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

Abstract

The southern house mosquito, Culex quinquefasciatus, has one of the most acute and eclectic olfactory systems of all mosquito species hitherto studied. Here, we used Illumina sequencing to identify olfactory genes expressed predominantly in antenna, mosquito's main olfactory organ. Less than 50% of the trimmed reads generated by high-quality libraries aligned to a transcript, but approximately 70% of them aligned to the genome. Differential expression analysis, which was validated by quantitative realtime PCR on a subset of genes, showed that approximately half of the 48 odorant-binding protein genes were enriched in antennae, with the other half being predominantly expressed in legs. Similar patterns were observed with chemosensory proteins, "plus-C" odorant-binding proteins, and sensory neuron membrane proteins. Transcripts for as many as 43 ionotropic receptors were enriched in female antennae, thus making the ionotropic receptor family the largest of antennae-rich olfactory genes, second only to odorant receptor (OR) genes. As many as 177 OR genes have been identified, including 36 unique transcripts. The unique OR genes differed from previously annotated ORs in internal sequences, splice variants, and extended N or C terminus. One of the previously unknown transcripts was validated by cloning and functional expression. When challenged with a large panel of physiologically relevant compounds, CquiOR95b responded in a dose-dependent manner to ethyl 2-phenylacteate, which was demonstrated to repel Culex mosquitoes, and secondarily to citronellal, a known insect repellent. This transcriptome study led to identification of key molecular components and a repellent for the southern house mosquito.RNA-Seq | citronellal polymorphism isoforms

Mosquito odorant receptor for DEET and methyl jasmonate

“…We therefore surmised that DEET must be detected by highly expressed odorant receptors (ORs) given that only a very small fraction of molecules released in the air would reach neurons housed in antennal sensilla (13). Two out of the top 10 putative OR genes enriched in female antennae compared with control tissues (14), CquiOR21 (formerly CquiOR10) (15) and CquiOR95 (14), have already been deorphanized, and one putative OR, CquiOR36, is probably a pseudogene. We cloned the other seven putative ORs, CquiOR55, CquiOR64, CquiOR93, CquiOR125, CquiOR132, CquiOR136, and CquiOR151.…”

“…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.…”

“…Having identified a DEET-sensitive OR highly expressed in mosquito female antennae (14) we tested whether DEET might mimic plant defense compound(s) with a long insect-plant evolutionary history, such as those in the jasmonate-signaling pathway (19). After all, DEET, a more recent synthetic counterpart developed by molecular modeling (2), picaridin, and methyl jasmonate share similar structural motifs, which are essential for activity (20), and methyl jasmonate is a repellent for the southern house mosquito, as well as ticks (21).…”

Transcriptomic identification of chemoreceptor genes in the red palm weevil Rhynchophorus ferrugineus

“…In addition, comp14522_c0 appeared to be enriched in the abdomen, and comp12012_c0 was expressed at higher level in the abdomen than in antennae. It is unlikely that proteins predominantly expressed in non-olfactory tissues play a role in odorant reception in antennae (Leal et al, 2013). These OR genes are enriched in non-olfactory tissues, suggesting that they may play an important role in the unexpected expression in non-chemosensory tissues.…”

Venom allergen 5is Associated With Deltamethrin Resistance inCulex pipiens pallens(Diptera: Culicidae)

“…The data were analyzed with 7300 System SDS Software v1.2.1 (Applied Biosystems, Foster City, CA). We chose b-actin (Canales et al 2009) and RsP7 (Leal et al 2013) as the internal normalization. The relative expression levels of each gene were calculated using the 2 -(DDCt) method (Livak and Schmittgen 2001).…”