Intracellular distribution and late endosomal effects of the ocular albinism type 1 gene product: consequences of disease-causing mutations and implications for melanosome biogenesis.
To investigate the function of ocular albinism type 1 (OA1), the gene responsible for X-linked ocular albinism, we employed a construct containing murine Oa1 fused to green fluorescent protein (GFP) in a heterologous COS cell expression system. The cellular distribution of wild-type (WT) Oa1 protein and Oa1 proteins reflecting mutations causing X-linked ocular albinism were examined. Comparison with different organelle markers revealed that Oa1-GFP localized to the late endolysosomal compartments. Some Oa1 mutant proteins failed to exit the endoplasmic reticulum (ER) (Class I mutants), while other mutants partially (Class II mutants) or fully (Class III mutants) exited the ER and trafficked to endolysosomal compartments. We observed that expression of WT Oa1-GFP in COS cells caused an apparent enlargement of late endosomes and a redistribution of the mannose-6-phosphate receptor (M6PR). None of the mutants displayed the full range of effects on the redistribution of M6PR exhibited by WT Oa1. The effects of Oa1 on late endosome structure and content are thus likely to reflect an important biological property of Oa1. We propose that OA1 is involved in reorganizing the endolysosomal compartment as a necessary step in ocular melanosome biogenesis.
The Ronald O. Perelman Department of Dermatology and the Department of Cell Biology, NYU School of Medicine, New York, NY 10016, USA.
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Rosenberg
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Orlow
D016117:Albinism, Ocular / Q000235:genetics*; D000818:Animals; D015703:Antigens, CD / Q000032:analysis; D019556:COS Cells; D002522:Chlorocebus aethiops; D003594:Cytoplasmic Granules / Q000502:physiology; D011992:Endosomes / Q000502:physiology; D005136:Eye Proteins / Q000235:genetics / Q000502:physiology*; D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins / Q000235:genetics; D051907:Lysosomal Membrane Proteins; D008247:Lysosomes / Q000502:physiology; D020460:Melanosomes / Q000235:genetics / Q000502:physiology*; D008562:Membrane Glycoproteins / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D051379:Mice; D016297:Mutagenesis, Site-Directed; D015388:Organelles / Q000502:physiology*; D010980:Platelet Membrane Glycoproteins / Q000032:analysis; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D060149:Tetraspanin 30
D015703:Antigens, CD; C554586:CD63 protein, human; C554587:Cd63 protein, mouse; D005136:Eye Proteins; C095276:GPR143 protein, human; D008164:Luminescent Proteins; D051907:Lysosomal Membrane Proteins; D008562:Membrane Glycoproteins; D010980:Platelet Membrane Glycoproteins; D011993:Recombinant Fusion Proteins; D060149:Tetraspanin 30; D049452:Green Fluorescent Proteins