Identification and characterization of an odorant receptor from the West Nile virus mosquito, Culex quinquefasciatus

Abstract

Members of the Culex pipens mosquito group including C. quinquefasciatus are responsible for the transmission of Bancroftian filarisis as well as West Nile Virus (WNV) in the United States. As is the case for other mosquitoes, the host preference of this disease vector relies on olfaction and accordingly mediated via G-protein coupled signal transduction pathways. Here, we identify and characterize CqOR7, the first candidate member of the odorant receptor gene family from C. quinquefasciatus. CqOR7 displays extremely high primary amino acid conservation with other apparent orthologs including AaOR7, from the Dengue virus vector mosquito Aedes aegypti, AgOR7 from the malaria vector Anopheles gambiae and DOr83b from the fruit fly Drosophila melanogaster that form an essential non-conventional odorant receptor sub-family. CqOR7 transcripts can be detected in adult chemosensory tissues and during several pre-adult stages of C. quinquefasciatus, and the CqOR7 protein is localized to characteristic olfactory tissues such as the antennae and maxillary palps as well as the proboscis, a typically gustatory appendage. These results suggest that CqOR7 and its orthologs are likely to play a role in the chemosensory processes of Culicine and other mosquitoes that underlie their vectorial capacity.

Fig. 1

Alignment of CqOr7 ortholog peptides using the single amino acid code. Identical residues are shaded and boxed. Transmembrane domains I–VII are indicated with black bars. Dotted line indicates peptide used for generating OR7 antiserum. For a list of genes and accession numbers see materials and methods.

Fig. 2

Expression of CqOR7 in pre-adult and adult C. quinquefasciatus. Lane as follows—early larvae (EL), late larvae (LL), early pupae (EP), late pupae (LP), female antennae (fAnt), female proboscis (fPro), female leg (fLeg), female body (fBody), male antennae (mAnt), male maxillary palp (mMP), male proboscis (mPro), male leg (mLeg), male body (mBody), negative control. RPS7 acts as positive control.

Fig. 3

Localization of CqOR7 protein in female C. quinquefasciatus antennae. Red is anti-AgOR7 marked with Cy3-labelled secondary antibody. Green is anti-horseradish peroxidase conjugated to FITC. (A) SEM of the first antenna segment ST—sensillum trichodica (scale bar is 40 µm). (B) SEM of the second antenna segment GP—grooved pegs, (scale bar is 40 µm). (C) CqOr7 labeling of the first antenna segment, arrows shows the labeling of a neuron cell body, (scale bar is 20 µm). (D) CqOr7 labeling of the second antenna segment, (scale bar is 20 µm). (E) control reaction using pre-immune serum as primary antibody, arrow shows an unlabeled sensillum trichodica (scale bar is 40 µm). (F) No CqOr7 labeling is observed in grooved peg (scale bar is 5 µm). (G) CqOr7 labeling of the first 6 antenna segments (scale bar is 40 µm).

Fig. 4

Localization of CqOR7 protein in female C. quinquefasciatus maxillary palp and proboscis. Red is anti-AgOR7 marked with Cy3-labeled secondary antibody. Green is anti-horseradish peroxidase conjugated with FITC. (A) SEM of a female C. quinquefasciatus maxillary palp CP—capitate pegs (scale bar is 25 µm). (B) CqOr7 labeling of the capitate pegs (scale bar is 25 µm). (C) SEM of a female C. quinquefasciatus proboscis region, arrow shows a distinct type of sensillum (scale bar is 5 µm). (D) CqOr7 is labeled in a distinct type of sensilla shown by arrow (scale bar is 20 µm).