Ingested dsRNAs trigger RNA interference (RNAi) in many invertebrates, including the nematode Caenorhabditis elegans. Here we show that the C. elegans apical intestinal membrane protein SID-2 is required in C. elegans for the import of ingested dsRNA and that, when expressed in Drosophila S2 cells, SID-2 enables the uptake of dsRNAs. SID-2-dependent dsRNA transport requires an acidic extracellular environment and is selective for dsRNAs with at least 50 base pairs. Through structure-function analysis, we identify several SID-2 regions required for this activity, including three extracellular, positively charged histidines. Finally, we find that SID-2-dependent transport is inhibited by drugs that interfere with vesicle transport. Therefore, we propose that environmental dsRNAs are imported from the acidic intestinal lumen by SID-2 via endocytosis and are released from internalized vesicles in a secondary step mediated by the dsRNA channel SID-1. Similar multistep mechanisms may underlie the widespread observations of environmental RNAi.
Graphical Abstract
Highlights
► SID-2 is required to import dsRNA from the acidic C. elegans intestinal lumen ► SID-2 expressed in S2 cells selectively uptakes dsRNA from acidic environments ► SID-2 function requires extracellular histidine residues and vesicle trafficking ► dsRNA imported by SID-2 likely becomes cytoplasmic via the dsRNA SID-1 channel
Present address: Department of Genetics, Harvard Medical School, and Department of Molecular Biology, Massachusetts General Hospital, Boston, MA 02114, USA