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Fig. 7 | BMC Evolutionary Biology

Fig. 7

From: Conservation and diversification of small RNA pathways within flatworms

Fig. 7

RNAi amplification, spreading and transcriptional gene silencing pathways. a Amplification pathway. RNA dependent RNA Polymerases (RdRP) employs the 3′ of the siRNA as primer to synthesis a new long dsRNA using the mRNA as template. PIR-1 and DRH-3 are required for Dicer to process long dsRNA, while RDE-3 intervenes in an intermediate step, stabilizing the product of the initial round of cleavage, allowing the amplification mediated by RdRPs. SMG genes, Mut-14 and Mut-16 act downstream of secondary siRNA generation. RNAi persists in the animals exposed to dsRNA for several days [5]. This persistence depends on SMG genes. The secondary siRNA with the Secondary Argonautes (SAGOs) produce a secondary siRISC complex. b Systemic spreading. The secondary siRNAs spread throughout other tissues inducing the systemic silencing of the target gene. c Co-transcriptional silencing and chromatin remodeling. A specialized Argonaute, NRDE-3, transports the secondary siRNA to the nucleus where produce co-transcriptional gene silencing and interacts with other factors to remodel the chromatin. Factors with homologous genes detected in flatworms are indicated (“Flatworm Distribution Code” box). A shape code was used to indicate predicted function of factors (“Protein Function Code” box)

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