title: Effect of genetic variation in a Drosophila model of diabetes-associated misfolded human proinsulin.
abstract: The identification and validation of gene-gene interactions is a major challenge in human studies. Here, we explore an approach for studying epistasis in humans using a Drosophila melanogaster model of neonatal diabetes mellitus. Expression of the mutant preproinsulin (hINS(C96Y)) in the eye imaginal disc mimics the human disease: it activates conserved stress-response pathways and leads to cell death (reduction in eye area). Dominant-acting variants in wild-derived inbred lines from the Drosophila Genetics Reference Panel produce a continuous, highly heritable distribution of eye-degeneration phenotypes in a hINS(C96Y) background. A genome-wide association study (GWAS) in 154 sequenced lines identified a sharp peak on chromosome 3L, which mapped to a 400-bp linkage block within an intron of the gene sulfateless (sfl). RNAi knockdown of sfl enhanced the eye-degeneration phenotype in a mutant-hINS-dependent manner. RNAi against two additional genes in the heparan sulfate (HS) biosynthetic pathway (ttv and botv), in which sfl acts, also modified the eye phenotype in a hINS(C96Y)-dependent manner, strongly suggesting a novel link between HS-modified proteins and cellular responses to misfolded proteins. Finally, we evaluated allele-specific expression difference between the two major sfl-intronic haplotypes in heterozygtes. The results showed significant heterogeneity in marker-associated gene expression, thereby leaving the causal mutation(s) and its mechanism unidentified. In conclusion, the ability to create a model of human genetic disease, map a QTL by GWAS to a specific gene, and validate its contribution to disease with available genetic resources and the potential to experimentally link the variant to a molecular mechanism demonstrate the many advantages Drosophila holds in determining the genetic underpinnings of human disease.
authors.affiliation: Department of Ecology and Evolution, The University of Chicago, Chicago, Illinois 60637.
authors.forename: Bin Z
authors.initials: BZ
authors.lastname: He
authors.forename: Michael Z
authors.initials: MZ
authors.lastname: Ludwig
authors.forename: Desiree A
authors.initials: DA
authors.lastname: Dickerson
authors.forename: Levi
authors.initials: L
authors.lastname: Barse
authors.forename: Bharath
authors.initials: B
authors.lastname: Arun
authors.forename: Bjarni J
authors.initials: BJ
authors.lastname: Vilhjálmsson
authors.forename: Pengyao
authors.initials: P
authors.lastname: Jiang
authors.forename: Soo-Young
authors.initials: SY
authors.lastname: Park
authors.forename: Natalia A
authors.initials: NA
authors.lastname: Tamarina
authors.forename: Scott B
authors.initials: SB
authors.lastname: Selleck
authors.forename: Patricia J
authors.initials: PJ
authors.lastname: Wittkopp
authors.forename: Graeme I
authors.initials: GI
authors.lastname: Bell
authors.forename: Martin
authors.initials: M
authors.lastname: Kreitman
mesh_terms: D000483:Alleles; D000818:Animals; D030801:Animals, Genetically Modified; D003920:Diabetes Mellitus / Q000235:genetics* / Q000378:metabolism; D004195:Disease Models, Animal; D029721:Drosophila Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D004331:Drosophila melanogaster; D004843:Epistasis, Genetic; D005123:Eye / Q000378:metabolism / Q000473:pathology; D005260:Female; D015870:Gene Expression; D055785:Gene Knockdown Techniques; D014644:Genetic Variation; D055106:Genome-Wide Association Study; D006497:Heparan Sulfate / Q000096:biosynthesis; D006801:Humans; D007438:Introns; D008297:Male; D009154:Mutation; D010641:Phenotype; D011384:Proinsulin / Q000737:chemistry / Q000235:genetics*; D017510:Protein Folding; D034622:RNA Interference; D015238:Sulfotransferases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: D029721:Drosophila Proteins; D006497:Heparan Sulfate; D011384:Proinsulin; D015238:Sulfotransferases; C500949:sfl protein, Drosophila
keywords: Drosophila; genome-wide association study; heparan sulfate proteoglycan; mutant insulin; sulfateless