Unusual Leucophore‐Like Cells Specifically Appear in the Lineage of Melanophores in the Periodic Albino Mutant of Xenopus laevis

In the periodic albino mutant (a^p/a^p) of Xenopus laevis, peculiar leucophore‐like cells appear in the skins of tadpoles and froglets, whereas no such cells are observed in the wild‐type (+/+). These leucophore‐like cells are unusual in (1) appearing white, but not iridescent, under incident light, (2) emitting green fluorescence under blue light, (3) exhibiting pigment dispersion in the presence of α‐melanocyte stimulating hormone (αMSH), and (4) containing an abundance of bizarre‐shaped, reflecting platelet‐like organelles. In this study, the developmental and ultrastructural characteristics of these leucophore‐like cells were compared with melanophores, iridophores and xanthophores, utilizing fluorescence stereomicroscopy, and light and electron microscopy. Staining with methylene blue, exposure to αMSH, and culture of neural crest cells were also performed to clarify the pigment cell type. The results obtained clearly indicate that: (1) the leucophore‐like cells in the mutant are different from melanophores, iridophores and xanthophores, (2) the leucophore‐like cells are essentially similar to melanophores of the wild‐type with respect to their localization in the skin and manner of response to αMSH, (3) the leucophore‐like cells contain many premelanosomes that are observed in developing melanophores, and (4) mosaic pigment cells containing both melanosomes specific to mutant melanophores and peculiar reflecting platelet‐like organelles are observed in the mutant tadpoles. These findings strongly suggest that the leucophore‐like cells in the periodic albino mutant are derived from the melanophore lineage, which provides some insight into the origin of brightly colored pigment cells in lower vertebrates.     

Ultrastructure of the dermal chromatophores in a lizard (Scincidae: Plestiodon latiscutatus) with conspicuous body and tail coloration

Microscopic observation of the skin of Plestiodon lizards, which have body stripes and blue tail coloration, identified epidermal melanophores and three types of dermal chromatophores: xanthophores, iridophores, and melanophores. There was a vertical combination of these pigment cells, with xanthophores in the uppermost layer, iridophores in the intermediate layer, and melanophores in the basal layer, which varied according to the skin coloration. Skin with yellowish-white or brown coloration had an identical vertical order of xanthophores, iridophores, and melanophores, but yellowish-white skin had a thicker layer of iridophores and a thinner layer of melanophores than did brown skin. The thickness of the iridophore layer was proportional to the number of reflecting platelets within each iridophore. Skin showing green coloration also had three layers of dermal chromatophores, but the vertical order of xanthophores and iridophores was frequently reversed. Skin showing blue color had iridophores above the melanophores. In addition, the thickness of reflecting platelets in the blue tail was less than in yellowish-white or brown areas of the body. Skin with black coloration had only melanophores.     

An Ultrastructural and Carotenoid Analysis of the Red Ventrum of the Japanese Newt,Cynops pyrrhogaster

The ventral skin of the wild Japanese newt Cynops pyrrhogaster is creamy at metamorphosis, but turns red when mature. The color of the ventral skin of laboratory (lab)‐reared newts stays yellow throughout their life. However, the mechanism for the red coloration of this animal still remains unknown. In this study, we have performed ultrastructural and carotenoid analyses of the red ventrum of wild and lab‐reared Japanese newts. Using electron microscopy, we observed a number of xanthophores having ring carotenoid vesicles (rcv) and homogenous carotenoid granules (hcg) in the ventral red skin of the wild newt. In the skin, β‐carotene and five other kinds of carotenoids were detected by thin‐layer chromatography (TLC). In the ventral yellow skin of lab‐reared newts, however, only β‐carotene and three other kinds of carotenoids were found. The total amount of carotenoids in the red skin of the wild adult newt was six times more than that of the yellow skin of the lab‐reared newt. Moreover, rcv were more abundant in xanthophores in red skin, but hcg were more abundant in yellow skin. These results, taken together, suggest that the presence of carotenoids in rcv in xanthophores is one of the critical factors for producing the red ventral coloration of the Japanese newt C. pyrrhogaster.     

Pigment cell differentiation in the fire-bellied toad,Bombina orientalis. I. Structural,chemical, and physical aspects of the adult pigment pattern

Wild-collected adults of Bombina orientalis are bright green dorsally and red to red-orange ventrally. As a prelude to an analysis of the differentiation of pigment cells in developing B. orientalis, we describe structural and chemical aspects of the fully differentiated pigment pattern of the “normal” adult. Structurally, differences between dorsal green and ventral red skin are summarized as follows: (1) Dorsal green skin contains a “typical” dermal chromatophore unit comprised of melanophores, iridophores, and xanthophores. Red skin contains predominantly carotenoid-containing xanthophores (erythrophores), and skin from black spot areas contains only melanophores. (2) In ventral red skin, there is also a thin layer of deep-lying iridophores that presumably are not involved in the observed color pattern. (3) Xanthophores of red and green skin are morphologically distinguishable from each other. Dorsal skin xanthophores contain both pterinosomes and carotenoid vesicles; ventral skin xanthophores contain only carotenoid vesicles. Carotenoid vesicles in dorsal xanthophores are much larger but less electron dense than comparable structures in ventral xanthophores. The presence of carotenes in ventral skin accounts for the bright red-orange color of the belly of this frog. Similar pigments are also present in green skin, but in smaller quantities and in conjunction with both colored (yellow) and colorless pteridines. From spectral data obtained for xanthophore pigments and structural data obtained from the size and arrangement of reflecting platelets in the iridophore layer, we attempt to explain the phenomenon of observed green color in B. orientalis.     

Formation of the adult pigment pattern in zebrafish requires leopard and obelix dependent cell interactions

Colour patterns are a prominent feature of many animals and are of high evolutionary relevance. In zebrafish, the adult pigment pattern comprises alternating stripes of two pigment cell types, melanophores and xanthophores. How the stripes are defined and a straight boundary is formed remains elusive. We find that mutants lacking one pigment cell type lack a striped pattern. Instead, cells of one type form characteristic patterns by homotypic interactions. Using mosaic analysis, we show that juxtaposition of melanophores and xanthophores suffices to restore stripe formation locally. Based on this, we have analysed the pigment pattern of two adult specific mutants: leopard and obelix. We demonstrate that obelix is required in melanophores to promote their aggregation and controls boundary integrity. By contrast, leopard regulates homotypic interaction within both melanophores and xanthophores, and interaction between the two, thus controlling boundary shape. These findings support a view in which cell-cell interactions among pigment cells are the major driving force for adult pigment pattern formation.     

Changes in the distribution of melanophores and xanthophores inTriturus alpestris embryos during their transition from the uniform to banded pattern

Summary The change in distribution of melanophores from stage 28+ (uniform melanophore pattern) to stage 34 (banded melanophore pattern) and the participation of xanthophores in these changes has been investigated inTriturus alpestris embryos by studying the social behaviour of single cells. While melanophores are clearly visible from outside the embryo at stage 28+, xanthophores cannot be recognized from the outside until after stage 34. In ultrathin sections of stage 34 embryos, xanthophores are observed alternating with melanophores in a zonal distribution (Epperlein 1982). Using detached pieces of dorsolateral trunk skin, which retain their chromatophores after detachment, the entire distribution of melanophores and xanthophores can be visualized in a scanning electron microscope (SEM). In ambiguous cases (early stages), cells were reprocessed for transmission electron microscopy (TEM) and the presence of the characteristic pigment organelles was assessed. In addition, xanthophores were specifically identified by pteridine fluorescence with dilute ammonia. Pteridines were also identified chromatographically in skin homogenates. The combination of these methods allowed precise identification and quantitative determination of melanophores and xanthophores. Both cell types were present as codistributed, biochemically differentiated cells at stage 28+. Changes in the pattern up to stage 34 were due to the rearrangement at the epidermal-mesodermal interface of a relatively fixed number of melanophores which became preferentially localised at the dorsal somite edge and at the lateral plate mesoderm, and to the distribution of an increasing number of xanthophores to subepidermal locations in the dorsal fin and between the melanophore bands. Concomitant was an increase in the thickness of the epidermal basement membrane and a change in shape of chromatophores from elongate via stellate to rosette shaped, which may be correlated with a shift from migratory to sessile phases.     

Different distribution of melanophores and xanthophores in early tailbud and larval stages inTriturus alpestris

Summary The subepidermal distribution of xanthophores and melanophores is investigated in embryos ofTriturus alpestris with a uniform (stage 28+) and a banded melanophore pattern (stage 35/36). In ultrathin head and trunk sections from stage 35/36 embryos which externally show longitudinal dorsal and lateral melanophore bands in the trunk and less compact continuations of the dorsal bands in the head, xanthophores were discovered in addition to melanophores. Melanophores contain melanosomes while xanthophores which are not externally visible, are recognized by their pterinosomes. Both chromatophore cell types are mutually exclusively distributed on the epidermal basement membrane (bm). Mesenchymal cells seemed not to be able to replace them, except on the bm of the corneal epithelium where there were only mesenchymal cells. In head and trunk sections from stage 28+ embryos which externally show a distribution of uniformly scattered melanophores on the dorsolateral halves, melanophores were found on the dorsolateral neural crest migration route. No epidermal bm was present and xanthophores were undetectable. In ventrolateral and ventral portions of embryos of both stages no chromatophores occurred. This investigation defines the histological localization of melanophores and xanthophores in embryos with a typical uniform and banded melanophore arrangement; a subsequent study analyzes when xanthophores appear and how they arrange with melanophores in alternating zones.     

Adult-type pigment cells,which color the ocular sides of flounders at metamorphosis,localize as precursor cells at the proximal parts of the dorsal and anal fins in early larvae

Flounders form left-right asymmetry in body coloration during metamorphosis through differentiation of adult-type melanophores and xanthophores on the ocular side. As the first step in investigating the formation of flounder body coloration asymmetry, in this study, we aimed to determine where the precursors of adult-type chromatophores distribute in larvae before metamorphosis. In Paralichthys olivaceus and Verasper variegatus, GTP cyclohydrolase 2 (gch2), a common marker of melanoblasts and xanthoblasts, was found to be transiently expressed in cells located along the bilateral skeletal muscles at the basal parts of the dorsal and anal fins of premetamorphic larvae. When V. variegatus larvae were fed with a strain of Artemia collected in Brazil, this gch2 expression was abolished and the differentiation of adult-type melanophores was completely inhibited, while the density of larval melanophores was not affected. In a cell trace test in which the cells at the basal part of the dorsal fin were labeled with DiI at the premetamorphic stage, adult-type melanophores labeled with DiI were found in the skin on the ocular side after metamorphosis. These data suggest that, in flounder larvae, adult-type melanophores are distributed at the basal parts of the dorsal and anal fins as unpigmented precursor cells.     

Tetraspanin 3c requirement for pigment cell interactions and boundary formation in zebrafish adult pigment stripes

Skin pigment pattern formation in zebrafish requires pigment‐cell autonomous interactions between melanophores and xanthophores, yet the molecular bases for these interactions remain largely unknown. Here, we examined the dali mutant that exhibits stripes in which melanophores are intermingled abnormally with xanthophores. By in vitro cell culture, we found that melanophores of dali mutants have a defect in motility and that interactions between melanophores and xanthophores are defective as well. Positional cloning and rescue identified dali as tetraspanin 3c (tspan3c), encoding a transmembrane scaffolding protein expressed by melanophores and xanthophores. We further showed that dali mutant Tspan3c expressed in HeLa cell exhibits a defect in N‐glycosylation and is retained inappropriately in the endoplasmic reticulum. Our results are the first to identify roles for a tetraspanin superfamily protein in skin pigment pattern formation and suggest new mechanisms for the establishment and maintenance of zebrafish stripe boundaries.     

Pigment cell mechanisms underlying dorsal color‐pattern polymorphism in the japanese four‐lined snake

To provide histological foundation for studying the genetic mechanisms of color‐pattern polymorphisms, we examined light reflectance profiles and cellular architectures of pigment cells that produced striped, nonstriped, and melanistic color patterns in the snake Elaphe quadrivirgata. Both, striped and nonstriped morphs, possessed the same set of epidermal melanophores and three types of dermal pigment cells (yellow xanthophores, iridescent iridophores, and black melanophores), but spatial variations in the densities of epidermal and dermal melanophores produced individual variations in stripe vividness. The densities of epidermal and dermal melanophores were two or three times higher in the dark‐brown‐stripe region than in the yellow background in the striped morph. However, the densities of epidermal and dermal melanophores between the striped and background regions were similar in the nonstriped morph. The melanistic morph had only epidermal and dermal melanophores and neither xanthophores nor iridophores were detected. Ghost stripes in the shed skin of some melanistic morphs suggested that stripe pattern formation and melanism were controlled independently. We proposed complete‐ and incomplete‐dominance heredity models for the stripe‐melanistic variation and striped, pale‐striped, and nonstriped polymorphisms, respectively, according to the differences in pigment‐cell composition and its spatial architecture. J. Morphol. 274:1353–1364, 2013. © 2013 Wiley Periodicals, Inc.     

Ultrastructural changes in the dermal chromatophore unit of Hyla arborea during color change

Summary The structural changes in the chromatophores of Hyla arborea related to changes in skin color were studied by electron microscopy and reflectance microspectrophotometry. During a change from a light to a darker green color, the melanosomes of the melanophores disperse and finally surround the iridophores and partly the xanthophores. The iridophores change from cup-shape to a cylindrical or conical shape with a simultaneous change in the orientation of the platelets from being parallel to the upper surface of the iridophores to being more irregular. The xanthophores change from lens-shape to plate-shape. The color change from green to grey seems always to go through a transitional black-green or dark olive green to dark grey. During this change the xanthophores migrate down between the iridophores, and in grey skins they are sometimes found beneath them. The pterinosomes gather in the periphery of the cell, while the carotenoid vesicles aggregate around the nucleus. The iridophores in grey skin are almost ball-shaped with concentric layers of platelets. A lighter grey color arises from a darker grey by an aggregation of melanosomes. The chromatophore values previously defined for Hyla cinerea are applicable in Hyla arborea, and the ultrastructural studies support the assumptions previously made to explain these values.The author wishes to thank Drs. P. Budtz, J. Dyck and L.O. Larsen for valuable discussions and J. Dyck for kindly providing the spectrophotometer granted him by the Danish National Science Foundation. The skilled technical assistance of Mrs. E. Schiøtt Hansen is gratefully acknowledged. Permission was granted by the Springer-Verlag to republish the illustrations of W.J. Schmidt (1920)     

The Role of Early Learning in Determining Shoaling Preferences Based on Visual Cues in the Zebrafish, Danio rerio

Social preferences for specific colour patterns learned in early development, termed imprinting, may influence social and mating decisions. Imprinting has been demonstrated in both birds and fish and has been proposed to play a role in speciation. We raised wild‐type zebrafish, Danio rerio, either with individuals of the same colour pattern, an alternative colour pattern (leopard), or a closely related, unpatterned species, D. albolineatus. We also cross‐reared individual ‘leopard’D. rerio and D. albolineatus with wild‐type D. rerio. We tested the prediction that Danio would prefer to shoal with fish of the colour pattern with which they had been raised, irrespective of their own appearance. Rearing condition affected shoaling preferences between D. rerio and D. albolineatus, with individuals of both colour patterns preferring to associate with shoals of the colour pattern with which they had been raised. The more subtle distinction between the wild‐type and ‘leopard’D. rerio colour patterns did not elicit a shoaling preference. Thus, zebrafish exhibit shoaling preferences based on visual cues, the effect being stronger when patterns are more distinct. There is a strong learned component to these preferences, although the extent to which they may influence mating decisions is unclear.     

An ultrastructural and carotenoid analysis of the red ventrum of the Japanese newt,Cynops pyrrhogaster

The ventral skin of the wild Japanese newt Cynops pyrrhogaster is creamy at metamorphosis, but turns red when mature. The color of the ventral skin of laboratory (lab)-reared newts stays yellow throughout their life. However, the mechanism for the red coloration of this animal still remains unknown. In this study, we have performed ultrastructural and carotenoid analyses of the red ventrum of wild and lab-reared Japanese newts. Using electron microscopy, we observed a number of xanthophores having ring carotenoid vesicles (rcv) and homogenous carotenoid granules (hcg) in the ventral red skin of the wild newt. In the skin, beta-carotene and five other kinds of carotenoids were detected by thin-layer chromatography (TLC). In the ventral yellow skin of lab-reared newts, however, only beta-carotene and three other kinds of carotenoids were found. The total amount of carotenoids in the red skin of the wild adult newt was six times more than that of the yellow skin of the lab-reared newt. Moreover, rcv were more abundant in xanthophores in red skin, but hcg were more abundant in yellow skin. These results, taken together, suggest that the presence of carotenoids in rcv in xanthophores is one of the critical factors for producing the red ventral coloration of the Japanese newt C. pyrrhogaster.     

Genetics of white color and iridophoroma in “Lemon Frost” leopard geckos

The squamates (lizards and snakes) are close relatives of birds and mammals, with more than 10,000 described species that display extensive variation in a number of important biological traits, including coloration, venom production, and regeneration. Due to a lack of genomic tools, few genetic studies in squamates have been carried out. The leopard gecko, Eublepharis macularius, is a popular companion animal, and displays a variety of coloration patterns. We took advantage of a large breeding colony and used linkage analysis, synteny, and homozygosity mapping to investigate a spontaneous semi-dominant mutation, “Lemon Frost”, that produces white coloration and causes skin tumors (iridophoroma). We localized the mutation to a single locus which contains a strong candidate gene, SPINT1, a tumor suppressor implicated in human skin cutaneous melanoma (SKCM) and over-proliferation of epithelial cells in mice and zebrafish. Our work establishes the leopard gecko as a tractable genetic system and suggests that a tumor suppressor in melanocytes in humans can also suppress tumor development in iridophores in lizards.     

The Pteridine Pathway in Zebrafish: Regulation and Specification during the Determination of Neural Crest Cell‐Fate

This review describes pteridine biosynthesis and its relation to the differentiation of neural crest derivatives in zebrafish. During the embryonic development of these fish, neural crest precursor cells segregate into neural elements, ectomesenchymal cells and pigment cells; the latter then diversifying into melanophores, iridophores and xanthophores. The differentiation of neural cells, melanophores, and xanthophores is coupled closely with the onset of pteridine synthesis which starts from GTP and is regulated through the control of GTP cyclohydrolase I activity. De novo pteridine synthesis in embryos of this species increases during the first 72‐h postfertilization, producing H₄biopterin, which serves as a cofactor for neurotransmitter synthesis in neural cells and for tyrosine production in melanophores. Thereafter, sepiapterin (6‐lactoyl‐7,8‐dihydropterin) accumulates as yellow pigment in xanthophores, together with 7‐oxobiopterin, isoxanthopterin and 2,4,7‐trioxopteridine. Sepiapterin is the key intermediate in the formation of 7‐oxopteridines, which depends on the availability of enzymes belonging to the xanthine oxidoreductase family. Expression of the GTP cyclohydrolase I gene (gch) is found in neural cells, in melanoblasts and in early xanthophores (xanthoblasts) of early zebrafish embryos but steeply declines in xanthophores by 42‐h postfertilization. The mechanism(s) whereby sepiapterin branches off from the GTP‐H₄biopterin pathway is currently unknown and will require further study. The surge of interest in zebrafish as a model for vertebrate development and its amenability to genetic manipulation provide powerful tools for analysing the functional commitment of neural crest‐derived cells and the regulation of pteridine synthesis in mammals.     

鳜皮肤图案中色素细胞的分布与排列

色素细胞是皮肤图案形成的基础,为了解鳜(Siniperca chuatsi)皮肤图案区域色素细胞的种类、分布及排列特征,采用光学显微镜与电子显微镜对鳜皮肤中图案区域、非图案区域及交界处皮肤的色素细胞进行显微及超显微结构观察。结果显示,鳜皮肤中含有黑色素细胞、黄色素细胞、红色素细胞及虹彩细胞,主要分布于表皮层和色素层。头部过眼条纹、躯干纵带、躯干斑块等图案区域皮肤表皮层与色素层均含有黑色素细胞,非图案区域仅表皮层含有少量黑色素细胞。躯干图案区域(纵带、斑块)皮肤色素层色素细胞分布层次明显,由外到内依次为黄色素细胞、红色素细胞、黑色素细胞和虹彩细胞,其中,虹彩细胞内反射小板较长,整齐水平排列;躯干非图案区域皮肤色素层由外到内依次为黄色素细胞、红色素细胞和虹彩细胞,其中,虹彩细胞内反射小板较短,无规则排列。头部过眼条纹色素层含有4种色素细胞,色素细胞数量较少,且无规则排列,其中,黑色素细胞内黑色素颗粒较大。交界处皮肤色素层黑色素细胞数量向非图案区域一侧逐渐减少,虹彩细胞数量逐渐增加。结果表明,鳜图案区域与非图案区域、不同图案区域的色素细胞分布与排列各不相同,本研究结果为鳜色素细胞图案化形成机制提供了基础资料。     

Chromatophores and color change in the lizard,Anolis carolinensis

Summary The skin of the lizard, Anolis carolinensis, changes rapidly from bright green to a dark brown color in response to melanophore stimulating hormone (MSH). Chromatophores responsible for color changes of the skin are xanthophores which lie just beneath the basal lamina containing pterinosomes and carotenoid vesicles. Iridophores lying immediately below the xanthophores contain regularly arranged rows of reflecting platelets. Melanophores containing melanosomes are present immediately below the iridophores. The ultrastructural features of these chromatophores and their pigmentary organelles are described. The color of Anolis skin is determined by the position of the melanosomes within the melanophores which is regulated by MSH and other hormones such as norepinephrine. Skins are green when melanosomes are located in a perinuclear position within melanophores. In response to MSH, they migrate into the terminal processes of the melanophores which overlie the xanthophores above, thus effectively preventing light penetration to the iridophores below, resulting in skins becoming brown. The structural and functional characteristics of Anolis chromatophores are compared to the dermal chromatophore unit of the frog.This study was supported in part by GB-8347 from the National Science Foundation.Contribution No. 244, Department of Biology, Wayne State University.The authors are indebted to Dr. Joseph T. Bagnara for his encouragement during the study and to Dr. Wayne Ferris for his advice and the use of his electron microscope laboratory.     

Physiological colour change in the Moorish gecko,Tarentola mauritanica (Squamata: Gekkonidae): effects of background,light, and temperature

Colour has many different functions in animals, such as an involvement in thermoregulation, crypsis, and social interactions. Species capable of physiological colour change may alter their coloration in response to ecological conditions. The Moorish gecko, Tarentola mauritanica, is capable of actively changing its body coloration. In the present study, we investigated colour change in this gecko as a function of background, temperature, and light. Our results demonstrate that the Moorish gecko indeed changes its dorsal colour in response to changes in environmental conditions. By contrast to several other reptilian species, this rapid colour change does not appear to be associated with thermoregulation. Background matching, however, did appear to be a prominent function, although illumination appears to be an essential trigger. Future research should concentrate on individual variation and its effectiveness with respect to antipredatory mechanisms. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ?? , ??–??.     

Cytoskeletal Architecture of Dermal Chromatophores of the Freshwater Teleost Oryzias latipes

Cytoskeletal construction of dermal chromatophores of Orgzias latipes was studied by immunofluorescence microscopy. A microtubule system was most prominent in melanophores where a large number of microtubules emanated from the center of the cell. Xanthophores had an arrangement basically similar to that of melanophores, though the radial pattern became more irregular in the peripheral region where intersecting wavy microtubules were quite frequent. Oval-shaped leucophores exhibited the least-developed microtubule system, where the limited number of microtubules formed a loose basket-like architecture. Intermediate filaments were ubiquitously present in all types of chromatophores and were found to be vimentin-immunoreactive. Examination of doubly-labeled cells indicated that vimentin filaments had similar distribution patterns with microtubules. Orderly arranged bundles of actin filaments were found only in xanthophores, while in melanophores and xanthophores, actin expression was diffuse without displaying a conspicuous filamentous organization. Colchicine treatment induced depolymerization of microtubules and retraction of dendrites in varying degrees in cells in culture and in situ. Melanophores in culture are very sensitive to the treatment while xanthophores appeared to be more resistant in respect to the maintenance of cell morphology.     

Studies of pigment transfer between Xenopus laevis melanophores and fibroblasts in vitro and in vivo1

Frog melanophores rapidly change colour by dispersion or aggregation of melanosomes. A long‐term colour change exists where melanosomes are released from melanophores and transferred to surrounding skin cells. No in vitro model for pigment transfer exists for lower vertebrates. Frog melanophores of different morphology exist both in epidermis where keratinocytes are present and in dermis where fibroblasts dominate. We have examined whether release and transfer of melanosomes can be studied in a melanophore‐fibroblast co‐culture, as no frog keratinocyte cell line exists. Xenopus laevis melanophores are normally cultured in conditioned medium from fibroblasts and fibroblast‐derived factors may be important for melanophore morphology. Melanin was exocytosed as membrane‐enclosed melanosomes in a process that was upregulated by α‐melanocyte‐stimulating hormone (α‐MSH), and melanosomes where taken up by fibroblasts. Melanosome membrane‐proteins seemed to be of importance, as the cluster‐like uptake pattern of pigment granules was distinct from that of latex beads. In vivo results confirmed the ability of dermal fibroblasts to engulf melanosomes. Our results show that cultured frog melanophores can not only be used for studies of rapid colour change, but also as a model system for long‐term colour changes and for studies of factors that affect pigmentation.