Submitted on March 5, 2008
Accepted on March 31, 2008
Endogenous siRNAs Derived from Transposons and mRNAs in Drosophila Somatic Cells
Megha Ghildiyal 1
, Hervé Seitz 1, Michael D. Horwich 1, Chengjian Li 1, Tingting Du 1, Soohyun Lee 2, Jia Xu 3, Ellen L.W. Kittler 4, Maria L. Zapp 4, Zhiping Weng 5, Phillip D. Zamore 1*
1 Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA 01605, USA.
2 Program in Bioinformatics, Boston University, Boston, MA 02215, USA.
3 Department of Biomedical Engineering, Boston University, Boston, MA 02215, USA.
4 Program in Molecular Medicine and Center for AIDS Research, University of Massachusetts Medical School, Worcester, MA 01605, USA.
5 Program in Bioinformatics and Integrative Biology, University of Massachusetts Medical School, Worcester, MA 01605, USA.
* To whom correspondence should be addressed.
Phillip D. Zamore , E-mail: phillip.zamore{at}umassmed.edu
These authors contributed equally to this work.
Small interfering RNAs (siRNAs) direct RNA interference (RNAi) in eukaryotes. In flies, somatic cells produce siRNAs from exogenous double-stranded RNA as a defense against viral infection. Here, we identify 21-nt long, endogenous siRNAs (endo-siRNAs) corresponding to transposons and heterochromatic sequences in the somatic cells of Drosophila melanogaster. We also detected endo-siRNAs complementary to mRNAs: these siRNAs disproportionately mapped to the complementary regions of overlapping mRNAs predicted to form dsRNA in vivo. Normal accumulation of somatic endo-siRNAs requires the siRNA-generating ribonuclease, Dicer-2, and the RNAi effector protein, Ago2. We propose that endo-siRNAs generated by the fly RNAi pathway silence selfish genetic elements in the soma much as piRNAs do in the germ line.
