Our results describe a complete and highly concordant map of both the molecular and cellular olfactory components on the maxillary palp of the adult female An. gambiae mosquito. These results also facilitate the understanding of how An. gambiae mosquitoes sense olfactory cues that might be exploited to compromise their ability to transmit malaria.

The proboscis is an important head appendage in insects that has primarily been thought to process gustatory information during food intake. Indeed, in Drosophila and other insects in which they have been identified, most gustatory receptors are expressed in proboscis neurons. Our previous characterization of the expression of AgOR7, a highly conserved odorant receptor (OR) of the Afrotropical malaria vector mosquito Anopheles gambiae in the labellum at the tip of the proboscis was suggestive of a potential olfactory function in this mosquito appendage. To test this hypothesis, we used electrophysiological recording and neuronal tracing, and carried out a molecular characterization of candidate OR expression in the labellum of A. gambiae. These studies have uncovered a set of labial olfactory responses to a small spectrum of human-related odorants, such as isovaleric acid, butylamine, and several ketones and oxocarboxylic acids. Molecular analyses indicated that at least 24 conventional OR genes are expressed throughout the proboscis. Furthermore, to more fully examine AgOR expression within this tissue, we characterized the AgOR profile within a single labial olfactory sensillum. This study provides compelling data to support the hypothesis that a cryptic set of olfactory neurons that respond to a small set of odorants are present in the mouth parts of hematophagous mosquitoes. This result is consistent with an important role for the labellum in the close-range discrimination of bloodmeal hosts that directly impacts the ability of A. gambiae to transmit malaria and other diseases.olfaction ͉ proboscis ͉ insect ͉ olfactory receptor neuron

Heat sensitivity is a sensory modality that plays a critical role in close-range host-seeking behaviors of adult female Anopheles gambiae, the principal Afrotropical vector for human malaria. An essential step in this activity is the ability to discriminate and respond to increases in environmental temperature gradients through the process of peripheral thermoreception. Here, we report on the characterization of the anopheline homolog of the transient receptor potential (TRP) A1/ANKTM1 channel that is consistent with its role as a heat-sensor in host-seeking adult female mosquitoes. We identify a set of distal antennal sensory structures that specifically respond to temperature gradients and express AgTRPA1. Functional characterization of AgTRPA1 in Xenopus oocytes supports its role in the molecular transduction of temperature gradients in An. gambiae, providing a basis for targeting mosquito heat responses as a means toward reducing malaria transmission.

To initiate a comprehensive investigation of chemosensory signal transduction downstream of odorant receptors, we identified and characterized the complete set of genes that encode G-protein α subunits in the genome of the malaria vector mosquito An. gambiae. Data are provided on the tissue-specific expression patterns of 10 corresponding aga-transcripts in adult mosquitoes and pre-imago developmental stages. Specific immunoreactivity in chemosensory hairs of female antennae provides evidence in support of the participation of a subset of AG αq isoforms in olfactory signal transduction in this mosquito. In contrast, AG αo is localized along the flagellar axon bundle but is absent from chemosensory sensilla, which suggests that this G-protein α subunit does not participate in olfactory signal transduction. Indexing terms RT-PCR; olfaction; insect; G-proteinOlfaction plays a critical role in modulating a wide range of behaviors across all insect taxa (for review, see Dahanukar et al., 2005;Rutzler and Zwiebel, 2005). Indeed, chemosensorydriven behaviors have profound effects on the capabilities of many insects to transmit a range of human and animal pathogens (reviewed by (Zwiebel and Takken, 2004). Following the identification of genes encoding candidate insect chemoreceptors in the Drosophila melanogaster genome (Clyne et al., 1999;Gao and Chess, 1999;Vosshall et al., 1999), several homologs have been identified in a number of nonmodel insects, including the malaria vector mosquito Anopheles gambiae (Fox et al., 2001;Hill et al., 2002). More recently, studies in D. melanogaster and other systems have facilitated functional characterization of members of this gene family (Chyb et al., 2003;Dobritsa et al., 2003; Hallem et al., 2004a,b;Sakurai et al., 2004;Goldman et al., 2005;Kreher et al., 2005;Nakagawa et al., 2005;Neuhaus et al., 2005). In a similar fashion to odorant receptors (ORs) in vertebrates and nematodes, insect ORs are thought to function by affecting the guanosine nucleotide exchange rate of heterotrimeric guanosine 5′-triphosphate (GTP) binding (G) proteins (Jones and Reed, 1989;Zwaal et al., 1997), although the precise mechanisms of NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript peripheral olfactory signal transduction remain unclear (for review, see Krieger and Breer, 1999;Rutzler and Zwiebel, 2005). In one study using the cockroach, exposure of antennal preparations to pheromone resulted in a rapid increase in inositol-1,4,5-trisphosphate (IP 3 ) levels . This effect can be inhibited by pertussis toxin, indicating that it is likely to be dependent on either a G αi or G αo heterotrimeric G-protein subunit . Moreover, the localization of G αq -proteins to the dendritic membrane of Bombyx mori olfactory receptor neurons further implicates these G-proteins in the generation of second-messenger signals in response to OR-odorant binding (Laue et al., 1997). Both reports suggest that at least some aspects of insect olfactory signal transduction involve phospholipas...