Ionotropic receptors mediate nitrogenous waste avoidance in Drosophila melanogaster

Abstract

Ammonia and its amine-containing derivatives are widely found in natural decomposition byproducts. Here, we conducted biased chemoreceptor screening to investigate the mechanisms by which different concentrations of ammonium salt, urea, and putrescine in rotten fruits affect feeding and oviposition behavior. We identified three ionotropic receptors, including the two broadly required IR25a and IR76b receptors, as well as the narrowly tuned IR51b receptor. These three IRs were fundamental in eliciting avoidance against nitrogenous waste products, which is mediated by bitter-sensing gustatory receptor neurons (GRNs). The aversion of nitrogenous wastes was evaluated by the cellular requirement by expressing Kir2.1 and behavioral recoveries of the mutants in bitter-sensing GRNs. Furthermore, by conducting electrophysiology assays, we confirmed that ammonia compounds are aversive in taste as they directly activated bitter-sensing GRNs. Therefore, our findings provide insights into the ecological roles of IRs as a means to detect and avoid toxic nitrogenous waste products in nature.

The taste of vitamin C in Drosophila

“…Therefore, we tested a repertoire of putative taste receptors (31 candidate Ir and nine candidate Gr loss‐of‐function mutants) via electrophysiology on L4 and L6 sensilla to elucidate the vitamin C receptors (Fig 2A and B). This included the broadly required Ir25a and Ir76b (Zhang et al , 2013; Chen & Amrein, 2017; Ganguly et al , 2017; Lee et al , 2018; Dhakal et al , 2021; Shrestha & Lee, 2021a; Xiao et al , 2022; Aryal et al , 2022a). Ir7a and Ir62a are required for sensing acetic acid and Ca 2+ , respectively (Lee et al , 2018; Rimal et al , 2019).…”

Chemosensory detection of aversive concentrations of ammonia and basic volatile amines in insects

“…A recent study has shown a requirement for three members of the Ir family (Ir51a, Ir25a and Ir76b) in activation of bitter neurons to nitrogenous waste compounds. 33 However, a determination of whether the observed inhibition is dependent on these or any other chemosensory receptors, or whether it is mediated by some other aspects of cellular function, awaits further molecular genetic investigation.…”

Protocol for binary food choice assays using Drosophila melanogaster

“…However, labellum and legs are the major taste organs, which mediate a major role in contact chemosensation in insects. The full benefit of this behavioral assay is realized when performed in combination with an electrophysiological assay that measures tastant-induced action potentials in gustatory receptor neurons (tip recordings) ( Aryal et al., 2022 ; Dhakal et al., 2021 ; Shrestha and Lee, 2021a ).…”

“…, 2022). Complete preference is indicated by P.I values of 1.0 and -1.0 while a P.I value of 0 indicates the absence of a bias between the two food choices ( Aryal et al., 2022 ; Dhakal et al., 2021 ; Shrestha and Lee, 2021b ; Shrestha et al., 2022 ).

Figure 1 Binary food choice assay (A) Photograph of 72-well microtiter plate containing red dye and blue dye mixed food for a binary food choice assay.

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“…In rare instances wherein a binary food choice assay cannot be performed due to poor food consumption, it may be possible to employ the proboscis extension response (PER) assay, which involves touching a positive tastant, such as sucrose, to taste sensilla, and observing the innate extension of the proboscis ( Dhakal et al., 2021 ; Rimal and Lee, 2019 ). However, this assay must be performed on single flies, as it is more time-consuming than binary food choice assays and requires more training to get consistent results.…”