Using Pox-Neuro (Poxn) Mutants in Drosophila Gustation Research: A Double-Edged Sword

Abstract

In Drosophila, Pox-neuro (Poxn) is a member of the Paired box (Pax) gene family that encodes transcription factors with characteristic paired DNA-binding domains. During embryonic development, Poxn is expressed in sensory organ precursor (SOP) cells of poly-innervated external sensory (p-es) organs and is important for specifying p-es organ identity (chemosensory) as opposed to mono-innervated external sensory (m-es) organs (mechanosensory). In Poxn mutants, there is a transformation of chemosensory bristles into mechanosensory bristles. As a result, these mutants have often been considered to be entirely taste-blind, and researchers have used them in this capacity to investigate physiological and behavioral functions that act in a taste-independent manner. However, recent studies show that only external taste bristles are transformed in Poxn mutants whereas all internal pharyngeal taste neurons remain intact, raising concerns about interpretations of experimental results using Poxn mutants as taste-blind flies. In this review, we summarize the value of Poxn mutants in advancing our knowledge of taste-enriched genes and feeding behaviors, and encourage revisiting some of the conclusions about taste-independent nutrient-sensing mechanisms derived from these mutants. Lastly, we highlight that Poxn mutant flies remain a valuable tool for probing the function of the relatively understudied pharyngeal taste neurons in sensing meal properties and regulating feeding behaviors.

Absolute ethanol intake predicts ethanol preference inDrosophila

“…Studies using other animals have similarly reported that rhesus monkeys will readily self-administer ethanol intravenously but not orally, and laboratory mice and rats that are not water or food deprived require specific induction protocols to start orally selfadministering various concentrations of ethanol (Meisch, 1977). Although Devineni and Heberlein (2009) reported that Drosophila poxn mutants lacking external chemosensilla show a preference for ethanol, poxn mutants have intact pharyngeal taste (Chen et al, 2018). Assessing ethanol preference in the absence of taste input using 'taste-blind' flies that lack both external and pharyngeal taste (Chen et al, 2019) might provide a better understanding of the behavioral response to the pharmacological effects of ethanol.…”

Combinatorial Pharyngeal Taste Coding for Feeding Avoidance in Adult Drosophila

“…Previous studies have used Poxn mutants to understand the role of pharyngeal sweet GRNs, which promote sugar consumption and local search behaviors (Murata et al, 2017; LeDue et al, 2015). To evaluate the role of the pharynx in feeding avoidance, we also took advantage of Poxn mutants, which serve as a good model for dissecting the function of pharyngeal taste without other confounding taste inputs (Chen et al, 2018). Specifically, we characterized feeding preferences of Poxn mutants in binary choice assays for various categories of aversive tastants, including high concentrations of tartaric acid and salt (Zhang et al, 2013; Charlu et al, 2013), as well as compounds perceived as bitter by humans and avoided by flies (Weiss et al, 2011).…”

“…Recently, we created receptor-to-neuron maps of pharyngeal taste organs, which revealed the presence of multiple classes of taste neurons (Chen and Dahanukar, 2017), consistent with the idea that the pharynx may independently assess food quality. To investigate how pharyngeal taste input affects feeding behaviors, we took advantage of Pox-neuro ( Poxn ) mutants, in which all external taste bristles are transformed into mechanosensory bristles (Awasaki and Kimura, 1997; Nottebohm et al, 1992) but all pharyngeal taste neurons are retained (Chen and Dahanukar, 2017; Chen et al, 2018). We first characterized feeding preference and food intake of Poxn mutants and found that behavioral avoidance of a diverse panel of bitter compounds, high concentrations of salt, and tartaric acid is similar to that of control flies.…”

A subset of brain neurons controls regurgitation in adult Drosophila melanogaster

“…One previous study showed that thermogenetic activation of Gr66a-expressing taste neurons in the mouthpart caused regurgitation (Kang et al, 2011), which raised the possibility that VT041723-GAL4 neurons receive input from pharyngeal Gr66a + GRNs. To test this possibility, we used Pox-neuro (Poxn) mutants in which all external taste hairs are transformed into mechanosensory hairs, leaving pharyngeal taste neurons intact (Chen et al, 2018;Chen and Dahanukar, 2017;Ledue et al, 2015). Consistent with our previous report (Chen and Dahanukar, 2017), Poxn mutants retained Ir76b + projections from the pharynx and a few taste pegs, while lacking projections from all external taste organs.…”