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Proc Natl Acad Sci U S A. 2019 Jul 16;116(29):14639-14644. doi: 10.1073/pnas.1903491116. Epub 2019 Jul 1.

Diversification of small RNA amplification mechanisms for targeting transposon-related sequences in ciliates.

Author information

1
Institute of Human Genetics, CNRS, University of Montpellier, 34090 Montpellier, France.
2
Institute of Human Genetics, CNRS, University of Montpellier, 34090 Montpellier, France kazufumi.mochizuki@igh.cnrs.fr.

Abstract

The silencing of repetitive transposable elements (TEs) is ensured by signal amplification of the initial small RNA trigger, which occurs at distinct steps of TE silencing in different eukaryotes. How such a variety of secondary small RNA biogenesis mechanisms has evolved has not been thoroughly elucidated. Ciliated protozoa perform small RNA-directed programmed DNA elimination of thousands of TE-related internal eliminated sequences (IESs) in the newly developed somatic nucleus. In the ciliate Paramecium, secondary small RNAs are produced after the excision of IESs. In this study, we show that in another ciliate, Tetrahymena, secondary small RNAs accumulate at least a few hours before their derived IESs are excised. We also demonstrate that DNA excision is dispensable for their biogenesis in this ciliate. Therefore, unlike in Paramecium, small RNA amplification occurs before IES excision in Tetrahymena This study reveals the remarkable diversity of secondary small RNA biogenesis mechanisms, even among ciliates with similar DNA elimination processes, and thus raises the possibility that the evolution of TE-targeting small RNA amplification can be traced by investigating the DNA elimination mechanisms of ciliates.

KEYWORDS:

DNA elimination; Tetrahymena; ciliate; small RNA; transposon silencing

PMID:
31262823
PMCID:
PMC6642352
[Available on 2020-01-01]
DOI:
10.1073/pnas.1903491116

Conflict of interest statement

The authors declare no conflict of interest.

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