Ultrastructure and regulation of color change in blue spots of leopard coral trout Plectropomus leopardus

The leopard coral trout generally exhibited numerous round, minute blue spots covering its head (about the size of nostril) and body (except ventral side). This is a characteristic that distinguishes them from similar species. Recently, however, we found the leopard coral trout with black spots. Here, the distribution and ultrastructure of chromatophores in the blue and black spots were investigated with light and transmission electron microscopies. The results showed that in the blue spots, two types of chromatophores are present in the dermis, with the light-reflecting iridophores located in the upper layer and the aggregated light-absorbing melanophores in the lower layer. Black spots have a similar chromatophore composition, except that the melanosomes within the melanophores disperse their dendritic processes to encircle the iridophores. Interestingly, after the treatment of forskolin, a potent adenylate cyclase activator, the blue spots on the body surface turned black. On the other hand, using the skin preparations in vitro, the electrical stimulation and norepinephrine treatment returned the spots to blue color again, indicating the sympathetic nerves were involved in regulating the coloration of blue spots. Taken together, our results revealed that the blue spots of the leopard coral trout can change color to black and vice versa, resulting from the differences in the distribution of melanosomes, which enriches our understanding of the body color and color changes of fishes.

Neural innervation as a potential trigger of morphological color change and sexual dimorphism in cichlid fish

Many species change their coloration during ontogeny or even as adults. Color change hereby often serves as sexual or status signal. The cellular and subcellular changes that drive color change and how they are orchestrated have been barely understood, but a deeper knowledge of the underlying processes is important to our understanding of how such plastic changes develop and evolve. Here we studied the color change of the Malawi golden cichlid (Melanchromis auratus). Females and subordinate males of this species are yellow and white with two prominent black stripes (yellow morph; female and non-breeding male coloration), while dominant males change their color and completely invert this pattern with the yellow and white regions becoming black, and the black stripes becoming white to iridescent blue (dark morph; male breeding coloration). A comparison of the two morphs reveals that substantial changes across multiple levels of biological organization underlie this polyphenism. These include changes in pigment cell (chromatophore) number, intracellular dispersal of pigments, and tilting of reflective platelets (iridosomes) within iridophores. At the transcriptional level, we find differences in pigmentation gene expression between these two color morphs but, surprisingly, 80% of the genes overexpressed in the dark morph relate to neuronal processes including synapse formation. Nerve fiber staining confirms that scales of the dark morph are indeed innervated by 1.3 to 2 times more axonal fibers. Our results might suggest an instructive role of nervous innervation orchestrating the complex cellular and ultrastructural changes that drive the morphological color change of this cichlid species.

Characterization and Biosynthesis of Lipids in Paulinella micropora MYN1: Evidence for Efficient Integration of Chromatophores into Cellular Lipid Metabolism

The chromatophores found in the cells of photosynthetic Paulinella species, once believed to be endosymbiotic cyanobacteria, are photosynthetic organelles that are distinct from chloroplasts. The chromatophore genome is similar to the genomes of α-cyanobacteria and encodes about 1,000 genes. Therefore, the chromatophore is an intriguing model of organelle formation. In this study, we analyzed the lipids of Paulinella micropora MYN1 to verify that this organism is a composite of cyanobacterial descendants and a heterotrophic protist. We detected glycolipids and phospholipids, as well as a betaine lipid diacylglyceryl-3-O-carboxyhydroxymethylcholine, previously detected in many marine algae. Cholesterol was the only sterol component detected, suggesting that the host cell is similar to animal cells. The glycolipids, presumably present in the chromatophores, contained mainly C16 fatty acids, whereas other classes of lipids, presumably present in the other compartments, were abundant in C20 and C22 polyunsaturated fatty acids. This suggests that chromatophores are metabolically distinct from the rest of the cell. Metabolic studies using isotopically labeled substrates showed that different fatty acids are synthesized in the chromatophore and the cytosol, which is consistent with the presence of both type I and type II fatty acid synthases, supposedly present in the cytosol and the chromatophore, respectively. Nevertheless, rapid labeling of the fatty acids in triacylglycerol and phosphatidylcholine by photosynthetically fixed carbon suggested that the chromatophores efficiently provide metabolites to the host. The metabolic and ultrastructural evidence suggests that chromatophores are tightly integrated into the whole cellular metabolism.

Contributions of Phenoxazone-Based Pigments to the Structure and Function of Nanostructured Granules in Squid Chromatophores

Understanding the structure-function relationships of pigment-based nanostructures can provide insight into the molecular mechanisms behind biological signaling, camouflage, or communication experienced in many species. In squid Doryteuthis pealeii, combinations of phenoxazone-based pigments are identified as the source of visible color within the nanostructured granules that populate dermal chromatophore organs. In the absence of the pigments, granules experience a reduction in diameter with the loss of visible color, suggesting important structural and functional features. Energy gaps are estimated from electronic absorption spectra, revealing highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) energies that are dependent upon the varying carboxylated states of the pigment. These results implicate a hierarchical mechanism for the bulk coloration in cephalopods originating from the molecular components confined within in the nanostructured granules of chromatophore organs.

Multiple pigment cell types contribute to the black, blue, and orange ornaments of male guppies (Poecilia reticulata)

The fitness of male guppies (Poecilia reticulata) highly depends on the size and number of their black, blue, and orange ornaments. Recently, progress has been made regarding the genetic mechanisms underlying male guppy pigment pattern formation, but we still know little about the pigment cell organization within these ornaments. Here, we investigate the pigment cell distribution within the black, blue, and orange trunk spots and selected fin color patterns of guppy males from three genetically divergent strains using transmission electron microscopy. We identified three types of pigment cells and found that at least two of these contribute to each color trait. Further, two pigment cell layers, one in the dermis and the other in the hypodermis, contribute to each trunk spot. The pigment cell organization within the black and orange trunk spots was similar between strains. The presence of iridophores in each of the investigated color traits is consistent with a key role for this pigment cell type in guppy color pattern formation.

A spring-matrix model for pigment translocation in the red ovarian chromatophores of the freshwater shrimp Macrobrachium olfersi (Crustacea, Decapoda)

A model for intracellular transport of pigment granules in the red ovarian chromatophores of the freshwater shrimp Macrobrachium olfersi is proposed on the basis of shifts in the equilibrium of resting forces acting on an elastic pigment matrix. The model describes a pigment-transport mechanism in which mechanochemical protein motors like kinesin and myosin alternately stretch and compress a structurally unified, elastic pigment matrix. Quantifiable properties of the spring-matrix obey Hooke's Law during the rapid phases of pigment aggregation and dispersion. The spring-like response of the pigment mass is estimated from previous kinetic experiments on pigment translocation induced by red pigment concentrating hormone, or by the calcium ionophore A23187. Both translocation effectors trigger an initial phase of rapid pigment aggregation, and their removal or washout after complete aggregation produces a phase of rapid pigment dispersion, followed by slow pigment translocation. The rapid-phase kinetics of pigment transport are in reasonable agreement with Hooke's Law, suggesting that such phases represent the release of kinetic energy, probably produced by the mechanochemical protein motors and stored in the form of matrix deformation during the slow phases of translocation. This semiquantitative model should aid in analyzing intracellular transport systems that incorporate an elastic component.

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.

Scanning Electrochemical Microscopy of the Photosynthetic Reaction Center of Rhodobacter sphaeroides in Different Environmental Systems

The present work uses a scanning electrochemical microscopy technique to study systems containing the membrane-bound reaction center protein (RC) from the purple photosynthetic bacteria Rhodobacter spheroides to chromatophores (spherical reorganization of cell membrane following its mechanical rupture) and liposomes (reconstituted membrane systems at lower degree of complexity). Scanning electrochemical microscopy is a useful tool to investigate redox processes involving a RC, because the effective heterogeneous rate constants for the redox reaction with different mediators can be measured. The technique is also able to provide information on the role of the outer cell membrane permeation on the kinetics of the electron-transfer processes and to obtain more insight into the nature of the species involved.

Ultrastructure of the skin melanophores and iridophores in paddlefish, Polyodon spathula

The ultrastructure of melanophores and iridophores of Polyodon spathula has been examined by transmission electron microscopy. In the skin, two types of chromatophores, melanophores and iridophores were founded. Melanophores were localized both in epidermis and dermis. Epidermal melanophores were present on the dorsal region of the trunk, sides, outer surface of the operculum and rostrum. Iridophores were founded in the dermis from ventral skin. The cytoplasm of iridophores is filled with reflecting platelets with variable orientation. The length of the long axis of the platelets varies from 1 to 2.10 microm.

The role of muscarinic receptors and intracellular Ca2+ in the spectral reflectivity changes of squid iridophores

In this paper we describe changes in spectral reflectivity of the light reflectors (iridophores) of the squid Alloteuthis subulata. The spectral changes that can be seen in living squid, can also be brought about by superfusing whole skin preparations with acetylcholine (ACh) (20 μmol l-1) and muscarine (30 μmol l-1) but not nicotine (up to 50 mmol l-1), suggesting that cholinergic muscarinic receptors are involved. Changing the osmolarity of the external solution had no effect on spectral reflectivity. To study the iridophores at the cellular level,iridophores were isolated enzymatically. Lucifer Yellow filled the iridophores uniformly, showing cellular individuality. Isolated iridophore cells were loaded with Fura-2 AM and cytoplasmic Ca2+ was recorded ratiometrically. Intracellular Ca2+ (resting concentration at 66.16 nmol l-1) increased transiently after addition of ACh (50 μmol l-1), muscarine (25 μmol l-1), but not nicotine (up to 5 mmol l-1). Ca2+ also increased when superfused with potassium chloride (10 mmol l-1) and caffeine (2.5 mmol l-1). Hypo- and hyperosmotic solutions had no effects on the cytoplasmic Ca2+. By presenting direct evidence that iridophores are polarised cellular structures containing Ca2+ stores and that they are activated via cholinergic muscarinic receptors, we demonstrate that Ca2+ is involved in the reflectivity changes of the iridophores of A. subulata. Specimens were prepared for transmission electron microscopy. It was found that the orientations of the plates with respect to the skin surface are in good agreement with the expected orientations based on the prediction that the iridophores act as multilayer reflectors.

Pigment cell organization in the hypodermis of zebrafish

Zebrafish have a characteristic horizontal-stripe pigment pattern made by a specific distribution of three types of pigment cells: melanophores, xanthophores, and iridophores. This pattern is a valuable model to investigate how the spatial patterns form during animal development. Although recent findings suggest that the interactions among the pigment cells play a key role, the particular details of these interactions have not yet been clarified. In this report, we performed transmission electron microscopic study to show the distribution, conformation, and how the cells contact with each other in the hypodermis. We found that the pigment cells form complex but ordered, layered structures in both stripe and interstripe regions. The order of the layered structures is kept strictly all through the hypodermal regions. Our study will provide basic information to investigate the mechanism of pigment pattern formation in zebrafish.

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.

Morphological color changes in fish: Regulation of pigment cell density and morphology

Pigment cells enable fish to change their coloration. It has been recognized that fish color changes can be divided into two categories; one is a physiological color change, which is attributed to rapid motile responses of chromatophores, and the other is a morphological color change, which results from changes in the morphology and density of chromatophores. Long-term adaptation of fish to a certain background can be a general cue to morphological color changes, and has been studied from the beginning of the 19th century. Although the motile mechanism and its control in fish chromatophores are now being elucidated, it is not yet clear how chromatophores change their density and what controls morphological color changes. In recent years, chromatophores, especially melanophores, have been shown to differentiate and to die by apoptosis under the influence of factors that regulate motile responses. Those factors are likely to utilize common intracellular signaling pathways used in part to regulate both types of color changes. In this article, after briefly reviewing the history of early studies, recent findings are discussed relevant to increases or decreases in chromatophores, and changes in their morphology. Finally, morphological color changes are discussed as physiological phenomena involved in the balance between differentiation and apoptosis of chromatophores.

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.

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.

The yellow mutation in the frog Rana rugosa: pigment organelle deformities in the three types of chromatophore

Crossing experiments revealed that a single recessive gene mutation (yellow) gives rise to the yellow phenotype of Rana rugosa in Japan. Ultrastructural observation of dermal chromatophores showed that the pigment organelles; melanosomes, pterinosomes, and reflecting platelets, all had structural deformities. This suggests that the yellow gene acts at the level of a primordial pigment organelle common to the three types of chromatophore.

Characterization of a novel filament system in goldfish xanthophores

We report the presence of a novel filament system in goldfish xanthophores using a monoclonal antibody (A2) made against 40-70 kD proteins derived from cytoskeletal preparations. On Western blots, this antibody recognized a 45 kD protein in xanthophore cell extracts. In cells with dispersed pigment, immunofluorescence staining of xanthophores revealed a uniform distribution of A2-reactive filaments. In cells with aggregated pigment, these filaments assumed a distinctively radial orientation, such that filaments emanated from the central pigment mass (CPM). At the electron microscopic level, immunogold labeling identified a filament system with a diameter of 7 nm. Overall, the cellular distribution of A2-reactive filaments was distinctly different from that of the other known components of the cytoskeleton, such as intermediate filaments, actin filaments, and microtubules. A2-reactive filaments also appeared resistant to agents known to perturb the cytoskeleton such as cytochalasin B, which depolymerized the actin filaments. When xanthophores were treated with vinblastine, shown to depolymerize microtubules and induce the collapse of intermediate filaments (vimentin and keratin) in other cell types, no effect on the A2 filament distribution was observed. On the other hand, treatment with calyculin A, a phosphatase inhibitor, converted A2 filaments into a wavy bundles, the effect of which was completely reversible by the removal of the drug from culture medium. These novel properties of A2 filaments, together with their reorganization in response to pigment translocation suggest that A2 filaments might play a yet unidentified role in intracellular organelle transport in these cells.

Ultrastructural and biochemical analysis of epidermal xanthophores and dermal chromatophores of the teleost Sparus aurata

We have studied the pigmentary system of the teleost Sparus aurata skin by electron microscopy and chromatographic analysis. Under electron microscopy, we found the dermis to contain the three major types of recognized chromatophores: melanophores, xanthophores and iridophores. Melanophores were more abundant in the dorsal region, whereas the iridophores were more abundant in the ventral region. The most important discovery was that of epidermal xanthophores. Epidermal xanthophores were the only chromatophores in the epidermis, something only found in S aurata and in a teleost species living in the Antartic sea. In contrast, the biochemical analysis did not establish any special characteristics: we found pteridine and flavin pigments located mostly in the pigmented dorsal region. Riboflavin and pterin were two of the most abundant coloured pigment types, but other colourless pigments such as xanthopterin and isoxanthopterin were also detected.

The erythrophore in the larval and adult dorsal skin of the brown frog, Rana ornativentris: its differentiation, migration, and pigmentary organelle formation

To determine whether or not the erythrophore originates from xanthophores in the dorsal skin of the brown frog, Rana ornativentris, we morphologically examined the differentiation and migration of the two chromatophore types and their pigmentary organelle formation. At an early tadpole stage, three kinds of chromatophores, xanthophores, iridophores, and melanophores, appeared in the subdermis, whereas the erythrophore did so just before the foreleg protrusion stage. By the middle of metamorphosis, most chromatophores other than erythrophores had migrated to the subepidermal space. Erythrophores, which appeared late in the subdermis, proliferated actively there during metamorphosis and finished moving into the subepidermal space by the completion of metamorphosis. Carotenoid vesicles and pterinosomes within the erythrophores and xanthophores showed several significant differences in structure. In xanthophores, carotenoid vesicles were abundant throughout life, whereas those in erythrophores decreased in number with the growth of the frogs. The fibrous materials contained in the pterinosomes were initially scattered but soon formed a concentric lamellar structure. In erythrophores, the lamellar structure began to form at the periphery of the organelles but at the center in xanthophores. In addition, the pterinosomes of erythrophores were uniform in size throughout development, while those of xanthophores showed a tendency to become smaller after metamorphosis. The pterinosomes of xanthophores were significantly larger than those of erythrophores. These findings suggest that an erythrophore is not a transformed xanthophore, although they resemble each other closely in many respects.

Malignant chromatophoroma in a canebrake rattlesnake (Crotalus horridus atricaudatus)

An adult female canebrake rattlesnake (Crotalus horridus atricaudatus) at Zoo Atlanta (Atlanta, Georgia, USA) had a subcutaneous mass on the left lateral abdomen. Microscopically, the tumor contained a pleomorphic population of cells with abundant intracytoplasmic brown to gold nonrefractile pigment (chromatophores), large stellate cells resembling neurons, and small stellate cells whose cytoplasmic processes formed a fibrillar matrix. The pigment stained black with the Fontana-Masson technique and was positive with the periodic acid-Schiff technique (prior to and after diastase treatment). Neuron-specific enolase was detected in the large stellate cells using an immunohistochemical staining technique. In addition, glial fibrillary acidic and S-100 proteins were detected in the chromatophores with immunohistochemical staining. The smaller stellate cells were strongly S-100 positive. Ultrastructurally, chromatophores contained intracytoplasmic structures composed of concentric lamellar membranes bordered by a triple-layer outer membrane. The morphology of these structures was compatible with pterinosomes. Three fluorescent pigments were isolated from the neoplasm by one-dimensional chromatography and characterized by spectrophotometry and spectrofluorometry.

The ultrastructure and innervation of muscles controlling chromatophore expansion in the squid, Loligo vulgaris

Squid chromatophores are organs of colour change, consisting of a pigment sac opened by contraction of 10-24 radial muscle fibres. The ultrastructure and innervation of these muscle fibres were examined by electron microscopy and diagramatic reconstructions made on the basis of serial ultra-thin sections. At the proximal end of the fibre, nearest the pigment sac a cortical myofilament zone surrounds 2 cores containing mitochrondria; further along the fibre these merge to form one central core. The myofilament zone forms a groove containing a nerve bundle consisting of 2 to 4 axons per muscle fibre. The axons are surrounded by glial cell processes, and either originate from a neighbouring fibre, or join the fibre at some point along its length. Axons twist around each other, forming a series of synapses with the muscle fibre. As many as 6-37 synapses exist along the length of each muscle fibre; the mean synapse interval is 9.05 microm, but the largest may be 123 microm. At the distal end of the muscles, the nerve is located towards the middle of the fibre, which it penetrates as the muscle splits up. Electron-lucent vesicles are present in all synaptic regions, but electron-dense vesicles are only found towards the distal end of the fibre. There is thus a possibility that more than one neurotransmitter is present in the nerves innervating chromatophores. Electron-lucent and dense-cored vesicles are not colocalised.

Ultrastructural immunogold localization of some organelle-transport relevant proteins in wholemounted permeabilized nonextracted goldfish xanthophores

By whole-cell transmission electron microscopy (WCTEM), we recently demonstrated that carotenoid droplets are transported by elongating or retracting endoplasmic reticular cisternae in goldfish xanthophores. Here we report that permeabilized xanthophores demonstrate immunogold reactivity against several proteins involved in organelle translocation. The gold labeling against beta-tubulin and the intermediate filament protein p45a were found on microtubules and intermediate filaments. Labeling with anti-actin was found on nonidentifiable structures, on vesicles of unknown origin, occasional labeling on carotenoid droplets, and on occasional microfilaments. Immunoreactivity was demonstrated with anti-p57 on the carotenoid droplet surface, confirming previous results (Lynch et al., 1986a,b). Labeling with anti-PCD6 subunit (of the inositol trisphosphate/ryanodine receptor) was demonstrated on carotenoid droplets suggesting they possess calcium channels. Anti-MAP 1C (dynein) immunolabeling was generally seen on club-shaped structures in the cytomatrix and on carotenoid droplets. Finally, immunogold labeling with anti-MAP 2a + 2b was seen on a meshwork of microfilaments and intermediate filaments. Finally, this is the first report of a WCTEM technique for permeabilized cells that reveals immunoreactive elements, organelles, and cytomatrix components without the additional requirements of extraction or fracturing.

A transmission electron microscopic (TEM) method for determining structural colors reflected by lizard iridophores

Iridescent tissue colors are thought to be produced by iridophores through the optical phenomenon of thin-layer interference. Land and others have shown that structural features, predominantly reflecting platelet width and the cytoplasmic spacing between layers of platelets, determine the wavelength of light maximally reflected by this mechanism in iridophores. Some researchers have used interference microscopy to estimate these structural parameters, but the most direct measurement technique should be transmission electron microscopy (TEM). Transmission electron microscopy (TEM) has associated processing artifacts (particularly cytoplasmic shrinkage) that preclude direct measurement of ultrastructure, but if a number of assumptions are made, reflected wavelengths can be predicted. A thin-layer interference model and its associated assumptions were tested using TEM measurements of iridophores from several brightly colored tissues of each of three lizards (Sceloporus jarrovi, S. undulatus erythrocheilus, and S. magister). In all the instances examined when the contribution of the pigments present were accounted for, tissue color corresponded with predicted iridophore reflectances from the model. Finally, if the model and its assumptions are assumed to be correct, the amount of iridophore cytoplasmic shrinkage as a result of TEM processing can be calculated.

Morphological characterization of three phenotypes of the isopod Armadillidium vulgare

The morphological characteristics and ommochrome quantity in the integument of red, white, and wild type (black-grey) Armadillidium vulgare were studied. The red phenotype was found to possess two kinds of immature ommochrome pigment granules within its pigment cells, in addition to mature pigment granules. The immature granules seemed to contain uniformly distributed fibrilles, or to have an electron-dense central region surrounded by an electron-lucent outer edge. Since these immature pigment granules were typically observed to be distributed along with the mature ones, and were also more easily extractable than the wild type's, it is hypothesized that ommochrome granule maturation in the red phenotype may occur slowly due to a defect in the pigment granule internal process which combines pigments with matrix proteins. Regarding the white phenotype, although its pigment cells were undeveloped, several large-sized vesicles containing a small amount of electron-dense material appeared in the pigment cell cytoplasm. The wild and red type males of A. vulgare were found to have an ommochrome content twice as large as that of the corresponding females, with no ommochrome pigment being detected in the white phenotype. The genetic relationship between the white and red phenotypes was discussed using as a basis the observed pigment granule structure.

The role of microtubules in pigment translocation in goldfish xanthophores

In xanthophores, microtubules were observed to radiate out from the microtubule organization center which was also the center of a central pigment mass. A similar pattern of microtubules was identified in both cells with dispersed or aggregated pigments. Brief vinblastine incubation, which depolymerized the microtubules of pigment-aggregated cells, failed to disrupt the central pigment mass. Subsequent removal of the vinblastine and the addition of ACTH dispersed pigment granules before the reassembly of microtubules. These results suggest that a radiating microtubular system is not essential to the maintenance or the dispersion of the aggregated pigment mass. Prolonged incubation with vinblastine eventually dispersed the aggregated pigment mass even in an ACTH-free medium, suggesting that certain components responsible for pigment association were finally destroyed by vinblastine. Moreover, these dispersed pigments could be induced to reaggregate into small clusters in the absence of microtubules, and finally into a large, tight aggregate when the microtubule system was fully reconstituted. We thus conclude that microtubules may serve to guide the centripedal movement of small pigment clusters toward the cell center, and they may not be essential to pigment dispersion and the maintenance of the central pigment mass.

Cytoskeletal architecture of dermal chromatophores of the freshwater teleost Oryzias latipes

Cytoskeletal construction of dermal chromatophores of Oryzias 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.

Pteridines in the yellow-colored chromatophores of the isopod, Armadillidium vulgare

Biochemical analyses of the dorsal integument of the isopod, Armadillidium vulgare, revealed that sepiapterin, biopterin, pterin, isoxanthopterin and uric acid accumulated in the yellow-colored chromatophores which are distinguishable from ommochrome chromatophores. The pattern of the yellow-colored chromatophores in the female is externally observable at the dorsal surface of the integument as yellow markings. In contrast, the yellow-colored chromatophores are not externally observable in the male, since they are covered by an ommochrome chromatophore layer. The content of both sepiapterin and biopterin in the male chromatophores was about two times greater than that in the female. The yellow-colored chromatophores were observable by light microscopy as pigmented granules. Electron microscopy showed that morphological properties of the granules were similar to those of pteridine granules which contain uric acid occurring in the silkworm integument. These facts indicate that both pteridines and uric acid in the integument of A. vulgare are localized in the pigmented granules of the yellow-colored chromatophores.

Does the introduction of a new player, the endoplasmic reticulum, create more or less confusion in understanding the mechanism(s) of pigmentary organelle translocations?

In 1925, Wilson listed, in his classic third edition of Cell in Development and Heredity, four theories for the morphological and physiological characteristics of cytoplasm; each theory provided some sort of explanation as to the mechanism(s) of organelle translocations. During the past twenty years, cell biologists have focused their attentions on the cell's cytoskeleton, microtrabecular lattice, and associated mechanochemical motors which drive organelles along cytoskeletal tracks. A number of cell types have been used to study organelle translocations, but chromatophores, pigment cells, from cold-blooded vertebrates have been one of the more popular models. This article reviews some of the research findings during the past twenty years, particularly those involving cytoplasmic elements: i.e, microfilaments, intermediate filaments, microtubules, and mechanochemical motors. In addition, it contrasts the proposed involvement of these elements in organelle translocations with the endoplasmic reticulum, a tubulovesicular organelle, which we recently demonstrated is responsible, through its elongation or retraction, for the translocations of carotenoid droplets in goldfish xanthophores and swordtail fish erythrophores. Here, the carotenoid droplets are not free in the cytoplasm and do not translocate via cytoskeletal tracks, but instead are attached to or are a part of the endoplasmic reticulum. On the other hand, carotenoid droplets of squirrel fish erythrophores are free in the cytoplasm and appear to translocate via microtubules. Finally, the rates of pigmentary organelle translocations are reviewed in light of the participation of the cytoskeletal elements with the endoplasmic reticulum.

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.

Ultrastructural analysis of iridophore organellogenesis in a lizard, Sceloporus graciosus (Reptilia: Phrynosomatidae)

Transmission electron microscopy (TEM) data from the ultrastructure of lizard skin iridophores (reflective dermal chromatophores) are used to illustrate the organellogenesis of small rectangular reflecting platelets, which are the color-generating components of these cells. During the development of reflecting platelets, crystals are deposited within double-membraned vesicles from electron-dense material located within the vesicles. The crystals are initially small but expanded lengthwise eventually to fill the vesicle that contains them. The inner membrane then tightly surrounds the crystal whereas the outer membrane is much more loosely associated with the inner-membrane-bound crystal. These observations allow discussion of the possible origin of the precursor double-membraned vesicles from endoplasmic reticulum (ER) and Golgi-derived vesicles. A model is proposed that incorporates our findings and other published reports to explain the origin of the precursor double-membraned vesicles via three alternative pathways.

Further evidence for synthesis of screening pigment granules involved in the photosensory membrane turnover of the crayfish photoreceptor

Photosensory membrane degradation in crayfish occurs at first in multi-vesicular bodies (MVBs) and then, with the aid of lysosomal enzymes, in lysosome related lamellar bodies. In organ culture experiments with the isolated crayfish retina (Orconectes limosus) small screening pigment-like granules became visible under the electron microscope in such lamellar bodies and suggested a possible relation of photosensory membrane degradation and screening pigment granule synthesis. Chloroquine, an inhibitor of lysosomal activity, when added to the culture medium reduced the appearance of screening pigment-like granules in lamellar bodies, but led to the appearance of these granules in mature MVB's, indicating the involvement of lysosomal enzymes in the formation of pigmented lamellar bodies. In a second set of experiments the effect of bright light on the screening pigment granule ultrastructure of crayfish phoreceptors was investigated. It was found that after bright light exposure large numbers of little screening pigment granules (0.15-0.3 microns) were located between or close to rhabdomeral microvilli that were not at these sites in crayfish kept under natural light. MVB's were also reduced in size, and among the little screening pigmentary organelles granules of different electron density and morphology appeared. Additionally, vesicle flux to little screening pigment granules was detected. The screening pigment granules of the little type did not seem to be transported close to or between the microvilli, but appeared to be synthesized at these sites within little MVBs.

Stimulation of cultured iridophores by amphibian ventral conditioned medium

That the ventral integument of adult frogs (Rana pipiens) contains factor(s) that stimulate iridophore expression (adhesion, morphologic appearance, proliferation) was demonstrated on iridophores derived from tadpoles of R. pipiens and Pachymedusa dacnicolor, and maintained in primary culture in a growth medium based upon Leibovitz's L-15. Experimental growth medium (VCM) conditioned by a one-hour exposure to pieces of ventral skin of adult R. pipiens induced iridophores to assume a broad and stellate appearance, to form confluent sheets, and to proliferate over a nine-day period. Iridophores in control medium assumed long thin profiles, detached easily, and exhibited no signs of proliferation. Unknown cells containing reflecting platelets and unusual other organelles appeared uniquely in chromatophore cultures of P. dacnicolor in VCM. The intense stimulation of iridophore expression in VCM is consistent with the known inhibitory effect of this medium on melanization and with its purported role in the determination of dorsal/ventral pigment patterns of amphibians. The results are discussed in terms of a prevailing theory about pigment cell origins and development.

Localization of pigment cells in cultured frog skin

The pigmentation pattern of ventral skin of the frog Rana esculenta consists mainly of melanophores and iridophores, rather than the three pigment cells (xanthophores, iridophores, and melanophores) which form typical dermal chromatophore units in dorsal skin. The present study deals with the precise localization and identification of the types of pigment cells in relation to their position in the dermal tracts of uncultured or cultured frog skins. Iridophores were observed by dark-field microscopy; both melanophores and iridophores were observed by transmission electron microscopy. In uncultured skins, three levels were distinguished in the dermal tracts connecting the subcutaneous tissue to the upper dermis. Melanophores and iridophores were localized in the upper openings of the tracts directed towards the superficial dermis (level 1). The tracts themselves formed level 2 and contained melanophores and a few iridophores. The inner openings of the tracts made up level 3 in which mainly iridophores were present. These latter openings faced the subcutaneous tissue In cultured skins, such pigment-cell distribution remained unchanged, except at level 2 of the tracts, where pigment cells were statistically more numerous; among these, mosaic pigment cells were sometimes observed.

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.

Ultrastructural observations of motile iridophores from the freshwater goby, Odontobutis obscura

The ultrastructure of "motile" iridophores of Odontobutis obscura and the changes in cell shape related to the motility were studied with electron microscopy. Various structural details were revealed by this method, and their importance is discussed. Of particular interest were the abundant microfilaments observed in the cortical cytoplasm. Cross-sectional profiles of iridophores showed that, in an iridophore in the dendritic state, the platelets were scattered randomly throughout the centrosphere and its processes, so that the centrosphere appeared to be rather flat. In the punctate state, the platelets were gathered, in groups or in stacks with regular arrangements, in the centrosphere, which appeared to be ovoid in shape. The most notable finding was that, at this time, the processes from which the platelets were lost remained there without retracting. The results indicates clearly that the motility of the goby iridophores involves the migration of platelets within the fixed contour of each cell and that no amoeboidal changes in the shapes of the cells occur.

[Histologic study of the lumbar glands of Pleurodema thaul (Amphibia, Anura, Leptodactylidae)]

Frogs of the Pleurodema thaul species have a pair of prominent elevated cutaneous glands dorsolaterally, just posterior to the sacrum, which are named lumbar glands. We have studied histologically these glands and found that their chromatophores are disposed mainly immediately under the epidermis structuring a dermal chromatophore unit. Similar to the other anuran macroglands, the lumbar glands are constituted basically by granular alveoli filled with secretion. The presence of these granular alveoli and the typical distribution of the dermal chromatophores to suggest a defensive role for the lumbar glands. In most of the amphibians granular alveoli contain secretions with toxicity for several vertebrates. On the other hand, chromatophores in this frog species, probably play an aposematic function, since their disposition on the skin permits that the lumbar glands might be taken for eyes, probably giving to an eventual predator the impression that it may be an animal of higher dimensions.

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.

Drug-induced and genetic hypermelanism: effects on pigment cell differentiation

Allopurinol, a drug that inhibits the enzyme xanthine dehydrogenase (XDH), is known to cause hypermelanism in the axolotl. The hypermelanistic condition that results from allopurinol treatment is similar in most respects to the phenotype that results from the action of the melanoid (m) gene in axolotls. On the basis of structural and biochemical studies, it now seems clear that genetic and drug-induced hypermelanism are the same in the following ways. 1) Both types of melanism result in the production of more than normal amounts of melanin and more melanin-containing cells (melanophores). 2) In both cases the amount of pteridine-associated yellow pigment declines during development, and this is associated directly with fine structural changes that occur within the pigment organelles (pterinosomes) of yellow pigment cells (xanthophores). 3) In both cases the hypermelanistic condition results in the suppression of reflecting pigment cell (iridophore) differentiation. 4) Both conditions have now been linked directly to depressed levels of XDH activity. Thus both genetic and drug-induced hypermelanism result in alterations in the normal differentiation of all three pigment cell types and the subsequent disruption of normal pigment pattern formation. The possible significance of these findings with regard to factors known or suspected to direct the migration and/or differentiation of neural crest-derived pigment cells is discussed.

Chromatophoromas in a pine snake

Iridophoroma and melanophoroma were diagnosed in an adult male pine snake. Light microscopic examination of irregularly thickened white and black portions of abnormal scales demonstrated two distinctive populations of pigment-containing cells. Pigment cells within abnormal-appearing white scales had needle-shaped granules that were dark amber in color while black portions were composed of pigment cells typical of melanophores, with dark black, round granules. Both populations of cells showed junctional activity, and clusters of both neoplastic pigment cell types were found in adjoining areas of the epidermis. By electron microscopy, the pigment cell with amber-colored granules contained reflecting platelet profiles typical of iridophores while pigment cells with dark round granules contained melanosomes. At a junctional area between abnormal white and black scales, mosaic chromatophores containing reflecting platelet profiles and melanosomes were observed. At 1 1/2 years following initial diagnosis, the snake died and neoplastic iridophores were found at multiple visceral sites; there was no evidence of metastases of melanophores to any organ. The two pigment cell tumors are believed to have developed from either stem cells destined to become iridophores and melanophores or from prexisting iridophores and melanophores in the dermis.

Lysed chromatophores: a model system for the study of bidirectional organelle transport

The development of procedures to lyse and reactivate pigment granule movements in chromatophores has provided the only information to date concerning the mechanisms by which cells regulate the direction of organelle transport. Continued analysis of motility in these models as well as in a reconstituted system containing only the pigment granules, the appropriate cytoskeletal structures, and defined soluble cell components should contribute to our understanding of the mechanisms by which protein phosphorylation and dephosphorylation or Ca2+ regulate direction of transport and to the identification and characterization of the force-generating proteins responsible for producing bidirectional organelle movements.

Immunofluorescence evidence for cytoskeletal rearrangement accompanying pigment redistribution in goldfish xanthophores

Immunofluorescence and phase-contrast microscopic studies of goldfish xanthophores with aggregated or dispersed pigment show two unusual features. First, immunofluorescence studies with anti-actin show punctate structures instead of filaments. These punctate structures are unique for the xanthophores and are absent from both goldfish dermal non-pigment cells and a dedifferentiated cell line (GEM-81) derived from a goldfish xanthophore tumor. Comparison of immunofluorescence and phase-contrast microscopic images with electron microscopic images of thin sections and of Triton-insoluble cytoskeletons show that these punctate structures represent pterinosomes with radiating F-actin. The high local concentration of actin around the pterinosomes results in strong localized fluorescence such that, when the images have proper brightness for these structures, individual actin filaments elsewhere in the cell are too weak in their fluorescence to be visible in the micrographs. Second, whereas immunofluorescence images with anti-tubulin show typical patterns in xanthophores with either aggregated or dispersed pigment, namely, filaments radiating out from the microtubule organizing center, immunofluorescence images with anti-actin or with anti-intermediate filament proteins show different patterns in xanthophores with aggregated versus dispersed pigment. In cells with dispersed pigment, the punctate structures seen with anti-actin are relatively evenly distributed in the cytoplasm, and intermediate filaments appear usually as a dense perinuclear band and long filaments elsewhere in the cytoplasm. In cells with aggregated pigment, both intermediate filaments and pterinosomes with associated actin are largely excluded from the space occupied by the pigment aggregate, and the band of intermediate filaments surrounds not only the nucleus but also the pigment aggregate. The patterns of distribution of the different cytoskeleton components, together with previous results from this laboratory, indicate that formation of the pigment aggregate depends at least in part on the interaction between pigment organelles and microtubules. The possibility that intermediate filaments may play a role in the formation/stabilization of the pigment aggregate is discussed.

Identification of pigment cells during early amphibian development (Triturus alpestris, Ambystoma mexicanum)

The purpose of the present investigation was to provide and apply a methodological manual with which the distribution, patterning and relationship of melanophores and xanthophores can be analyzed during early amphibian development. For demonstration of the methods, which include ultrastructural, histochemical and biochemical approaches, Triturus alpestris and Ambystoma mexicanum (axolotl) embryos are used. These two species differ conspicuously in their larval pigment patterns, showing alternating melanophore bands in horizontal (T. alpestris) and vertical (axolotl) arrangements. With transmission- and scanning electron microscopy melanophores and xanthophores were distinguished by their different pigment organelles and surface structures. The presence of phenol oxidase (tyrosinase) was used to reveal externally invisible or faintly visible melanophores by applying an excess of 3,4 dihydroxy-phenylalanine (dopa). Xanthophores were made visible in fixed and living embryos by demonstrating their pterin fluorescence. In addition, pterins were analyzed by HPLC in embryos before and after pigmentation was visible.

Effects of exogenous guanosine on chromatophore differentiation in the axolotl

Guanosine is shown to dramatically alter the pigment phenotype of axolotls by suppressing melanization and enhancing the biosynthesis and deposition of purine-derived pigments. Phenotypic changes caused by guanosine are manifested by altered chromatophore differentiation patterns such that few black pigment cells (melanophores) differentiate (and those that do are punctate and necrotic in appearance), whereas the development of yellow (xanthophore) and reflecting (iridophore) pigment cells is enhanced. Mechanisms for changes in chromatophore differentiation, and thus pattern formation, are discussed, including the possibility that pigment cells may undergo transdifferentiation in vivo.

Differentiation of neural crest cells of Xenopus laevis in clonal culture

Clonal cultures were performed with the use of neural crest cells and their derivatives, chromatophores, from Xenopus laevis in order to elucidate the state of commitment in early embryogenesis. Neural crest cells that outgrew from neural tube explants were isolated and plated at clonal density. Cloned neural crest cells differentiated and gave rise to colonies that consisted of 1) only melanophores, 2) only xanthophores, or 3) melanophores and xanthophores. Xanthophores and iridophores, which differentiated in vitro, were also isolated and cloned. Cloned xanthophores proliferated in a stable fashion and did not lose their properties. On the other hand, cloned iridophores converted into melanophores as they proliferated. These results suggest that there is heterogeneity in the state of commitment of neural crest cells immediately after migration with regard to chromatophore differentiation and that iridophore determination is relatively labile (at least in vitro), whereas melanophore and xanthophore phenotypes are stable.

Polarized pigment granule transport occurs in the absence of microtubules in squirrelfish erythrophores: studies of the effects of estramustine

We have re-examined the involvement of microtubules in the process of pigment granule transport in squirrelfish erythrophores in situ (i.e. on scales). Light-microscopic studies revealed that following exposure to 5 microM-nocodazole for 1 h at 4 degrees C erythrophores retained an ability to aggregate and disperse their pigment uniformly, though at reduced rates. Serial thick-section stereo high-voltage electron-microscopic studies showed that the entire microtubule population was removed by drug treatment and that the microtubules were not reassembled as a result of pigment translocation processes in the presence of reduced levels of nocodazole (0.4 microM). Immunofluorescence microscopic studies confirmed that nocodazole (0.5-1 microM) produced rapid disassembly of the microtubules. Whole-mount electron-microscopic studies showed that the pigment granules were suspended in a cross-linking network of 3–10 nm filaments, which appeared to support ordered pigment transport in situ in the absence of microtubules. Drug inhibition studies showed that micromolar levels of estramustine, a novel anti-MAPs (microtubule-associated proteins) drug, reversibly inhibited pigment transport. The results suggest that an estramustine-sensitive cytomatrix component might produce polarized pigment transport in intact erythrophores.

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.

Evidence that MAP-2 may be involved in pigment granule transport in squirrel fish erythrophores

We have demonstrated the presence of MAP-2 in squirrel fish erythrophores using SDS-PAGE, immunoblot, and immunoprecipitation techniques. The monoclonal antibodies used (AP-9, -13, -14) were raised against distinct antigenic sites on Chinese hamster brain MAP-2. Immunoprecipitation studies demonstrated that all three antibodies bind a 300 K protein found in crude cell extracts and in partially purified MAP fractions isolated from erythrophores of the squirrel fish Holocentrus rufus. Immunofluorescent studies confirmed that the 300 K protein was present in cultured erythrophores. Studies of cells induced to aggregate and disperse their pigment granules revealed that the 300 K protein comigrated with the pigment, suggesting that the 300 K protein may constitute part of the "alpha-cytomatrix" involved in pigment translocations.

Production of crystallins and lens-like structures in differentiation-induced neoplastic pigment cells (goldfish erythrophoroma cells) in vitro

We examined the crystallins present in lens-like cell aggregates produced by goldfish erythrophoroma (tumors of integumental erythrophores) cells in vitro using a combination of Sephadex-G-200 gel filtration, one- and two-dimensional sodium-dodecyl-sulfate/polyacryl-amide gel electrophoresis, immunoblotting, and indirect immunofluorescence assays. The two studied neoplastic pigment cell lines, GEM 81 and GEM 218, formed small, spherical, transparent cell aggregates, resembling lentoid bodies, within the cell mounds of monolayer cultures after treatment with dimethylsulfoxide (DMSO) and autologous serum. Partial purification of a water-soluble extract of such lens-like cell aggregates and subsequent immunoblotting using antibodies (polyclonal) against newt whole lens proteins revealed the presence of about 20 unequivocally conjugated peptides with molecular masses of 19-27 kilodaltons. From their antigenicity and their behavior during gel filtration and electrophoresis, most of these peptides were identified as either alpha- or beta-form crystallins. Immunofluorescence microscopy using antibodies to newt whole lens proteins revealed intense fluorescence in the lens-like cell aggregates formed by these erythrophoroma cells, whereas the cell mounds in cultures of the same cell lines that had not been subjected to differentiation induction were almost unlabeled. Thus, goldfish erythrophoroma cells appear to be capable of crystallin production as well as the formation of lens-like cell aggregates upon the induction of differentiation. There is little available information indicating that normal pigment cells are capable of lens formation and crystallin synthesis during vertebrate ontogeny, and thus it is possible that neoplastic transformation of pigment cells is associated with the acquisition of the ability to produce crystallins.

The structure of the pigment cells in the turtle Trionyx sinensis

A light and transmission electron microscopic study of the pigment cells (chromatophores) revealed the presence of three types of cells, namely: melanophores, xanthophores or erythrophores, and iridophores. The melanophores contained eumelanin containing organelles, the melanosomes and iridophores showed reflecting platelets, whereas, the xanthophores contained pterinosomes. Quantitatively melanophores appeared in large numbers and were widely distributed, ranging from the skin to many internal viscera, whereas iridophores were few and xanthophores very rare.