Organelle-autonomous regulation of size and number: OA1 receptor sustains Pmel17 expression

One of the main themes of cell biology is the regulation of intracellular organelles number and the correct size preservation. Melanosome biogenesis is a good example of organelle maturation, and the Ocular Albinism type I, that displays a specific morphological phenotype characterized by enlarged melanosomes in the Retinal Pigment Epithelium and in the skin melanocytes, is an useful model to clarify some of these aspects. In this disease, the macromelanosome represents the abnormal growth of a single organelle. Our studies provide a potential molecular mechanism about the role of OA1 protein concerning the control of melanosome size and number. OA1 influences Mitf transcription amount. In Oa1 knockout melanocytes, as well as in silenced cells, the considerable decrease of Mitf does not determine a pigmentation gross alteration, but it provokes an abnormal expression of PMEL17, a key protein of the melanosome biogenesis. With these results, we found evidences that the control of melanin synthesis and of the rate of new melanosome biogenesis rely on different independent control factors.