A spatial map of antennal-expressed olfactory ionotropic receptors in the malaria mosquito

The malaria mosquito Anopheles coluzzii uses odors to guide various behaviors such as host-seeking. The detection of behaviorally relevant odors is mediated by a diverse family of receptors including the olfactory Ionotropic Receptors (IRs). Olfactory receptors are expressed on olfactory neurons, with the mosquito antennae representing the main olfactory appendage for detecting volatile chemical cues from the environment. It is currently unknown how many neurons across the antenna express a certain IR, or how these IR-expressing neurons are spatially arranged. Here, we performed whole mount fluorescent in situ hybridization of all IRs expressed in the antennae. The organization of IR-positive cells within an antennal segment (flagellomere) appeared stereotyped across multiple antennae. The spatial map of IR-expressing neurons revealed that the antenna might be organized into proximal and distal functional domains. Highly expressed tuning (odor-binding) IRs exhibit distinct co-localization patterns with cognate IR co-receptor(s) in a combinatorial fashion that might predict their functional properties. These findings reveal organizing principles of Anopheles IR-expressing neurons in the mosquito which might underlie their functional contribution to the detection of behaviorally relevant odors.