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''Tetrahymena'' are free-living ciliate protozoa that can also switch from commensalistic to pathogenic modes of survival. They are common in freshwater ponds. ''Tetrahymena'' species used as model organisms in biomedical research are ''T. thermophila'' and ''T. pyriformis''. == ''T. thermophila'': a model organism in experimental biology == As a ciliated protozoan, ''Tetrahymena thermophila'' 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 they both 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. Because ''Tetrahymena'' can be grown in a large quantity in the laboratory with ease, it has been a great source for biochemical analysis for years, specifically for enzymatic activities and purification of sub-cellular components. In addition, with the advancement of genetic techniques it has become an excellent model to study the gene function ''in vivo''. The recent sequencing of the macronucleus genome should ensure that ''Tetrahymena'' will be continuously used as a model system. ''Tetrahymena thermophila'' exists in 7 different sexes (mating types) that 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. Studies on ''Tetrahymena'' have contributed to several scientific milestones including: # First cell which showed synchronized division, which led to the first insights into the existence of mechanisms which control the cell cycle.〔(Tetrahymena Genome Sequencing White Paper )〕 # Identification and purification of the first cytoskeleton based motor protein such as ''dynein''.〔 # Aid in the discovery of ''lysosomes'' and ''peroxisomes''.〔 # Early molecular identification of somatic genome rearrangement.〔 # Discovery of the molecular structure of ''telomeres'', ''telomerase'' enzyme, the templating role of telomerase RNA and their roles in cellular senescence and chromosome healing (for which a Nobel Prize was won).〔 # Nobel Prize–winning co-discovery (1989, in Chemistry) of catalytic ribonucleic acid (''ribozyme'').〔 # Discovery of the function of histone acetylation.〔 # Demonstration of the roles of posttranslational modification such as acetylation and glycylation on tubulins and discovery of the enzymes responsible for some of these modifications (glutamylation) # Crystal structure of 40S ribosome in complex with its initiation factor eIF1 # First demonstration that two of the "universal" stop codons, UAA and UAG, will code for the amino acid glutamine in some eukaryotes, leaving UGA as the only termination codon in these organisms. # Discovery of self-splicing RNA. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「tetrahymena」の詳細全文を読む スポンサード リンク
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