GIBBS, Allen G.; VANIER, Cheryl H.; Univ. of Arizona; Univ. of Arizona: Gene expression in desiccated and starved Drosophila

We studied the effects of desiccation stress on gene expression patterns in Drosophila melanogaster. Because desiccation involves the removal of both food and water, we used two control treatments: flies with water but no food (starved control) and with food and water (fed control). We exposed male flies to 1-7 hours of stress, isolated RNA, and investigated gene expression patterns using cDNA microarrays. At a P-value of 0.001 (differential expression of 5-6 genes expected by chance), the number of differentially expressed genes relative to the first time point increased, up to ~200 genes after seven hours. Down-regulated genes included lysosomal proteins and metabolic enzymes, suggesting that flies respond to stress by reducing protein turnover and metabolic rates. We expected to identify two major sets of genes. Starved and desiccated flies should differ from fed flies in the expression of genes involved in the response to food stress. Desiccated flies should additionally differ from both control treatments in a suite of desiccation-specific genes. However, the expected sets of starvation- and desiccation-related genes were not observed. Instead, after seven hours desiccated flies differed from fed flies in the expression of 98 genes, and from starved flies in the expression of 86 completely different genes. Our results indicate that starvation and desiccation affect different physiological and biochemical processes, and that desiccation is not simply starvation in the absence of water. Thus, previous desiccation selection experiments in Drosophila may have used an inappropriate control treatment.