Biology:Last eukaryotic common ancestor

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Reconstruction of LECA.[1] Key:
1) Nucleus with nucleolus and eu/heterochromatin
2) Endoplasmic reticulum
3) Peroxisome
4) Endo/lysosome, ESCRT system
5) Golgi apparatus
6) Endo/exocytosis, actin-based
7) Pseudo/Filopodium
8) Sterol-based membrane; G3P + ester bond phospholipids
9) Microtubule-based cytoskeleton and organising centre
10) Basal bodies
11) Vacuoles
12) Iron-sulphur cluster biosynthesis via the CIA system
13) Mitochondria
14) Flagella, microtubule-based

The last eukaryotic common ancestor (LECA) is the hypothetical most recent common ancestor of all living eukaryotes – organisms whose cells have a nucleus, around 2 billion years ago. The process by which the LECA came into being, eukaryogenesis, is not understood in detail, but is thought to have involved symbiogenesis, the coming together of an archaean and a bacterium which formed the cell's mitochondria.

The LECA's structure and function have been reconstructed by comparing the genomes of modern eukaryotes. This has led biologists to propose that the LECA was a complex cell with a nucleus with a nucleolus and eu/heterochromatin, an endoplasmic reticulum, peroxisomes, endo- and lysosomes, the ESCRT system, a Golgi apparatus, actin-based endo- and exocytosis, pseudopodia or filopodia, sterol-based membranes, G3P + ester bond phospholipids, a microtubule-based cytoskeleton with an organising centre, basal bodies, vacuoles, iron-sulphur cluster biosynthesis via the CIA system, mitochondria, and microtubule-based flagella.

Context

Life arose on Earth once it had cooled enough for oceans to form. That developed into the last universal common ancestor (LUCA), an organism which had ribosomes and the genetic code, some 3.5-4 billion years ago. It gave rise to two domains of life, the bacteria and the archaea. From among these small-celled ancestors arose the eukaryotes, with a much wider range of cell sizes, and more complex cells with nuclei, a cytoskeleton, and an endomembrane system.[2][3] The eukaryotes form a third domain that contains all complex cells and most types of multicellular organisms, including the animals, plants, and fungi.[4][5]

The last eukaryotic common ancestor (LECA) is the hypothetical most recent common ancestor of all living eukaryotes, around 2 billion years ago,[4][5] and was most likely a biological population.[6]

It is not known how the bacteria and archaea gave rise to the LECA (and hence to all later eukaryotes) in the process of eukaryogenesis, as the fossil record of ancient single-celled organisms is fragmentary. Instead biologists have focused on reconstructing the properties of the LECA from what is known of the genomes of different lineages of modern eukaryotes.[1]

Structure and function

Organelles

It is believed, on the basis of study of the genomes of different lineages of modern eukaryotes, to have been a single cell with a nucleus, at least one centriole and cilium, facultatively aerobic mitochondria, sex (meiosis and syngamy), a dormant cyst with a cell wall of chitin or cellulose, and peroxisomes.[1][7][8] All of these features are unique to the eukaryotes. Some modern eukaryotes such as myxomycetes are syncitial, with multiple nuclei: this has been suggested as a feature of the LECA.[9]

It has been proposed that the LECA fed by phagocytosis, engulfing other organisms,[7][8] though this has been disputed.[10] The LECA has been described as having "spectacular cellular complexity".[11] Its cell was divided into compartments such as the Golgi apparatus, the endoplasmic reticulum, and the nuclear envelope.[11] It appears to have inherited a set of endosomal sorting complex proteins that enable membranes to be remodelled, including pinching off vesicles to form endosomes.[12]

Genetic mechanisms

In eukaryotes, unlike in prokaryotes, the mechanisms for transcribing DNA into RNA, and then for translating the RNA into proteins, were separated, permitting extensive RNA processing and allowing the expression of genes to become more complex.[13] It had mechanisms for reshuffling its genetic material, and possibly for manipulating its own evolvability. All of these gave the LECA "a compelling cohort of selective advantages".[11]

Eukaryotic sex

Sex in eukaryotes is a composite process, consisting of meiosis and fertilisation, which can be coupled to reproduction.[14] Dacks and Roger proposed on the basis of a phylogenetic analysis that facultative sex was likely present in the common ancestor of all eukaryotes.[15][16] Early in eukaryotic evolution, about 2 billion years ago, organisms needed a solution to the major problem that oxidative metabolism releases reactive oxygen species that damage the genetic material, DNA.[14] Eukaryotic sex provides a process, homologous recombination during meiosis, for using informational redundancy to repair such DNA damage.[14]

Response to injury

Since several immune mechanisms involved in the response to injury are widely shared among modern eukaryotes, it has been suggested that they were present in the LECA. These mechanisms include receptors, calcium signalling, reactive oxygen species, adenosine triphosphate release, kinase cascades, and oxylipin signalling.[17][18] Single-celled eukaryotes, such as choanoflagellates, substantially share the pathways found in plants and animals for detecting damage and pathogens.[19] Extracellular adenosine triphosphate is a signal that promotes healing of wounds to the epithelium in animals. The signal is detected by a P2X receptor.[18]

Thibaut Brunet and Detlev Arendt propose that the LECA possessed a calcium-based wound healing response. They argue that the mechanism's purpose was to detect and heal a potentially fatal opening in the cell membrane. They propose that it worked by detecting an inflow of calcium ions, which provoked a contraction in muscle-like actomyosin proteins. This in turn caused vesicles to fuse with the cell membrane (exocytosis), healing the opening and preventing the cell from splitting open.[20]

  • How the last eukaryotic common ancestor may have detected and repaired a hole in its membrane[21]

References

  1. ↑ 1.0 1.1 1.2 Richards, Thomas A.; Eme, Laura; Archibald, John M.; Leonard, Guy; Coelho, Susana M. et al. (25 November 2024). "Reconstructing the last common ancestor of all eukaryotes". PLOS Biology 22 (11). doi:10.1371/journal.pbio.3002917. PMID 39585925. 
  2. ↑ McGrath, Casey (31 May 2022). "Highlight: Unraveling the Origins of LUCA and LECA on the Tree of Life". Genome Biology and Evolution 14 (6). doi:10.1093/gbe/evac072. 
  3. ↑ Weiss, Madeline C.; Sousa, F. L.; Mrnjavac, N. et al. (2016). "The physiology and habitat of the last universal common ancestor". Nature Microbiology 1 (9): 16116. doi:10.1038/nmicrobiol.2016.116. PMID 27562259. http://complexityexplorer.s3.amazonaws.com/supplemental_materials/3.6+Early+Metabolisms/Weiss_et_al_Nat_Microbiol_2016.pdf. 
  4. ↑ 4.0 4.1 Gabaldón, T. (October 2021). "Origin and Early Evolution of the Eukaryotic Cell". Annual Review of Microbiology 75 (1): 631–647. doi:10.1146/annurev-micro-090817-062213. PMID 34343017. 
  5. ↑ 5.0 5.1 Woese, C. R.; Kandler, Otto; Wheelis, Mark L. (June 1990). "Towards a natural system of organisms: proposal for the domains Archaea, Bacteria, and Eucarya". Proceedings of the National Academy of Sciences 87 (12): 4576–4579. doi:10.1073/pnas.87.12.4576. PMID 2112744. Bibcode: 1990PNAS...87.4576W. 
  6. ↑ O'Malley, Maureen A.; Leger, Michelle M.; Wideman, Jeremy G.; Ruiz-Trillo, Iñaki (18 February 2019). "Concepts of the last eukaryotic common ancestor". Nature Ecology & Evolution 3 (3): 338–344. doi:10.1038/s41559-019-0796-3. PMID 30778187. Bibcode: 2019NatEE...3..338O. 
  7. ↑ 7.0 7.1 Leander, B. S. (May 2020). "Predatory protists". Current Biology 30 (10): R510–R516. doi:10.1016/j.cub.2020.03.052. PMID 32428491. Bibcode: 2020CBio...30.R510L. 
  8. ↑ 8.0 8.1 Strassert, Jürgen F. H.; Irisarri, Iker; Williams, Tom A.; Burki, Fabien (25 March 2021). "A molecular timescale for eukaryote evolution with implications for the origin of red algal-derived plastids". Nature Communications 12 (1): 1879. doi:10.1038/s41467-021-22044-z. PMID 33767194. Bibcode: 2021NatCo..12.1879S. 
  9. ↑ Skejo, Josip (2022). Reconstruction of the Last Eukaryotic Common Ancestor by cladistic and phylogenetic approach. University of Zagreb (PhD thesis). https://repozitorij.pmf.unizg.hr/object/pmf:11310. 
  10. ↑ Bremer, Nico; Tria, Fernando D. K.; Skejo, Josip; Garg, Sriram G.; Martin, William F. (31 May 2022). "Ancestral State Reconstructions Trace Mitochondria But Not Phagocytosis to the Last Eukaryotic Common Ancestor". Genome Biology and Evolution 14 (6). doi:10.1093/gbe/evac079. PMID 35642316. 
  11. ↑ 11.0 11.1 11.2 Koumandou, V. Lila; Wickstead, Bill; Ginger, Michael L.; van der Giezen, Mark; Dacks, Joel B.; Field, Mark C. (2013). "Molecular paleontology and complexity in the last eukaryotic common ancestor". Critical Reviews in Biochemistry and Molecular Biology 48 (4): 373–396. doi:10.3109/10409238.2013.821444. PMID 23895660. 
  12. ↑ Makarova, Kira S.; Yutin, Natalya; Bell, Stephen D.; Koonin, Eugene V. (6 September 2010). "Evolution of diverse cell division and vesicle formation systems in Archaea". Nature Reviews Microbiology 8 (10): 731–741. doi:10.1038/nrmicro2406. PMID 20818414. 
  13. ↑ Martin, William; Koonin, Eugene V. (2006). "Introns and the origin of nucleus–cytosol compartmentalization". Nature 440 (7080): 41–45. doi:10.1038/nature04531. PMID 16511485. Bibcode: 2006Natur.440...41M. 
  14. ↑ 14.0 14.1 14.2 Horandl, E.; Speijer, D. (7 February 2018). "How oxygen gave rise to eukaryotic sex". Proceedings of the Royal Society B: Biological Sciences 285 (1872). doi:10.1098/rspb.2017.2706. PMID 29436502. Bibcode: 2018RSPSB.28572706H. 
  15. ↑ Dacks, J.; Roger, A. J. (1999). "The first sexual lineage and the relevance of facultative sex". Journal of Molecular Evolution 48 (6): 779–783. doi:10.1007/pl00013156. PMID 10229582. Bibcode: 1999JMolE..48..779D. 
  16. ↑ "Attraction and sex among our microbial Last Eukaryotic Common Ancestors". The Atlantic. 11 November 2020. https://www.theatlantic.com/science/archive/2020/11/how-do-single-celled-organisms-have-sex/617072/. 
  17. ↑ Hernández-Oñate, M. A.; Herrera-Estrella, A. (2015). "Damage response involves mechanisms conserved across plants, animals and fungi". Current Genetics 61 (3): 359–372. doi:10.1007/s00294-014-0467-5. PMID 25572693. 
  18. ↑ 18.0 18.1 Lee, Elizabeth E. L.; O'Malley-Krohn, Isabel; Edsinger, Eric; Wu, Stephanie; Malamy, Jocelyn (1 November 2023). "Epithelial wound healing in Clytia hemisphaerica provides insights into extracellular ATP signaling mechanisms and P2XR evolution". Scientific Reports 13 (1). doi:10.1038/s41598-023-45424-5. PMID 37914720. Bibcode: 2023NatSR..1318819L. "these organisms [cnidarians] can reveal the evolutionary origin of wound healing mechanisms and likely identify mechanisms that are conserved across the tree of life.". 
  19. ↑ Rennolds, Corey W.; Bely, Alexandra E. (29 September 2022). "Integrative biology of injury in animals". Biological Reviews 98 (1): 34–62. doi:10.1111/brv.12894. PMID 36176189. 
  20. ↑ Brunet, Thibaut; Arendt, Detlev (5 January 2016). "From damage response to action potentials: early evolution of neural and contractile modules in stem eukaryotes". Philosophical Transactions of the Royal Society B 371 (371 (1685)). doi:10.1098/rstb.2015.0043. 20150043. PMID 26598726. 
  21. ↑ Brunet & Arendt 2016.



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