Gonadulin: A novel insulin-like peptide involved in oviposition in Rhodnius prolixus, a vector of chagas disease

Insulin-like peptides (ILPs) are vital hormones involved in a wide range of physiological processes in all organisms. In insects, insulin signalling has been reported to be involved mainly in detecting and interpreting nutrient levels for egg production. Based on publicly available transcriptomes, a new ILP named gonadulin has been reported and suggested to be expressed by the gonads (hence its name). Although the identification of gonadulin establishes its existence, its physiological relevance remains poorly understood. Rhodnius prolixus is an obligate hematophagous insect and a primary vector of Trypanosoma cruzi, the etiological agent of Chagas disease. In this study on R. prolixus we report for the first time the participation of gonadulin in reproductive performance of an hemipteran. By RT-qPCR, we find that the R. prolixus gonadulin (Rhopr-gonadulin) transcript is highly expressed in the reproductive system, particularly in the calyx, a structure through which eggs pass into the lumen of the lateral oviducts. Using Fluorescence in situ Hybridization (FISH) we confirm the location of the Rhopr-gonadulin transcript in the calyx. Interestingly, when the Rhopr-gonadulin signaling cascade is impaired using RNA interference (RNAi), eggs are retained primarily in the ovarioles and calyx, and thus oviposition is inhibited. Overall, the results support the hypothesis of Rhopr-gonadulin acting in an autocrine or paracrine way, in order to enable oviposition. Understanding the physiological mechanisms of reproductive performance in R. prolixus can shed light on potential targets for effective production of biopesticides by translational research, thereby controlling insect populations and transmission of the disease.