Strains of Drosophila melanogaster differ in alcohol tolerance

Phenotypic and transcriptional response to selection for alcohol sensitivity in Drosophila melanogaster

Gene-expression profiling combined with selection for genetically divergent Drosophila lines either highly sensitive or resistant to ethanol exposure has been used to identify candidate genes that affect alcohol sensitivity, including 23 novel genes that have human orthologs.

Background

Alcoholism is a complex disorder determined by interactions between genetic and environmental risk factors. Drosophila represents a powerful model system to dissect the genetic architecture of alcohol sensitivity, as large numbers of flies can readily be reared in defined genetic backgrounds and under controlled environmental conditions. Furthermore, flies exposed to ethanol undergo physiological and behavioral changes that resemble human alcohol intoxication, including loss of postural control, sedation, and development of tolerance.

Results

We performed artificial selection for alcohol sensitivity for 35 generations and created duplicate selection lines that are either highly sensitive or resistant to ethanol exposure along with unselected control lines. We used whole genome expression analysis to identify 1,678 probe sets with different expression levels between the divergent lines, pooled across replicates, at a false discovery rate of q < 0.001. We assessed to what extent genes with altered transcriptional regulation might be causally associated with ethanol sensitivity by measuring alcohol sensitivity of 37 co-isogenic P-element insertional mutations in 35 candidate genes, and found that 32 of these mutants differed in sensitivity to ethanol exposure from their co-isogenic controls. Furthermore, 23 of these novel genes have human orthologues.

Conclusion

Combining whole genome expression profiling with selection for genetically divergent lines is an effective approach for identifying candidate genes that affect complex traits, such as alcohol sensitivity. Because of evolutionary conservation of function, it is likely that human orthologues of genes affecting alcohol sensitivity in Drosophila may contribute to alcohol-associated phenotypes in humans.

Membrane lipid physiology and toxin catabolism underlie ethanol and acetic acid tolerance in Drosophila melanogaster

Drosophila melanogaster has evolved the ability to tolerate and utilize high levels of ethanol and acetic acid encountered in its rotting-fruit niche. Investigation of this phenomenon has focused on ethanol catabolism, particularly by the enzyme alcohol dehydrogenase. Here we report that survival under ethanol and acetic acid stress in D. melanogaster from high- and low-latitude populations is an integrated consequence of toxin catabolism and alteration of physical properties of cellular membranes by ethanol. Metabolic detoxification contributed to differences in ethanol tolerance between populations and acclimation temperatures via changes in both alcohol dehydrogenase and acetyl-CoA synthetase mRNA expression and enzyme activity. Independent of changes in ethanol catabolism, rapid thermal shifts that change membrane fluidity had dramatic effects on ethanol tolerance. Cold temperature treatments upregulated phospholipid metabolism genes and enhanced acetic acid tolerance, consistent with the predicted effects of restoring membrane fluidity. Phospholipase D was expressed at high levels in all treatments that conferred enhanced ethanol tolerance, suggesting that this lipid-mediated signaling enzyme may enhance tolerance by sequestering ethanol in membranes as phophatidylethanol. These results reveal new candidate genes underlying toxin tolerance and membrane adaptation to temperature in Drosophila and provide insight into how interactions between these phenotypes may underlie the maintenance of latitudinal clines in ethanol tolerance.

Differences in the effect of ethanol on fertility and viability components among laboratory strains of Drosophila melanogaster

We studied the effect of ethanol on several fitness components in six Drosophila melanogaster strains. Mating success, fecundity, egg-to-larva, egg-to-pupa and egg-to-adult survival and the number of emerging adults were estimated in a single series of experiments. The strains either had different combinations of genetic background and Adh genotypes with identical OdhF genotype or different Adh-Odh two-locus genotypes with similar genetic background. Ethanol had the greatest effect on mating success and fecundity, while its influence was lower on survival. When the experimental conditions were contrasted to the natural environment of the flies the most significant results were the ones related to fecundity and larval survival. Ethanol had the highest selective effect on fecundity. The genetic factors contributed substantially to the variation in the fertility and viability components. The Adh locus hardly influenced mating success while it had a sizable effect on fecundity and on all survival components. The influence of Adh on fecundity greatly depended on the other genetic factors. Genetic background had the largest influence on the different survival components. The influence of the Odh locus was mostly observed through the Adh-Odh interaction.