Altered hsrω lncRNA levels in activated Ras background further enhance Ras activity in Drosophila eye and induces more R7 photoreceptors

Abstract

We exploited the high Ras activity induced differentiation of supernumerary R7 cells in Drosophila eyes to examine if hsr{omega} lncRNAs influence active Ras signaling. Surprisingly, either down- or up-regulation of hsr{omega} lncRNAs in sev-GAL4>RasV12 expressing eye discs resulted in complete pupal lethality and substantially greater increase in R7 photoreceptor number at the expense of cone cells. Enhanced nuclear p-MAPK and presence of sev-GAL4 driven RasV12 bound RafRBDFLAG in cells not expressing the sev-GAL4 driver indicated non-cell autonomous spread of Ras signaling when hsr{omega} levels were co-altered. RNA-sequencing revealed that down-and up-regulation of hsr{omega} transcripts in sev-GAL4>RasV12 expressing eye discs elevated transcripts of positive or negative modulators, respectively, of Ras signaling so that either condition enhances it. Altered hsr{omega} transcript levels in sev-GAL4>RasV12 expressing discs also affected sn/sno/sca RNAs and some other RNA processing transcript levels. Post-transcriptional changes due to the disrupted intra-cellular dynamicity of omega speckle associated hnRNPs and other RNA-binding proteins that follow down- or up-regulation of hsr{omega} lncRNAs appear to be responsible for the further elevated Ras signaling. Cell autonomous and non-autonomous enhancement of Ras signaling by lncRNAs like hsr{omega} has implications for cell signaling during high Ras activity commonly associated with some cancers.\n\nHighlightsOur findings highlight roles of hsr{omega} lncRNAs in conditionally modulating the important Ras signaling pathway and provide evidence for cell non-autonomous Ras signaling in Drosophila eye discs.