Impact of Gene Copy Number Variation on Anesthesia in Drosophila melanogaster 

Abstract

Background Chromosomal deletions and duplications, which result in halving or doubling of copy number in a block of genes, are an important source of variation between individuals. Phenotypic effects of copy number variation are commonly observed but, to our knowledge, effects on sensitivity to volatile anesthetics have not been assessed in any organism. Methods The potency with which halothane depresses the righting reflex of fruit flies was measured in congenic Drosophila strains, each of which was heterozygous for a deletion of average size ~ 400 kb. Over 200 strains were examined, thereby scanning~half of the fly genome. Results Although the vast majority of deletion heterozygotes were indistinguishable from the control, eight had significantly altered sensitivity to halothane. Genetic tests supported the hypothesis that the change in anesthetic sensitivity was due to reduction in copy number and not adventitious mutations in the strains. Among the eight outliers, the difference in halothane potency ranged from a 25% increase to a 15% decrease. When these lines were tested with enflurane, isoflurane and sevoflurane, changes of similar magnitude but distinctive patterns were found. Conclusions Variation in gene copy number has a significant impact on anesthetic sensitivity in Drosophila melanogaster. The level of transcription of a few genes must thus be limiting for a normal response to volatiles. Since coupling between gene copy and gene expression is universal and since the components of the fly’s nervous system are highly conserved, our work provides a rationale for investigating the clinical impact of copy number variation.

Behavioral and electrophysiological analysis of general anesthesia in 3 background strains ofDrosophila melanogaster

“…There are numerous studies reporting Drosophila mutant strains with different anesthetic sensitivities. [12][13][14][15][16][26][27][28][29][30][31][32] Differences in general anesthesia sensitivities of different CS stocks has also been previously noted, 12 and individual background strains have been characterized for their anesthetic sensitivity for specific endpoints, 33 but a direct comparison across a range of endpoints in commonly used background strains has not been reported. In this study, we asked 2 broad questions: do different background strains display different sensitivity to isoflurane, and are any differences systemic across various endpoints in different life stages?…”

Genetic Effects inDrosophilaon the Potency of Diverse General Anesthetics: A Distinctive Pattern of Altered Sensitivity

“…These “potency ratios”, which are >1 for hypersensitive lines and <1 for lines that are relatively resistant to halothane, are reported together with their 95% confidence limits in Table 1. Another way to gauge the size of the mutant phenotype is to convert the potency ratios into the percentage by which the mutant EC50 differs from that of the control line (Alone et al, 2009); these values are also reported in Table 1.…”

“…The potency with which volatile anesthetics depress the righting/climbing reflex of flies was determined by evaluating the distribution test as described above, but using multiple drug concentrations (Alone et al, 2009). In this paradigm, the starting anesthetic concentration was chosen to be low enough that almost no flies failed to escape the bottom of the testing tube.…”

Drosophila Ryanodine Receptors Mediate General Anesthesia by Halothane

“…The reactive climbing assay, also known as the distribution test, was performed as described previously 18 . Male flies aged 3-7 days were collected and sorted under carbon dioxide anesthesia, and allowed to recover for one day.…”