RNA activation in insects: The targeted activation of endogenous and exogenous genes

Advances in structural-guided modifications of siRNA

To date, the US Food and Drug Administration (FDA) has approved six small interfering RNA (siRNA) drugs: patisiran, givosiran, lumasiran, inclisiran, vutrisiran, and nedosiran, serving as compelling evidence of the promising potential of RNA interference (RNAi) therapeutics. The successful implementation of siRNA therapeutics is improved through a combination of various chemical modifications and diverse delivery approaches. The utilization of chemically modified siRNA at specific sites on either the sense strand (SS) or antisense strand (AS) has the potential to enhance resistance to ribozyme degradation, improve stability and specificity, and prolong the efficacy of drugs. Herein, we provide comprehensive analyses concerning the correlation between chemical modifications and structure-guided siRNA design. Various modifications, such as 2'-modifications, 2',4'-dual modifications, non-canonical sugar modifications, and phosphonate mimics, are crucial for the activity of siRNA. We also emphasize the essential strategies for enhancing overhang stability, improving RISC loading efficacy and strand selection, reducing off-target effects, and discussing the future of targeted delivery.

RNA Interference in Insects: From a Natural Mechanism of Gene Expression Regulation to a Biotechnological Crop Protection Promise

Insect pests rank among the major limiting factors in agricultural production worldwide. In addition to direct effect on crops, some phytophagous insects are efficient vectors for plant disease transmission. Large amounts of conventional insecticides are required to secure food production worldwide, with a high impact on the economy and environment, particularly when beneficial insects are also affected by chemicals that frequently lack the desired specificity. RNA interference (RNAi) is a natural mechanism gene expression regulation and protection against exogenous and endogenous genetic elements present in most eukaryotes, including insects. Molecules of double-stranded RNA (dsRNA) or highly structured RNA are the substrates of cellular enzymes to produce several types of small RNAs (sRNAs), which play a crucial role in targeting sequences for transcriptional or post-transcriptional gene silencing. The relatively simple rules that underlie RNAi regulation, mainly based in Watson-Crick complementarity, have facilitated biotechnological applications based on these cellular mechanisms. This includes the promise of using engineered dsRNA molecules, either endogenously produced in crop plants or exogenously synthesized and applied onto crops, as a new generation of highly specific, sustainable, and environmentally friendly insecticides. Fueled on this expectation, this article reviews current knowledge about the RNAi pathways in insects, and some other applied questions such as production and delivery of recombinant RNA, which are critical to establish RNAi as a reliable technology for insect control in crop plants.

RNA activation in ticks

RNA activation (RNAa) is a burgeoning area of research in which double-stranded RNAs (dsRNAs) or small activating RNAs mediate the upregulation of specific genes by targeting the promoter sequence and/or AU-rich elements in the 3'- untranslated region (3'-UTR) of mRNA molecules. So far, studies on the phenomenon have been limited to mammals, plants, bacteria, Caenorhabditis elegans, and recently, Aedes aegypti. However, it is yet to be applied in other arthropods, including ticks, despite the ubiquitous presence of argonaute 2 protein, which is an indispensable requirement for the formation of RNA-induced transcriptional activation complex to enable a dsRNA-mediated gene activation. In this study, we demonstrated for the first time the possible presence of RNAa phenomenon in the tick vector, Haemaphysalis longicornis (Asian longhorned tick). We targeted the 3'-UTR of a novel endochitinase-like gene (HlemCHT) identified previously in H. longicornis eggs for dsRNA-mediated gene activation. Our results showed an increased gene expression in eggs of H. longicornis endochitinase-dsRNA-injected (dsHlemCHT) ticks on day-13 post-oviposition. Furthermore, we observed that eggs of dsHlemCHT ticks exhibited relatively early egg development and hatching, suggesting a dsRNA-mediated activation of the HlemCHT gene in the eggs. This is the first attempt to provide evidence of RNAa in ticks. Although further studies are required to elucidate the detailed mechanism by which RNAa occurs in ticks, the outcome of this study provides new opportunities for the use of RNAa as a gene overexpression tool in future studies on tick biology, to reduce the global burden of ticks and tick-borne diseases.