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.



Bright LJ, Kambesis N and Nelson SB (2010) Comprehensive analysis reveals dynamic and evolutionary plasticity of Rab GTPases and membrane traffic in Tetrahymena thermophila. PLoS Genetics 6: e1001155.

Brunk CF, Lee LC, Tran AB and Li J (2003) Complete sequence of the mitochondrial genome of Tetrahymena thermophila and comparative methods for identifying highly divergent genes. Nucleic Acids Research 31: 1673–1682.

Chalker DL, Fuller P and Yao MC (2005) Communication between parental and developing genomes during Tetrahymena nuclear differentiation is likely mediated by homologous RNAs. Genetics 169: 149–160.

Cheng CY, Vogt A, Mochizuki K and Yao MC (2010) A domesticated piggyBac transposase plays key roles in heterochromatin dynamics and DNA cleavage during programmed DNA deletion in Tetrahymena thermophila. Molecular Biology of the Cell 21: 1753–1762.

Chilcoat ND, Elde NC and Turkewitz AP (2001) An antisense approach to phenotype‐based gene cloning in Tetrahymena. Proceedings of the National Academy of Sciences of the USA 98: 8709–8713.

Cole ES, Cassidy‐Hanley D, Hemish J, Tuan G and Bruns PJ (1997) A mutational analysis of conjugation in Tetrahymena thermophila. I. Phenotypes affecting early development: meiosis to nuclear selection. Developmental Biology 189: 215–232.

Couvillion MT, Lee SR, Hogstad B et al. (2009) Sequence, biogenesis, and function of diverse small RNA classes bound to the Piwi family proteins of Tetrahymena thermophila. Genes & Development 23: 2016–2032.

Coyne RS, Thiagarajan M, Jones KM et al. (2008) Refined annotation and assembly of the Tetrahymena thermophila genome sequence through EST analysis, comparative genomic hybridization, and targeted gap closure. BMC Genomics 9: 562.

Doerder FP (1979) Regulation of macronuclear DNA content in Tetrahymena thermophila. Journal of Protozoology 26: 28–35.

Eisen JA, Coyne RS, Wu M et al. (2006) Macronuclear genome sequence of the ciliate Tetrahymena thermophila, a model eukaryote. PLoS Biology 4(9): e286.

Frankel J (2008) What do genic mutations tell us about the structural patterning of a complex single‐celled organism? Eukaryotic Cell 7: 1617–1639.

Gu L, Gaertig J, Stargell L and Gorovsky MA (1995) Gene‐specific signal transduction between microtubules and tubulin genes in Tetrahymena thermophila. Molecular and Cellular Biology 15: 5173–5179.

Guo F, Gooding AR and Cech TR (2004) Structure of the Tetrahymena ribozyme: base triple sandwich and metal ion at the active site. Molecular Cell 16: 351–362.

Haddad A and Turkewitz AP (1997) Analysis of exocytosis mutants indicates close coupling between regulated secretion and transcription activation in Tetrahymena. Proceedings of the National Academy of Sciences of the USA 94: 10675–10680.

Honts JE and Williams NE (2003) Novel cytoskeletal proteins in the cortex of Tetrahymena. Journal of Eukaryotic Microbiology 50: 9–14.

Howard‐Till RA and Yao MC (2006) Induction of gene silencing by hairpin RNA expression in Tetrahymena thermophila reveals a second small RNA pathway. Molecular and Cellular Biology 26(23): 8731–8742. Epub 2006 Sep 25.

Karrer K (2000) Tetrahymena genetics: two nuclei are better than one. In: Asai DJ and Forney JD (eds) Tetrahymena thermophila. Methods in Cell Biology, vol. 62, pp. 127–186. Orlando, FL: Academic Press.

Katz LA, Snoeyenbos‐West O and Doerder FP (2006) Patterns of protein evolution in Tetrahymena thermophila: implications for estimates of effective population size. Molecular Biology and Evolution 23: 608–614.

Miao W, Xiong J, Bowen J et al. (2009) Microarray analyses of gene expression during the Tetrahymena thermophila life cycle. PLoS ONE 4: e4429.

Mochizuki K and Gorovsky MA (2004) Small RNAs in genome rearrangement in Tetrahymena. Current Opinion in Genetics and Development 14: 181–187.

Moradian MM, Beglaryan D, Skozylas JM and Kerikorian V (2007) Complete mitochondrial genome sequence of three Tetrahymena species reveals mutation hot spots and accelerated nonsynonymous substitutions in Ymf genes. PLoS ONE 2: e650.

Nanney DL and Simon EM (2000) Laboratory and evolutionary history of Tetrahymena thermophila. In: Asai DJ and Forney JD (eds) Tetrahymena thermophila. Methods in Cell Biology, vol. 62, pp. 3–25. Orlando, FL: Academic Press.

Pearson CG and Winey M (2009) Basal body assembly in ciliates: the power of numbers. Traffic 10: 461–471.

Rusconi CP and Cech TR (1996) The anticodon is the signal sequence for mitochondrial import of glutamine tRNA in Tetrahymena. Genes & Development 10: 2870–2880.

Smith JC, Northey JG, Garg J et al. (2005) Robust method for proteome analysis by MS/MS using an entire translated genome: demonstration on the ciliome of Tetrahymena thermophila. Journal of Proteome Research 4: 909–919.

Stemm‐Wolf A, Morgan G, Giddings TH Jr et al. (2005) Basal body duplication and maintenance require one member of the Tetrahymena thermophila centrin gene family. Molecular Biology of the Cell 16: 3606–3619.

Stover NA, Krieger CJ, Binkley G et al. (2006) Tetrahymena Genome Database (TGD): a new genomic resource for Tetrahymena thermophila research. Nucleic Acids Research 34: D500–503.

Sweeney R, Fan Q and Yao MC (1996) Antisense ribosomes: rRNA as a vehicle for antisense RNAs. Proceedings of the National Academy of Sciences of the USA 93: 8518–8523.

Thazhath R, Jerka‐Dziadosz M, Duan J et al. (2004) Cell context‐specific effects of the β‐tubulin glycylation domain on assembly and size of microtubular organelles. Molecular Biology of the Cell 15: 4136–4147.

Turkewitz AP (2004) Out with a bang! Tetrahymena as a model system to study secretory granule biogenesis. Traffic 5: 63–68.

Witkin KL and Collins K (2004) Holoenzyme proteins required for the physiological assembly and activity of telomerase. Genes and Development 18: 1107–1118.

Xiong J, Lu X, Lu Y et al. (2011a) Tetrahymena Gene Expression Database (TGED): a resource of microarray data and co‐expression analyses for Tetrahymena. Science China Life Sciences 54: 65–67.

Xiong J, Yuan D, Fillingham JS et al. (2011b) Gene network landscape of the ciliate Tetrahymena thermophila. PLoS ONE 6: e20124.

Yao MC and Chao JL (2005) RNA‐guided DNA deletion in Tetrahymena: an RNAi‐based mechanism for programmed genome rearrangements. Annual Review of Genetics 39: 537–559.

Yao MC, Fuller P and Xi X (2003) Programmed DNA deletion as an RNA‐guided system of genome defence. Science 300: 1581–1584.

Further Reading

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.

Cech TR (1986) RNA as an enzyme. Scientific American 255: 64–74.

Coombs GH, Vickerman K, Sleigh MA and Warren A (eds) (1998) Evolutionary Relationships Among Protozoa. Dordrecht, NE: Kluwer Academic Publishers.

Elliott AM (ed.) (1973) Biology of Tetrahymena. Stroudsburg, PA: Dowden, Hutchinson, and Ross.

Frankel J (1989) Pattern Formation: Ciliate Studies and Models. New York: Oxford University Press.

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.

Hausmann K and Bradbury PC (eds) (1996) Ciliates: Cells as Organisms. Stuttgart: Verlag.

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.

Contact Editor close
Submit a note to the editor about this article by filling in the form below.

* Required Field

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]