Systemic RNA interference (RNAi) in Caenorhbaditis elegans requires
sid-1,
sid-3, and
sid-5 Injected, expressed, or ingested double-stranded RNA (dsRNA) is transported between cells, enabling RNAi in most tissues, including the germline and progeny (parental RNAi). A recent report claims that parental RNAi also requires the yolk receptor
rme-2 Here, we characterize the role of the sid genes and
rme-2 in parental RNAi. We identify multiple independent paths for maternal dsRNA to reach embryos and initiate RNAi. We showed previously that maternal and embryonic
sid-1 contribute independently to parental RNAi. Here we demonstrate a role for embryonic
sid-5, but not
sid-2 or
sid-3 in parental RNAi. We also find that maternal
rme-2 contributes to but is not required for parental RNAi. We determine that parental RNAi by feeding occurs nearly exclusively in adults. We also introduce 5-ethynyluridine to densely internally label dsRNA, avoiding complications associated with other labeling strategies such as inhibition of normal dsRNA trafficking and separation of label and RNA. Labeling shows that yolk and dsRNA do not co-localize following endocytosis, suggesting independent uptake, and furthermore dsRNA appears to rapidly progress through the RAB-7 endocytosis pathway independently of
sid-1 activity. Our results support the premise that although
sid-1 functions in multiple roles, it alone is central and absolutely required for inheritance of silencing RNAs.