The taste system enables animals to identify different water-soluble chemicals in their niches, enabling them to ingest nutritive food materials and reject toxic and noxious chemicals. The sense of taste is modulated both by internal factors like physiological state as well as external factors like presence of harmful contaminants in the food. Here we studied different factors that can modulate the taste system in flies. First, we studied yeast response in flies. Food preference for yeast is visible only in female flies and is dependent on mating state. Although earlier studies have explained mating realted physiological changes that are responsible for the dietary switch following mating, the cellular and molecular basis of yeast feeding was unknown. We found that a subset of free amino acids to be required for the feeding preference for yeast. We further identified tarsal taste neurons that are sensitive to amino acids.
We discovered that Ir76b an ionotropic receptor is necessary for amino acid taste. It combines with other Irs like Ir20a and other factors to confer amino acid sensitivity.
Nutritional imbalance changes dietary requirements in flies. They need to ingest more of the nutrient they are deprived of to maintain nutritional homeostasis. These changed requirements lead to changes in the taste preferences of flies. In order to study the compensatory changes following nutrient deprivation, we fed the flies with two different types of food viz. sugar deprived/yeast enriched and yeast deprived/sugar enriched. Feeding with both sugar deprived/yeast enriched food increased preferences and sensitivity for sugar while decreasing preferences for amino acids. While feeding with sugar enriched/yeast deprived food decreased their preferences and sensitivity for sugar at the same time decreasing their preferences for amino acids. We identified a Dop2R dependent mechanism to be responsible for compensatory changes following feeding with sugar deprived/ yeast enriched diet. Compensatory changes upon feeding with sugar enriched/ yeast deprived diet however required dilp5, an insulin like peptide.
Furthermore, we found that both sweet taste neuron and low salt taste neurons are inhibited with increasing pH of the taste solution. Also, presence of high concentrations of different salts lead to decreased activity of the sweet taste neurons.
Taken together all the above discoveries will be helpful in understanding how food choice is regulated in flies.