Classification Chromatophore

1 classification

1.1 xanthophores , erythrophores
1.2 iridophores , leucophores
1.3 melanophores
1.4 cyanophores

classification

the term chromatophore adopted (following sangiovanni s chromoforo) name pigment-bearing cells derived neural crest of cold-blooded vertebrates , cephalopods. word comes greek words chrōma (χρῶμα) meaning colour, , phoros (φόρος) meaning bearing . in contrast, word chromatocyte (cytos (κύτος) meaning cell ) adopted cells responsible colour found in birds , mammals. 1 such cell type, melanocyte, has been identified in these animals.

it in 1960s chromatophores enough understood enable them classified based on appearance. classification system persists day, though biochemistry of pigments may more useful scientific understanding of how cells function.

colour-producing molecules fall 2 distinct classes: biochromes , structural colours or schemochromes . biochromes include true pigments, such carotenoids , pteridines. these pigments selectively absorb parts of visible light spectrum makes white light while permitting other wavelengths reach eye of observer. structural colours produced various combinations of diffraction, reflection or scattering of light structures scale around quarter of wavelength of light. many such structures interfere wavelengths (colours) of light , transmit others, because of scale, produce iridescence, creating different colours when seen different directions.

whereas chromatophores contain pigments or reflecting structures (except when there has been mutation, in albinism), not pigment-containing cells chromatophores. haem, example, biochrome responsible red appearance of blood. found in red blood cells (erythrocytes), generated in bone marrow throughout life of organism, rather being formed during embryological development. therefore, erythrocytes not classified chromatophores.

a veiled chameleon, chamaeleo calyptratus. structural green , blue colours generated overlaying chromatophore types reflect filtered light.


xanthophores , erythrophores

chromatophores contain large amounts of yellow pteridine pigments named xanthophores; red/orange carotenoids termed erythrophores. however, vesicles containing pteridine , carotenoids found in same cell, in case overall colour depends on ratio of red , yellow pigments. therefore, distinction between these chromatophore types not clear.

most chromatophores can generate pteridines guanosine triphosphate, xanthophores appear have supplemental biochemical pathways enabling them accumulate yellow pigment. in contrast, carotenoids metabolised , transported erythrophores. first demonstrated rearing green frogs on diet of carotene-restricted crickets. absence of carotene in frogs diet meant red/orange carotenoid colour filter not present in erythrophores. made frogs appear blue instead of green.

iridophores , leucophores

iridophores, called guanophores, pigment cells reflect light using plates of crystalline chemochromes made guanine. when illuminated generate iridescent colours because of diffraction of light within stacked plates. orientation of schemochrome determines nature of colour observed. using biochromes coloured filters, iridophores create optical effect known tyndall or rayleigh scattering, producing bright-blue or -green colours.

a related type of chromatophore, leucophore, found in fish, in particular in tapetum lucidum. iridophores, utilize crystalline purines (often guanine) reflect light. unlike iridophores, however, leucophores have more organized crystals reduce diffraction. given source of white light, produce white shine. xanthophores , erythrophores, in fish distinction between iridophores , leucophores not obvious, but, in general, iridophores considered generate iridescent or metallic colours, whereas leucophores produce reflective white hues.

melanophores

at bottom mutant zebrafish larva fails synthesise melanin in melanophores, @ top non-mutant, wildtype larva

melanophores contain eumelanin, type of melanin, appears black or dark-brown because of light absorbing qualities. packaged in vesicles called melanosomes , distributed throughout cell. eumelanin generated tyrosine in series of catalysed chemical reactions. complex chemical containing units of dihydroxyindole , dihydroxyindole-2-carboxylic acid pyrrole rings. key enzyme in melanin synthesis tyrosinase. when protein defective, no melanin can generated resulting in types of albinism. in amphibian species there other pigments packaged alongside eumelanin. example, novel deep (wine) red-colour pigment identified in melanophores of phyllomedusine frogs. subsequently identified pterorhodin, pteridine dimer accumulates around eumelanin core, , present in variety of tree frog species australia , papua new guinea. while other lesser-studied species have complex melanophore pigments, nevertheless true majority of melanophores studied date contain eumelanin exclusively.

humans have 1 class of pigment cell, mammalian equivalent of melanophores, generate skin, hair, , eye colour. reason, , because large number , contrasting colour of cells make them easy visualise, melanophores far studied chromatophore. however, there differences between biology of melanophores , of melanocytes. in addition eumelanin, melanocytes can generate yellow/red pigment called phaeomelanin.

the purple-striped dottyback, pseudochromis diadema, generates violet stripe unusual type of chromatophore.


cyanophores

nearly vibrant blues in animals , plants created structural coloration rather pigments. however, types of synchiropus splendidus possess vesicles of cyan biochrome of unknown chemical structure in cells named cyanophores. although appear unusual in limited taxonomic range, there may cyanophores (as further unusual chromatophore types) in other fish , amphibians. example, brightly coloured chromatophores undefined pigments found in both poison dart frogs , glass frogs, , atypical dichromatic chromatophores, named erythro-iridophores have been described in pseudochromis diadema.