viral Elements in Animal Genomes". PLoS Genet. 6: e1001191. doi:10.1371/journal.pgen.1001191. PMC 2987831Freely accessible. PMID 21124940. 
  8. ^ "Ancient "Fossil" Virus Shows Infection to Be Millions of Years Old", by Katherine Harmon, Scientific American, September 29, 2010
  9. ^ Taylor, D. J.; J. Bruenn (2009). "The evolution of novel fungal genes from non-retroviral RNA viruses". BMC Biology. 7: 88. doi:10.1186/1741-7007-7-88. 
  10. ^ Koonin, E. (2010). "Taming of the shrewd: novel eukaryotic genes from RNA viruses". BMC Biology. 8: 2. doi:10.1186/1741-7007-8-2. 
  11. ^ "How to Resurrect an Extinct Retrovirus", Scientific American, November 2, 2006