Tetrahymena thermophila

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Tetrahymena thermophila
Tetrahymena thermophila.png
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Clade: Diaphoretickes
Clade: SAR
Clade: Alveolata
Phylum: Ciliophora
Class: Oligohymenophorea
Order: Hymenostomatida
Family: Tetrahymenidae
Genus: Tetrahymena
Species:
T. thermophila
Binomial name
Tetrahymena thermophila
Nanney & McCoy, 1976

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

Contents

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 helping to understand the mechanisms of function of certain genes. [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 at first considered to be a form of 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, which usually only have 2. [4] : 84 

Taxonomy

T. thermophila along with other Tetrahymena species were originally lumped together as a single species called Tetrahymena 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 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 has allowed 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 the expression of the gene for the DNA repair enzyme Rad51. [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 fission but it also engages in "conjugation", in which two cells come together and exchange gametes. Conjugation results in zygotes (one in each cell), and the zygotes go on to develop into the two separate nuclei of each cell, while the old nuclei are destroyed. [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 Tetrahymena cannot mate with its own type. 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 has been 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, a piece of RNA that can catalyze a reaction, in this case self-splice from a primary transcript without the help of proteins. [21] : 82  Cech later also 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] Later the cryo-EM structure of telomerase was first reported in T. thermophila, to be followed a few years later by the cryo-EM structure of telomerase in humans. [27]

The first report of Histone acetyltransferase (HAT) activity was reported in this species in the year 1995. [28] The first type A HAT was discovered in this species. [29]

Related Research Articles

<span class="mw-page-title-main">Meiosis</span> Cell division producing haploid gametes

Meiosis (; from Ancient Greek μείωσις 'lessening', is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, the sperm or egg cells. It involves two rounds of division that ultimately result in four cells, each with only one copy of each chromosome. Additionally, prior to the division, genetic material from the paternal and maternal copies of each chromosome is crossed over, creating new combinations of code on each chromosome. Later on, during fertilisation, the haploid cells produced by meiosis from a male and a female will fuse to create a zygote, a cell with two copies of each chromosome again.

<i>Caenorhabditis elegans</i> Free-living species of nematode

Caenorhabditis elegans is a free-living transparent nematode about 1 mm in length that lives in temperate soil environments. It is the type species of its genus. The name is a blend of the Greek caeno- (recent), rhabditis (rod-like) and Latin elegans (elegant). In 1900, Maupas initially named it Rhabditides elegans. Osche placed it in the subgenus Caenorhabditis in 1952, and in 1955, Dougherty raised Caenorhabditis to the status of genus.

<span class="mw-page-title-main">Chromosomal crossover</span> Cellular process

Chromosomal crossover, or crossing over, is the exchange of genetic material during sexual reproduction between two homologous chromosomes' non-sister chromatids that results in recombinant chromosomes. It is one of the final phases of genetic recombination, which occurs in the pachytene stage of prophase I of meiosis during a process called synapsis. Synapsis begins before the synaptonemal complex develops and is not completed until near the end of prophase I. Crossover usually occurs when matching regions on matching chromosomes break and then reconnect to the other chromosome.

<i>Tetrahymena</i> Genus of single-celled organisms

Tetrahymena is a genus of free-living ciliates, examples of unicellular eukaryotes. The genus Tetrahymena is the most widely studied member of its phylum. It can produce, store and react with different types of hormones. Tetrahymena cells can recognize both related and hostile cells.

<span class="mw-page-title-main">Genetic recombination</span> Production of offspring with combinations of traits that differ from those found in either parent

Genetic recombination is the exchange of genetic material between different organisms which leads to production of offspring with combinations of traits that differ from those found in either parent. In eukaryotes, genetic recombination during meiosis can lead to a novel set of genetic information that can be further passed on from parents to offspring. Most recombination occurs naturally and can be classified into two types: (1) interchromosomal recombination, occurring through independent assortment of alleles whose loci are on different but homologous chromosomes ; & (2) intrachromosomal recombination, occurring through crossing over.

<span class="mw-page-title-main">Telomerase</span> Telomere-restoring protein active in the most rapidly dividing cells

Telomerase, also called terminal transferase, is a ribonucleoprotein that adds a species-dependent telomere repeat sequence to the 3' end of telomeres. A telomere is a region of repetitive sequences at each end of the chromosomes of most eukaryotes. Telomeres protect the end of the chromosome from DNA damage or from fusion with neighbouring chromosomes. The fruit fly Drosophila melanogaster lacks telomerase, but instead uses retrotransposons to maintain telomeres.

The ribosomal DNA consists of a group of ribosomal RNA encoding genes and related regulatory elements, and is widespread in similar configuration in all domains of life. The ribosomal DNA encodes the non-coding ribosomal RNA, integral structural elements in the assembly of ribosomes, it's importance making it the most abundant section of RNA found in cells of eukaryotes. Additionally, these segments includes regulatory sections, such as an promotor specific to the RNA polymerase I, as well as both transcribed and non-transcribed spacer segments.

<span class="mw-page-title-main">Synaptonemal complex</span> Protein structure

The synaptonemal complex (SC) is a protein structure that forms between homologous chromosomes during meiosis and is thought to mediate synapsis and recombination during prophase I during meiosis in eukaryotes. It is currently thought that the SC functions primarily as a scaffold to allow interacting chromatids to complete their crossover activities.

<span class="mw-page-title-main">Homologous recombination</span> Genetic recombination between identical or highly similar strands of genetic material

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Subtelomeres are segments of DNA between telomeric caps and chromatin.

<span class="mw-page-title-main">Nuclear dimorphism</span>

Nuclear dimorphism is a term referred to the special characteristic of having two different kinds of nuclei in a cell. There are many differences between the types of nuclei. This feature is observed in protozoan ciliates, like Tetrahymena, and some foraminifera. Ciliates contain two nucleus types: a macronucleus that is primarily used to control metabolism, and a micronucleus which performs reproductive functions and generates the macronucleus. The compositions of the nuclear pore complexes help determine the properties of the macronucleus and micronucleus. Nuclear dimorphism is subject to complex epigenetic controls. Nuclear dimorphism is continuously being studied to understand exactly how the mechanism works and how it is beneficial to cells. Learning about nuclear dimorphism is beneficial to understanding old eukaryotic mechanisms that have been preserved within these unicellular organisms but did not evolve into multicellular eukaryotes.

<span class="mw-page-title-main">Holliday junction</span> Branched nucleic acid structure

A Holliday junction is a branched nucleic acid structure that contains four double-stranded arms joined. These arms may adopt one of several conformations depending on buffer salt concentrations and the sequence of nucleobases closest to the junction. The structure is named after Robin Holliday, the molecular biologist who proposed its existence in 1964.

Microbial genetics is a subject area within microbiology and genetic engineering. Microbial genetics studies microorganisms for different purposes. The microorganisms that are observed are bacteria and archaea. Some fungi and protozoa are also subjects used to study in this field. The studies of microorganisms involve studies of genotype and expression system. Genotypes are the inherited compositions of an organism. Genetic Engineering is a field of work and study within microbial genetics. The usage of recombinant DNA technology is a process of this work. The process involves creating recombinant DNA molecules through manipulating a DNA sequence. That DNA created is then in contact with a host organism. Cloning is also an example of genetic engineering.

<span class="mw-page-title-main">Carol W. Greider</span> American molecular biologist and Nobel laureate

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<span class="mw-page-title-main">Telomerase RNA component</span> NcRNA found in eukaryotes

Telomerase RNA component, also known as TR, TER or TERC, is an ncRNA found in eukaryotes that is a component of telomerase, the enzyme used to extend telomeres. TERC serves as a template for telomere replication by telomerase. Telomerase RNAs differ greatly in sequence and structure between vertebrates, ciliates and yeasts, but they share a 5' pseudoknot structure close to the template sequence. The vertebrate telomerase RNAs have a 3' H/ACA snoRNA-like domain.

<span class="mw-page-title-main">Ciliate</span> Taxon of protozoans with hair-like organelles called cilia

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<span class="mw-page-title-main">Synthesis-dependent strand annealing</span>

Synthesis-dependent strand annealing (SDSA) is a major mechanism of homology-directed repair of DNA double-strand breaks (DSBs). Although many of the features of SDSA were first suggested in 1976, the double-Holliday junction model proposed in 1983 was favored by many researchers. In 1994, studies of double-strand gap repair in Drosophila were found to be incompatible with the double-Holliday junction model, leading researchers to propose a model they called synthesis-dependent strand annealing. Subsequent studies of meiotic recombination in S. cerevisiae found that non-crossover products appear earlier than double-Holliday junctions or crossover products, challenging the previous notion that both crossover and non-crossover products are produced by double-Holliday junctions and leading the authors to propose that non-crossover products are generated through SDSA.

<span class="mw-page-title-main">R-loop</span> Three-stranded nucleic acid structure

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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. 1 2 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. 1 2 3 4 Tetrahymena Thermophila. Academic Press. 2012-10-22. ISBN   978-0-12-385968-6.
  5. 1 2 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. 1 2 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. 1 2 3 Reeve, Eric C. R. (2014-01-14). Encyclopedia of Genetics. Routledge. ISBN   978-1-134-26357-8.
  9. 1 2 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. 1 2 3 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. 1 2 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. 1 2 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. 1 2 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. Vol. 9. Royal Society of Chemistry. pp. vii–ix. doi:10.1039/9781849732512-FP007. ISBN   978-1-84973-094-5. PMID   22010266.{{cite book}}: |journal= ignored (help)
  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. ↑ Wang Y, Sušac L, Feigon J (2019). "Structural Biology of Telomerase". Cold Spring Harbor Perspectives in Biology . 11 (12): a032383. doi:10.1101/cshperspect.a032383. PMC   6886448 . PMID   31451513.
  28. ↑ 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.
  29. ↑ Proteins in Eukaryotic Transcription. Elsevier. 2004-03-19. p. 182. ISBN   978-0-08-052241-8.
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