Study of the transcriptional response to intoxication by Cry toxins in Aedes aegypti midgut

Worldwide rise of Dengue fever and Chikungunya cases highlights the importance of efficient control of mosquito populations, such as with the insecticidal Cry-toxins from Bacillus thuringiensis. Exposure to Cry toxins has been seen to induce transcriptional response in insects, but information in Aedes aegypti is limited. We performed a 12 h intoxication assay with a Cry11Aa LC₅₀ dose and conducted RNAseq analysis on the mRNA from dissected midgut tissue of toxin-exposed larvae. Differential expression analysis showed stronger transcriptional response with prolonged Cry11Aa intoxication. After short times of toxin ingestion repression of cell division and transmembrane transport was observed. Longer exposure times induced functions related to vesicular traffic, cellular morphogenesis, protein folding and lipid biosynthesis. Several induced functions and genes indicate a strong role of small GTPases of the Rho, ARF and RAB subfamilies in the response to Cry toxins, linking them to transduction via PIP3 as well as MAP kinases. At the longest time of intoxication oxidative stress functions, synthesis of antimicrobial peptides, and some ABC transporters were repressed. RT-qPCR analysis of intoxication curves with Wt and mutant Cry11Aa toxins validate RNAseq results, but also indicate that functional pore formation is required to trigger the response mechanisms. This knowledge will help us understand mosquito responses of midgut recovery to Cry toxin and may point out specific genes that could be targeted by other strategies such as RNAi or gene knock-out to increase Cry toxin efficiency against mosquitoes.