PROJECT SUMMARY Cocaine Use Disorder (CUD) represents a significant public health and socioeconomic concern. Cocaine is involved in 40% of drug-related emergency room visits, and rates of cocaine overdose in the United States are climbing steadily. Yet, the genetic underpinnings that predispose to CUD remain poorly understood. Twin studies on the genetics of CUD provide heritability estimates between 42-79%. However, significant heritability estimates do not indicate which genes are involved, and how they might be functionally relevant. Genome-wide association studies (GWAS) of CUD are limited by inability to control environmental factors; the haplotype structure of the human genome limiting mapping precision; and small sample sizes due to difficulty recruiting participants because of criminalization of cocaine use. Model organisms such as the fruit fly Drosophila melanogaster offer a cost-effective alternative where sample size, environment, and genetic background can be controlled. Cocaine binds to the dopamine transporter of Drosophila as it does in humans, eliciting cocaine-induced locomotor phenotypes. GWAS in Drosophila are facilitated by the Drosophila melanogaster Genetic Reference Panel (DGRP), an expanding collection of wild-derived, inbred, fully sequenced lines that provide a living library of natural variation. It is my goal to use the DGRP and a systems genetics approach to uncover the genetic underpinnings of cocaine-related phenotypes. In Specific Aim 1, I will investigate the impact of genetic background on cocaine preference by screening 600 DGRP lines for cocaine preference using the microplate feeder assay. I will then perform a GWAS, utilizing whole genome sequence data to identify genetic variants associated with cocaine preference. I will perform gene ontology and KEGG orthology pathway enrichment analyses, as well as construct genetic interaction networks to implicate genes and pathways involved in cocaine preference. In Specific Aim 2, I will quantify the behavioral and transcriptomic effects of cocaine exposure in DGRP lines with extreme cocaine preference. For 25 DGRP lines that exhibit cocaine preference and 25 lines near the population average, I will assess effects of cocaine on sensorimotor integration upon repeated exposures. In Specific Aim 3, I will functionally validate candidate genes and variants associated with cocaine preference using RNA interference and out-of-sample testing of DGRP lines, respectively. Completion of these aims will result in a systems genetics model of cocaine preference in Drosophila with translational potential for human cocaine use disorder. This project will train me in advanced systems genetics techniques and analyses and prepare me for a professional career in the study of the genetics of substance use disorders.