Multi-Species Gene Networks and Drosophila Ethanol Sedation

Alcohol use disorders (AUDs) are major health issues with few known genetic explanations. This project used the fruit fly (Drosophila melanogaster) model to identify genes and gene networks that influence alcohol intoxication, a phenotype related to alcohol abuse in humans. We used bioinformatic tools to build gene networks based on 24 published Drosophila ethanol-responsive genes with human orthologs. We then assessed the role of these networks in ethanol sedation by testing two of the networks seeded on IP3K2, a gene that regulates calcium signaling, and CG14630, a gene involved in carnitine biosynthesis. We knocked down several genes in each of the networks using RNAi and tested the knockdown flies in a behavioral assay for ethanol sedation. Nervous system RNAi expression against 7 of 20 genes in the IP3K2 network and 4 of 30 genes in the CG14630 network significantly affected the sensitivity of flies to ethanol. To determine whether the hit rates in these two networks were greater than would be expected by random chance alone, we also assessed the effects of nervous system RNAi targeting a random set of fly genes. Unexpectedly, the fraction of randomly selected genes that affected ethanol sensitivity in a primary screen was comparable to or even larger than that from bioinformatically-derived gene networks. Our data are consistent with two possibilities that are not mutually exclusive. One possibility is that there are a very large number of genes that impact ethanol sedation and our bioinformatic analyses did not substantially enrich for these genes. A second possibility is that expression of RNAi could influence ethanol sedation independent of target gene knock-down. These two possibilities will be examined in future experiments