The ocular albinism type 1 protein, an intracellular G protein-coupled receptor, regulates melanosome transport in pigment cells.
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.
Palmisano
Ilaria
I
San Raffaele Scientific Institute, DIBIT, Milan, Italy.
Bagnato
Paola
P
Palmigiano
Angela
A
Innamorati
Giulio
G
Rotondo
Giuseppe
G
Altimare
Domenico
D
Venturi
Consuelo
C
Sviderskaya
Elena V
EV
Piccirillo
Rosanna
R
Coppola
Massimiliano
M
Marigo
Valeria
V
Incerti
Barbara
B
Ballabio
Andrea
A
Surace
Enrico M
EM
Tacchetti
Carlo
C
Bennett
Dorothy C
DC
Schiaffino
Maria Vittoria
MV
D016117:Albinism, Ocular / Q000235:genetics / Q000378:metabolism; D000818:Animals; D003599:Cytoskeleton / Q000502:physiology; D005136:Eye Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008544:Melanocytes / Q000378:metabolism* / Q000473:pathology / Q000648:ultrastructure; D020460:Melanosomes / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D008854:Microscopy, Electron; D010857:Pigment Epithelium of Eye / Q000166:cytology / Q000378:metabolism*; D043562:Receptors, G-Protein-Coupled / Q000235:genetics / Q000378:metabolism*
D005136:Eye Proteins; C095276:GPR143 protein, human; C506821:Gpr143 protein, mouse; D008562:Membrane Glycoproteins; D043562:Receptors, G-Protein-Coupled