Tetrahymena thermophila belongs to the Alveolates, a
major evolutionary branch of eukaryotic protists composed of three primary
lineages: Ciliates (e.g., Tetrahymena and
Paramecium), Dinoflagellates (e.g., Symbiodinium, the coral endosymbiont,
and Alexandrium, which causes
paralytic shellfish poisoning) and the exclusively parasitic Apicomplexa (e.g.,
Plasmodium falciparum, the causative
agent of malaria). Tetrahymena thermophila is a ciliated
protozoan belonging to a free-living, fresh-water genus that is highly
successful ecologically. No free-living alveolate genome has been sequenced.
Since
1923, when Nobel Laureate Andre Lwoff succeeded in growing Tetrahymena in pure culture, two sibling species of the genus Tetrahymena (pyriformis and thermophila)
have been used as microbial animal
models. With the development of genetic methods in T. thermophila in the 1950's, this has become the species of choice
throughout the field.
Tetrahymena has typical eukaryotic
biology. Its ultrastructure, cell physiology, development, biochemistry,
genetics, and molecular biology have been extensively investigated. This
organism displays a degree of cellular structural
and functional complexity comparable to that of human and other metazoan cells.
Consistent with this, analyses of mRNA complexity and very recent EST projects
have confirmed that, at the molecular level, Tetrahymena's rich and complex genome conserves a rich set of
ancestral eukaryotic functions. In addition, Tetrahymena’s special elaborations of certain basic eukaryotic
mechanisms have facilitated discoveries opening the door to major new fields of
fundamental research, including:
- First cell whose division
was synchronized, leading to the first insights into the
existence of cell cycle control mechanisms.
- Identification and purification
of the first cytoskeletal motor, dynein, and determination of directional
activity.
- Participation in the
discovery of lysosomes and peroxisomes.
- One of earliest molecular
descriptions of programmed 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.
- Nobel-prize winning
co-discovery of catalytic RNA (ribozymes);
- Discovery of the function
of histone acetylation in transcription.
The
richness of Tetrahymena's biology
makes it a genetic unicellular animal model organism "for all
seasons." An impressive array of novel molecular genetic technologies
places Tetrahymena at the forefront
of experimental, in vivo functional
genomics research, and complements a wealth of favorable biological features.
Availability of the Tetrahymena genome sequence will have major benefits
in molecular bioscience and biotechnology. Areas of impact include 1)
fundamental biological and biomedical research; 2) finding the function of
predicted human genes with homologs in Tetrahymena but not in yeast; 3)
value for experimental functional genomics and 4) informing the biology of
other alveolates, including pathogens of major medical or agricultural
significance. These areas of impact are described in greater detail in the Appendix of the Concept Paper submitted to the
Trans-NIH NonMammalian Models Committee in November 2001.
Updated
2/02