The PIWI proteins SMEDWI-2 and SMEDWI-3 are required for stem cell function and piRNA expression in planarians
Abstract
PIWI proteins are expressed in germ cells in a wide variety of metazoans, where they participate in the synthesis and function of a novel class of small RNAs called PIWI associated RNAs (piRNAs). One function of piRNAs is to preserve the integrity of the germline genome by silencing transposons, though they also participate in epigenetic and post-transcriptional gene regulation. In the planarian Schmidtea mediterranea, the PIWI proteins SMEDWI-1 and SMEDWI-2 are expressed in neoblasts and SMEDWI-2 is required for regeneration and homeostasis. Here, we identify a diverse population of ∼32-nucleotide small RNAs that strongly resemble vertebrate and insect piRNAs and map to hundreds of thousands of loci in the S. mediterranea genome. The expression of these RNAs occurs predominantly in neoblasts and is not restricted to the germline. RNAi knockdown of either SMEDWI-2 or a newly identified PIWI protein, SMEDWI-3, impairs regeneration and homeostasis and decreases the levels of both piRNAs and neoblasts. Therefore, SMEDWI-2 and SMEDWI-3 are required for piRNA expression, regeneration, and neoblast function in S. mediterranea.
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Footnotes
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Reprint requests to: Brenton R. Graveley, Department of Genetics and Developmental Biology, University of Connecticut Stem Cell Institute, University of Connecticut Health Center, 263 Farmington Avenue, Farmington, CT 06030-3301, USA; e-mail: graveley{at}neuron.uchc.edu; fax: (860) 679-8345; or Gene W. Yeo, Crick–Jacobs Center for Theoretical and Computational Biology, Salk Institute, 10010 North Torrey Pines Road, La Jolla, CA 92037, USA; e-mail: geneyeo{at}salk.edu; fax: (858) 597-0824.
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Article published online ahead of print. Article and publication date are at http://www.rnajournal.org/cgi/doi/10.1261/rna.1085008.
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- Received February 25, 2008.
- Accepted March 10, 2008.
- Copyright © 2008 RNA Society
