RNAi pathways in Drosophila

RNAi pathways in Drosophila. (a) The antiviral siRNA pathway. Dicer-2 cuts dsRNA into siRNAs, which are loaded into an Argonaute-containing RISC that targets RNA for degradation. (b) The miRNA pathway. Primary miRNAs are transcribed from the genome, processed by Drosha and Dicer-1 into mature miRNAs. These are loaded into the Argonaute-containing effector complex (RISC), which binds mRNAs and recruits additional factors to inhibit translation. (c) The ‘ping-pong’ model of TE silencing in the Drosophila germ line. Aubergine and Argonaute-3 (Piwi family Argonautes) alternately cleave sense (red) and antisense (blue) transcripts from TEs, guided by piRNAs generated in the other half of the cycle. Cleavage both inactivates the transcript and generates the 5′ end of a new piRNA. The new piRNA-precursor is bound by the partner Piwi family member and the 3′ end degraded and then modified by the addition of a methyl group (Me). The nuclear localization of Piwi suggests that it might mediate heterochromatin assembly (). It is unknown how this occurs, but one possibility is that the active Piwi complex binds nascent TE transcripts to recruit heterochromatin factors (). Recently, a fourth pathway has been identified, which targets TE transcripts in both the soma and the germ line, using Dcr-2 and Ago-2 from the antiviral pathway, but Loqs from the miRNA pathway (; ).

Publication

The evolution of RNAi as a defence against viruses and transposable elements. (2009) Darren J. Obbard, et al. Philos Trans R Soc Lond B Biol Sci. 2009 Jan 12;364(1513):99-115. Figure: F1. All organisms Drosophila melanogaster Homo sapiens

Disease mentions