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First published online September 19, 2006
Journal of Experimental Biology 209, 3837-3850 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02448

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

Kristi L. Montooth^1,*, Kyle T. Siebenthall² and Andrew G. Clark²

¹ Department of Ecology and Evolutionary Biology, Brown University, Providence, RI 02912, USA
² Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA

View larger version (31K): [in a new window]   Fig. 1. Systems of genes/enzymes underlying ethanol metabolism and lipid-derived signaling pathways, along with the regulatory effects of the sterol regulatory element binding protein (dSREBP). The two parallel curved lines represent the plasma membrane. AcCoAS, acetyl-CoA synthetase; ADH, alcohol dehydrogenase; ALDH, acetaldehyde dehydrogenase; DAG, diacylglycerol; PC, phosphatidylcholine; PE, phosphatidylethanolamine; PEth, phosphatidylethanol; PLD, phospholipase D; PPAP, phosphatidate phosphatase.

View larger version (25K): [in a new window]   Fig. 2. Correlation between ethanol and acetic acid tolerances across species of Drosophila and populations of D. melanogaster. Points represent the lethal dose of toxin causing a 50% male mortality (LD50) in each genetic line. Error bars represent 95% confidence intervals for LD50 values. Australian population data are from flies acclimated to and tested at 15°C. All others are from a survey of tolerances in flies reared and assayed at 24°C.

View larger version (16K): [in a new window]   Fig. 3. ADH activities and ethanol tolerances for each Adh genotypic class. Lines are categorized as having only the Adh-F allele (F, N=5 lines), only the Adh-S allele (S, N=5 lines) or having both alleles (F&S, N=10 lines). Data are least square means ± 1 standard error. The inset contains Adh expression data (1/Ct) for the three genotype classes.

View larger version (18K): [in a new window]   Fig. 4. Mortality curves for extreme high and low ethanol tolerant lines acclimated to and assayed at 26°C. Symbols represent the two replicate observations for each line at each of five ethanol concentrations. Lines with 95% confidence intervals (horizontal bars) are fits from probit regressions from which we obtained estimates of LD50.

View larger version (22K): [in a new window]   Fig. 5. Population and temperature acclimation effects on ethanol tolerance (A), the ethanol catabolic enzymes, ADH (B), AcCoAS (C) and two putative AcCoAS-encoding loci (D). Shown are least square means ± 1 standard error and significant fixed effects from mixed-model ANOVAs. Fold expression changes were calculated from serial dilution standard curves. *P<0.05, **P<0.01, ***P<0.001, ****P<0.0001.

View larger version (18K): [in a new window]   Fig. 6. Phosphatidylethanolamine (PE) biosynthesis pathway (A) and the population and temperature acclimation effects on expression of genes encoding enzymes in this pathway, as well as a fatty acid desaturase (B). Shown are least square means ± 1 standard error and significant fixed effects from mixed-model ANOVAs. Units of expression are (1/Ct)x1000. Fold expression changes were calculated from serial dilution standard curves. CDPET, CDP-ethanolamine diglyceride transferase; PECT, phosphoethanolamine cytidylyltransferase; SPLY, sphinganine-1-phosphate lyase. *P<0.05, **P<0.01, ****P<0.0001.

View larger version (18K): [in a new window]   Fig. 7. Population and temperature acclimation effects on activity (A) and expression (B) of the lipid-mediated signaling enzyme, phospholipase D (PLD). Shown are least square means ± 1 standard error and significant fixed effects from mixed-model ANOVAs. Fold expression changes were calculated from serial dilution standard curves. *P<0.05, ****P<0.0001.

View larger version (23K): [in a new window]   Fig. 8. The effect of rapid thermal shifts on ethanol tolerance. Flies reared at 26°C and shifted to 15°C (left) had increased ethanol tolerance, whereas flies reared at 15°C and shifted to 26°C (right) had decreased tolerance. Data are least square means ± 1 standard error.

View larger version (17K): [in a new window]   Fig. 9. The effects of a rapid thermal shift from 26°C to 15°C, which should increase membrane rigidity, on the expression of genes involved in phosphatidylethanolamine (PE) biosynthesis (A; Sply, Cdpet), membrane lipid signaling (B; Pld, Wun) and encoding a putative AcCoAS (C; CG6432). Shown are least square means ± 1 standard error and significant fixed effects of TExpose(TRear) from mixed-model ANOVAs. Units of expression are (1/Ct)x1000. Fold expression changes were calculated from serial dilution standard curves. **P<0.01, ***P<0.001, ****P<0.0001.

View larger version (19K): [in a new window]   Fig. 10. The response of acetic acid tolerance (A) and dSrebp expression (B) to temperature acclimation. Shown are least square means ± 1 standard error and significant fixed effects. *P<0.05, ****P<0.0001.