, 2009, Clyne et al., 1999, Miller and Carlson, 2010, Ray et al., 2007, Ray et al., 2008 and Tichy et al., 2008). Mechanisms of receptor gene choice were elucidated in part by identifying upstream-regulatory elements that were common to coexpressed Or genes.

The receptor-to-neuron map that we have established for the taste system lays a foundation for identifying regulatory Crizotinib nmr elements shared by coexpressed Gr genes, which in turn may elucidate mechanisms of receptor gene choice in the taste system. It will be interesting to determine whether the mechanisms used in the olfactory and taste systems are similar. In principle the design of the Drosophila taste system could have been extremely simple. Every sensillum could be identical, and all sensilla could report uniformly the valence of each tastant, e.g., positive for most sugars and negative for bitter compounds. Such a design would be economical to encode in the genome and to execute during development. The design of the Drosophila olfactory system is not so simple. Physiological analysis VEGFR inhibitor of the fly has identified ≥17 functionally distinct types of olfactory sensilla ( Clyne et al., 1997, de Bruyne et al., 1999, de Bruyne

et al., 2001, Elmore et al., 2003, van der Goes van for Naters and Carlson, 2007 and Yao et al., 2005). This design allows for the combinatorial coding of odors. A recent study of the Drosophila larva defined an odor space in which each dimension represents the response of each component of olfactory input ( Kreher et al., 2008). The distance between two odors in this space was proportional to the perceptual relationship

between them. In principle, a coding space of high dimension may enhance sensory discrimination and allow for a more adaptive behavioral response to a sensory stimulus. Here we have found that the fly’s taste system is similar to its olfactory system in that its sensilla fall into at least five functionally distinct types, four of which respond to bitter stimuli. This heterogeneity provides the basis for a combinatorial code for tastes and for a multidimensional taste space. A recent report has suggested that flies cannot discriminate between pairs of bitter stimuli when applied to leg sensilla (Masek and Scott, 2010); it will be interesting to extend such analysis to the labellum and especially to examine pairs of stimuli that have been shown to activate distinct populations of neurons.