Ultrastructure of the chromatophores of Palaemon affinis Heilprin (crustacea: decapoda). The structural basis of pigment migration

The relationships between pigment granules and the prominent smooth endoplasmic reticulum in the chromatophores of the shrimp, Palaemon affinis Heilprin, were investigated by transmission electron microscopy. Different types of pigment granules within the chromatophores were found to exhibit a close structural continuity with the cisternal membranes. The membranes of membrane-bound pigment granules were seen to be continuous with those of the ER cisternae, while pigment granules lacking membranes appear to adhere to the external cisternal surfaces. The reticulum, which seems to form a network enmeshing the pigment granules, is proposed to be part of a continuum linking these granules with their translocating force.     

The fine structure of odonata chromatophores

The appearance, fine structure and pigment composition of the epidermal chromatophores of mature Austrolestes annulosus (Lestidae) are described and compared with the developing chromatophores of teneral Austrolestes and the mature chromatophores of Diphlebia lestoides (Amphipterygidae) and Ischnura heterosticta (Caenagrionidae). Mature chromatophores contain masses of near spherical light-scattering bodies and larger irregularly shaped pigment vesicles. These effect colour change by migrating in opposite directions, through a system of interconnecting granular endoplasmic reticulum tubules. The pigment, a mixture of xanthommatin and dihydroxanthommatin, has a liquid or gelatinous consistency. Developing chromatophores of teneral insects lack light-scattering bodies and well-defined migratory pigment vesicles, but contain irregular masses of pigment of similar chemical composition.     

Association of kinesin and myosin with pigment granules in crustacean chromatophores

Chromatic adaptation in crustaceans results from the differential distribution of colored pigment granules within their chromatophores consequent to cell signaling by neurosecretory peptides. However, the force transducing, mechanochemical protein motors responsible for granule translocation, and their molecular mechanisms of action, are not well understood. The present study uses immunocytochemical techniques and a motility assay in vitro to demonstrate that protein motors from the kinesin and myosin superfamilies are stably associated with membrane-bounded pigment granules in the red, ovarian chromatophores of the freshwater, palaemonid shrimp, Macrobrachium olfersii. Monoclonal antibodies against conventional kinesin heavy chain, and an anti-myosin whole serum, labeled pigment-containing fragments prepared from homogenates of chromatophores with fully dispersed or aggregated pigments: this finding infers a permanent association between the protein motors and the pigment granules, and suggests that such motors may be regulated while bound to their cargos. The pigment aggregator appears to be a myosin since the anti-myosin whole serum attenuated hormonally triggered pigment aggregation in the motility assay in vitro, and induced pigment hyper-dispersion in some chromatophores. Western blots of the chromatophore-containing, ovarian tissue homogenate demonstrated protein bands consistent with myosin II and myosin XII, either of which may be the pigment aggregator. This study provides the first direct evidence for myosin and kinesin protein motors directly and stably associated with pigment granules in crustacean chromatophores, and may represent the first successful isolation of myosin class XII.     

The morphology of dermal chromatophores in the infrared-reflecting glass-frog Centrolenella fleischmanni

The morphology and organization of chromatophores in the neotropical glass-frog, Centrolenella fleischmanni (family Centrolenidae), were studied with both light and electron microscopes. Four types of pigment cells are described in the dorsal skin. The fine structure of two chromatophores corresponds to the typical amphibian xanthophore and iridophore; one is similar to the unusual melanophore found in phyllomedusine hylids; the fourth cell type is unlike any chromatophore previously described. Pigment granules in the unusual chromatophore are moderately electron-dense and have an irregular shape, suggesting a fluid composition. This pigment appears to be laid down in organelles similar in appearance to pterinosomes. The organization of pigment cells in this species differs from that of other green, leaf-sitting frogs in that there are few discrete groups resembling “dermal chromatophore units.” It is suggested that the unusual new pigment cell contributes significantly to the overall green color of C. fleischmanni.     

The effect of temperature on the light-induced pigment movement in fish corneal chromatophores.

Corneal chromatophores of unusual morphology were used for studies on the influence of temperature on the intracellular pigment movement in two species of marine fish from different temperature zones: the tropical puffer, Canthigaster cinctus, and boreal whitespotted greenling, Hexagrammos stelleri. It was shown that both dispersion under bright illumination and aggregation at darkening are slower or decrease at lower temperatures when examined in the range of 12-27 degrees C. The mean speed of the pigment translocations in the individual cell process was 0.38 micron/s at the highest temperature examined, with a range of 0.17-1.0 micron/s. Near the middle of the temperature range, the dynamic characteristics of cell pigment movement in tropical and boreal species were rather close, suggesting that there would be little divergent adaptations with respect to the mechanisms of the pigment transport. Corneal chromatophores are considered as a new promising model for cell motility studies.     

Light-induced alterations in cell shape and pigment displacement in chromatophores of the sea urchin Centrostephanus longispinus

Summary Alterations in cell shape of the light-sensitive chromatophores of Centrostephanus longispinus are described. Upon illumination a centrifugal pigment movement starts within extremely thin filopodia which radiate from the cell body. With continued pigment migration the cellular processes increase in length and diameter and give the cell an irregular stellate appearance. Pigment movement within the cellular processes is discontinuous in space and time and may occur independently in single filopodia. The motion of single granules shows characteristic features of a saltatory movement.     

Direct reception of light by chromatophores of lower vertebrates

Rapid color changes of lower vertebrates are caused by the motile activities of pigment cells (chromatophores) present in the skin tissue. Chromatophore motility is generally regulated by neural and/or by endocrine systems. However, in some cases, light also induces pigment aggregation or dispersion directly, which suggests the existence of visual pigments in chromatophores. In fact, some opsins, including melanopsin, have been identified. This article reviews light-sensitive chromatophores of lower vertebrates. Photoreceptive molecules (visual pigments) and signal transduction of light via a GTP-binding protein (G protein) are also discussed.     

The involvement of calmodulin in motile activities of fish chromatophores

1. Effects of W-7 and W-5, calmodulin antagonists, on the pigment aggregation within melanophores and coloring response of iridophores were examined in the blue damselfish, Chrysiptera cyanea.2. W-7 was found to antagonize norepinephrine-induced responses of the chromatophores, whereas W-5 had only a slight effect on inhibition of the responses.3. H-7, a specific antagonist of protein kinase C, did not arrest the responses of melanophores and iridophores at all.4. The chromatophores responded normally to norepinephrine in Ca²⁺, Mg²⁺-free saline solution.5. These results indicate that it is a Ca²⁺/calmodulin-regulated enzyme and not protein kinase C that is involved in motile activities of fish chromatophores. Ca²⁺ may be supplied from an intracellular store.     

A large photoreactive particle from Chromatium vinosum chromatophores

Large photoreactive particles from Chromatium vinosum are obtained pure and in high yield by using a mixture of detergents at high ionic strength to dissociate the chromatophore membrane. The particles contain all of the secondary electron acceptor of the chromatophores and about half of the cytochrome. Their content of ubiquinone is greatly enriched as compared with chromatophores. The individual particles have an estimated molecular weight of between 650 000 and 810 000.Gel electrophoresis of the preparation in sodium dodecylsulfate shows polypeptides with molecular weights of 50–45 000, 30 000, 27 000, 22 000 and 12 000. The 50–45 000 components are cytochromes. The 30 000, 27 000 and 22 000 components may be analogous to the triad of polypeptides present in Rhodopseudomonas spheroides reaction centers. The non-cytochrome components are partly soluble in chloroform/methanol.Aggregates of particles appear in these preparations. Electron microscopy of the aggregates demonstrates rectilinear lattices of isodiametric particles, 120 Å in diameter. These sheet-like structures are one unit thick and typically contain 9–16 members. They appear to arise by aggregation during isolation but are probably similar to native aggregates apparent within chromatophores after treatment with detergents at low salt concentration.     

The adaptive significance of chromatophores in the Arctic under-ice amphipod Apherusa glacialis

Solar radiation is a crucial factor governing biological processes in polar habitats. Containing harmful ultraviolet radiation (UVR), it can pose a threat for organisms inhabiting surface waters of polar oceans. The present study investigated the physiological color change in the obligate sympagic amphipod Apherusa glacialis mediated by red-brown chromatophores, which cover the body and internal organs of the species. Short-term experimental exposure to photosynthetic active radiation (PAR) led to pigment dispersal in the chromatophores, resulting in darkening of the animal. Irradiation in the PAR range (400–700 nm) was identified as the main trigger with high light intensities evoking marked responses within 15 min. After exposure to high PAR, darkness led to a slow aggregation of pigments in the cell center after 24 h. Experiments revealed no statistically significant change in coloration of the animal when exposed to different background colors nor UV radiation. Our results point to a dose- and time-dependent photoprotective role of chromatophores in the amphipod, presuming a shielding effect from harmful radiation in a dispersed state. The reversible nature of the physiological color change enables the species to adapt dynamically to prevailing light conditions and thereby minimize the cost of increased conspicuousness toward visually hunting predators.     

Mitotic and pigment-translocating activities of cultured chromatophores of the guppy, Lebistes reticulatus

Using Ham's F-12 medium, an in vitro culture system permitting cellular survival for over 6 months has been developed for the chromatophores of the guppy. In this culture system, the various types of chromatophores (melanophores, erythrophores and xanthophores) migrated out of the explanted tail fin tissue, retained their pigmentation, and displayed both mitotic and pigment-translocating activities. The mitotic activity was evident during the first 3 or 4 weeks in culture, whereas the pigment-translocating ability persisted for 16 weeks. The cultured chromatophores of male fish displayed pigment aggregation in response to adrenergic agents (epinephrine and norepinephrine) and pigment dispersion in response to alpha-melanocyte stimulating hormone (alpha-MSH), cyclic AMP and dibutyryl cyclic AMP. Cyclic GMP did not elicit pigment-translocating responses in any of the chromatophores.     

Calcium movements during pigment aggregation in freshwater shrimp chromatophores

Pigment granule migration within crustacean chromatophores provides an excellent model with which to investigate cytoplasmic movements, given the antagonistic, neurosecretory peptide regulation of granule translocation, and the absence of innervation in these large, brightly colored cells. Red pigment-concentrating hormone (RPCH) induces pigment aggregation in shrimp chromatophores via an increase in intracellular Ca2+; however, how this increase is brought about is not known. To examine the putative Ca2+ movements leading to pigment translocation in red, ovarian chromatophores of the freshwater shrimp, Macrobrachium olfersii, this study manipulates intra- and extracellular Ca2+ employing ER Ca2+-ATPase inhibitors, ryanodine-sensitive, ER Ca2+ channel blockers, and EDTA/EGTA-buffered A23187/Ca2+-containing salines. Our findings reveal that during pigment aggregation, cytosolic Ca2+ apparently increases from an intracellular source, the abundant SER, loaded by the SERCA and released through ryanodine-sensitive receptor/channels, triggered by capacitative calcium influx and/or calcium-induced calcium release mechanisms. Aggregation also depends on external calcium, which may modulate RPCH/receptor coupling. Such calcium-regulated pigment movements form the basis of a complex system of chromatic adaptation, which confers selective advantages like camouflage and protection against ultra-violet radiation to this palaemonid shrimp.     

Improvement of photosynthesis in zooxanthellate corals by autofluorescent chromatophores

Autofluorescent chromatophores were detected in 17 out of 71 zooxanthellate coral species studied. Chromatophores are localized either in the oral gastrodermic (endoderm) or oral epidermis (ectoderm). The pigment granules within the chromatophores (0.5–1.0 m in diameter) show a brilliant light-blue/turquoise autofluorescence (emission between 430 and 500 nm) after excitation with light of 365–410 nm. All species where the autofluorescent gastrodermal chromatophores form a compact layer, embedding the zooxanthellae, belong to the family Agariciidae. In contrast, some species of the Faviidae (2), Pectiniidae (1) and Mussidae (1) were found to have distinct, autofluorescent chromatophores in the oral epidermis. Autofluorescent pigments of the host may enhance photosynthesis of the symbionts as in Leptoseris fragilis. Short wavelength irradiance, less suitable for photosynthesis, is transformed by host pigments into longer wavelengths which are photosynthetically more effective. Thus, host species possessing autofluorescent chromatophores might have selective advantage over non-fluorescent species, and have the potential to survive in light-limited habitats. Furthermore, the daily period of photosynthesis is extended, thus increasing the energy supply and enhancing the deposition of skeletal carbonate. The absence or presence of chromatophores may have value in taxonomy and could putatively be of plalaeontological and palaeoecological interest.     

Intrinsic curvature properties of photosynthetic proteins in chromatophores

In purple bacteria, photosynthesis is carried out on large indentations of the bacterial plasma membrane termed chromatophores. Acting as primitive organelles, chromatophores are densely packed with the membrane proteins necessary for photosynthesis, including light harvesting complexes LH1 and LH2, reaction center (RC), and cytochrome bc₁. The shape of chromatophores is primarily dependent on species, and is typically spherical or flat. How these shapes arise from the protein-protein and protein-membrane interactions is still unknown. Now, using molecular dynamics simulations, we have observed the dynamic curvature of membranes caused by proteins in the chromatophore. A membrane-embedded array of LH2s was found to relax to a curved state, both for LH2 from Rps. acidophila and a homology-modeled LH2 from Rb. sphaeroides. A modeled LH1-RC-PufX dimer was found to develop a bend at the dimerizing interface resulting in a curved shape as well. In contrast, the bc₁ complex, which has not been imaged yet in native chromatophores, did not induce a preferred membrane curvature in simulation. Based on these results, a model for how the different photosynthetic proteins influence chromatophore shape is presented.     

Fish chromatophores as cytosensors in a microscale device: detection of environmental toxins and bacterial pathogens

Fish chromatophores from Betta splendens are used as the cytosensor element in the development of a portable microscale device capable of detecting certain environmental toxins and bacterial pathogens by monitoring changes in pigment granule distribution. The adaptation of chromatophores to a microscale environment has required the development of enabling technologies to produce miniaturized culture chambers, to integrate microfluidics for sample delivery, to miniaturize image capture, and to design new statistical methods for image analyses. Betta splendens chromatophores were selected as the cytosensor element because of their moderate size, their toleration of close contact, and most importantly, for their responses to a broad range of chemicals and pathogenic bacteria. A miniaturized culture chamber has been designed that supports chromatophore viability for as long as 3 months, and that can be easily transported without damage to the cells. New statistical methods for image analyses have been developed that increase sensitivity and also decrease the time required for detection of significant changes in pigment granule distribution. Betta chromatophores have been tested for their responses to selected pathogenic bacteria and chemical agents. We discuss in detail the aggregation of pigment granules seen when chromatophores are incubated with Bacillus cereus, a common cause of food poisoning. Also described are the more subtle responses of chromatophores to a class of environmental chemical toxins, polynuclear aromatic hydrocarbons. We show that the chromatophores are able to detect the presence of certain polynuclear aromatic hydrocarbons at concentrations lower than the Environment Protection Agency (EPA) 550.1 standards.     

Ultrastructural observations on changes in cell shape in chromatophores of the sea urchin Centrostephanus longispinus

Summary Alterations in cell shape of the light-sensitive chromatophores of the sea urchin Centrostephanus longispinus were studied by scanning- and transmission electron microscopy. Transition of the aggregated to the dispersed state is accompanied by incorporation of vesicles into the membrane of the pigment cell. During dispersion a system of microtubules originating from centriole-like structures is established throughout the stellate cell. Within restricted areas of the cell, cytoplasmic differentiation and condensation is found. The possible functional significance of the findings is briefly discussed.     

The effects of two physiological salines, Locke's and van Harreveld's, on the midgut red chromatophores of the freshwater shrimp, Caridina denticulata

It was reported previously that the red chromatophores on the midgut of a freshwater shrimp, Caridina denticulata, are affected by Locke's and van Harreveld's solutions differently, i.e., the pigment disperses in Locke's solution and concentrates with the addition of crude eyestalk extract, but in Harreveld's solution the chromatophores do not change in the saline alone nor do they respond to eyestalk extract. The differences were probably due to the osmotic pressure and Mg ion concentrations of the two solutions not being the same. Harreveld's solution is commonly used as a physiological saline for freshwater crustaceans such as crayfish. Consequently, this solution was employed at first in a previous study (Miyawaki and Tsuruda, 1985). But this solution completely inhibited pigment migration in the chromatophores. But when Locke's solution was subsequently tried, migration of the pigment in the midgut chromatophores occurred. It seemed worthwhile to examine further the effects of both solutions on these chromatophores. The results of this study are presented below.     

Observations on the ultrastructure and distribution of chromatophores in the skin of chelonians

Alibardi, L. 2011. Observations on the ultrastructure and distribution of chromatophores in the skin of chelonians. —Acta Zoologica (Stockholm) 00 :1–11. The cytology and distribution of chromatophores responsible for skin pigmentation in chelonians is analyzed. Epidermal melanocytes are involved in the formation of dark spots or stripes in growing shelled and non‐shelled skin. Melanocytes rest in the basal layer of the epidermis and transfer melanosomes into keratinocytes during epidermal growth. Dermal melanophores and other chromatophores instead remain in the dermis and form the gray background of the skin. When dermal melanophores condense, they give origin to the dense spots or stripes in areas where no epidermal melanocytes are present. In the latter case, the epidermis and the corneous layer are transparent and reveal the dermal distribution of melanophores and other chromatophores underneath. As a result of this basic process of distribution of pigment cells, the dark areas visible in scales can have a double origin (epidermal and dermal) or a single origin (epidermal or dermal). Xanthophores, lipophores, and a cell containing both pterinosomes and lipid droplets are sparse in the loose dermis while iridophores are rarely seen in the skin of chelonians analyzed in the present study. Xanthophores and lipophores contribute to form the pale, yellow or oranges hues present among the dark areas of the skin in turtles.     

Fusion of chromatophores derived from Rhodopseudomonas sphaeroides

Fusion of chromatophores, the photosynthetic membrane vesicles isolated from the intracytoplasmic membranes of Rhodopseudomonas sphaeroides, was achieved by the use of poly(ethylene glycol) 6000 as fusogen. Ultracentrifugation, electron microscopy, intrinsic density and isotope labeling were used to demonstrate chromatophore fusion. Although studies of the flash-induced shift in the carotenoid absorbance spectrum indicated that the membrane was rendered leaky to ions by either the fusion procedure or the increased size of the fused products, the orientation and integrity of fused chromatophores were otherwise demonstrated to be identical to control chromatophores by freeze-fracture electron microscopy, proteolytic enzyme digestion, enzymatic radioiodination, and transfer of chromatophore phospholipids mediated by phospholipid exchange protein extracted from Rps. sphaeroides.     

Action of chlorophyllase purified from rye seedlings on light-harvesting bacteriochlorophyll of chromatophores and spheroplasts from Rhodospirillum rubrum

1. The chlorophyllase [EC 3.1.1.14] purified from greened rye seedlings hydrolyzed the bacteriochlorophyll isolated from Rhodospirillum rubrum, but not the pigment bound to the membrane of chromatophores or spheroplasts from the bacterium. 2. Acetone, if added at such concentrations that the bound bacteriochlorophyll would not be solubilized, enabled the enzyme to hydrolyze the bound pigment. The acetone concentrations required for half the maximum hydrolysis rates were 16% with chromatophores and 7% with spheroplasts. 3. The enzymic hydrolysis of the bound bacteriochlorophyll in the presence of acetone removed bacteriochlorophyllide from the membrane, leaving its esterifying alcohol, possibly all-trans-geranylgeraniol, in situ. 4. Washing of chromatophores with 30% acetone removed about 10% of the bound bacteriochlorophyll. The bound pigment remaining after washing was not hydrolyzed by the enzyme unless acetone was added. 5. It seems possible that light-harvesting bacteriochlorophyll was mostly, if not all, bound to the inner surface of chromatophores (the outer surface of spheroplasts), having its esterifying alcohol residue buried in the membrane and its porphyrin residue emerging from the membrane into the inside solution; thus, chlorophyllase could not make contact with the ester linkage between the esterifying alcohol and porphyrin moieties of the pigment unless the esterifying alcohol residue was partly exposed.