Probably functions as cargo-recognition protein that couples cytoplasmic vesicles to the transport machinery (PubMed:22940130, PubMed:22275436, PubMed:30174147). Plays a role in hair pigmentation, a process that involves shedding of melanosome-containing vesicles from melanocytes, followed by phagocytosis of the melanosome-containing vesicles by keratinocytes (PubMed:15550542, PubMed:3410303, PubMed:22753477). Functions on melanosomes as receptor for RILP and the complex formed by RILP and DCTN1, and thereby contributes to retrograde melanosome transport from the cell periphery to the center (PubMed:22940130, PubMed:22275436). Overexpression causes accumulation of late endosomes and/or lysosomes at the microtubule organising center (MTOC) at the center of the cell (PubMed:19240024, PubMed:30174147). Probably binds cholesterol and requires the presence of cholesterol in membranes to function in microtubule-mediated retrograde organelle transport (PubMed:30174147). Binds phosphatidylinositol 3-phosphate, phosphatidylinositol 4-phosphate, phosphatidylinositol 5-phosphate and phosphatidylinositol 3,5-bisphosphate, but not phosphatidylinositol 3,4-bisphosphate or phosphatidylinositol 4,5-bisphosphate (PubMed:19240024). Required for normal phagosome clearing and normal activation of lysosomal enzymes in lysosomes from retinal pigment epithelium cells (PubMed:19240024). Required for normal degradation of the lipofuscin component N-retinylidene-N-retinylethanolamine (A2E) in the eye (PubMed:19240024). May function in membrane fusion and regulate the biogenesis of disk membranes of photoreceptor rod cells (Probable). Identified in a complex with RILP and DCTN1; interacts directly with RILP, but does not interact directly with DCTN1 (PubMed:22275436). Interacts with PRPH2 (PubMed:17260955). Localizes to the inner segment and basal outer segment of rods in the retina. Detected in melanocytes (PubMed:15550542). Expressed in retina, in retinal pigment epithelium (at protein level) (PubMed:17260955, PubMed:19240024). Widely expressed with higher expression in skin, heart, liver, testis and thymus (PubMed:15550542). Detected in retina, in retinal pigment epithelium cells (PubMed:19240024). Detected throughout embryogenesis, from 7 dpc to 17 dpc. Palmitoylated. Palmitoylation is required to maintain the protein at the melanosome membrane. Dilute mice carry a hypomorphic allele of Myo5a, resulting in melanosome clustering in the center of the cell. This causes decreased light absorption and an apparent dilution of coat color. The hair color of mice that are deficient for both Myo5a and Mreg appears nearly normal, but the abnormal clustering of the melanosomes persists (PubMed:15550542, PubMed:3410303, PubMed:22753477). Likewise, mice deficient for Rab27a or Mreg have a gray coat, while mice deficient for Mreg and Rab27a, or Mreg and Mlph, have a hair coat that appears nearly black (PubMed:3410303). In spite of melanosome clustering, shedding of melanosome-containing vesicles and their uptake by adjacent keratinocytes is restored in mice that are deficient for both Myo5a and Mreg (PubMed:22753477). RNAi-mediated knockdown of Mreg in cultured Rab27a-deficient melanocytes restores normal melanosome location at the cell periphery. In cultured wild-type melanocytes melanosomes are dispersed at the cell periphery, and RNAi-mediated knockdown of Mreg has no effect on melanosome location (PubMed:22275436). In mice lacking Mreg, the number of phagosomes in retinal pigment epithelial cells displays a normal, rapid increase after the onset of light, but then decreases much more slowly than in wild-type (PubMed:19240024). Eyecups from 9 and 12 month old mutant mice display increased levels of the lipofuscin component N-retinylidene-N-retinylethanolamine (A2E) (PubMed:19240024). Belongs to the melanoregulin family.