Knockdown of a Mosquito Odorant-binding Protein Involved in the Sensitive Detection of Oviposition Attractants

Abstract

Odorant-binding proteins (OBPs) were discovered almost three decades ago, but there is still considerable debate regarding their role(s) in insect olfaction, particularly due to our inability to knockdown OBPs and demonstrate their direct phenotypic effects. By using RNA interference (RNAi), we reduced transcription of a major OBP gene, CquiOBP1, in the antennae of the Southern house mosquito, Culex quinquefasciatus. Previously, we had demonstrated that the mosquito oviposition pheromone (MOP) binds to CquiOBP1, which is expressed in MOP-sensitive sensilla. Antennae of RNAi-treated mosquitoes showed significantly lower electrophysiological responses to known mosquito oviposition attractants than the antennae of water-injected, control mosquitoes. While electroantennogram (EAG) responses to MOP, skatole, and indole were reduced in the knockdowns, there was no significant difference in the EAG responses from RNAi-treated and water-injected mosquito antennae to nonanal at all doses tested. These data suggest that CquiOBP1 is involved in the reception of some oviposition attractants, and that high levels of OBPs expression are essential for the sensitivity of the insect’s olfactory system.

Insect olfaction from model systems to disease control

“…CquiOBP1 binds the oviposition pheromone as well as other odorants (138,145). In a recent study, RNAi knockdown of CquiOBP1 resulted in a reduced electrophysiological response to oviposition pheromone and some, but not all, of the nonpheromonal odorants that bind to this OBP (49). This result provides an interesting opportunity to investigate the role of an OBP in the behavioral response to nonpheromonal odorants, an unresolved question in the field.…”

“…However, OBPs seem likely to play roles in the dynamics of olfactory response and in olfactory sensitivity. Two recent studies have reported decreased electrophysiological responses to odorants when an OBP was targeted with RNAi (48,49), and variations in behavioral responses to odorants have been associated with polymorphisms in OBP genes (50,51).…”

“…Because RNAi knockdown of an OBP resulted in decreased electrophysiological responses to some odorants (48,49), it will be interesting to examine the behavioral effects of such manipulations from the standpoint of technology as well as science. Targeting of OBPs that bind pheromones deserves special attention; precedent for this approach comes from the phenotypic effects observed from genetic disruption of LUSH (52) and CquiOBP1, which binds the oviposition pheromone of C. quinquefasciatus (49,145). Screens for molecules that interact with such OBPs could yield agents that disrupt mating or oviposition behavior.…”

Crystal and solution structures of an odorant-binding protein from the southern house mosquito complexed with an oviposition pheromone

“…CquiOBP1 bound MOP with high affinity at high pH but showed no affinity at low pH (8). OBPs essential role for odorant reception in C. quinquefasciatus has been demonstrated by RNA interference experiments in which reduction of CquiOBP1 expression led to lower sensitivity for the detection of oviposition attractants, including MOP (12). Using CquiOBP1 as a molecular target in a reverse chemical ecology approach (10), we identified C. quinquefasciatus oviposition attractants (8), which are now commercially available for monitoring and surveillance.…”

Live calcium imaging ofAedes aegyptineuronal tissues reveals differential importance of chemosensory systems for life-history-specific foraging strategies

“…Finally, these GCaMP6s/+/+ mosquitoes and GCaMP6s/Gr3-/-and GCaMP6s/orco5-/-mutants could provide additional information and strategies for the control of disease-vector mosquitoes. Female mosquitoes may use olfactory indicators of larval habitat quality to choose oviposition sites [69] . A better understanding of chemosensory cues that elicit strong responses in larvae could help identify new attractants for use in oviposition traps, or oviposition deterrents for use in homes and outdoor water containers.…”