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Graphical

Melanosome

Definition

The melanosome is a melanin-containing organelle found in melanocytes and melanophores. Fish and amphibians possess specialized cells, called melanophores, which contain hundreds of melanin-filled pigment granules, termed melanosomes. The sole function of these cells is pigment aggregation in the center of the cell or dispersion throughout the cytoplasm. This alternative transport of pigment allows the animal to effect color changes important for camouflage and social interactions. Melanophores transport their pigment in response to extracellular cues: neurotransmitters in the case of fish and hormonal stimuli in the case of frogs. In both cases, melanosome dispersion is induced by elevation of intracellular cAMP levels, while aggregation is triggered by depression of cAMP. The regulatory mechanisms downstream of these second-messengers are poorly understood. Mammalian melanocytes also produce melanosomes but, unlike melanophores, pigment in these cells is transported to the cell periphery for subsequent exocytosis to surrounding epithelial cells.

Category

› Cellular component

GOi

melanosome [ GO:0042470 ]