Functional analysis of Orco and odorant receptors in odor recognition in Aedes albopictus

Abstract

BackgroundAedes albopictus is a globally invasive mosquito and a major vector of arboviruses, including dengue, Zika and Chikungunya. Olfactory-related behaviors, particularly host-seeking, offer opportunities to disrupt the disease-transmission process. A better understanding of odorant receptors (ORs) may assist in explaining host selection and location, and contribute to novel strategy of vector control.MethodsBased on previous prediction of 158 putative odorant receptors by Ae. albopictus genome analysis, 29 AalORs were selected for tissue-specific expression profiles in the present study. AalOrco (AalOR7), AalOR10 and AalOR88, highly expressed in female olfactory tissues, were chosen for further structure predictions as well as functional validation including calcium imaging assay in human embryonic kidney (HEK293) cells and RNA interference assay in Ae. albopictus. We also conducted electrophysiological and behavioral assays in mosquitoes after RNA interference of the three genes to determine their roles in host-seeking.ResultsThe results support previous conclusions that individual conventional (ORXs) and Orco can form heteromeric complexes to recognize odorants and respond to components of human volatiles in HEK293 cells. The reduction of AalOrco transcript levels led to a significant decrease in host-seeking and confusion in host preference. In contrast, AalOR10 and AalOR88 knockdown mosquitoes showed no significant behavioral differences compared with controls. The functions of conventional ORs at least AalOR10 and AalOR88 are abolished with inhibited expression of the Orco gene orthologs, along with the concomitant relevant olfactory behavior.ConclusionsCombining structural and functional data, we conclude that the product of the Orco gene in this mosquito is crucial for transmitting olfactory signaling and conventional ORs contribute directly to odorant recognition. Our results provide insight into the linkage between odorant receptors and host-seeking in this important vector species.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-016-1644-9) contains supplementary material, which is available to authorized users.

Expression and Localization of Olfactory Receptor AcerOr1 from Chinese Honey Bee, Apis cerana cerana (Hymenoptera, Apidae)

“…The developmental and tissue-specific expression profiles of conventional odorant receptors, are highly distinct and species-specific; for example, AgOR1 is expressed specifically in female Anopheles gambiae [13] and AgOR4 is highly expressed in the antennae [14]. AalOR7, AalOR10, and AalOR88 were detected significantly and specifically in female antennae [15]. Among the 57 odorant receptor genes in Drosophila, 32 are specifically expressed in the antenna, with seven being exclusively expressed in the maxillary palp, and one in both the antenna and maxillary palp.…”

Peer Review #3 of "Expressional and functional interactions of two Apis cerana cerana olfactory receptors (v0.2)"

“…Based on membrane topology analysis of the AcerOrc2 sequences, we showed that the CaM-binding domain residue in ICL2 was found to be highly conserved. This domain has been studied in Drosophila melanogaster 336 SAIKYWVER 344 (Mukunda et al, 2014) and in Aedes albopictus, 329 SAIKYWVER 337 (Liu et al, 2016), and this sequence conservation indicates that CaM activity in ICL2 plays a crucial functional role in the formation of functional ion channels by AcerOr2. In addition, the Tyr residue Y469 in AcerOr2 TM7 is conserved in B. mori (Y464) (Tatsuro et al, 2012) and L. lucorum (Y463) (Zhou et al, 2014) and has been confirmed to be critical for ion function, whereas conventional AcerOr1 does not have this sequence.…”

Neuro-Olfactory Regulation and Salivary Actions: A Coordinated Event for Successful Blood-Feeding Behavior of Mosquitoes

“…Further experimental evidence suggested that mosquito ORs act as ligand-gated ion channels comprising of heteromeric complexes of two subunits [38,39]. One subunit is highly conserved and known as olfactory receptor co-receptors (Orco), and the other subunit is largely divergent in terms of number as well as amino acid sequences (Orx) [31,[40][41][42]. Pilot studies of the OR gene repertoire primarily in Drosophila melanogaster [35] and later in mosquitoes [42,43] suggest that despite having a limited number of ORs, mosquitoes can respond to an array of varied chemicals depending on the specific demand at different life cycle stages [44].…”