A Drosophila Model to Investigate Natural Variation Effect in Response to Expression of A Human Misfolded Protein. Bin He¹, Michael Ludwig¹, Soo-Young Park², Pengyao Jiang¹, Cecelia Miles³, Levi Barse¹, Desiree Dickerson¹, Sarah Carl¹, Graeme Bell², Martin Kreitman¹. 1) Department of Ecology & Evolution, The University of Chicago, Chicago, IL; 2) Department of Medicine, The University of Chicago, Chicago, IL; 3) Biology Department, Augustana College, Sioux Falls, SD.

   Identifying the genetic variants and the underlying molecular mechanism for disease variability is crucial in both complex and Mendelian disease. However, its progress has been hampered by the mapping resolution and further experimental challenges in human, leaving many basic questions unanswered: what types of variants? how do they act and interact? Here we present a novel approach to the genetic investigation of a complex disease trait, featuring high mapping resolution and experimental tractability in a Drosophila model of human disease. The approach uses natural genetic variation in Drosophila to screen for modifying loci in a sensitized disease background, created by expressing a mutant (disease-causing) form of human proinsulin in the developing eye imaginal disc, causing neuro-degeneration in the eye that mimics the -cell death in human patients. Crossing this transgenic line to a panel of 178 inbred lines of D. melanogaster resulted in a continuous distribution of the disease phenotype. GWAS in 154 sequenced lines identified multiple loci, with the strongest signal fine-mapped to a 400bp region in the intron of the gene sulfateless (sfl). RNAi knock-down of sfl enhanced the eye phenotype in a mutant-proinsulin-dependent manner; the same approach identified two more genes in the Heparan Sulfate Proteoglycan (HSPG) pathway, to which sfl belongs, strongly suggesting a previously unknown link between HSPG and cell response to misfolded protein. Finally, we used pyro-sequencing to show evidence of allele-specific expression associated with the sfl intronic variants, revealing the potential mechanism of the non-coding variants in regulating the host-gene expression.