title: Melanophilin, the product of the leaden locus, is required for targeting of myosin-Va to melanosomes.
abstract: The formation of complex subcellular organelles requires the coordinated targeting of multiple components. Melanosome biogenesis in mouse melanocytes is an excellent model system for studying the coordinated function of multiple gene products in intracellular trafficking. To begin to order events in melanosome biogenesis and distribution, we employed the classical coat-color mutants ashen, dilute, and leaden, which affect melanosome distribution, but not melanin synthesis. The loci have been renamed Rab27a, Myo5a, and Mlph for their gene products. While each of the three loci has been shown to be required for melanosome distribution, the point(s) at which each acts is unknown. We have utilized primary melanocytes to examine the interdependencies between rab27a, myosin-Va, and melanophilin. The localization of rab27a to melanosomes did not require the function of either myosin-Va or melanophilin, but leaden function was required for the association of myosin-Va with melanosomes. In leaden melanocytes permeabilized before fixation, myosin-Va immunoreactivity was greatly attenuated, suggesting that myosin-Va is free in the cytoplasm. Finally, we have complemented both the leaden and ashen phenotypes by cell fusion and observed redistribution of mature melanosomes in the absence of both protein and melanin synthesis. Together, our data suggest a model for the initial assembly of the machinery required for melanosome distribution.
authors.affiliation: McLaughlin Research Institute, 1520 23rd St South, Great Falls, MT 59405, USA.
authors.forename: D William
authors.initials: DW
authors.lastname: Provance
authors.forename: Ted L
authors.initials: TL
authors.lastname: James
authors.forename: John A
authors.initials: JA
authors.lastname: Mercer
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D002352:Carrier Proteins / Q000737:chemistry* / Q000378:metabolism*; D002478:Cells, Cultured; D019084:Fluorescent Antibody Technique, Indirect; D020460:Melanosomes / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D008856:Microscopy, Fluorescence; D009154:Mutation; D018995:Myosin Heavy Chains / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D024701:Myosin Type V / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D010641:Phenotype; D020691:rab GTP-Binding Proteins / Q000378:metabolism; D000075745:rab27 GTP-Binding Proteins
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; C492410:MLPH protein, human; C435724:Mlph protein, mouse; C513082:Myo5a protein, mouse; D000075745:rab27 GTP-Binding Proteins; D024701:Myosin Type V; C512962:Rab27a protein, mouse; D018995:Myosin Heavy Chains; D020691:rab GTP-Binding Proteins