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Epigenetics of Ciliates

Epigenetic Regulation and Epigenomics

  1. Jason A. Motl,
  2. Annie W. Shieh,
  3. Douglas L. Chalker

Published Online: 15 MAR 2012

DOI: 10.1002/3527600906.mcb.201100024

Encyclopedia of Molecular Cell Biology and Molecular Medicine

Encyclopedia of Molecular Cell Biology and Molecular Medicine

How to Cite

Motl, J. A., Shieh, A. W. and Chalker, D. L. 2012. Epigenetics of Ciliates. Encyclopedia of Molecular Cell Biology and Molecular Medicine. .

Author Information

  1. Washington University in St Louis, Biology Department, St Louis, Missouri, USA

Publication History

  1. Published Online: 15 MAR 2012

Abstract

Genetic studies of ciliated protozoa delivered some of the earliest evidence that epigenetic mechanisms play profound roles in determining phenotype. The nuclear dimorphism of these unconventional unicellular organisms has provided a rich context within which to uncover epigenetic mechanisms that regulate genome activities. Comparisons of the chromatin of the transcriptionally active somatic genome and the silent germline have revealed that histone modifications and specialized variants are important regulatory mechanisms, allowing homologous sequences to exist in different states. However, these genomes do not just differ in epigenetic characteristics; they have major structural differences, the result of developmentally programmed DNA rearrangements that occur during nuclear differentiation. These rearrangements eliminate between 15% and 95% of a ciliate's germline-derived DNA to create a streamlined genome that is devoid of most repetitive elements. More recent investigations have revealed that homologous noncoding RNAs (ncRNAs) and RNA interference mechanisms play essential roles in guiding these DNA rearrangements by mediating a comparison of the genome content of the current somatic genome to that in the germline. Continuing research into the process of DNA elimination in ciliates shows promise to provide new insights into the potential of ncRNAs to remodel genomes during development.

Keywords:

  • Nuclear dimorphism;
  • Micronucleus (Mic);
  • Macronucleus (Mac);
  • Conjugation;
  • Autogamy;
  • Internal eliminated sequences (IESs);
  • DNA elimination;
  • Transposons;
  • RNA interference;
  • Heterochromatin