2009 Volume 78 Issue 1 Pages 1_33-1_37
Double-stranded RNA (dsRNA) induces various biological responses in eukaryotic cells. Sequence-specific RNA interference (RNAi) is highly conserved throughout eukaryotic organisms. In mammalian cells, long dsRNA is known to have sequence-nonspecific gene silencing effect by activating several cellular pathways. As for insect cells, only the smallest amount of information has been reported so far. Here, we investigate the sequence-nonspecific effect of dsRNA on gene expression in a lepidopteran cell line, silkworm Bombyx mori BmN4. Cells were cotransfected with long dsRNA and a reporter plasmid expressing luciferase or β-galactosidase, and measured for the activities of each enzyme. dsRNAs which are not homologous to the target gene reduced the reporter activity in a concentration-dependent manner, albeit its effective concentration was considerably higher than that caused by dsRNA homologous to the target gene. The sequence-nonspecific repression by non-homologous dsRNAs was further confirmed using dsRNAs complementary to several genes from some organisms such as silkworm, fruit fly and human, as well as a synthetic dsRNA, polyinosinic-polycytidylic acid (poly(I:C)). Since the sequence-independent effect by long dsRNA was also observed in another lepidopteran cell line, fall armyworm Spodoptera frugiperda Sf21, it may be one of the conserved immune responses among lepidopteran insects.
