Tetrahymena

Robert S Coyne, J. Craig Venter Institute, Rockville, Maryland, USA

Published online: November 2011

DOI: 10.1002/9780470015902.a0001972.pub3

Tetrahymena is a genus of mostly free-living ciliated protozoa that is intensively employed to investigate and solve fundamental problems in molecular, cellular and developmental biology. Like all ciliates, Tetrahymena contains separate germline and somatic nuclei, known as the micronucleus and macronucleus, respectively. The macronucleus is derived from a copy of the micronucleus through a process that involves extensive programmed whole-genome rearrangement and is under intensive study. The most highly developed experimental model species is Tetrahymena thermophila, which can be readily manipulated using the tools of genetics, molecular biology, cell biology and biochemistry. Notable discoveries made using Tetrahymena include the structure of telomeres and telomerase, self-splicing RNA, the first microtubular motor and the link between histone acetylation and gene regulation. The approximately 104 Megabase macronuclear genome of T. thermophila has been sequenced and annotated; the micronuclear genome sequence will be completed soon.

Key Concepts:

  • Tetrahymena are large, elaborate eukaryotic cells with many experimental advantages and well-suited to the study of cellular structure, division and development.
  • Tetrahymena have been studied for nearly a century and been the source of a number of groundbreaking discoveries.
  • A characteristic feature of Tetrahymena, and the basis of much biological interest, is the separation of germline and somatic genetic functions into separate nuclei.
  • Programmed genome rearrangement in Tetrahymena shares common mechanistic features with heterochromatic gene silencing in other eukaryotes.
  • Applying the modern tools of genomics and proteomics has facilitated research with Tetrahymena and opened up new areas of investigation.

Keywords: Tetrahymena; ciliated protozoa; Tetrahymena genetics; ciliated protozoa; ciliate genomics; ciliate molecular biology; ciliate cell biology

Figure 1. A schematic diagram of the organisation of Tetrahymena. The anterior end of the cell is oriented upwards, and the ventral (oral) surface of the cell faces the viewer. Seven of the total of 18–21 ciliary rows are seen, with basal bodies shown as dots next to longitudinally oriented microtubule bands. Cilia are drawn emerging from the basal bodies of one of the ciliary rows and omitted from the other rows. For further explanation, see the text.
Figure 2. Structural features of the ventral surface of Tetrahymena at different stages of the cell division process. The micronucleus (Mic) and macronucleus (Mac) are shown in each of these diagrams, as well as the three major cortical landmarks, the oral apparatus (OA), cytoproct (Cyp) and contractile vacuole pores (CVP), plus the ‘reference’ ciliary row connecting the OA and the Cyp. (a) A nondeveloping cell. (b) A cell that has begun micronuclear mitosis and formation of an oral primordium (OP). (c) A cell in which the micronucleus has divided and a fission zone (FZ) has formed with a new cytoproct (nCyp) and new contractile vacuole pores (nCVP) anterior to it. The new oral apparatus has interrupted the reference ciliary row. (d) A cell undergoing macronuclear and cell division. For further explanation, see the text.
Figure 3. A greatly simplified schematic showing selected stages of conjugation in Tetrahymena. The macronucleus (Mac) and micronucleus (Mic) are shown in all diagrams, with different colours used to indicate a difference in genotype. Vegetative cells are shown at the left, conjugating cells undergoing pronuclear exchange in the centre and exconjugants that have formed new heterozygous micronuclei and macronuclei on the right. Relevant processes that are not illustrated in this diagram are written in at appropriate places. For explanation, see the text.
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 Further Reading
    book Asai DJ and Forney JD (eds) (2000) Tetrahymena thermophila. Methods in Cell Biology, vol. 62. Orlando, FL: Academic Press.
    Blackburn EH (2005) Telomeres and telomerase: their mechanisms of action and effects of altering their functions. FEBS Letters 579: 859–862.
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    book Coombs GH, Vickerman K, Sleigh MA and Warren A (eds) (1998) Evolutionary Relationships Among Protozoa. Dordrecht, NE: Kluwer Academic Publishers.
    book Elliott AM (ed.) (1973) Biology of Tetrahymena. Stroudsburg, PA: Dowden, Hutchinson, and Ross.
    book Frankel J (1989) Pattern Formation: Ciliate Studies and Models. New York: Oxford University Press.
    book Gall JG (1986) The Molecular Biology of Ciliated Protozoa. Orlando, FL: Academic Press.
    Greider CW (1996) Telomere length regulation. Annual Review of Biochemistry 65: 337–365.
    book Hausmann K and Bradbury PC (eds) (1996) Ciliates: Cells as Organisms. Stuttgart: Verlag.
    book Nanney DL (1980) Experimental Ciliatology: An Introduction to Genetic and Developmental Analysis in Ciliates. New York: Wiley.
    Orias E (2000) Toward sequencing the Tetrahymena genome: exploiting the gift of nuclear dimorphism. Journal of Eukaryotic Microbiology 47: 328–333.
    Raikov I (1995) Structure and genetic organization of the polyploid macronucleus of ciliates: a comparative review. Acta Protozoologica 34: 151–171.
    Turkewitz AP, Orias E and Kapler G (2002) Functional genomics: the coming of age of Tetrahymena thermophila. Trends in Genetics 18: 35–40.

Related Sub-Topics:

Composition and Structure of Microbial Cells | Genomes and Chromosomes | Microbial Evolution and Taxonomy | Protozoa
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Article Title: Tetrahymena
 
How to Cite close
Coyne, Robert S(Nov 2011) Tetrahymena. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0001972.pub3]