Gene silencing mediated by RNAi depends on short interfering RNAs and micro RNAs. These RNAs have unique selleck products features, namely a defined size of 19 21 pb, and characteristic two nucleo tide single stranded 3 overhangs and 5 monophosphate groups. Although RNAi off target effects were shown in horn flies, most sequence alignments resulted in homology regions of 11 bp only and in some cases no homology 11 bp was found. These results suggested differences in RNAi specificity and sensitivity, a fact that needs to be fully characterized to understand and efficiently use RNAi in horn flies and other organisms. The aim of this study was to conduct a functional genomics study in female horn flies combining EST ana lysis with RNAi. Therefore, we will focus the discussion on unigene functional groups characterized by RNAi.

Serine proteases Serine proteases are a group of endopeptidases involved in several processes such as digestion, immune response, blood clotting and inflammation. In female horn flies, 10% of the assembled unigenes, containing more than 500 ESTs, were identified as serine proteases. In agree ment with these results, Guerrero et al. recently showed that serine proteases are differentially expressed in fly adult stages when compared to larvae. Significant gene knockdown was not obtained for any of the genes targeted by dsRNA injection in this group. Conse quently, RNAi did not affect fly mortality or oviposition. In other arthropods, silencing of serine proteases expression by RNAi showed that these proteins are involved in blood digestion, oocyte maturation, develop ment and immune response.

Protease inhibitors The protease inhibitor genes identified in female horn flies corresponded to serpins, inhibitors of serine pro teases and thus involved in the same biological pro cesses discussed before for serine proteases. A horn fly serine protease inhibitor gene was previously cloned and characterized, suggesting that these genes may be involved in the control of fly endogenous and pathogen proteases. In mosquitoes, serpin RNAi affected insect immune response. The elastase inhibitor gene knockdown significantly increased horn fly mortal ity at 12, 24 and 36 hpi. Thus, the effect of elastase inhi bitor RNAi described here in horn flies may be the result of impaired fly protease control and or the effect of increased Brefeldin_A susceptibility to persistent pathogen infec tions resulting from diminished immune response. Vitellogenin VTGs constitute a multigene superfamily encoding for egg yolk precursor proteins expressed in the females of arthropods and other oviparous organisms.