RNA helicase Belle/DDX3 regulates transgene expression in Drosophila

• DOI: 10.1016/j.ydbio.2016.02.014
• Publication Date: 2016-02-20T08:05:08Z
• Authors: Pang-Kuo Lo; Yi-Chun Huang; John S. Poulton; Nicholas Leake; William H. Palmer; Daniel Vera; Gengqiang Xie; Stephen Klusza; Wu-Min Deng
• Keywords: 0301 basic medicine; 03 medical and health sciences; Mutation; Animals; Drosophila Proteins; Drosophila; Cell Biology; Gene Silencing; Transgenes; Molecular Biology; RNA Helicases; Developmental Biology

Belle (Bel), the Drosophila homolog of the yeast DEAD-box RNA helicase DED1 and human DDX3, has been shown to be required for oogenesis and female fertility. Here we report a novel role of Bel in regulating the expression of transgenes. Abrogation of Bel by mutations or RNAi induces silencing of a variety of P-element-derived transgenes. This silencing effect depends on downregulation of their RNA levels. Our genetic studies have revealed that the RNA helicase Spindle-E (Spn-E), a nuage RNA helicase that plays a crucial role in regulating RNA processing and PIWI-interacting RNA (piRNA) biogenesis in germline cells, is required for loss-of-bel-induced transgene silencing. Conversely, Bel abrogation alleviates the nuage-protein mislocalization phenotype in spn-E mutants, suggesting a competitive relationship between these two RNA helicases. Additionally, disruption of the chromatin remodeling factor Mod(mdg4) or the microRNA biogenesis enzyme Dcr-1 also rescued the transgene-silencing phenotypes in bel mutants, suggesting the involvement of chromatin remodeling and microRNA biogenesis in loss-of-bel-induced transgene silencing. Finally we showed that genetic inhibition of Bel function led to the de novo generation of piRNAs from the transgene region inserted in the genome, suggesting a potential piRNA-dependent mechanism that may mediate transgene silencing as Bel function is inhibited. Our findings have demonstrated a novel involvement of Bel in regulating transgene expression and its loss triggers a transgene silencing mechanism mediated by protein regulators implicated in RNA processing, piRNA biogenesis, chromatin remodeling and the microRNA pathway.