A mosquito-specific antennal protein is critical for the attraction to human odor in the malaria vector Anopheles gambiae

Involvement of a Microplusin-like Gene (HlonML-1) in the Olfactory Chemosensation of Haemophysalis longicornis: Expression, RNA Silencing, and Behavioral Implications

The study of tick olfaction is relatively new compared to that of insects, and the molecular mechanisms involved remain poorly understood. Despite several potential chemosensory genes identified in multiple tick species, these are yet to be validated through independent functional experiments. In this research, we cloned and analyzed a microplusin-like gene, HlonML-1, and investigated its role in the chemosensory activities of H. longicornis. The results showed that this gene's amino acid sequences lack histidine residues essential for antimicrobial activity, and it is evolutionarily linked to putative chemosensory microplusins in ticks. Gene expression analyses indicated that HlonML-1 was significantly more abundant in ticks exposed to potential attractants and in the forelegs of H. longicornis than in non-exposed ticks and the hindlegs, respectively. Tick forelegs support the Haller's organ, which is a sensory structure mostly specialized for chemosensation. Furthermore, Y-tube olfactometer assays indicated that silencing HlonML-1 significantly impaired adult ticks' ability to detect selected odors, while their gustatory-related behavior remained unaffected compared to the control groups. Given its unique sequences, relative abundance in chemosensory tissues, and impact on odor detection, HlonML-1 is likely involved in the olfactory chemosensation of H. longicornis. Future research validating putative chemosensory microplusins in the genomes of various tick species may enhance our understanding of their olfactory functions in tick and lead to the identification of new molecular targets for developing tick repellents.

Evidence for a role of SNMP2 and antennal support cells in sensillum lymph clearance processes of moth pheromone-responsive sensilla

In insect antenna, following the activation of olfactory sensory neurons, odorant molecules are inactivated by enzymes in the sensillum lymph. How the inactivation products are cleared from the sensillum lymph is presently unknown. Here we studied the role of support cells (SCs) and the so-called sensory neuron membrane protein 2 (SNMP2), a member of the CD36 family of lipid transporters abundantly expressed in SCs, in sensillum lymph clearance processes in the moths Heliothis virescens and Bombyx mori. In these species, the sex pheromone components are inactivated to long-chain fatty acids. To approach a role of SNMP2 in the removal of such inactivation products, we analyzed the uptake of a fluorescent long-chain fatty acid analog into a newly generated HvirSNMP2-expressing cell line. We found an increased uptake of the analog into SNMP2-cells compared to control cells, which could be blocked by the CD36 protein inhibitor, SSO. Furthermore, analyses of sensilla from antenna treated with the fatty acid analog indicated that SNMP2-expressing SCs are able to take up fatty acids from the sensillum lymph. In addition, sensilla from SSO-pretreated antenna of B. mori showed reduced removal of the fluorescent analog from the sensillum lymph. Finally, we revealed that SSO pretreatment of male silkmoth antenna significantly prolonged the duration of the female pheromone-induced wing-fluttering behavior, possibly as a result of impaired lymph clearance processes. Together our findings in H. virescens and B. mori support a pivotal role of olfactory SCs in sensillum lymph maintenance processes and suggest an integral role of SNMP2 in the removal of lipophilic "waste products" such as fatty acids resulting from sex pheromone inactivation.