title: Identification of Atg2 and ArfGAP1 as Candidate Genetic Modifiers of the Eye Pigmentation Phenotype of Adaptor Protein-3 (AP-3) Mutants in Drosophila melanogaster.
abstract: The Adaptor Protein (AP)-3 complex is an evolutionary conserved, molecular sorting device that mediates the intracellular trafficking of proteins to lysosomes and related organelles. Genetic defects in AP-3 subunits lead to impaired biogenesis of lysosome-related organelles (LROs) such as mammalian melanosomes and insect eye pigment granules. In this work, we have performed a forward screening for genetic modifiers of AP-3 function in the fruit fly, Drosophila melanogaster. Specifically, we have tested collections of large multi-gene deletions--which together covered most of the autosomal chromosomes-to identify chromosomal regions that, when deleted in single copy, enhanced or ameliorated the eye pigmentation phenotype of two independent AP-3 subunit mutants. Fine-mapping led us to define two non-overlapping, relatively small critical regions within fly chromosome 3. The first critical region included the Atg2 gene, which encodes a conserved protein involved in autophagy. Loss of one functional copy of Atg2 ameliorated the pigmentation defects of mutants in AP-3 subunits as well as in two other genes previously implicated in LRO biogenesis, namely Blos1 and lightoid, and even increased the eye pigment content of wild-type flies. The second critical region included the ArfGAP1 gene, which encodes a conserved GTPase-activating protein with specificity towards GTPases of the Arf family. Loss of a single functional copy of the ArfGAP1 gene ameliorated the pigmentation phenotype of AP-3 mutants but did not to modify the eye pigmentation of wild-type flies or mutants in Blos1 or lightoid. Strikingly, loss of the second functional copy of the gene did not modify the phenotype of AP-3 mutants any further but elicited early lethality in males and abnormal eye morphology when combined with mutations in Blos1 and lightoid, respectively. These results provide genetic evidence for new functional links connecting the machinery for biogenesis of LROs with molecules implicated in autophagy and small GTPase regulation.
authors.affiliation: Department of Human Genetics, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, United States of America.
authors.forename: Imilce A
authors.initials: IA
authors.lastname: Rodriguez-Fernandez
authors.affiliation: Department of Human Genetics, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, United States of America.
authors.forename: Esteban C
authors.initials: EC
authors.lastname: Dell'Angelica
mesh_terms: D000818:Animals; D001343:Autophagy; D000071183:Autophagy-Related Proteins; D002874:Chromosome Mapping; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase / Q000235:genetics* / Q000502:physiology; D029721:Drosophila Proteins / Q000235:genetics* / Q000502:physiology*; D004331:Drosophila melanogaster / Q000235:genetics* / Q000502:physiology; D019143:Evolution, Molecular; D005136:Eye Proteins / Q000235:genetics / Q000502:physiology; D005260:Female; D020558:GTP Phosphohydrolases / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D020690:GTPase-Activating Proteins / Q000235:genetics / Q000502:physiology*; D017353:Gene Deletion; D018507:Gene Expression Regulation, Developmental; D057898:Hemizygote; D008247:Lysosomes / Q000378:metabolism; D008297:Male; D008957:Models, Genetic; D009154:Mutation; D010641:Phenotype; D017956:Photoreceptor Cells, Invertebrate / Q000502:physiology; D010858:Pigmentation / Q000235:genetics*; D020691:rab GTP-Binding Proteins
chemical_list: C000608612:ArfGAP1 protein, Drosophila; C550900:Atg2 protein, Drosophila; D000071183:Autophagy-Related Proteins; C550346:BLOS1 protein, Drosophila; D029721:Drosophila Proteins; D005136:Eye Proteins; D020690:GTPase-Activating Proteins; C070334:Ribosomal protein P0, Drosophila; D020558:GTP Phosphohydrolases; C471560:Rab32 protein, Drosophila; D020691:rab GTP-Binding Proteins; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase