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Nature Reviews Molecular Cell Biology 9, 673–678 (1 September 2008) | doi:10.1038/nrm2479

Endogenous small interfering RNAs in animals

Katsutomo Okamura & Eric C. Lai

Until recently, only nematodes among animals had a well-defined endogenous small interfering RNA (endo-siRNA) pathway. This has changed dramatically with the recent discovery of diverse intramolecular and intermolecular substrates that generate endo-siRNAs in Drosophila melanogaster and mice. These findings suggest broad and possibly conserved roles for endogenous RNA interference in regulating host-gene expression and transposable element transcripts. They also raise many questions regarding the biogenesis and function of small regulatory RNAs in animals.