Morphological and biochemical characterization of goldfish erythrophores and their pterinosomes

Development and genetics of red coloration in the zebrafish relative Danio albolineatus

Animal pigment patterns play important roles in behavior and, in many species, red coloration serves as an honest signal of individual quality in mate choice. Among Danio fishes, some species develop erythrophores, pigment cells that contain red ketocarotenoids, whereas other species, like zebrafish (D. rerio) only have yellow xanthophores. Here, we use pearl danio (D. albolineatus) to assess the developmental origin of erythrophores and their mechanisms of differentiation. We show that erythrophores in the fin of D. albolineatus share a common progenitor with xanthophores and maintain plasticity in cell fate even after differentiation. We further identify the predominant ketocarotenoids that confer red coloration to erythrophores and use reverse genetics to pinpoint genes required for the differentiation and maintenance of these cells. Our analyses are a first step toward defining the mechanisms underlying the development of erythrophore-mediated red coloration in Danio and reveal striking parallels with the mechanism of red coloration in birds.

Pterin-based pigmentation in animals

Pterins are one of the major sources of bright coloration in animals. They are produced endogenously, participate in vital physiological processes and serve a variety of signalling functions. Despite their ubiquity in nature, pterin-based pigmentation has received little attention when compared to other major pigment classes. Here, we summarize major aspects relating to pterin pigmentation in animals, from its long history of research to recent genomic studies on the molecular mechanisms underlying its evolution. We argue that pterins have intermediate characteristics (endogenously produced, typically bright) between two well-studied pigment types, melanins (endogenously produced, typically cryptic) and carotenoids (dietary uptake, typically bright), providing unique opportunities to address general questions about the biology of coloration, from the mechanisms that determine how different types of pigmentation evolve to discussions on honest signalling hypotheses. Crucial gaps persist in our knowledge on the molecular basis underlying the production and deposition of pterins. We thus highlight the need for functional studies on systems amenable for laboratory manipulation, but also on systems that exhibit natural variation in pterin pigmentation. The wealth of potential model species, coupled with recent technological and analytical advances, make this a promising time to advance research on pterin-based pigmentation in animals.

Goldfish: an old and new model system to study vertebrate development, evolution and human disease

The goldfish (Carassius auratus) is a domesticated cyprinid teleost closely related to the crucian carp. Goldfish domestication occurred in South China around 1,000 years ago. At least 180 variants and 70 genetically established strains are currently produced. These strains possess diverse phenotypes in body shape, colouration, scales, and fin, eye and hood morphology. These include biologically interesting phenotypes that have not been observed in mutants of zebrafish or medaka. In addition, goldfish strains have been maintained in a non-wild environment for several hundreds of generations, and certain goldfish strains have phenotypes similar to some human diseases. The recent progress in the assembly of the whole-genome sequence of goldfish provides strong tools for a genetic analysis of these phenotypes. The whole-genome duplication (WGD) event occurred in the goldfish genome 8-14 million years ago; this is one of the latest WGD in vertebrates. Goldfish are a useful model for studying genome evolution after the WGD event. This review focuses on the potential for goldfish as a model system in understanding the molecular basis of vertebrate development and evolution and human diseases.

Role of ABC transporters White, Scarlet and Brown in brown planthopper eye pigmentation

The brown planthopper ATP-binding cassette (ABC) proteins White (W), Scarlet (St) and Brown (Bw) belong to the ABC transporter superfamily and are responsible for the transportation of guanine and tryptophan precursors of eye pigments. In the present study, the brown planthopper White (NlW), S t(NlSt) and Bw (NlBw) genes were cloned, and subsequent phylogenetic analysis showed that these genes are clustered with their respective homologues, with a genetic relationship observed between NlW and its Bemisia tabaci homologue having the highest similarity. Sequence alignments showed that these three proteins have a highly conserved Walker A domain, an ABC "signature sequence" and a Walker B domain. QRT-PCR demonstrated that W, St and Bw are highly expressed in the head of long-winged males and are highly expressed in both egg and male. Adult eye colour was altered after the downregulation of NlW, NlSt and NlBw in the 1st to 3rd instar nymph. The eye colours of emerged adults became white, dark and red after injection of dsNlW, dsNlSt and dsNlBw, respectively. The eye pigment content assay revealed that xanthommatin and pteridine were significantly decreased after the injection of dsRNAs, and the range of variation was inversely correlated with nymph age. The present study provides a theoretical basis for understanding the function of ABC transporters at the molecular and biochemical levels.

Comparative transcriptome analysis of molecular mechanism underlying gray-to-red body color formation in red crucian carp (Carassius auratus, red var.)

Red crucian carp (Carassius auratus red var.) is an ornamental fish with vivid red/orange color. It has been found that the adult body color of this strain forms a gray-to-red change. In this study, skin transcriptomes of red crucian carp are first obtained for three different stages of body color development, named by gray-color (GC), color-variation (CV), and red-color (RC) stages, respectively. From the skins of GC, CV, and RC, 103,229; 108,208; and 120,184 transcripts have been identified, respectively. Bioinformatics analysis reveals that 2483, 2967, and 4473 unigenes are differentially expressed between CV and GC, RC and CV, and RC and GC, respectively. A part of the differentially expressed genes (DEGs) are involved in the signaling pathway of pigment synthesis, such as the melanogenesis genes (Mitfa, Pax3a, Foxd3, Mc1r, Asip); tyrosine metabolism genes (Tyr, Dct, Tyrp1, Silva, Tat, Hpda); and pteridine metabolism genes (Gch, Xdh, Ptps, Tc). According to the data of transcriptome and quantitative PCR, the expression of Mitfa and its regulated genes which include the genes of Tyr, Tyrp1, Dct, Tfe3a, and Baxα, decreases with gray-to-red change. It is suggested that Mitfa and some genes, being related to melanin synthesis or melanophore development, are closely related to the gray-to-red body color transformation in the red crucian carp. Furthermore, the DEGs of cell apoptosis and autophagy pathway, such as Tfe3a, Baxα, Hsp70, Beclin1, Lc3, Atg9a, and Atg4a, might be involved in the melanocytes fade away of juvenile fish. These results shed light on the regulation mechanism of gray-to-red body color transformation in red crucian carp, and are helpful to the selective breeding of ornamental fish strains.

Lipid droplet biology and evolution illuminated by the characterization of a novel perilipin in teleost fish

Perilipin (PLIN) proteins constitute an ancient family important in lipid droplet (LD) formation and triglyceride metabolism. We identified an additional PLIN clade (plin6) that is unique to teleosts and can be traced to the two whole genome duplications that occurred early in vertebrate evolution. Plin6 is highly expressed in skin xanthophores, which mediate red/yellow pigmentation and trafficking, but not in tissues associated with lipid metabolism. Biochemical and immunochemical analyses demonstrate that zebrafish Plin6 protein targets the surface of pigment-containing carotenoid droplets (CD). Protein kinase A (PKA) activation, which mediates CD dispersion in xanthophores, phosphorylates Plin6 on conserved residues. Knockout of plin6 in zebrafish severely impairs the ability of CD to concentrate carotenoids and prevents tight clustering of CD within carotenoid bodies. Ultrastructural and functional analyses indicate that LD and CD are homologous structures, and that Plin6 was functionalized early in vertebrate evolution for concentrating and trafficking pigment.

DOI:http://dx.doi.org/10.7554/eLife.21771.001

Comparison of pigment cell ultrastructure and organisation in the dermis of marble trout and brown trout, and first description of erythrophore ultrastructure in salmonids

Skin pigmentation in animals is an important trait with many functions. The present study focused on two closely related salmonid species, marble trout (Salmo marmoratus) and brown trout (S. trutta), which display an uncommon labyrinthine (marble-like) and spot skin pattern, respectively. To determine the role of chromatophore type in the different formation of skin pigment patterns in the two species, the distribution and ultrastructure of chromatophores was examined with light microscopy and transmission electron microscopy. The presence of three types of chromatophores in trout skin was confirmed: melanophores; xanthophores; and iridophores. In addition, using correlative microscopy, erythrophore ultrastructure in salmonids was described for the first time. Two types of erythrophores are distinguished, both located exclusively in the skin of brown trout: type 1 in black spot skin sections similar to xanthophores; and type 2 with a unique ultrastructure, located only in red spot skin sections. Morphologically, the difference between the light and dark pigmentation of trout skin depends primarily on the position and density of melanophores, in the dark region covering other chromatophores, and in the light region with the iridophores and xanthophores usually exposed. With larger amounts of melanophores, absence of xanthophores and presence of erythrophores type 1 and type L iridophores in the black spot compared with the light regions and the presence of erythrophores type 2 in the red spot, a higher level of pigment cell organisation in the skin of brown trout compared with that of marble trout was demonstrated. Even though the skin regions with chromatophores were well defined, not all the chromatophores were in direct contact, either homophilically or heterophilically, with each other. In addition to short-range interactions, an important role of the cellular environment and long-range interactions between chromatophores in promoting adult pigment pattern formation of trout are proposed.

Gene Expression Variations of Red-White Skin Coloration in Common Carp (Cyprinus carpio)

Teleosts have more types of chromatophores than other vertebrates and the genetic basis for pigmentation is highly conserved among vertebrates. Therefore, teleosts are important models to study the mechanism of pigmentation. Although functional genes and genetic variations of pigmentation have been studied, the mechanisms of different skin coloration remains poorly understood. The koi strain of common carp has various colors and patterns, making it a good model for studying the genetic basis of pigmentation. We performed RNA-sequencing for red skin and white skin and identified 62 differentially expressed genes (DEGs). Most of them were validated with RT-qPCR. The up-regulated DEGs in red skin were enriched in Kupffer's vesicle development while the up-regulated DEGs in white skin were involved in cytoskeletal protein binding, sarcomere organization and glycogen phosphorylase activity. The distinct enriched activity might be associated with different structures and functions in erythrophores and iridophores. The DNA methylation levels of two selected DEGs inversely correlated with gene expression, indicating the participation of DNA methylation in the coloration. This expression characterization of red-white skin along with the accompanying transcriptome-wide expression data will be a useful resource for further studies of pigment cell biology.

Localization of sepiapterin reductase in pigment cells of Oryzias latipes

Body colors of poikilothermal vertebrates are derived from three distinct types of pigment cells, melanophores, erythro/xanthophores and irido/leucophores. It is well known that melanin in melanophores is synthesized by tyrosinase within a specific organelle termed the melanosome. Although sepiapterin reductase (SPR) is an important enzyme involved in metabolizing biopterin and sepiapterin (a conspicuous pteridine as a coloring pigment in xanthophores) the distribution of SPR has not been shown in pigment cells. An antibody raised in rabbits against rat SPR was used to demonstrate the presence of SPR in pigment cells of Oryzias latipes. This study, which used immunohistochemistry with fluorescence or peroxidase/diaminobenzidine as markers, revealed that SPR could be detected readily in xanthophores, but only faintly in melanophores. These results suggest that sepiapterin is metabolized within xanthophores. Moreover, these experiments show that a protein sharing immunological cross-reactivity with rat SPR is located in teleost O. latipes xanthophores, which is significant considering the relationship of pteridine metabolism between poikilothermal vertebrates and mammals. Further progress in investigations of the roles of pteridines in vertebrates will be promoted by using these fish which can be bred in mass rather easily in the laboratory.

Morphological studies on the mechanisms of pigmentary organelle transport in fish xanthophores and melanophores

Pigmentary organelle translocations within fish chromatophores undergo physiological color changes when exposed to external signals. Chromatophores can be isolated in high yields, and their pigmentary organelles can be tracked readily by microscopy. The combined efforts of morphology and biomolecular chemistry have led to the identification of and determination of the interrelationships between cytoskeletal elements and accessory proteins, motor molecules, cytomatrix, and pigmentary organelles of various sizes. Fish chromatophores have been classified as fast, intermediate, and slow translocators, based on the relative numbers of microtubules. Studies on cultured goldfish (Carassius auratus L.) xanthophores for over 20 years have demonstrated that in this slow translocator, tubulovesicular structures of the smooth endoplasmic reticular (SER) cisternae are involved in the disperson and aggregation of associated carotenoid droplets (CD) with some involvement of cytoskeletal elements. Killifish (Fundulus heteroclitus L.) melanophore, a fast translocator, was also examined. Recent work demonstrates a bright fluorescent "starburst"-like spot that we call an actin filament-organizing center (AFOC) with radiating microfilaments, akin to the microtubule-organizing center (MTOC) with radiating microtubules. Melanosomes translocate single-file on microtubules and are not associated with SER cisternae. Slower CD dispersion or aggregation in goldfish xanthophores seems to be predominantly microfilament-based transport, or microfilament- and microtubule-based transport, respectively. Faster melanosome translocations in killifish melanophores are based on microtubules, with our evidence indicating microfilament involvement. Neural crest-derived chromatophores are models for vesicular transport in axons, and immunocytochemical and imaging technologies may help to elucidate the cellular transport mechanisms.

Calponin, caldesmon, and chromatophores: The smooth muscle connection

Observations on pigment translocations in fish chromatophores and speculations on the chemo-mechanical transduction processes responsible for the recorded chromatosome motilities are briefly reviewed. The presence of the two smooth muscle proteins caldesmon and calponin is confirmed by immunocytochemistry for melanophores and iridophores of the Antarctic fishes Pagothenia borchgrevinki and Trematomus bernacchii. Troponin, a typical vertebrate skeletal muscle protein is absent from the chromatophores of the two fish species. It is suggested that calponin's role, in the presence of Ca(2+) and calmodulin, is that of a modulator and that caldesmon, a molecule that competes with calponin for actin binding sites, is in a position in which it can switch on and off Ca(2+)-dependent contractility and relaxation. Freshly caught Antarctic fish are receiving conflicting signals, when hauled from the dark under-ice to the bright above-ice environment (nor-adrenaline secretion promoting aggregation, but exposure to bright light bringing on pigment dispersion); it is in such situations that the two proteins in question could play important roles. The precise nature of their involvement still needs to be worked out, but the fact that they do exist in the chromatophores at all, appears to have an ontogenetic background.

Brightly colored pigmentation in lower vertebrates: wonder searching its mechanisms and significance in the context of phylogeny

This is a biographical sketch of my research and its related personal episodes with respect to brightly colored pigmentation in lower vertebrates. It includes a brief story of the studies on; (a) pterinosomes as a specific site of pteridine deposition in xanthophores or erythrophores of fish and amphibians, (b) a mosaic phenotype of chromatophores occurring in the reptiles and its implication for their developmental origin and differentiation mechanisms, (c) erythrophoroma as a tumor of erythrophores in goldfish, (d) the pluripotentials of erythrophoroma cells for expression of neural crest-derived characters in vitro, (e) pigment disorders occurring in hatchery-raised flounders and (f) recognition of pigment cell types by murine tyrosinase genes transfected into an orange-colored variant of medaka fish. Some of the personal affairs associated with the history of the Japanese community for pigment cell research were described to illustrate the background of these studies.

Cutaneous biology and diseases of fish

The normal structure and function of the piscine integument reflects the adaptation of the organism to the physical, chemical, and biological properties of the aquatic environment, and the natural history of the organism. Because of the intimate contact of fish with the environment, cutaneous disease is relatively more common in fish than in terrestrial vertebrates and is one of the primary disease conditions presented to the aquatic animal practitioner. However, cutaneous lesions are generally nonspecific and may be indicative of disease that is restricted to the integument or a manifestation of systemic disease. Regardless, a gross and microscopic examination of the integument is simple to perform, but is highly diagnostic and should always be included in the routine diagnostic effort of the aquatic animal practitioner, especially since various ancillary diagnostic procedures are either not practical or lack predictive value in fish. The purpose of this article is to provide an overview of normal cutaneous biology prior to consideration of specific cutaneous diseases in fish.

Involvement of pteridines in the body coloration of the isopod Armadillidium vulgare

The pteridine content was measured as a function of age in Armadillidium vulgare, and the fine structure of the pteridine-containing granules in the integument was examined in relation to pteridine content. Yellow chromatophores are an essential component of the cream-markings, which are a defining feature of the female A. vulgare. Four kinds of pteridines in the integument including a yellow pigment (sepiapterin) were determined by HPLC. The body color of the red phenotype of A. vulgare varies from dark red to yellowish red and was formerly thought to be due to the quality and quantity of ommochrome pigment. Our analysis of the pteridine content in the integument of this phenotype revealed a significant change in sepiapterin content per body weight with age. Sepiapterin content per body weight decreased gradually with age, while that of biopterin tended to increase with age. Ultrastructural observations of the pigment granules in the yellow chromatophores revealed a corresponding change in the fine structure of pigment granules. In the older adults, some of the electron-dense fibrous materials in the pteridine-containing granules was concentrically arranged, and in the younger adults, most of pteridine-containing granules were electron-lucent. The role of pteridine quality in determining the structure of pteridine-containing granules is discussed.

Deficiency of the gene B impairs differentiation of melanophores in the medaka fish, Oryzias latipes: fine structure studies

In an orange-colored variant of the medaka fish, Oryzias latipes, which is homozygous for b allele, the melanophores represent a tissue-specific differentiation, manifesting an amelanotic appearance in the skin, an incomplete melanogenesis in the choroid and the peritoneum, and mosaic phenotype-like melano-iridophores in the peritoneum. In a wild-type strain of this species carrying the B gene, all melanophores are terminally differentiated irrespective of the tissues in which they are located. This indicates that the deficiency of B gene impairs the differentiation of melanophores in the medaka. Electron microscopy disclosed that the deficiency of B gene causes deterioration of melanogenesis to occur inside the melanosomes and that the manner of deterioration in the melanophores in the skin, the choroid and the peritoneum is different. The ubiquitous occurrence of reflecting platelet-laden melanophores in the peritoneum of this variant and the total absence of a mosaicism in pigment cells of the wild-type strain indicate that the deficiency of B gene predestines melanoblasts distributed in this tissue to an ambiguous state with regard to their differentiation. Little difference is observed between melanosomes maturation in pigment epithelial cells of the orange-colored variant and the wild-type strain, indicating an innocent role of the B gene in their differentiation.

Pigments and ultrastructures of pigment cells in xanthic sailfin mollies (Poecilia latipinna)

Electron micrographs of skin from xanthic (gold) sailfin mollies revealed numerous xanthophores, as well as scattered melanophores. The melanophores were seen to contain premelanosomes in various stages of development. This is consistent with the fact that xanthic mollies have been shown to be tyrosinase positive. Melanosomes in xanthic mollies appear to develop by one of two pathways: 1) from an endoplasmic reticulum-derived vesicle which develops an internal lamellar framework, and 2) by fusion of multiple Golgi-derived vesicles which lack an internal lamellar framework. Analysis of the pigments in the skin of the xanthic mollies identified four colorless pteridine pigments (xanthopterin, isoxanthopterin, neopterin, and pterin) and a carotenoid with an absorbance spectrum similar to beta-carotene. It appears that, unlike some other poeciliid fishes, sailfin mollies do not use pteridine pigments for orange coloration. Rather, they appear to rely primarily on carotenoids.

Pigmentary system of the adult alpine salamander Salamandra atra atra (Laur., 1768)

The pigmentary system of the skin from adult specimens of the black alpine salamander Salamandra atra atra was investigated by light microscope, electron microscope, and biochemical studies. Results were compared with those obtained in previous study of the subspecies Salamandra atra aurorae. Unlike Salamandra atra aurorae, which presents epidermal xanthophores and iridophores, Salamandra atra atra is completely melanized, presenting only epidermal and dermal melanophores. The melanosomes in both the epidermis and the dermis appear to derive from a multivesicular premelanosome similar to that in the goldfish, and the epidermal melanosomes are smaller than those in the dermis. Premelanosomes with an internal lamellar matrix were not observed. The biochemical results have shown that in the ethanol extracts obtained from the skin in toto and from the melanosomes, pteridines and flavins are always present and are the same as those extracted from the black skin areas of Salamandra atra aurorae.

Biosynthetic pathways of pteridines and their association with phenotypic expression in vitro in normal and neoplastic pigment cells from goldfish

The distribution of GTP-cyclohydrolase I, pyruvoyl tetrahydropterin (dysopropterin) synthase, and pyruvoyl tetrahydropterin reductase in goldfish erythrophores, melanophores, and erythrophoroma cells in vitro has been revealed by specific biochemical assays. The activity of pyruvoyl tetrahydropterin synthase in the erythrophores is nearly the same as that in rat kidney and pineal gland. Results of the simultaneous quantification of unconjugated pteridines (biopterin, sepiapterin, neopterin, and pterin) by HPLC indicate that the total amounts of these derivatives present in these cells and in the respective culture media are closely correlated with the activities of these enzymes. These findings imply that these cells are capable of the autonomous synthesis of pteridines, which most likely proceeds from GTP to 6-lactoyl-5,6,7,8-tetrahydropterin (reduced sepiapterin), via dihydroneopterin triphosphate and pyruvoyl tetrahydropterin, through reactions catalyzed by these enzymes. A comparison of pteridine metabolism between clones of the stem cell type and the yellow-pigmented clones induced from erythrophoroma cells suggests that brightly colored pigmentation involves two separate phases: the biosynthesis of pteridines and their deposition in the pigment organelles. The presence of the highly active pteridine-synthesizing enzymes in melanophores and melanogenic erythrophoroma cells strongly suggests a loose commitment to the expression of pigment phenotypes in this species.

Pigmentary system of the adult alpine salamander Salamandra atra aurorae (Trevisan, 1982)

The pigmentary system of skin from adult specimens of the amphibian urodele Salamandra atra aurorae was investigated by light microscope, electron microscope, and biochemical studies. Yellow (dorsum and head) and black (flank and belly) skin was tested. Three chromatophore types are present in yellow skin: xanthophores, iridophores, and melanophores. Xanthophores are located in the epidermis whereas iridophores and melanophores are found in the dermis. Xanthophores contain types I, II, and III pterinosomes. Some pterinosomes are very electron-dense. Black skin has a single type of chromatophore: the melanophores. Some melanophores are located in the epidermis. In contrast to the dermal melanophores, these present, in addition to typical melanosomes, organelles with different morphology and vesicles having a limiting membrane and containing little amorphous material. Both skin types present some pteridines and flavins, though they are qualitatively and quantitatively more abundant in yellow skin extracts.

Dermal and epidermal chromatophores of the Antarctic teleost Trematomus bernacchii

The physiological response and ultrastructure of the pigment cells of Trematomus bernacchii, an Antarctic teleost that lives under the sea ice north of the Ross Ice Shelf, were studied. In the integument, two types of epidermal chromatophores, melanophores and xanthophores, were found; in the dermis, typically three types of chromatophores--melanophores, xanthophores, and iridophores--were observed. The occurrence of epidermal xanthophore is reported for the first time in fish. Dermal melanophores and xanthophores have well-developed arrays of cytoplasmic microtubules. They responded rapidly to epinephrine and teleost melanin-concentrating hormone (MCH) with pigment aggregation and to theophylline with pigment dispersion. Total darkness elicited pigment aggregation in the majority of dermal xanthophores of isolated scales, whereas melanophores remained dispersed under both light and dark conditions. Pigment organelles of epidermal and dermal xanthophores that translocate during the pigmentary responses are carotenoid droplets of relatively large size. Dermal iridophores containing large reflecting platelets appeared to be immobile.

Neural crest cell differentiation and carcinogenesis: capability of goldfish erythrophoroma cells for multiple differentiation and clonal polymorphism in their melanogenic variants

Multiple differentiation shown by a single cell line (GEM 81) of goldfish erythrophoroma (tumors of integumental erythrophores) cells after administration of chemical induction in vitro includes 1) melanogenesis, 2) formation of reflecting platelets, 3) synthesis of pteridines heterogeneous to this species, 4) formation of dermal skeletons such as teeth and fin rays, 5) production of neuronal characters, and 6) genesis of lentoid bodies. Melanogenic cells, highest in inducibility, also show remarkable phenotypic diversification in their cell morphology, pigmentation, and physiologic response. In this paper, the following findings are presented; a) multiple differentiation shown by erythrophoroma cells occurs on a clonal basis, making whole component cells of a given induced colony strikingly similar in their cell characters, and b) induced melanogenic clones manifest a remarkable polymorphism in their melanosome ultrastructure and receptor composition associated with motile response. The divergence covers concentric lamellar, multivesicular, fibrillar, and macroglobular types for the former, and a varying combination of receptors for epinephrine, melanin concentrating hormone (MCH), and melatonin for the latter. Because a spectrum of phenotypes expressed by differentiation-induced erythrophoroma cells is restricted to those of neural crest origin (except lentoid bodies) and polymorphism in induced melanized cells is composed mostly of a collection of a variety of known melanogenic characters, it is presumed that erythrophoroma cells are capable of multiple differentiation within the commitment as neural crest cells.

Pigment cells and pigment cell tumors in fish

The three basic pigment cell types found in poikilothermic vertebrates, melanocytes (melanin-producing cells), erythrophores (red or yellow pigment cells), and iridophores (iridescence-producing cells), are derived from neural crest. Neoplasms of pigment cells in fish are also of three phenotypes, melanomas (melanophoromas), erythrophoromas, and iridophoromas, showing the phenotypes of their corresponding normal pigment cells. These pigment cell tumors are among the most common types in bony fish and seem to be more common in fish than in mammals, including humans. Moreover, there are no mammalian neoplasms corresponding to erythrophoromas and iridophoromas in fish. The complexities in the nature and classification of pigment cell tumors in fish will be discussed on the basis of a survey of our collection of these tumors at the Cancer Institute. The etiology of pigment cell tumors in fish is obscure. In order to know whether activated oncogene is involved in the genesis of erythrophoromas in goldfish, the ras genes from normal and erythrophoroma cells were cloned and their nucleotide sequences were compared. The goldfish ras gene and human ras genes showed striking homology. However, no point mutation at the 12th codon was observed in ras genes isolated from erythrophoromas. Besides pigment cell tumors in fish, abnormal pigmentation or depigmentation in flounders associated with diseased conditions is also described.

Induction of xanthophores from non-pigmented dermal cells of xanthic goldfish in vitro

To identify precursor cells of xanthophores (xanthoblasts), non-pigmented cells without any phenotypic traits as pigment cells were isolated from the dermal tissue of xanthic goldfish with an adult color pattern and cultured in a medium containing 1 mM db-cAMP or 0.25 U/ml ACTH and 10% carp serum. These non-pigmented cells differentiated into xanthophores which showed a dendritic morphology and contained a large quantity of fluorescent pteridines and numerous vesicular inclusions. Sepiapterin was the major component, and the vesicles contained fuzzy material in addition to small membranous elements. The fluorescent pattern and the morphological characteristics indicated that the differentiated pigment cells were xanthophores of larval type.

Cyclic nucleotide levels of the photosensitive irises of Bufo marinus and Lophius

The sphincter pupillae muscle of several species contracts autonomously after light directly strikes the iris. The response is initiated by isomerization of rhodopsin in the sarcolemma. Light-induced release of CA2+ from internal stores is one step in the transduction process. The levels of cyclic AMP and cyclic GMP were measured after irises were stimulated by light. Stimulation by light does not produce measurable or consistent changes in the levels of either cyclic AMP or cyclic GMP within the photosensitive irises of at least two species, Bufo marinus and Lophius.

Ultrastructure of the extracutaneous pigment cells in the plaice (Pleuronectes platessa, L., Teleostei)

The extracutaneous pigment cell system of the plaice (Pleuronectes platessa L.) was examined by light and electron microscopy in selected regions, including two cutaneous regions for comparison. The extracutaneous pigmentation consists of guanocytes and melanocytes with differing distributions within the body. The eyeless side lacks melanocytes. The pigment cells are differentiated as very flat elements with long processes. They display an affinity for loose connective tissue at boundary layers such as the peritoneal epithelium, organ capsules or blood vessels, to which they are parallelly arranged at a very constant distance. In some locations guanocytes are intimately associated with melanocytes forming "reduced chromatophore units". Extracutaneous pigment cells are poor in mitochondria, endoplasmic reticulum, microfilaments, caveolae intracellulares, ribosomes and glycogen granules, all of which are more abundant in cutaneous pigment cells and pigment cells of the eye. In extracutaneous guanocytes the crystals are loosely arranged parallel to the cell surface, in cutaneous guanocytes perpendicular. Cells with rod-like vesicular cisternae are described as "guanoblasts". No single pigment cell was found exhibiting different types of pigment granules. The varying colors of extracutaneous pigmentation arise from varying combinations of guanocytes and melanocytes in addition to the color of the tissue itself.

Melanogenesis in genetically determined pigment cell tumors of platyfish and platyfish-swordtail hybrids: correlation between tyrosine activity and degree of malignancy

In the genetically determined pigment cell tumors of platyfish and platyfish-swordtail hybrids, the degree of malignancy of pigment cells which have been neoplastically transformed by a tumor gene (Tu) depends on the type and number of certain regulating genes (R). In the present study, the tyrosinase activities in tumors of different degrees of malignancy (black spots, premelanomas, melanomas) have been determined. The results demonstrate a close correlation between the level of tyrosinase activity and the degree of malignancy. Spot patterns consisting of completely differentiated (benign) Tu-transformed cells show no tyrosinase activity. Premelanomas containing a few incompletely differentiated (malignant) Tu-transformed cells in addition to many differentiated ones show moderate tyrosinase activities. Melanomas which contain increasing numbers of incompletely differentiated cells with increasing growth rates show high to extremely high tyrosinase activities. Thus, the tyrosinase levels present in these tumors can be used as an indicator for the degree of differentiation and, thereby, for the degree of malignancy of the neoplastically transformed pigment cells.

Genetic control of cell differentiation in platyfish-swordtail melanomas

In certain fish hybrids, malignant transformation of pigment cells is due to the presence of a tumor gene (Tu), the action of which is controlled by several regulatory elements. Absence of these controlling genes causes rapid proliferation of the Tu-transformed cells and ultimately results in melanoma formation. One of these genes has been identified as a differentiation gene (Diff), since it seems to control the differentiation of the transformed pigment cells. Light and electron microscopy of Tu-transformed cells of fish differing in the dosage of Diff, and the determination of tyrosinase activity in homogenates of the respective tissues revealed that the degree of cellular differentiation depends on the dosage of Diff present in the genome. It is concluded that the gene Diff promotes the differentiation of malignant melanoma cells into benign melanophores.

Hormone-induced dispersion or aggregation of carotenoid-containing smooth endoplasmic reticulum in cultured xanthophores from the goldfish, Carrassius auratus L

A novel organelle movement is described in goldfish xanthophores. Smooth endoplasmic reticulum, containing carotenoids pigments, undergo MSH or c-AMP-induced dispersion. This dispersion is independent of RNA and protein synthesis, not modulated by c-GMP and inhibited by cytochalasin B but only at the relatively high concentration of 10 mug/ml. Epinephrine induces aggregation, a process that is inhibited by colchicine. These results suggest, but do not prove, the involvement of microfilaments in dispersion and microtubules in the aggregation of carotenoid-containing endoplasmic reticulum.

Cytochemical characterization of goldfish (Carassius auratus L.) dermis with special reference to the pigment cells

The dermal cells in grey, xanthic, and white goldfish integuments were cytochemically characterized for the following enzymatic activities: tyrosinase, DOPA-oxidase, cytochrome oxidase, monoamine oxidase, peroxidase, non-specific esterase, cholinesterase, NAD-diaphorase, NADP-diaphorase, aryl sulfatase, nucleotide phosphodiesterase, beta-glucuronidase, acid phosphatase, alkaline phosphatase, adenosine triphosphatase, thiamine pyrophosphatase, glucose-6-phosphatase, aldolase, as well as succinate, malate, isocitrate, glutamate, glucose-6-phosphate, 6-phosphogluconate, alpha-glycerophosphate, alcohol, lactate, and beta-hydroxybutyrate dehydrogenases. It was found that the epidermis was a significant barrier to the access of cytochemical reaction substrates. Removal of the epidermal barrier provided dermal cell localizations of enzymatic activities which were reproducible. Further, alterations in reaction times and temperatures from the mammalian methodology provided conditions fe various integumental cells were compared for possible interrelationships. The basic foundations for future work with the dermis of poikilothermic vertebrates on an experimental basis were established. In addition, a previously undescribed non-pigmented dermal cell, the "x"-cell, was found to have enzymatic characteristics similar to both melanophores and lipophores. The "x"-cell may be the common precursor of both types of pigment cells.

Fine structure of goldfish xanthophore

Images