Tetrahymena are free-living ciliate protozoa that can also switch from commensalistic to pathogenic modes of survival. They are common in fresh-water. 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 striking nuclear dimorphism: two types of cell nuclei, a large, somatic macronucleus and a small, germline micronucleus, exist in a single cell at the same time and carry out different functions with distinct cytological and biochemical properties. This unique versatility allows scientists to use Tetrahymena to identify several key factors regarding gene expression and genome integrity. In addition, Tetrahymena possesses hundreds of cilia and has complicated microtubule structures, making it also an ideal model to elucidate the diversity and functions of microtubule systems.
Since Tetrahymena can be easily cultured in a large quantity in the laboratory, for years it has been a great source for biochemical analysis of important enzymatic activities and for purification of sub-cellular components. In addition, advanced molecular genetic techniques have been developed, including DNA-mediated transformation, gene 'knock-out' and 'knock-in' by homologous recombination, epitope tagging and inducible/repressible gene expression, making it an excellent model to study the gene function in vivo. Recently, the whole macronuclear genome has been sequenced, which should promise Tetrahymena to be continuously utilized as a model system in the genomic and post-genomic era.
Studies on Tetrahymena have contributed to several scientific milestones:
1. Methods in Cell Biology Volume 62: Tetrahymena thermophila, Edited by David J. Asai and James D. Forney. (2000). By Academic Press ISBN 0-12-544164-9
2. Collins, K. and Gorovsky, M.A. (2005). Tetrahymena thermophila Curr Biol. 15: R317-8.
3. Eisen JA, Coyne RS, Wu M, Wu D, Thiagarajan M, et al. (2006) Macronuclear Genome Sequence of the Ciliate Tetrahymena thermophila, a Model Eukaryote. PLoS Biol 4(9): e286
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