Pharyngeal sense organs drive robust sugar consumption in Drosophila.

Emily E Ledue,Michael D Gordon,Anupama Dahanukar,Aera Y Jung,Yu-Chieh Chen

doi:10.1038/ncomms7667

Emily E Ledue, Michael D Gordon + Show 3 more

Open Access

https://doi.org/10.1038/ncomms7667

Copy DOI

Abstract

The fly pharyngeal sense organs lie at the transition between external and internal nutrient sensing mechanisms. Here, we investigate the function of pharyngeal sweet gustatory receptor neurons (GRNs), demonstrating that they express a subset of the nine previously identified sweet receptors and respond to stimulation with a panel of sweet compounds. We show that pox-neuro (poxn) mutants lacking taste function in the legs and labial palps have intact pharyngeal sweet taste, which is both necessary and sufficient to drive preferred consumption of sweet compounds by prolonging ingestion. Moreover, flies putatively lacking all sweet taste show little preference for nutritive or non-nutritive sugars in a short-term feeding assay. Together, our data demonstrate that pharyngeal sense organs play an important role in directing sustained consumption of sweet compounds, and suggest that post-ingestive sugar sensing does not effectively drive food choice in a simple short-term feeding paradigm.

Highlights

The fly pharyngeal sense organs lie at the transition between external and internal nutrientsensing mechanisms
Mapping was based on the examination of green fluorescent protein (GFP) expression in the labral sense organ (LSO), VCSO and DCSO of flies carrying each gustatory receptor (Gr)-GAL4 or GrLexA driver, as well as analysis of GFP expression in flies carrying two different drivers
Gr43a-GAL4 and Gr64e-GAL4 offer two tools to explore the physiological and behavioural roles of the pharyngeal sense organs. Both are expressed in all identified candidate pharyngeal sweet neurons, as well as gustatory receptor neurons (GRNs) in the legs; Gr64e-GAL4 is expressed in the taste hairs and taste pegs of the labellum, while Gr43a-GAL4 lacks labellar expression, but is expressed in sugar-sensing neurons in the protocerebrum[13,16,17,30]

Summary

Introduction

The fly pharyngeal sense organs lie at the transition between external and internal nutrientsensing mechanisms. Our data demonstrate that pharyngeal sense organs play an important role in directing sustained consumption of sweet compounds, and suggest that post-ingestive sugar sensing does not effectively drive food choice in a simple short-term feeding paradigm. Adult Drosophila express sweet taste receptors in gustatory receptor neurons (GRNs) located in the legs, labellum and a set of three pharyngeal sense organs collectively referred to as the internal mouthparts[1]. Gr5a, Gr61a and Gr64a–64f, are closely related in sequence and are the defining members of a clade of insect sweet taste receptors[14] Both expression and functional analyses suggest that sweet GRNs co-express multiple sweet receptors[4,10,11,13,15]. If poxn mutants have functional pharyngeal taste sensilla, this could account for their observed preference for caloric sugars[21,22]

Methods

Results

Conclusion