The mouse ocular albinism 1 gene product is an endolysosomal protein.
To gain insight into the role of Oa1, the mouse homolog of the human X-linked ocular albinism 1 protein, its properties and subcellular localization were investigated. Antiserum raised against an expressed segment of the Oa1 protein recognized a band of approximately 48 kDa in immunoblots of extracts of cultured mouse melan-a melanocytes, but not of cells of non-melanocyte origin. When melanocyte extracts were treated with glycopeptidase F, a approximately 44 kDa band appeared. Like the melanogenic enzyme tyrosinase, expression of Oa1 was stimulated by alpha-melanocyte stimulating hormone and inhibited by agouti signal protein. Upon density gradient centrifugation of organelles of melan-a cells, Oa1 protein colocalized with the late endosomal/lysosomal marker Lamp1, but only partial overlap was observed with melanosomal proteins in the high density region of the gradient. Immunofluorescence staining revealed that neither endogenous Oa1 nor an Oa1-green fluorescent protein fusion product colocalized with the melanosomal protein tyrosinase related protein-1 in the cell periphery. In contrast, colocalization of Oa1 and Oa1-green fluorescent protein fusion product with Lamp1 was extensive throughout the cell. These results indicate that Oa1 is a melanocyte-specific integral membrane glycoprotein localized to late endosomes/lysosomes but not mature melanosomes. Considering the microscopic findings in patients with X-linked ocular albinism 1, we speculate that Oa1 may play a role in the trafficking of vesicles to developing melanosomes.
Samaraweera
P
P
The Ronald O. Perelman Department of Dermatology, NYU School of Medicine, New York, NY 10016, USA.
Shen
B
B
Newton
J M
JM
Barsh
G S
GS
Orlow
S J
SJ
D016117:Albinism, Ocular / Q000235:genetics*; D000818:Animals; D002478:Cells, Cultured; D018076:DNA, Complementary; D004591:Electrophoresis, Polyacrylamide Gel; D005455:Fluorescent Antibody Technique; D006031:Glycosylation; D008247:Lysosomes / Q000737:chemistry*; D008544:Melanocytes / Q000737:chemistry; D051379:Mice; D008810:Mice, Inbred C57BL; D018613:Microscopy, Confocal; D014442:Monophenol Monooxygenase / Q000276:immunology; D016133:Polymerase Chain Reaction; D011506:Proteins / Q000737:chemistry*; D011817:Rabbits
D018076:DNA, Complementary; D011506:Proteins; D014442:Monophenol Monooxygenase