title: The protein O-glucosyltransferase Rumi modifies eyes shut to promote rhabdomere separation in Drosophila.
abstract: The protein O-glucosyltransferase Rumi/POGLUT1 regulates Drosophila Notch signaling by adding O-glucose residues to the Notch extracellular domain. Rumi has other predicted targets including Crumbs (Crb) and Eyes shut (Eys), both of which are involved in photoreceptor development. However, whether Rumi is required for the function of Crb and Eys remains unknown. Here we report that in the absence of Rumi or its enzymatic activity, several rhabdomeres in each ommatidium fail to separate from one another in a Notch-independent manner. Mass spectral analysis indicates the presence of O-glucose on Crb and Eys. However, mutating all O-glucosylation sites in a crb knock-in allele does not cause rhabdomere attachment, ruling out Crb as a biologically-relevant Rumi target in this process. In contrast, eys and rumi exhibit a dosage-sensitive genetic interaction. In addition, although in wild-type ommatidia most of the Eys protein is found in the inter-rhabdomeral space (IRS), in rumi mutants a significant fraction of Eys remains in the photoreceptor cells. The intracellular accumulation of Eys and the IRS defect worsen in rumi mutants raised at a higher temperature, and are accompanied by a ∼50% decrease in the total level of Eys. Moreover, removing one copy of an endoplasmic reticulum chaperone enhances the rhabdomere attachment in rumi mutant animals. Altogether, our data suggest that O-glucosylation of Eys by Rumi ensures rhabdomere separation by promoting proper Eys folding and stability in a critical time window during the mid-pupal stage. Human EYS, which is mutated in patients with autosomal recessive retinitis pigmentosa, also harbors multiple Rumi target sites. Therefore, the role of O-glucose in regulating Eys may be conserved.
authors.affiliation: Program in Genes & Development, The University of Texas Graduate School of Biomedical Sciences, Houston, Texas, United States of America; Department of Molecular & Human Genetics, Baylor College of Medicine, Houston, Texas, United States of America.
authors.forename: Amanda R
authors.initials: AR
authors.lastname: Haltom
authors.affiliation: Department of Molecular & Human Genetics, Baylor College of Medicine, Houston, Texas, United States of America.
authors.forename: Tom V
authors.initials: TV
authors.lastname: Lee
authors.affiliation: Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, New York, United States of America.
authors.forename: Beth M
authors.initials: BM
authors.lastname: Harvey
authors.affiliation: Department of Molecular & Human Genetics, Baylor College of Medicine, Houston, Texas, United States of America; Program in Developmental Biology, Baylor College of Medicine, Houston, Texas, United States of America.
authors.forename: Jessica
authors.initials: J
authors.lastname: Leonardi
authors.affiliation: Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States of America.
authors.forename: Yi-Jiun
authors.initials: YJ
authors.lastname: Chen
authors.affiliation: Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States of America.
authors.forename: Yang
authors.initials: Y
authors.lastname: Hong
authors.affiliation: Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, New York, United States of America.
authors.forename: Robert S
authors.initials: RS
authors.lastname: Haltiwanger
authors.affiliation: Program in Genes & Development, The University of Texas Graduate School of Biomedical Sciences, Houston, Texas, United States of America; Department of Molecular & Human Genetics, Baylor College of Medicine, Houston, Texas, United States of America; Program in Developmental Biology, Baylor College of Medicine, Houston, Texas, United States of America.
authors.forename: Hamed
authors.initials: H
authors.lastname: Jafar-Nejad
mesh_terms: D000818:Animals; D029721:Drosophila Proteins / Q000235:genetics* / Q000378:metabolism; D004331:Drosophila melanogaster / Q000235:genetics; D005136:Eye Proteins / Q000235:genetics* / Q000378:metabolism; D055879:Gene Knock-In Techniques; D005947:Glucose / Q000378:metabolism; D005964:Glucosyltransferases / Q000235:genetics* / Q000378:metabolism; D006031:Glycosylation; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D010786:Photoreceptor Cells / Q000378:metabolism* / Q000473:pathology; D051880:Receptors, Notch / Q000235:genetics; D012174:Retinitis Pigmentosa / Q000235:genetics* / Q000473:pathology; D015398:Signal Transduction / Q000235:genetics
chemical_list: D029721:Drosophila Proteins; D005136:Eye Proteins; D008565:Membrane Proteins; D051880:Receptors, Notch; C064360:crb protein, Drosophila; C514625:eys protein, Drosophila; D005964:Glucosyltransferases; C527374:Rumi protein, Drosophila; D005947:Glucose