Eocyte hypothesis

Karyota
Ignicoccus hospitalis (and its symbiote Nanoarchaeum equitans)
Scientific classification
Domain: Archaea or Arkarya
(unranked): Karyota
Lake et al. 1988[1]
Domain & Regnum
Synonyms
  • proto-eukaryotic group
  • Karyotes

The Eocyte hypothesis is a biological classification that indicates eukaryotes emerged within the prokaryotic Crenarchaeota (formerly known as eocytes), a phylum within the archaea. This hypothesis was originally proposed by James A. Lake and colleagues in 1984 based on the discovery that the shapes of ribosomes in the Crenarchaeota and eukaryotes are more similar to each other than to either bacteria or the second major kingdom of archaea, the Euryarchaeota.[2][3]

The eocyte hypothesis gained considerable attention after its introduction due to the interest in determining the origin of the eukaryotic cell. This hypothesis has primarily been in contrast with the three-domain system introduced by Carl Woese in 1977. Additional evidence supporting the eocyte hypothesis was published in the 1980s, but despite fairly unequivocal evidence, support waned in favor of the three-domain system.[1][2]

With advancements in genomics, the eocyte hypothesis experienced a revival beginning in the mid-2000s. As more archaeal genomes were sequenced, numerous genes coding for eukaryotic traits have been discovered in various archaean phyla, seemingly providing support for the eocyte hypothesis. In addition to a Crenarchaeal origin of eukaryotes, some studies have suggested that eukaryotes may also have originated in the Thaumarchaeota.[2][4][5][6][7] A superphylum - TACK - has been proposed that includes the Thaumarchaeota, Crenarchaeota, and other groups of archaea[8], so that this superphylum may be related to the origin of eukaryotes.

As a result of metagenomic analysis of material found nearby hydrothermal vents, another superphylum -- Asgard -- has been named and proposed to be more closely related to the original eukaryote and a sister group to TACK more recently.[9] The eocyte tree root may be located in the RNA World, that is the root organism may have been a Ribocyte (aka Ribocell). For cellular DNA and DNA handling an "out of virus" scenario has been proposed, i. e. string genetic information in DNA may have been an invention performed by viruses later handed over to Ribocytes twice, once transforming them into bacteria and once transforming them into archaea.[10][11] All these findings do not change the eocyte tree as given here in principle, but zoom into a higher resolution of it.

Eocyte hypothesis

References

  1. 1 2 Lake, James A. (1988). "Origin of the eukaryotic nucleus determined by rate-invariant analysis of rRNA sequences". Nature. 331 (6152): 184–186. Bibcode:1988Natur.331..184L. doi:10.1038/331184a0. PMID 3340165.
  2. 1 2 3 Archibald, John M. (23 December 2008). "The eocyte hypothesis and the origin of eukaryotic cells". PNAS. 105 (51): 20049–20050. Bibcode:2008PNAS..10520049A. doi:10.1073/pnas.0811118106. PMC 2629348. Retrieved 5 October 2012.
  3. ↑ Lake, James A.; Henderson, Eric; Oakes, Melanie; Clark, Michael W. (June 1984). "Eocytes: A new ribosome structure indicates a kingdom with a close relationship to eukaryotes". PNAS. 81 (12): 3786–3790. Bibcode:1984PNAS...81.3786L. doi:10.1073/pnas.81.12.3786. PMC 345305. PMID 6587394. Retrieved 5 October 2012.
  4. ↑ Kelly, S.; Wickstead, B.; Gull, K. (2011). "Archaeal phylogenomics provides evidence in support of a methanogenic origin of the Archaea and a thaumarchaeal origin for the eukaryotes" (PDF). Proceedings of the Royal Society B. 278: 1009–1018. doi:10.1098/rspb.2010.1427. PMC 3049024. PMID 20880885. Retrieved 5 October 2012.
  5. ↑ Poole, Anthony M.; Neumann, Nadja (2011). "Reconciling an archaeal origin of eukaryotes with engulfment: a biologically plausible update of the Eocyte hypothesis" (PDF). Research in Microbiology. 162: 71–76. doi:10.1016/j.resmic.2010.10.002. Retrieved 5 October 2012.
  6. ↑ Guy, Lionel; Ettema, Thijs J. G. (December 2011). "The archaeal 'TACK' superphylum and the origin of eukaryotes". Trends in Microbiology. 19 (12): 580–587. doi:10.1016/j.tim.2011.09.002. PMID 22018741. Retrieved 5 October 2012.
  7. ↑ Cox, Cymon J.; Foster, Peter G.; Hirt, Robert P.; Harris, Simon R.; Embley, T. Martin (23 December 2008). "The archaebacterial origin of eukaryotes". PNAS. 105: 20356–20361. Bibcode:2008PNAS..10520356C. doi:10.1073/pnas.0810647105. PMC 2629343. PMID 19073919. Retrieved 5 October 2012.
  8. ↑ Guy, L.; Ettema, T.J. (19 December 2011). "The archaeal 'TACK' superphylum and the origin of eukaryotes". Trends Microbiol. 19 (12): 580–587. doi:10.1016/j.tim.2011.09.002. PMID 22018741.
  9. ↑ Zaremba-Niedzwiedzka, K; et al. (2017). "Asgard archaea illuminate the origin of eukaryotic cellular complexity". Nature. 541: 353–358. Bibcode:2017Natur.541..353Z. doi:10.1038/nature21031.
  10. ↑ P. Forterre, M. Krupovic: The Origin of Virions and Virocells: The Escape Hypothesis Revisited. In: G. Witzany (Ed.): Viruses: Essential Agents of Life, Seite 43-60, Springer Link, September 25, 2012. ISBN 978-94-007-4898-9 (Print) 978-94-007-4899-6 (Online), DOI 10.1007/978-94-007-4899-6
  11. ↑ Patrick Forterre: Evolution - Die wahre Natur der Viren, in: Spektrum August 2017, S. 37 (Online-Artikel vom 19. Juli 2017) (German)


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