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 (OA), cytoproct (Cyp) and (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 (OP). (c) A cell in which the micronucleus has divided and a (FZ) has formed with a (nCyp) and (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

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Coyne, Robert S(Nov 2011) Tetrahymena. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0001972.pub3]