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Fig. 1 | Parasites & Vectors

Fig. 1

From: RNAi gene knockdown in the poultry red mite, Dermanyssus gallinae (De Geer 1778), a tool for functional genomics

Fig. 1

Summary of RNA interference (RNAi) pathways identified in Dermanyssus gallinae. RNAi pathways are based on those described in Tetranychus urticae and Drosophila melanogaster with core RNAi pathway enzymes either present (red) or absent (grey) in D. gallinae. siRNA pathway: double-stranded RNA (dsRNA; either viral or experimentally introduced) is processed by Dicer-2 (Dcr-2) into 21- to 23-nucleotide small interfering RNAs (siRNAs) and loaded into the RNA-induced silencing complex (RISC) complex. Argonaute (Ago) cleaves the passenger strand of the siRNA and retains the guide strand which guides the active siRISC complex to the target mRNA. Full complementarity between the guide siRNA strand and target mRNA leads to cleavage of the mRNA. miRNA pathway: The microRNA (miRNA) gene is transcribed in the nucleus to generate pri-miRNA that is then cleaved by the enzymes Drosha and Pasha to form a pre-miRNA. The pre-miRNA is transported to the cytoplasm through Exportin-5 (XPO5) and cleaved by Dicer-1 (Dcr-1)/Loquacious (loqs) complex to yield miRNA. The miRNA is loaded into the RISC complex, and Ago cleaves the passenger strand of the miRNA and retains the guide strand which guides the active miRISC complex to the target mRNA. Partial complementarity between the guide strand and target mRNA leads to either translation repression or cleavage of the mRNA. miRNAs usually target several genes, with shared sequences in the 3′ untranslated region (UTR). In both pathways siRNAs and miRNAs are amplified by the RNA-dependent RNA polymerase (RdRP). piRNA pathway: The P-element-induced wimpy testis (piwi)-interacting RNA (piRNA) pathway functions in germline cells to protect against transposable elements. Antisense piRNAs are transcribed from repetitive elements in genomic DNA (gDNA) and processed by zucchini (zuc) into 26- to 32-nucleotide primary piRNAs. Primary piRNAs associate with either piwi or aubergine (aub). Piwi-associated piRNAs are translocated to the nucleus, while aub-associated piRNAs cleave cytoplasmic transposon transcripts and trigger a ‘ping-pong’ piRNA amplification. Following transposon, transcript cleavage argonaute-3 (ago3) is loaded with secondary piRNAs which in turn produce piRNAs that associate with aub, resulting in silencing of cytoplasmic transposon transcripts

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