The variability of dsRNA-induced RNA interference is well documented with some insects very amenable to this method of regulating gene expression while are others are very much less so. The factors involved in this variation are known to some extent but which factors are of primary importance.
Wang et al. explore this variation in four insect species – Periplaneta americana, Zophobas atratus, Locusta migratoria and Spodoptera litura
Using the chitinase gene from each of the species as a reporter of RNA interference the authors both injected and fed chitinase dsRNA to the 4 species.
The doses of dsRNA administered were chosen to result in approximately the same concentration of dsRNA in the hemolymph of each insect.
All of the species tested were sensitive to RNA interference although not equally. P. americana was most sensitive to RNAi following injection with an 82% reduction in chitinase transcript levels. In Z. atratus the reduction was 78%, L. migratoria – 76% and S. litura – only 20%.
Feeding dsRNA resulted in a 47% and 29% reduction in chitinase transcript levels in P. americana and Z. atratus, respectively, while there was little effect seen in L. migratoria – 5% and S. litura -1%.
Wang et al. were interested in the dynamics of dsRNA accumulation and degradation in the hemolymph and used not only ds-chitinase RNA but also ds-EGFP RNA. Interestingly the dynamics are quite different the species tested. For example, after feeding dsRNA to S. litura peak dsRNA in the hemolymph was observed after only about 8 minutes and quickly declined . In P. americana, peak dsRNA concentration in the hemolymph was reached approximately 1 hour post feeding and disappeared during the next hour.
Wang et al. tested the capacity of midgut juices and hemolymph to degrade dsRNA and found that the observed sensitivity of each of the tested species was negatively correlated to the dsRNA degradative capacity of the midgut and hemolymph.
This is an interesting study that harmonizes with various observations reported in the literature and nicely illustrates that improvement in dsRNA mediated RNAi in some species will require methods to mitigate dsRNA degradation in the midgut and in the hemolymph.
Wang K, Peng Y, Pu J, Fu W, Wang J, Han Z (2016). Variation in RNAi efficacy among insect species is attributable to dsRNA degradation in vivo. Insect Biochem Mol Biol. 2016 Jul 20;77:1-9. doi: 10.1016/j.ibmb.2016.07.007. [Epub ahead of print]