Tetrahymena thermophila | |
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Scientific classification ![]() | |
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]
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
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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
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
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]
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.
The species reproduces by asexual fission but it also engages in "conjugation", in which two cells come together and exchanged 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]
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]
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]
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.
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.
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.
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.
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.
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.
Neurospora crassa is a type of red bread mold of the phylum Ascomycota. The genus name, meaning 'nerve spore' in Greek, refers to the characteristic striations on the spores. The first published account of this fungus was from an infestation of French bakeries in 1843.
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.
Homologous recombination is a type of genetic recombination in which genetic information is exchanged between two similar or identical molecules of double-stranded or single-stranded nucleic acids.
Subtelomeres are segments of DNA between telomeric caps and chromatin.
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.
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.
Carolyn Widney Greider is an American molecular biologist and Nobel laureate. She joined the University of California, Santa Cruz as a Distinguished Professor in the department of molecular, cell, and developmental biology in October 2020.
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.
The ciliates are a group of alveolates characterized by the presence of hair-like organelles called cilia, which are identical in structure to eukaryotic flagella, but are in general shorter and present in much larger numbers, with a different undulating pattern than flagella. Cilia occur in all members of the group and are variously used in swimming, crawling, attachment, feeding, and sensation.
Chilodonella uncinata is a single-celled organism of the ciliate class of alveoles. As a ciliate, C. uncinata has cilia covering its body and a dual nuclear structure, the micronucleus and macronucleus. Unlike some other ciliates, C. uncinata contains millions of minichromosomes in its macronucleus while its micronucleus is estimated to contain 3 chromosomes. Childonella uncinata is the causative agent of Chilodonelloza, a disease that affects the gills and skin of fresh water fish, and may act as a facultative of mosquito larva.
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.
Colpidium colpoda are free-living ciliates commonly found in many freshwater environments including streams, rivers, lakes and ponds across the world. Colpidium colpoda is also frequently found inhabiting wastewater treatment plants. This species is used as an indicator of water quality and waste treatment plant performance.
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