Transcriptional Networks for Alcohol Sensitivity in Drosophila melanogaster

Abstract

Understanding the genetic architecture of polygenic traits requires investigating how complex networks of interacting molecules mediate the effect of genetic variation on organismal phenotypes. We used a combination of P-element mutagenesis and analysis of natural variation in gene expression to predict transcriptional networks that underlie alcohol sensitivity in Drosophila melanogaster. We identified 139 unique P-element mutations (124 in genes) that affect sensitivity or resistance to alcohol exposure. Further analyses of nine of the lines showed that the P-elements affected expression levels of the tagged genes, and P-element excision resulted in phenotypic reversion. The majority of the mutations were in computationally predicted genes or genes with unexpected effects on alcohol phenotypes. Therefore we sought to understand the biological relationships among 21 of these genes by leveraging genetic correlations among genetically variable transcripts in wild-derived inbred lines to predict coregulated transcriptional networks. A total of 32 ''hub'' genes were common to two or more networks associated with the focal genes. We used RNAi-mediated inhibition of expression of focal genes and of hub genes connected to them in the network to confirm their effects on alcohol-related phenotypes. We then expanded the computational networks using the hub genes as foci and again validated network predictions. Iteration of this approach allows a stepwise expansion of the network with simultaneous functional validation. Although coregulated transcriptional networks do not provide information about causal relationships among their constituent transcripts, they provide a framework for subsequent functional studies on the genetic basis of alcohol sensitivity.

Functional roles for redox genes in ethanol sensitivity in Drosophila

“…The identification of specific ethanolregulated TFs linked to neuronal development and redox processes provide the starting point for the development of transcription networks for ethanol responses. Co-regulated transcription networks for a set of 21 Drosophila genes with functions in ethanol sensitivity have been predicted in a recent study (Morozova et al 2011). This work showed genes involved in nervous system development were present in extended networks of ethanol sensitivity and resistance genes.…”

“…Evidence of a role for redox genes in ethanol responses (specifically those in the oxidative phosphorylation gene ontology class) has also been shown in predicted transcriptional networks associated with increased sensitivity to ethanol (Morozova et al 2011). Ethanol-induced oxidative stress has been reported widely, and is an imbalance in a cell's redox reactions associated with increases in reactive oxygen species (ROS) or decreases in antioxidant defences such as glutathione (González et al 2007).…”

“…These upregulated genes work to rescue cells from oxidative stress and its consequences such as protein misfolding, apoptosis and ageing. Whilst such data can be used to predict transcription networks of ethanol response genes in Drosophila (Morozova et al 2011), the future lies in mapping these networks and associated interactions to the human population, with the ultimate aim of identifying genetic factors for alcohol use disorders such as alcoholism.…”

Genetic architecture of natural variation in visual senescence in Drosophila

“…Drosophila melanogaster has emerged as a powerful genetic model system for the study of complex human disorders (15) including Alzheimer's disease (16), Parkinson's disease (17), Huntington's disease (18), ocular hypertension (6), retinal degeneration (7), longevity (19), sleep patterns (20), aggressive behaviors (21)(22)(23)(24), and sensitivity to alcohol (25)(26)(27)(28)(29)(30). Natural populations of Drosophila harbor substantial genetic variation for quantitative traits (31)(32)(33)(34).…”

Genetics and genomics of alcohol sensitivity

“…A P -element insertional mutagenesis screen for alcohol sensitivity revealed that almost 30 % of the P -element insertions tested affected the trait, indicating that a large fraction of the genome contributes to alcohol sensitivity and predicting extensive pleiotropy (Morozova et al 2011; Fig. 2).…”