Atypical strategies for cuticle pigmentation in the blood-feeding hemipteran Rhodnius prolixus

Gene Editing in the Chagas Disease Vector Rhodnius prolixus by Cas9-Mediated ReMOT Control

Rhodnius prolixus is currently the model vector of choice for studying Chagas disease transmission, a debilitating disease caused by Trypanosoma cruzi parasites. However, transgenesis and gene editing protocols to advance the field are still lacking. Here, we tested protocols for the maternal delivery of CRISPR-Cas9 (clustered regularly spaced palindromic repeats/Cas-9 associated) elements to developing R. prolixus oocytes and strategies for the identification of insertions and deletions (indels) in target loci of resulting gene-edited generation zero (G0) nymphs. We demonstrate successful gene editing of the eye color markers Rp-scarlet and Rp-white, and the cuticle color marker Rp-yellow, with highest effectiveness obtained using Receptor-Mediated Ovary Transduction of Cargo (ReMOT Control) with the ovary-targeting BtKV ligand. These results provide proof of concepts for generating somatic mutations in R. prolixus and potentially for generating germ line-edited lines in triatomines, laying the foundation for gene editing protocols that could lead to the development of novel control strategies for vectors of Chagas disease.

Efficient DIPA-CRISPR-mediated knockout of an eye pigment gene in the white-backed planthopper, Sogatella furcifera

Although CRISPR/Cas9 has been widely used in insect gene editing, the need for the microinjection of preblastoderm embryos can preclude the technique being used in insect species with eggs that are small, have hard shells, and/or are difficult to collect and maintain outside of their normal environment. Such is the case with Sogatella furcifera, the white-backed planthopper (WBPH), a significant pest of Oryza sativa (rice) that oviposits inside rice stems. Egg extraction from the stem runs the risk of mechanical damage and hatching is heavily influenced by the micro-environment of the rice stem. To bypass these issues, we targeted embryos prior to oviposition via direct parental (DIPA)-CRISPR, in which Cas9 and single-guide RNAs (sgRNAs) for the WBPH eye pigment gene tryptophan 2,3-dioxygenase were injected into the hemocoel of adult females. Females at varying numbers of days posteclosion were evaluated to determine at what stage their oocyte might be most capable of taking up the gene-editing components. An evaluation of the offspring indicated that the highest G0 gene-edited efficacy (56.7%) occurred in females injected 2 d posteclosion, and that those mutations were heritably transmitted to the G1 generation. This study demonstrates the potential utility of DIPA-CRISPR for future gene-editing studies in non-model insect species and can facilitate the development of novel pest management applications.

Genome editing of the vermilion locus generates a visible eye color marker for Oncopeltus fasciatus

Insects display a vast array of eye and body colors. Genes encoding products involved in biosynthesis and deposition of pigments are ideal genetic markers, contributing, for example, to the power of Drosophila genetics. Oncopeltus fasciatus is an emerging model for hemimetabolous insects, a member of the piercing-sucking feeding order Hemiptera, that includes pests and disease vectors. To identify candidate visible markers for O. fasciatus, we used parental and nymphal RNAi to identify genes that altered eye or body color while having no deleterious effects on viability. We selected Of-vermilion for CRISPR/Cas9 genome editing, generating three independent loss-of-function mutant lines. These studies mapped Of-vermilion to the X-chromosome, the first assignment of a gene to a chromosome in this species. Of-vermilion homozygotes have bright red, rather than black, eyes and are fully viable and fertile. We used these mutants to verify a role for Of-xdh1, ortholog of Drosophila rosy, in contributing to red pigmentation using RNAi. Rather than wild-type-like red bodies, bugs lacking both vermilion and xdh1 have bright yellow bodies, suggesting that ommochromes and pteridines contribute to O. fasciatus body color. Our studies generated the first gene-based visible marker for O. fasciatus and expanded the genetic toolkit for this model system.

Arylalkylamine N-acetyltransferase 1 gene (AANAT1) regulates cuticle pigmentation and ovary development of the adult oriental fruit fly, Bactrocera dorsalis

The arylalkylamine N-acetyltransferase (AANAT) enzymes catalyze the acetyl-CoA-dependent acetylation of an amine or arylalkylamine, which is involved in important biological processes of insects. Here, we carried out the molecular and biochemical identification of an arylalkylamine N-acetyltransferase (AANAT) from the oriental fruit fly, Bactrocera dorsalis. Using a bacterial expression system, we expressed and purified the encoded recombinant BdorAANAT1-V3 protein. The purified recombinant protein acts on a wide range of substrates, including dopamine, tyramine, octopamine, serotonin, methoxytryptamine, and tryptamine, and shows similar substrate affinity (i.e., K_m values: 0.16-0.26 mM) except for serotonin (K_m = 0.74 mM) and dopamine (K_m = 0.84 mM). Transcriptional profile analysis of BdorAANAT1 revealed that this gene is most prevalent in adults and abundant in the adult brain, gut, and ovary. Using the CRISPR/Cas9 technique, we successfully obtained a BdorAANAT1 knockout strain based on a wild-type strain (WT). Compared with the WT, the cuticle color of larvae and pupae is normal; however, in adult mutants, the yellow region of their thorax is darkly pigmented, and two black spots were evident at the abdomen's end. Moreover, the female BdorAANAT1 knockout mutant had a smaller ovary than the WT, and laid far fewer eggs. Loss of function of BdorAANAT1 caused by RNAi with mature adult females in which the reproductive system is fully developed had no effect on their fecundity. Altogether, these results indicate that BdorAANAT1 regulates ovary development. Our findings provide evidence for the insect AANAT1 modulating adult cuticle pigmentation and female fecundity.