Transgenic expression of Nix converts genetic females into males and allows automated sex sorting in Aedes albopictus

Célia Lutrat,Jérémy Bouyer,Eric Marois,Roenick P. Olmo,Thierry Baldet

doi:10.1038/s42003-022-03165-7

Abstract

Aedes albopictus is a major vector of arboviruses. Better understanding of its sex determination is crucial for developing mosquito control tools, especially genetic sexing strains. In Aedes aegypti, Nix is the primary gene responsible for masculinization and Nix-expressing genetic females develop into fertile, albeit flightless, males. In Ae. albopictus, Nix has also been implicated in masculinization but its role remains to be further characterized. In this work, we establish Ae. albopictus transgenic lines ectopically expressing Nix. Several are composed exclusively of genetic females, with transgenic individuals being phenotypic and functional males due to the expression of the Nix transgene. Their reproductive fitness is marginally impaired, while their flight performance is similar to controls. Overall, our results show that Nix is sufficient for full masculinization in Ae. albopictus. Moreover, the transgene construct contains a fluorescence marker allowing efficient automated sex sorting. Consequently, such strains constitute valuable sexing strains for genetic control.

Highlights

Aedes albopictus is a major vector of arboviruses
The Nix-expressing transgenic Ae. albopictus lines presented in this work confirm that Nix is necessary and sufficient to initiate the male sex determination cascade in Ae. albopictus
They demonstrate that a short version of Nix comprising only the first two exons and the first intron is sufficient for complete masculinization

Summary

Introduction

Aedes albopictus is a major vector of arboviruses. Better understanding of its sex determination is crucial for developing mosquito control tools, especially genetic sexing strains. Stable transgenic expression of Nix in Ae. aegypti has been shown to be sufficient for converting all genetic females into phenotypic fertile males, confirming its role[24] These phenotypic males were unable to fly, most likely because they lacked myo-sex, another gene closely linked to the M-locus encoding a male-specific flight muscle myosin. Nix disruption using CRISPR/Cas[9] leads to partial feminization of males, confirming the role of Nix as the M-factor in this species[22] It remains to be shown whether Ae. albopictus Nix alone is sufficient for masculinization and if genetic females transformed into phenotypic males by transgenic expression of Nix would be fertile and able to fly. We generated transgenic Ae. albopictus mosquitoes expressing the four main Nix isoforms in genetic females and showed that all can induce partial to complete masculinization Some of these lines constitute valuable genetic sexing strains, allowing high-throughput sex sorting at the neonate stage

Methods

Results

Conclusion