In Situ Tip-recordings Found No Evidence for an Orco-based Ionotropic Mechanism of Pheromone-transduction in Manduca Sexta
Overview
Authors
Affiliations
The mechanisms of insect odor transduction are still controversial. Insect odorant receptors (ORs) are 7TM receptors with inverted membrane topology. They colocalize with a conserved coreceptor (Orco) with chaperone and ion channel function. Some studies suggest that insects employ exclusively ionotropic odor transduction via OR-Orco heteromers. Other studies provide evidence for different metabotropic odor transduction cascades, which employ second messenger-gated ion channel families for odor transduction. The hawkmoth Manduca sexta is an established model organism for studies of insect olfaction, also due to the availability of the hawkmoth-specific pheromone blend with its main component bombykal. Previous patch-clamp studies on primary cell cultures of M. sexta olfactory receptor neurons provided evidence for a pheromone-dependent activation of a phospholipase Cβ. Pheromone application elicited a sequence of one rapid, apparently IP3-dependent, transient and two slower Ca(2+)-dependent inward currents. It remains unknown whether additionally an ionotropic pheromone-transduction mechanism is employed. If indeed an OR-Orco ion channel complex underlies an ionotropic mechanism, then Orco agonist-dependent opening of the OR-Orco channel pore should add up to pheromone-dependent opening of the pore. Here, in tip-recordings from intact pheromone-sensitive sensilla, perfusion with the Orco agonist VUAA1 did not increase pheromone-responses within the first 1000 ms. However, VUAA1 increased spontaneous activity of olfactory receptor neurons Zeitgebertime- and dose-dependently. We conclude that we find no evidence for an Orco-dependent ionotropic pheromone transduction cascade in M. sexta. Instead, in M. sexta Orco appears to be a slower, second messenger-dependent pacemaker channel which affects kinetics and threshold of pheromone-detection via changes of intracellular Ca(2+) baseline concentrations.
Modulation of the NO-cGMP pathway has no effect on olfactory responses in the antenna.
Prelic S, Getahun M, Kaltofen S, Hansson B, Wicher D Front Cell Neurosci. 2023; 17:1180798.
PMID: 37305438 PMC: 10248080. DOI: 10.3389/fncel.2023.1180798.
Altered functional properties of the codling moth Orco mutagenized in the intracellular loop-3.
Bobkov Y, Walker Iii W, Cattaneo A Sci Rep. 2021; 11(1):3893.
PMID: 33594162 PMC: 7887336. DOI: 10.1038/s41598-021-83024-3.
Fandino R, Haverkamp A, Bisch-Knaden S, Zhang J, Bucks S, Nguyen T Proc Natl Acad Sci U S A. 2019; 116(31):15677-15685.
PMID: 31320583 PMC: 6681710. DOI: 10.1073/pnas.1902089116.
Insect Pheromone Receptors - Key Elements in Sensing Intraspecific Chemical Signals.
Fleischer J, Krieger J Front Cell Neurosci. 2018; 12:425.
PMID: 30515079 PMC: 6255830. DOI: 10.3389/fncel.2018.00425.
The Two Main Olfactory Receptor Families in , ORs and IRs: A Comparative Approach.
Gomez-Diaz C, Martin F, Garcia-Fernandez J, Alcorta E Front Cell Neurosci. 2018; 12:253.
PMID: 30214396 PMC: 6125307. DOI: 10.3389/fncel.2018.00253.