Localization and Mutant Analysis of the Anopheles coluzzii Ammonium Transporter AcAmt
Ammonia is one of the principal kairomones originating from humans and plays an essential role in host-seeking/preference and other behaviors of the anthropophilic malaria vector mosquito Anopheles coluzzii. Despite its importance in directing host-seeking/preference, the mechanisms underlying ammonia detection in the mosquito olfactory system remain largely unknown while studies in Drosophila melanogaster have revealed a prominent role for the ammonium transporter (DmAmt) in modulating antennal responses to ammonia. In addition, localization of DmAmt in antennal sensilla to auxiliary cells surrounding the ammonia sensory neurons led to the hypothesis that its role was to clear excess ammonium ions in the sensillar lymph. Here advanced genetic tools, including the binary Q system and CRISPR/Cas9 system, have been employed to examine the spatial localization of the An. coluzzii ammonium transporter (AcAmt) and to generate AcAmt mutants which were characterized using a range of phenotypic assessments. In adult antennae, AcAmt-derived signals are observed in both non-neuronal auxiliary cells and in sensory neurons in ammonia-responsive basiconic and coeloconic sensilla. In the maxillary palps, labella, and tarsi, AcAmt appears restricted to sensory neurons. AcAmt-/- mutants displayed a series of reproductive deficits, while in contrast to D. melanogaster, no significant differences were observed across a range of peripheral sensory neuron responses to ammonia and other odorants between wild-type and AcAmt-/- females. These studies demonstrate that in contrast to the studies of its Drosophila ortholog, AcAmt is expressed heterogeneously across mosquito’s sensory appendages where it supports a novel mechanism for sensing volatile ammonia that may be unique to mosquitoes.