Changes in gene expression accompanying induction of ethanol tolerance in larvae: a microarray study. B.C. Caletka , J.D. Fry. Dept Biol, Univ Rochester, Rochester, NY.

   Ethanol is an important resource and toxin for wild D. melanogaster populations. In embryos and larvae, ethanol tolerance is inducible: embryos that develop in the presence of ethanol give rise to larvae with substantially higher ethanol tolerance than those not exposed to ethanol. We used whole-genome cDNA microarrays (Affymetrix) to characterize the gene expression changes that occur in response to ethanol. Embryos were allowed to develop while partly immersed in either 12% ethanol or water, and RNA was extracted from the resulting larvae (~2000) within 45 minutes of hatching. Three arrays were hybridized with RNA from each treatment, and a mixed-model analysis was used to compare signal intensities between treatments for each gene separately. About 125 genes showed a significant treatment effect at the 0.0001 level, compared to the ~1 that would be expected by chance. Of these, about twice as many were downregulated by ethanol as upregulated. The list of significantly (P < 0.0001) upregulated genes did not include many with a clear role in ethanol metabolism or tolerance. However, alcohol dehydrogenase, an aldehyde dehydrogenase (CG3752), and acetyl-coA synthase were significantly upregulated at 0.01 > P > 0.0001; these catalyze the first through third steps in ethanol degradation, respectively. Hsp70, the major stress-inducible protein, showed a non-significant (P = 0.08) response to ethanol, consistent with the results of a preliminary experiment using a reporter construct. Although analysis is still in progress, the results suggest that induction of ethanol tolerance occurs as a specific response to ethanol, rather than as a generalized stress response. In addition, the down-regulation of many genes may account for the observed ca. one hour delay of hatching of ethanol-treated eggs.