title: Melanoregulin, product of the dsu locus, links the BLOC-pathway and OA1 in organelle biogenesis.
abstract: Humans with Hermansky-Pudlak Syndrome (HPS) or ocular albinism (OA1) display abnormal aspects of organelle biogenesis. The multigenic disorder HPS displays broad defects in biogenesis of lysosome-related organelles including melanosomes, platelet dense granules, and lysosomes. A phenotype of ocular pigmentation in OA1 is a smaller number of macromelanosomes, in contrast to HPS, where in many cases the melanosomes are smaller than normal. In these studies we define the role of the Mreg(dsu) gene, which suppresses the coat color dilution of Myo5a, melanophilin, and Rab27a mutant mice in maintaining melanosome size and distribution. We show that the product of the Mreg(dsu) locus, melanoregulin (MREG), interacts both with members of the HPS BLOC-2 complex and with Oa1 in regulating melanosome size. Loss of MREG function facilitates increase in the size of micromelanosomes in the choroid of the HPS BLOC-2 mutants ruby, ruby2, and cocoa, while a transgenic mouse overexpressing melanoregulin corrects the size of retinal pigment epithelium (RPE) macromelanosomes in Oa1(ko/ko) mice. Collectively, these results suggest that MREG levels regulate pigment incorporation into melanosomes. Immunohistochemical analysis localizes melanoregulin not to melanosomes, but to small vesicles in the cytoplasm of the RPE, consistent with a role for this protein in regulating membrane interactions during melanosome biogenesis. These results provide the first link between the BLOC pathway and Oa1 in melanosome biogenesis, thus supporting the hypothesis that intracellular G-protein coupled receptors may be involved in the biogenesis of other organelles. Furthermore these studies provide the foundation for therapeutic approaches to correct the pigment defects in the RPE of HPS and OA1.
authors.affiliation: Neurobiology, Neurodegeneration & Repair Laboratory, National Eye Institute, Bethesda, Maryland, United States of America.
authors.forename: Rivka A
authors.initials: RA
authors.lastname: Rachel
authors.forename: Kunio
authors.initials: K
authors.lastname: Nagashima
authors.forename: T Norene
authors.initials: TN
authors.lastname: O'Sullivan
authors.forename: Laura S
authors.initials: LS
authors.lastname: Frost
authors.forename: Frank P
authors.initials: FP
authors.lastname: Stefano
authors.forename: Valeria
authors.initials: V
authors.lastname: Marigo
authors.forename: Kathleen
authors.initials: K
authors.lastname: Boesze-Battaglia
mesh_terms: D033942:Adaptor Proteins, Vesicular Transport; D016117:Albinism, Ocular / Q000235:genetics* / Q000473:pathology; D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002829:Choroid / Q000378:metabolism / Q000473:pathology / Q000648:ultrastructure; D018628:Gene Dosage / Q000235:genetics; D056426:Genetic Loci / Q000235:genetics*; D022861:Hermanski-Pudlak Syndrome / Q000235:genetics; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D020460:Melanosomes / Q000378:metabolism / Q000473:pathology / Q000648:ultrastructure; D051379:Mice; D008822:Mice, Transgenic; D008954:Models, Biological; D009154:Mutation / Q000235:genetics; D053141:Organelle Size; D015388:Organelles / Q000378:metabolism*; D010857:Pigment Epithelium of Eye / Q000378:metabolism / Q000473:pathology / Q000648:ultrastructure; D021381:Protein Transport; D033921:Vesicular Transport Proteins
chemical_list: D033942:Adaptor Proteins, Vesicular Transport; D002352:Carrier Proteins; C554282:Hps6 protein, mouse; D047908:Intracellular Signaling Peptides and Proteins; D033921:Vesicular Transport Proteins; C518334:melanoregulin protein, mouse