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Review
. 2022 Apr 2;13(4):354.
doi: 10.3390/insects13040354.

Time-Dependent Odorant Sensitivity Modulation in Insects

Hao Guo  1 , Dean P Smith  2
Affiliations
Review

Time-Dependent Odorant Sensitivity Modulation in Insects

Hao Guo et al. Insects. .

Abstract

Insects use olfaction to detect ecologically relevant chemicals in their environment. To maintain useful responses over a variety of stimuli, olfactory receptor neurons are desensitized to prolonged or high concentrations of stimuli. Depending on the timescale, the desensitization is classified as short-term, which typically spans a few seconds; or long-term, which spans from minutes to hours. Compared with the well-studied mechanisms of desensitization in vertebrate olfactory neurons, the mechanisms underlying invertebrate olfactory sensitivity regulation remain poorly understood. Recently, using a large-scale functional screen, a conserved critical receptor phosphorylation site has been identified in the model insect Drosophila melanogaster, providing new insight into the molecular basis of desensitization in insects. Here, we summarize the progress in this area and provide perspectives on future directions to determine the molecular mechanisms that orchestrate the desensitization in insect olfaction.

Keywords: Drosophila melanogaster; desensitization; odorant receptors; olfactory receptor neurons; sensitivity.

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Conflict of interest statement

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

Figures

Figure 1
Figure 1
Conservation of the S289 phosphorylation site of Orco across different insect species. The amino acid sequences of Orco were downloaded from the National Center for Biotechnology Information (NCBI): flies D. melanogaster (NP_524235.2) and Ceratitis capitata (NP_001266301.1); mosquitoes Anopheles gambiae (XP_041762121.1) and Culex quinquefasciatus (ABB29301.1); moth Helicoverpa armigera (ADQ13177.1); parasitoid Campoletis chlorideae (AKO69815.1); ant: Harpegnathos saltator (XP_011139767.1); beetle Tribolium castaneum (CAM84014.1).
Figure 2
Figure 2
Schematic diagram of the process of long-term desensitization in D. melanogaster. (1) At rest state, S289 is phosphorylated by PKC98E, and the olfactory receptor channel is sensitive to the odorant stimulation. (2) The ligands bind to the receptors and open the channel, leading to the influx of calcium and (3) the generation of strong action potentials. (4) When the presence of stimuli is prolonged, the accumulating intracellular calcium activates unknown phosphatase(s) that dephosphorylate Orco S289. (5) This dephosphorylation gradually desensitizes the odorant receptor channels, which is reflected by the inhibited electrophysiological response to odorant stimuli (6).
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