Processing of Drosophila endo-siRNAs depends on a specific Loquacious isoform
- Rui Zhou1,4,
- Benjamin Czech2,4,
- Julius Brennecke2,5,
- Ravi Sachidanandam2,6,
- James A. Wohlschlegel3,
- Norbert Perrimon1 and
- Gregory J. Hannon2
- 1Harvard Medical School, Department of Genetics, Howard Hughes Medical Institute, Boston, Massachusetts 02115, USA
- 2Watson School of Biological Sciences, Howard Hughes Medical Institute, Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724, USA
- 3Department of Biological Chemistry, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, California 90095, USA
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↵4 These authors contributed equally to this work.
Abstract
Drosophila melanogaster expresses three classes of small RNAs, which are classified according to their mechanisms of biogenesis. MicroRNAs are ∼22–23 nucleotides (nt), ubiquitously expressed small RNAs that are sequentially processed from hairpin-like precursors by Drosha/Pasha and Dcr-1/Loquacious complexes. MicroRNAs usually associate with AGO1 and regulate the expression of protein-coding genes. Piwi-interacting RNAs (piRNAs) of ∼24–28 nt associate with Piwi-family proteins and can arise from single-stranded precursors. piRNAs function in transposon silencing and are mainly restricted to gonadal tissues. Endo-siRNAs are found in both germline and somatic tissues. These ∼21-nt RNAs are produced by a distinct Dicer, Dcr-2, and do not depend on Drosha/Pasha complexes. They predominantly bind to AGO2 and target both mobile elements and protein-coding genes. Surprisingly, a subset of endo-siRNAs strongly depend for their production on the dsRNA-binding protein Loquacious (Loqs), thought generally to be a partner for Dcr-1 and a cofactor for miRNA biogenesis. Endo-siRNA production depends on a specific Loqs isoform, Loqs-PD, which is distinct from the one, Loqs-PB, required for the production of microRNAs. Paralleling their roles in the biogenesis of distinct small RNA classes, Loqs-PD and Loqs-PB bind to different Dicer proteins, with Dcr-1/Loqs-PB complexes and Dcr-2/Loqs-PD complexes driving microRNA and endo-siRNA biogenesis, respectively.
Keywords
- Drosophila melanogaster
- Dicer
- double-stranded RNA-binding proteins (dsRBPs)
- Loquacious
- endo-siRNA processing
- transposon silencing
Footnotes
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Reprint requests to: Gregory J. Hannon, Watson School of Biological Sciences, Howard Hughes Medical Institute, Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724, USA; e-mail: hannon{at}cshl.edu; fax: (516) 367-8874.
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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.1611309.
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- Received February 19, 2009.
- Accepted June 30, 2009.
- Copyright © 2009 RNA Society