Many types of mammalian cells contain a specific repertoire of secretory organelles that are essential for their specialized function within the organism. Abnormal biogenesis of these organelles can cause a variety of human diseases. We are focused into the study of the molecular mechanisms of organelle biogenesis by exploiting the original model represented by Ocular albinism type 1 (OA1), an X-linked disorder characterized by severe reduction of visual acuity, retinal hypopigmentation, and the presence of giant melanosomes in the skin and eyes. The OA1 protein is a pigment cell specific membrane glycoprotein, displaying structural and functional features of G protein-coupled receptors (GPCRs). However, in contrast to all other canonical GPCRs, OA1 is not localized to the plasma membrane, but is targeted to an intracellular organelle, the melanosome. Thus, OA1 represents the first example so far of an exclusively intracellular GPCR, supporting the hypothesis that GPCR-mediated signal transduction systems might also operate at the internal membranes to regulate processes such as organelle biogenesis, transport and secretion.