The mouse ocular albinism 1 gene product is an endolysosomal protein

Exp Eye Res. 2001 Mar;72(3):319-29. doi: 10.1006/exer.2000.0962.


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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Albinism, Ocular / genetics*
  • Animals
  • Cells, Cultured
  • DNA, Complementary
  • Electrophoresis, Polyacrylamide Gel
  • Fluorescent Antibody Technique
  • Glycosylation
  • Lysosomes / chemistry*
  • Melanocytes / chemistry
  • Mice
  • Mice, Inbred C57BL
  • Microscopy, Confocal
  • Monophenol Monooxygenase / immunology
  • Polymerase Chain Reaction
  • Proteins / chemistry*
  • Rabbits


  • DNA, Complementary
  • Proteins
  • Monophenol Monooxygenase