Silent, generic and plant kairomone sensitive odorant receptors from the Southern house mosquito

Abstract

The Southern house mosquito Culex quinquefasciatus has the largest repertoire of odorant receptors (ORs) of all mosquitoes and dipteran species whose genomes have been sequenced to date. Previously, we have identified and de-orphanized two ORs expressed in female antennae, CquiOR2 and CquiOR10, which are sensitive to oviposition attractants. In view of a new nomenclature for the Culex genome (VectorBase) we renamed these ORs as CquiOR21 (formerly CquiOR10) and CquiOR121 (CquiOR2). In addition, we selected ORs from six different phylogenetic groups for deorphanization. We cloned four of them by using cDNA from female antennae as a template. Attempts to clone CquiOR87 and CquiOR110 were unsuccessful either because they are pseudogenes or are not expressed in adult female antennae, the main olfactory tissue. By contrast, CquiOR1, CquiOR44, CquiOR73, and CquiOR161 were highly expressed in female antennae. To de-orphanize these ORs, we employed the Xenopus oocyte recording system. CquiORx-CquiOrco-expressed oocytes were challenged with a panel of 90 compounds, including known oviposition attractants, human and vertebrate host odorants, plant kairomones, and naturally occuring repellents. While CquiOR161 did not respond to any test compound in two different laboratories, CquiOR1 showed the features of a generic OR, with strong responses to 1-octen-3-ol and other ligands. CquiOR44 and CquiOR73 showed preference to plant-derived terpenoids and phenolic compounds, respectively. While fenchone was the best ligand for the former, 3,5-dimethylphenol elicited the strongest responses in the latter. The newly de-orphanized ORs may be involved in reception of plant kairomones and/or natural repellents.

Mosquito odorant receptor for DEET and methyl jasmonate

“…We cloned the other seven putative ORs, CquiOR55, CquiOR64, CquiOR93, CquiOR125, CquiOR132, CquiOR136, and CquiOR151. We screened them for a DEET receptor by using the Xenopus oocyte recording system, as previously done to deorphanize multiple Culex ORs (9,(14)(15)(16)(17). CquiOR136•CquiOrco-expressing oocytes were mainly activated by DEET, PMD, IR3535, picaridin, and two other repellents, γ-octalactone and 3-octanol ( Fig.…”

Differential expression of olfactory genes in the southern house mosquito and insights into unique odorant receptor gene isoforms

“…Our initial estimate of 158 OR genes (6) and the report of 180 putative OR genes, along with the comprehensive genome analysis (5), were updated to 130 putative OR genes (7). Our current studies with the discovery of unique genes and isoforms suggests a repertoire of 177 Cx.. quiquefasciatus OR genes, including CquiOrco.…”

“…We now know that the major peripheral olfactory proteins involved in the reception of odorants in insects are the odorant-binding proteins (OBPs), chemosensory proteins (CSPs), odorant-degrading enzymes (ODEs), odorant receptors (ORs), ionotropic receptors (IRs), and sensory neuron membrane proteins (SNMPs) (4). The southern house mosquito may possess one of the most, if not the most, acute olfactory system in mosquitoes (3) and has the largest repertoire of putative odorant receptors (ORs) of all dipteran species whose genomes have been hitherto sequenced (5)(6)(7). Given the diversity of olfactory genes involved in reception of semiochemicals, our understanding of the molecular basis of olfaction heavily depends on genomic data.…”

“…quinquefasciatus and related Culex pipiens complex mosquitoes have a very high degree of polymorphism and the highest density of single nucleotide polymorphism (SNP) of all mosquito species studied thus far (8). Thus, genetic differences between the Johannesburg strain (the source of genome sequences) and our California strain has retarded progress in our attempts to isolate, clone, and deorphanize ORs on the basis of genomic data (7,9), particularly given the number of potential pseudogenes and genes unlikely to be expressed in female antennae. Here, we used next generation…”

Odorant receptor-based discovery of natural repellents of human lice

“…Using the pGEMHE-PhumOR plasmids as templates, capped cRNAs were synthesized with mMACHINE T7 Kit following the manufacturer's instructions (Xu et al, 2013). Purified OR cRNAs were re-suspended in nuclease-free water at 200 ng/ml and 18.4 nl of cRNAs were microinjected with the same amount of PhumOrco cRNA into stage V or VI X. laevis oocytes (purchased from EcoCyte Bioscience, Austin, TX).…”