Evolutionary differences in food preference rely on Gr64e, a receptor for glycerol

Abstract

Very little is known about how stimuli that are typically not rich in sugars, such as beer, trigger attractive gustatory responses in Drosophila. We identified a member of the gustatory receptor family, Gr64e, as a receptor that is required for feeding preference for beer and other sources that have fermenting yeast. We found that Gr64e is required for neuronal and behavioral responses to glycerol, an abundant component of growing yeast and fermentation products. Ectopic expression of Gr64e in an olfactory neuron conferred responsiveness to glycerol. We also found that Drosophila species that are predicted to carry pseudogenes of Gr64e had reduced glycerol sensitivity. Our results provide insight into the molecular mechanisms of feeding acceptance of yeast products and raise the possibility that Gr64e contributes to specific evolutionary variations in appetitive selectivity across Drosophila species.

Detection of sweet tastants by a conserved group of insect gustatory receptors

“…We selected the CO 2 -sensing ab1C olfactory neuron for ectopic expression of Grs based on our previous study (12). The ab1C neuron, housed with three other neurons in ab1 large basoconic sensilla in the fly antenna, is unique in that it expresses Gr21a and Gr63a but no members of the Or or Ir gene families (20,21,26,27).…”

“…Several lines of evidence suggest that one or more of the remaining six receptors are coexpressed with Gr5a in sweet neurons of the fly labellum (8)(9)(10)12). Genetic analysis for some of these other Grs suggests that they are also necessary for responses to sweet tastants, although the breadth of sugar response defects can vary between different Gr mutants (12)(13)(14).…”

“…We recently expressed Gr64e in the Gr21a/Gr63a CO 2 -sensing neuron in the olfactory system and showed that it confers sensitivity to glycerol (12). Here we investigate how tastants are detected by the entire repertoire of sweet taste receptors in Drosophila.…”

Identification of neurons responsible for feeding behavior in the Drosophila brain

“…In previous studies, poxn null mutants were found to be completely devoid of sweet sensory input [38,39], whereas the GRN blocking flies may have partially retained the ability to sense sweetness because not all of the sugar sensing neurons were blocked by using one Gr-Gal4 line [24,30]. This led to the enhanced water consumption (Figure 2A).…”

“…In contrast, Gr64a is essential for the detection of multiple other sugars, including sucrose, glucose, and maltose [24,26,29]. More recent studies demonstrate that Gr64e is a receptor for glyce-rol [30] and Gr64f, as a co-receptor, functions with Gr5a and Gr64a to detect most sugars [25].…”