Patterns of expression regulation were apparent for genes that function in olfaction, heat-shock responses, and immunity. In Drosophila, genes specific to olfaction include the odorant receptor (OR) family of 60 genes and the odorant-binding protein (OBP) family of 51 genes. OBPs are found in the fluid of the sensillum surrounding the dendrites of the OR neurons (Hallem et al., 2006). We observed a large, graded, and coordinated down-regulation of many but not all olfactory-specific genes following ethanol exposure (Fig. 2G). Examples of down-regulated olfactory genes include those coding for the olfactory co-receptor Or83b, the OBPs Lush and OS-E, and the pheromone-binding proteins Pbprp1, Pbprp3, Pbprp4, and Pbprp5 (Table S1). Exposure of flies to high concentration ethanol vapor results in activity-dependent olfactory neuron apoptosis and olfactory organ damage that is always accompanied by a blackening of the main olfactory organ, the third segment of the antennae (R.L. French, personal communication). Exposing flies to ethanol vapor under conditions identical to those used for our microarray study resulted in blackening of only 0.5% of antennae (n = 216). These data suggest that the
