Pigment_translocation Chromatophore

fish , frog melanophores cells can change colour dispersing or aggregating pigment-containing bodies.

many species able translocate pigment inside chromatophores, resulting in apparent change in body colour. process, known physiological colour change, studied in melanophores, since melanin darkest , visible pigment. in species relatively thin dermis, dermal melanophores tend flat , cover large surface area. however, in animals thick dermal layers, such adult reptiles, dermal melanophores form three-dimensional units other chromatophores. these dermal chromatophore units (dcu) consist of uppermost xanthophore or erythrophore layer, iridophore layer, , basket-like melanophore layer processes covering iridophores.

both types of melanophore important in physiological colour change. flat dermal melanophores overlay other chromatophores, when pigment dispersed throughout cell skin appears dark. when pigment aggregated toward centre of cell, pigments in other chromatophores exposed light , skin takes on hue. likewise, after melanin aggregation in dcus, skin appears green through xanthophore (yellow) filtering of scattered light iridophore layer. on dispersion of melanin, light no longer scattered , skin appears dark. other biochromatic chromatophores capable of pigment translocation, animals multiple chromatophore types can generate spectacular array of skin colours making use of divisional effect.

a single zebrafish melanophore imaged time-lapse photography during pigment aggregation

the control , mechanics of rapid pigment translocation has been studied in number of different species, in particular amphibians , teleost fish. has been demonstrated process can under hormonal or neuronal control or both , many species of bony fishes known chromatophores can respond directly environmental stimuli visible light, uv-radiation, temperature, ph, chemicals, etc. neurochemicals known translocate pigment include noradrenaline, through receptor on surface on melanophores. primary hormones involved in regulating translocation appear melanocortins, melatonin, , melanin-concentrating hormone (mch), produced in pituitary, pineal gland, , hypothalamus, respectively. these hormones may generated in paracrine fashion cells in skin. @ surface of melanophore, hormones have been shown activate specific g-protein-coupled receptors that, in turn, transduce signal cell. melanocortins result in dispersion of pigment, while melatonin , mch results in aggregation.

numerous melanocortin, mch , melatonin receptors have been identified in fish , frogs, including homologue of mc1r, melanocortin receptor known regulate skin , hair colour in humans. has been demonstrated mc1r required in zebrafish dispersion of melanin. inside cell, cyclic adenosine monophosphate (camp) has been shown important second messenger of pigment translocation. through mechanism not yet understood, camp influences other proteins such protein kinase drive molecular motors carrying pigment containing vesicles along both microtubules , microfilaments.