Journal Article

The ocular albinism type 1 protein, an intracellular G protein-coupled receptor, regulates melanosome transport in pigment cells

Ilaria Palmisano, Paola Bagnato, Angela Palmigiano, Giulio Innamorati, Giuseppe Rotondo, Domenico Altimare, Consuelo Venturi, Elena V. Sviderskaya, Rosanna Piccirillo, Massimiliano Coppola, Valeria Marigo, Barbara Incerti, Andrea Ballabio, Enrico M. Surace, Carlo Tacchetti, Dorothy C. Bennett and Maria Vittoria Schiaffino

in Human Molecular Genetics

Volume 17, issue 22, pages 3487-3501
Published in print November 2008 | ISSN: 0964-6906
Published online August 2008 | e-ISSN: 1460-2083 | DOI: http://dx.doi.org/10.1093/hmg/ddn241
The ocular albinism type 1 protein, an intracellular G protein-coupled receptor, regulates melanosome transport in pigment cells

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The protein product of the ocular albinism type 1 gene, named OA1, is a pigment cell-specific G protein-coupled receptor exclusively localized to intracellular organelles, namely lysosomes and melanosomes. Loss of OA1 function leads to the formation of macromelanosomes, suggesting that this receptor is implicated in organelle biogenesis, however the mechanism involved in the pathogenesis of the disease remains obscure. We report here the identification of an unexpected abnormality in melanosome distribution both in retinal pigment epithelium (RPE) and skin melanocytes of Oa1-knock-out (KO) mice, consisting in a displacement of the organelles from the central cytoplasm towards the cell periphery. Despite their depletion from the microtubule (MT)-enriched perinuclear region, Oa1-KO melanosomes were able to aggregate at the centrosome upon disruption of the actin cytoskeleton or expression of a dominant-negative construct of myosin Va. Consistently, quantification of organelle transport in living cells revealed that Oa1-KO melanosomes displayed a severe reduction in MT-based motility; however, this defect was rescued to normal following inhibition of actin-dependent capture at the cell periphery. Together, these data point to a defective regulation of organelle transport in the absence of OA1 and imply that the cytoskeleton might represent a downstream effector of this receptor. Furthermore, our results enlighten a novel function for OA1 in pigment cells and suggest that ocular albinism type 1 might result from a different pathogenetic mechanism than previously thought, based on an organelle-autonomous signalling pathway implicated in the regulation of both membrane traffic and transport.

Journal Article.  9957 words.  Illustrated.

Subjects: Genetics and Genomics

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