Selecting one of several mating types through gene segment joining and deletion in Tetrahymena thermophila

PLoS Biol. 2013;11(3):e1001518. doi: 10.1371/journal.pbio.1001518. Epub 2013 Mar 26.


The unicellular eukaryote Tetrahymena thermophila has seven mating types. Cells can mate only when they recognize cells of a different mating type as non-self. As a ciliate, Tetrahymena separates its germline and soma into two nuclei. During growth the somatic nucleus is responsible for all gene transcription while the germline nucleus remains silent. During mating, a new somatic nucleus is differentiated from a germline nucleus and mating type is decided by a stochastic process. We report here that the somatic mating type locus contains a pair of genes arranged head-to-head. Each gene encodes a mating type-specific segment and a transmembrane domain that is shared by all mating types. Somatic gene knockouts showed both genes are required for efficient non-self recognition and successful mating, as assessed by pair formation and progeny production. The germline mating type locus consists of a tandem array of incomplete gene pairs representing each potential mating type. During mating, a complete new gene pair is assembled at the somatic mating type locus; the incomplete genes of one gene pair are completed by joining to gene segments at each end of germline array. All other germline gene pairs are deleted in the process. These programmed DNA rearrangements make this a fascinating system of mating type determination.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Reproduction / genetics
  • Reproduction / physiology*
  • Tetrahymena thermophila / genetics
  • Tetrahymena thermophila / physiology*

Grant support

This work is supported by the National Science Foundation, USA (MCB-1025069) to EO and (U.S. NSF IGERT DGE-02-21715) to Linda Petzold in support of MJL; Knowledge Innovation Program of the Chinese Academy of Sciences (KSCX2-EW-G-6-4) and National Natural Science Foundation of China (31071993) to MW; Tri-Counties Blood Bank Postdoctoral Fellowship to M.D.C. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.