The piRNA pathway in host-pathogen interaction: Aedes albopictus and arboviruses

Aedes albopictus is an aggressive invasive species and a competent vector for over 20 arboviruses, including Chikungunya, Dengue and Zika viruses. Understanding the molecular and cellular interactions between viruses and vectors is key to implement transmission-blocking strategies to prevent viral outbreaks. However, the mechanisms that shape vector competence are poorly understood. Recent evidence reveals that the genomes of Aedes spp. harbour fragmented viral sequences which produce PIWI-interacting RNAs (piRNAs), suggesting a role in vector competence. Current knowledge of the piRNA pathway in Ae. albopictus is limited, and its possible role in the establishment of persistent infections widely unknown.

We combined cutting-edge bioinformatic analyses based on next-generation sequencing data with molecular biology and virology techniques to characterise the main genes of the piRNA pathway in this mosquito species, assess their polymorphisms and analyse their expression throughout mosquito development and following infection with the Chikungunya and Dengue-1 viruses.

We identified seven piwi genes which displayed high levels of polymorphism across populations and signs of adaptive evolution. Superposition of protein homology models indicate high structure similarity among all Piwi proteins, with high levels of amino acid conservation in the inner regions devoted to RNA binding. On the contrary, solvent-exposed surfaces showed low conservation, with sites under positive selection. Infection experiments indicated specific responses depending on viral species, time of infection and mosquito tissue, highlighting distinct roles for specific Piwi proteins.

In conclusion, this work helps define the role of the piRNA pathway in persistent arboviral infections and understand the evolutionary divergence among piwi proteins.