Tetrahymena thermophila

Tetrahymena thermophila is a species of Ciliophora in the family Tetrahymenidae.[1] It is a free living protozoa and occurs in fresh water.[2]

Tetrahymena thermophila
Scientific classification
Kingdom: Chromista
Superphylum: Alveolata
Phylum: Ciliophora
Class: Oligohymenophorea
Order: Hymenostomatida
Family: Tetrahymenidae
Genus: Tetrahymena
Species:
T. thermophila
Binomial name
Tetrahymena thermophila
Nanney & McCoy, 1976

There is little information on the ecology and natural history of this species,[3] but it is the most widely known and widely studied species in the genus Tetrahymena.[4]: 12  The species has been used as a model organism for molecular and cellular biology.[5] It has also helped in the discovery of new genes as well as help to understand the mechanisms of certain genes functions.[6] Studies on this species have contributed to major discoveries in biology.[5]

For example, the MAT locus found in this species has provided a foundation for the evolution of mating systems.[7]: 6–7 

The species was first considered to be Tetrahymena pyriformis.[8]: 258  T. malaccensis is the closest relative toT. thermophila.[4]: 284 

Characteristics

It is about 50 μm long. One famous trait this species is known for is that has 7 different mating types, unlike most eukaryotic organisms, who usually only have 2.[4]: 84 

Taxonomy

T. thermophila along with other Tetrahymena species were originally lumped together as a single species called T. pyriformis. With T. thermophila first being called T. pyriformis variety 1 and then T. pyriformis syngen 1.[6] It was later renamed to T. thermophila in 1974.[9]: 4 

Genetics

Tetrahymena thermophila has a large genome with about 200 million nucleotides[10]: 181  and 27 thousand genes in its nuclear genome.[11]

It also exhibits nuclear dimorphism: two types of cell nuclei. They have a bigger, non-germline macronucleus and a small, germline micronucleus in each cell at the same time and these two carry out different functions with distinct cytological and biological properties. This unique versatility allows scientists to use Tetrahymena to identify several key factors regarding gene expression and genome integrity. In addition, Tetrahymena possess hundreds of cilia and has complicated microtubule structures, making it an optimal model to illustrate the diversity and functions of microtubule arrays.[12]

DNA repair

When T. thermophila is exposed to UV light it results in a greater than 100-fold increase in Rad51 gene expression.[13] Treatment with the DNA alkylating agent methyl methanesulfonate also resulted in substantially elevated Rad 51 protein levels. These findings suggest that ciliates such as T. thermophila utilize a Rad51-dependent recombinational pathway to repair damaged DNA.

The Rad51 recombinase of T. thermophila is a homolog of the Escherichia coli RecA recombinase. In T. thermophila, Rad51 participates in homologous recombination during mitosis, meiosis and in the repair of double-strand breaks.[14] During conjugation, Rad51 is necessary for completion of meiosis. Meiosis in T. thermophila appears to employ a Mus81-dependent pathway that does not use a synaptonemal complex and is considered secondary in most other model eukaryotes.[15] This pathway includes the Mus81 resolvase and the Sgs1 helicase. The Sgs1 helicase appears to promote the non-crossover outcome of meiotic recombinational repair of DNA,[16] a pathway that generates little genetic variation.

Reproduction

The species reproduces by asexual reproduction with binary fission and conjugation.[17] In nature the species is an outbreeder.[8]: 259 

Tetrahymena thermophila has 7 mating types determined by a single locus with various alleles.[18]: 361  The mating types are named I, II, III, IV, V, VI and VII.[19]

The mating types can reproduce in 21 different combinations, and a single Tetrahymena cannot reproduce sexually with itself. Each organism "decides" which sex it will become during mating, through a stochastic process.[12]

Occurrence

The species lives in freshwater.[17] It usually lives in streams, ponds, and lakes.[8]: 258 

The phylogeography of the species is fairly unexplored, it has been observed along the eastern coast of the United States. But it has not been observed in other continents[3] with it currently only being reported in North America.[4]: 280  However it is said to have an occurrence across the world.[19]

History

Since the 1930s it has been known that the species has 7 mating types.[20]

Immobilized antigens were found in this species were first explored by workers in Ray Owen’s lab.[9]: 14 

In 1953, the MAT locus in this species was first described by David L. Nanney.[12]

In 1982, the group 1 intron was discovered located in the rRNA transcript of this species[21]: 82  by Thomas Cech and his coworks.[22]: 205  This was considered the first ribozyme that can self-splice from a primary transcript without the help of proteins.[21]: 82  Cech also later on discovered enzymatic RNA in this species.[23]

Telomerase and telomeres were first discovered in this species as well[24] by Elizabeth Blackburn and Carol Greider.[25][26]

The first report of HAT activity was reported in this species in the year 1995.[27] As well as the first type A HAT was discovered in this species.[28]

References
  1. "Tetrahymena thermophila" at the Encyclopedia of Life
  2. "Points to Address in a White Paper". www.lifesci.ucsb.edu. Retrieved 2021-10-14.
  3. Katz, Laura A.; Snoeyenbos-West, Oona; Doerder, F. Paul (2006-03-01). "Patterns of Protein Evolution in Tetrahymena thermophila: Implications for Estimates of Effective Population Size". Molecular Biology and Evolution. 23 (3): 608–614. doi:10.1093/molbev/msj067. ISSN 0737-4038. PMID 16308338.
  4. Tetrahymena Thermophila. Academic Press. 2012-10-22. ISBN 978-0-12-385968-6.
  5. Eisen, Jonathan A.; Coyne, Robert S.; Wu, Martin; Wu, Dongying; Thiagarajan, Mathangi; Wortman, Jennifer R.; Badger, Jonathan H.; Ren, Qinghu; Amedeo, Paolo; Jones, Kristie M.; Tallon, Luke J. (2006-08-29). "Macronuclear Genome Sequence of the Ciliate Tetrahymena thermophila, a Model Eukaryote". PLOS Biology. 4 (9): e286. doi:10.1371/journal.pbio.0040286. ISSN 1545-7885. PMC 1557398. PMID 16933976.
  6. Ruehle, Marisa D.; Orias, Eduardo; Pearson, Chad G. (June 2016). "Tetrahymena as a Unicellular Model Eukaryote: Genetic and Genomic Tools". Genetics. 203 (2): 649–665. doi:10.1534/genetics.114.169748. ISSN 0016-6731. PMC 4896184. PMID 27270699.
  7. Druzhinina, Irina S.; Kubicek, Christian P. (2016-03-18). Environmental and Microbial Relationships. Springer. ISBN 978-3-319-29532-9.
  8. Reeve, Eric C. R. (2014-01-14). Encyclopedia of Genetics. Routledge. ISBN 978-1-134-26357-8.
  9. Tetrahymena Thermophila. Academic Press. 1999-09-08. ISBN 978-0-08-052495-5.
  10. Johnson, Norman A. (2007-07-06). Darwinian Detectives: Revealing the Natural History of Genes and Genomes. Oxford University Press. ISBN 978-0-19-804189-4.
  11. Rogers, Scott Orland (2016-09-15). Integrated Molecular Evolution. CRC Press. ISBN 978-1-4822-3092-5.
  12. Cervantes MD, Hamilton EP, Xiong J, Lawson MJ, Yuan D, Hadjithomas M, et al. (2013). "Selecting one of several mating types through gene segment joining and deletion in Tetrahymena thermophila". PLOS Biology. 11 (3): e1001518. doi:10.1371/journal.pbio.1001518. PMC 3608545. PMID 23555191.
  13. Campbell C, Romero DP (July 1998). "Identification and characterization of the RAD51 gene from the ciliate Tetrahymena thermophila". Nucleic Acids Research. 26 (13): 3165–72. doi:10.1093/nar/26.13.3165. PMC 147671. PMID 9628914.
  14. Marsh TC, Cole ES, Stuart KR, Campbell C, Romero DP (April 2000). "RAD51 is required for propagation of the germinal nucleus in Tetrahymena thermophila". Genetics. 154 (4): 1587–96. doi:10.1093/genetics/154.4.1587. PMC 1461009. PMID 10747055.
  15. Chi J, Mahé F, Loidl J, Logsdon J, Dunthorn M (March 2014). "Meiosis gene inventory of four ciliates reveals the prevalence of a synaptonemal complex-independent crossover pathway". Molecular Biology and Evolution. 31 (3): 660–72. doi:10.1093/molbev/mst258. PMID 24336924.
  16. Lukaszewicz A, Howard-Till RA, Loidl J (November 2013). "Mus81 nuclease and Sgs1 helicase are essential for meiotic recombination in a protist lacking a synaptonemal complex". Nucleic Acids Research. 41 (20): 9296–309. doi:10.1093/nar/gkt703. PMC 3814389. PMID 23935123.
  17. Orias, Eduardo; Cervantes, Marcella D.; Hamilton, Eileen P. (2011). "Tetrahymena thermophila, a unicellular eukaryote with separate germline and somatic genomes". Research in Microbiology. 162 (6): 578–586. doi:10.1016/j.resmic.2011.05.001. ISSN 0923-2508. PMC 3132220. PMID 21624459.
  18. Chandler, Michael; Gellert, Martin; Lambowitz, Alan M.; Rice, Phoebe A.; Sandmeyer, Suzanne B. (2020-07-24). Mobile DNA III. John Wiley & Sons. ISBN 978-1-55581-921-7.
  19. Marshall, Michael. "Zoologger: The hairy beast with seven fuzzy sexes". New Scientist. Retrieved 2021-10-13.
  20. Quirk, Trevor (2013-03-27). "How a microbe chooses among seven sexes". Nature. doi:10.1038/nature.2013.12684. ISSN 1476-4687. S2CID 179307103.
  21. Teplow, David B. (2018-10-16). Progress in Molecular Biology and Translational Science. Academic Press. ISBN 978-0-12-816236-1.
  22. Sigel, Astrid; Sigel, Helmut; Sigel, Roland K. O. (2011). Structural and Catalytic Roles of Metal Ions in RNA. Metal Ions in Life Sciences. Vol. 9. Royal Society of Chemistry. pp. vii–ix. doi:10.1039/9781849732512-FP007. ISBN 978-1-84973-094-5. PMID 22010266.
  23. Jurga, Stefan; Barciszewski, Jan (2020-10-01). The Chemical Biology of Long Noncoding RNAs. Springer Nature. p. 132. ISBN 978-3-030-44743-4.
  24. Bucala, Richard; Lee, Patty J. (2015-12-08). The Aging Lungs: Mechanisms and Clinical Sequelae. World Scientific. p. 432. ISBN 978-981-4635-01-1.
  25. Corey, David R. (2009-12-24). "Telomeres and Telomerase: From Discovery to Clinical Trials". Chemistry & Biology. 16 (12): 1219–1223. doi:10.1016/j.chembiol.2009.12.001. ISSN 1074-5521. PMC 2810624. PMID 20064431.
  26. Chadwick, Derek J.; Cardew, Gail (2008-04-30). Telomeres and Telomerase. John Wiley & Sons. p. 20. ISBN 978-0-470-51544-0.
  27. Vidal, Cecilio J. (2010-10-13). Post-Translational Modifications in Health and Disease. Springer Science & Business Media. p. 372. ISBN 978-1-4419-6382-6.
  28. Proteins in Eukaryotic Transcription. Elsevier. 2004-03-19. p. 182. ISBN 978-0-08-052241-8.
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