Sex- and tissue-specific expression of chemosensory receptor genes in a hawkmoth

Abstract

For the nocturnal hawkmoth Manduca sexta, olfactory and gustatory cues are essential for finding partners, food, and oviposition sites. Three chemosensory receptor families, odorant receptors (ORs), ionotropic receptors (IRs), and gustatory receptors (GRs) are involved in the detection of these stimuli. While many chemosensory receptor genes have been identified, knowledge of their expression profile in potentially chemoreceptive organs is incomplete. Here, we studied the expression patterns of chemosensory receptors in different tissues including the antennae, labial palps, proboscis, legs, wings and ovipositor. We compared the receptors’ expression in female and male moths both before and after mating by using the NanoString platform. This tool allowed us to measure expression levels of chemosensory receptor genes in a single reaction using probes designed against 71 OR, 29 IR and 49 GR transcripts. In all tissues investigated, we detected expression of genes from all three receptor families. The highest number of receptors was detected in the antennae (92), followed by the ovipositor (59), while the least number was detected in the hindlegs (21). The highest number of OR genes were expressed in the antennae (63), of which 24 were specific to this main olfactory organ. The highest number of IRs were also expressed in the antennae (16), followed by the ovipositor (15). Likewise, antennae and ovipositor expressed the highest number of GRs (13 and 14). Expression of the OR co-receptor MsexORCo, presumably a prerequisite for OR function, was found in the antennae, labial palps, forelegs and ovipositor. IR co-receptors MsexIR25a and MsexIR76b were expressed across all tested tissues, while expression of the IR co-receptor MsexIR8a was restricted to antennae and ovipositor. Comparing the levels of all 149 transcripts across the nine tested tissues allowed us to identify sex-biased gene expression in the antennae and the legs, two appendages that are also morphologically different between the sexes. However, none of the chemosensory receptors was differentially expressed based on the moths’ mating state. The observed gene expression patterns form a strong base for the functional characterization of chemosensory receptors and the understanding of olfaction and gustation at the molecular level in M. sexta.

Identification and analysis of odorant receptors expressed in the two main olfactory organs, antennae and palps, of Schistocerca americana

“…This overlap is different from the case of Drosophila, in which ORs expressed in antenna and palp are mutually exclusive 48 . However, observations from other species including the dipteran A. gambiae 47 , the lepidopteran M. sexta 49 , the orthopterans L. migratoria 46 and S. gregaria 50 , and our results, show substantial overlap of OR types expressed in both structures, suggesting that OR mutually exclusive expression of ORs in antenna and palp tissues of Drosophila appears to be exceptional.…”

“…Similar organ-specific differences have been observed in other insects. For example, in L. migratoria , of 149 putative OR genes identified, only 11 have been found in the palps 46 ; in A. gambiae , of ~ 80 putative ORs, only 13 are in the palps 47 ; in D. melanogaster , of 62 ORs, only seven are present in the palps 48 ; in M. sexta , of 70 OR genes tested, 17 are found in the mouthparts 49 .…”

Chemosensory Receptor Expression in the Abdomen Tip of the Female Codling Moth, Cydia pomonella L. (Lepidoptera: Tortricidae)

“…Among these results, mating effect was restricted to only a few receptors; OR47 and OR63 were observed to be downregulated after mating, while OR70 was observed to be upregulated. This contrasts to M. sexta, in which a mating effect on OR expression in the ovipositor was not observed [55]. OR63 is found within the expanded novel PR clade; downregulation in the abdomen tip after mating suggests it may function in mediating mating or other reproductive behaviors unrelated to oviposition.…”

“…Based upon a combination of transcriptomic and RT-PCR analyses, transcripts encoding 32 ORs, 21 GRs, and 15 IRs were confirmed to be expressed in the female adult moth abdomen tip, which are among the highest reported counts to date within Lepidoptera. Comparably, in M. sexta, expression of 30 ORs, 14 GRs, and 15 IRs was reported specifically for the ovipositor tissue [55], while in the PG-OV of Helicoverpa assulta, 22 ORs, 6 GRs, and 13 IRs were identified in a transcriptomic study, and in the PG-OV of S. frugiperda, 12 ORs, 4 GRs, and 10 IRs were revealed. We were not able to detect or confirm expression in female adult abdomen tips for 11 of the 37 ORs nor one of the GRs and three of the IRs identified in the abdomen-tip transcriptome.…”

“…For GRs, comparisons were made to sets from B.mori [50], Heliconius melpomene [46], and Plutella xylostella [51]. For IRs, comparisons were made to sets from Acyrthosiphon pisum, Apis mellifera, B. mori, Drosophila melanogaster, and Tribolium castaneum [52]; in an attempt to provide greater resolution of phylogenetic relationships for novel CpomIRs, a secondary IR phylogeny was produced utilizing most insect IR/iGluR sequences from the dataset of Croset et al, 2010 [52] as well as novel divergent IRs recently reported for S. littoralis [53], and previously reported IRs from other lepidoptera including E. postvitanna [48], M. sexta [54,55], and Danaus plexippus [56]. Amino acid sequences for each gene family were aligned using MAFFT online version 7.220 (https://mafft.cbrc.jp/alignment/server/, accessed on 12 December 2023) through the FFT-NS-I iterative refinement method, with JTT200 scoring matrix, "leave gappy regions" set, and other default parameters [57].…”