Gene editing reveals obligate and modulatory components of the CO receptor complex in the malaria vector mosquito, Anopheles coluzzii.

The sensitivity to volatile carbon dioxide (CO) produced by humans and other animals is a critical component in the host preference behaviors of the malaria vector mosquito Anopheles coluzzii. The molecular receptors responsible for the ability to sense CO are encoded by three putative gustatory receptor (Gr) genes (Gr22,23,24) which are expressed in a distinctive array of sensory neurons housed in maxillary palp capitate peg sensilla of An. coluzzii. Despite the identification of these components and subsequent studies, there is a paucity of understanding regarding the respective roles of these three GRs in the mosquito's CO transduction process. To address this, we have used CRISPR/Cas9-based gene editing technique combined with in vivo electrophysiological recordings to directly examine the role of Gr22,23,24 in detecting CO in An. coluzzii. These studies reveal that both Gr23 and Gr24 are absolutely required to maintain in vivo CO sensitivity while, in contrast, Gr22 knock out mutants are still able to respond to CO stimuli albeit with significantly weaker sensitivity. Our data supports a model in which Gr22 plays a modulatory role to enhance the functionality of Gr23/24 complexes that are responsible for CO sensitivity of mosquitoes.