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The skin discoloration of squid subjected to frozen storage negatively affects market price. In this study, various alkali treatments were investigated for effects on red granules and yellow pigments of squid skin and corresponding mechanisms were investigated at the tissue, cellular and molecular level. A significant colour improvement was observed when subjected to a pH 12 treatment, supported by decreased Δb* and increased Δa* values. Neither lower nor harsher alkali treatments than pH 12 can not obtain such results. HE staining and the UV-vis spectrum suggest that the improved red colour in skin was ascribed to the release of red pigment granules from damaged chromatophores by alkaline treatment and the release of red pigments in alkaline aqueous solutions from granules. However, based on TEM and particle size analysis, an excessive alkali treatment of pH 13 would degrade granules into smaller particles. The degradation of yellowness pigments indicated high sensitivity to alkali environments according to HPLC results. This study provides a valuable reference for improving the colour appearance of squid skin subjected to frozen storage., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Chromatophore organs in cephalopod skin are known to produce ultra-fast changes in appearance for camouflage and communication. Light-scattering pigment granules within chromatocytes have been presumed to be the sole source of coloration in these complex organs. We report the discovery of structural coloration emanating in precise register with expanded pigmented chromatocytes. Concurrently, using an annotated squid chromatophore proteome together with microscopy, we identify a likely biochemical component of this reflective coloration as reflectin proteins distributed in sheath cells that envelop each chromatocyte. Additionally, within the chromatocytes, where the pigment resides in nanostructured granules, we find the lens protein Ω- crystallin interfacing tightly with pigment molecules. These findings offer fresh perspectives on the intricate biophotonic interplay between pigmentary and structural coloration elements tightly co-located within the same dynamic flexible organ - a feature that may help inspire the development of new classes of engineered materials that change color and pattern.

Rapid, simple, and low-cost screening procedures are necessary for the detection of harmful compounds in the effluent that flows out of point sources such as industrial outfall. The present study investigated the effects on a novel sensor of harmful compounds such as KCN, phenol, and herbicides such as 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), 2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine (atrazine), and 2-N-tert-butyl-4-N-ethyl-6-methylsulfanyl-1,3,5-triazine-2,4-diamine (terbutryn). The sensor employed an electrode system that incorporated the photocurrent of intra-cytoplasmic membranes (so-called chromatophores) prepared from photosynthetic bacteria and linked using carbon paste electrodes. The amperometric curve (photocurrent-time curve) of photo-induced electron transfer from chromatophores of the purple photosynthetic bacterium Rhodobacter sphaeroides to the electrode via an exogenous electron acceptor was composed of two characteristic phases: an abrupt increase in current immediately after illumination (I₀), and constant current over time (Ic). Compared with other redox compounds, 2,5-dichloro-1,4-benzoquinone (DCBQ) was the most useful exogenous electron acceptor in this system. Photo-reduction of DCBQ exhibited Michaelis-Menten-like kinetics, and reduction rates were dependent on the amount of DCBQ and the photon flux intensity. The Ic decreased in the presence of KCN at concentrations over 0.05 μM (=μmol·dm(-3)). The I₀ decreased following the addition of phenol at concentrations over 20 μM. The Ic was affected by terbutryn at concentrations over 10 μM. In contrast, DCMU and atrazine had no effect on either I₀ or Ic. The utility of this electrode system for the detection of harmful compounds is discussed.

Chromatophores are pigment-bearing cells of lower vertebrates, including fish that cater for the ability of individual animals to shift body coloration and pattern. Color change provides dynamic camouflage and various kinds of communication. It is also a spectacular example of phenotypic plasticity, and of significant importance for adaptation and survival in novel environments. Through different cellular mechanisms, color change can occur within minutes or more slowly over weeks. Chromatophores have different pigment types and are located not only in the skin, but also in the eyes and internally. While morphological color change, including seasonal color change, has received a lot of interest from evolutionary biologists and behavioral ecologists, the more rapid physiological color change has been largely a research subject for cell physiologists. In this cross-disciplinary review, we have highlighted emerging trends in pigment cell research and identified unsolved problems for future research., (Copyright © 2016. Published by Elsevier Inc.)

Many chameleons, and panther chameleons in particular, have the remarkable ability to exhibit complex and rapid colour changes during social interactions such as male contests or courtship. It is generally interpreted that these changes are due to dispersion/aggregation of pigment-containing organelles within dermal chromatophores. Here, combining microscopy, photometric videography and photonic band-gap modelling, we show that chameleons shift colour through active tuning of a lattice of guanine nanocrystals within a superficial thick layer of dermal iridophores. In addition, we show that a deeper population of iridophores with larger crystals reflects a substantial proportion of sunlight especially in the near-infrared range. The organization of iridophores into two superposed layers constitutes an evolutionary novelty for chameleons, which allows some species to combine efficient camouflage with spectacular display, while potentially providing passive thermal protection.

The chromatophores of Rhodobacter (Rb.) sphaeroides represent a minimal bio-energetic system, which efficiently converts light energy into usable chemical energy. Despite extensive studies, several issues pertaining to the morphology and molecular architecture of this elemental energy conversion system remain controversial or unknown. To tackle these issues, we combined electron microscope tomography, immuno-electron microscopy and atomic force microscopy. We found that the intracellular Rb. sphaeroides chromatophores form a continuous reticulum rather than existing as discrete vesicles. We also found that the cytochrome bc1 complex localizes to fragile chromatophore regions, which most likely constitute the tubular structures that interconnect the vesicles in the reticulum. In contrast, the peripheral light-harvesting complex 2 (LH2) is preferentially hexagonally packed within the convex vesicular regions of the membrane network. Based on these observations, we propose that the bc1 complexes are in the inter-vesicular regions and surrounded by reaction center (RC) core complexes, which in turn are bounded by arrays of peripheral antenna complexes. This arrangement affords rapid cycling of electrons between the core and bc1 complexes while maintaining efficient excitation energy transfer from LH2 domains to the RCs., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Chromatophores are the pigment-containing cells in the skins of animals such as fish and cephalopods which have chromomorphic (colour-changing) and controllable goniochromic (iridescent-changing) properties. These animals control the optical properties of their skins for camouflage and, it is speculated, for communication. The ability to replicate these properties in soft artificial skin structures opens up new possibilities for active camouflage, thermal regulation and active photovoltaics. This paper presents the design and implementation of soft and compliant artificial chromatophores based on the cutaneous chromatophores in fish and cephalopods. We demonstrate artificial chromatophores that are actuated by electroactive polymer artificial muscles, mimicking the radially orientated muscles found in natural chromatophores. It is shown how bio-inspired chromomorphism may be achieved using both areal expansion of dielectric elastomer structures and by the hydrostatic translocation of pigmented fluid into an artificial dermal melanophore.

Bacteriophytochromes (BphPs) are biliverdin IXα-containing photoreceptors that photoconvert between red (Pr) and far-red (Pfr) absorbing states. BphPs are one half of a two-component system that transmits a light signal to a histidine kinase domain and then to a gene-response regulator. In Rhodopseudomonas palustris, synthesis of a light-harvesting complex (LH4) is controlled by two BphPs (RpBphP2 and RpBphP3). Despite their high sequence identity (52%), their absorption spectra are very different. The spectra of RpBphP2 exhibit classic Pr-to-Pfr photoconversion, whereas RpBphP3 quenches and a high-energy Pnr state emerges [Giraud et al. (2005), J. Biol. Chem. 280, 32389-32397]. Crystallization of the chromophore-binding domain (CBD) of RpBphP2 (RpBphP2-CBD) proved to be difficult and the structure of RpBphP3-CBD was used to crystallize RpBphP2-CBD* using homologue-directed mutagenesis. The structure shows that dimerization is an important factor in successful crystallization of RpBphP2-CBD* and arises from an N136R mutation. Mutations at this site correlate with an ability to dimerize in other truncated BphPs and may also be important for full-length dimer formation. Comparison of the RpBphP3-CBD and RpBphP2-CBD* biliverdin IXα pockets revealed that the former has additional hydrogen bonding around the B and D pyrrole rings that may constrain photoconversion to Pfr, resulting in a strained photoexcited Pnr state.

Spacing variation of adjoining reflecting thin films in iridophore is responsible for the variable interference color in the paracheirodon innesi. On the basis of this phenomenon, colloidal crystal thin films with different structures are fabricated from monodisperse poly(styrene-methyl methacrylate-acrylic acid) (PSMA) colloids. The relationship between the colors and structures of the films is investigated and discussed according to the principle of light interference. A two-layer colloidal film having uniform color is researched and it displays diverse colors before and after swelling by styrene (St), which can be used to mimic the variable structural color of the paracheirodon innesi.

Bacterial photosynthetic membranes, also known as chromatophores, are tightly packed with integral membrane proteins that work together to carry out photosynthesis. Chromatophores display a wide range of cellular morphologies; spherical, tubular, and lamellar chromatophores have all been observed in different bacterial species, or with different protein constituents. Through recent computational modeling and simulation, it has been demonstrated that the light-harvesting complexes abundant in chromatophores induce local membrane curvature via multiple mechanisms. These protein complexes assemble to generate a global curvature and sculpt the chromatophores into various cellular-scale architectures.

Although motile iridophores in the longitudinal stripes of neon tetra skin are under control of the sympathetic nervous system, they also respond to light directly and show circadian color changes. Using neon tetra skin, we found that the photoresponse of iridophores depends on light intensity, and that light near 500 nm is most effective. RT-PCR demonstrated the expression of mRNAs encoding rhodopsin and two kinds of cone opsins (Pi-green1 and Pi-green2) in neon tetra skin where the light-sensitive iridophores exist. These mRNAs are also expressed in the lateral eyes. The cone opsin genes, Pi-green1 and Pi-green2, show high similarity with the g101 and g103 genes of unique green cone opsins (belonging to the MWS/LWS group) of the blind Mexican cavefish. These results show that Pi-green1, Pi-green2, and/or rhodopsin may play important roles in the photoresponse of neon tetra iridophores, which are most sensitive to light near 500 nm.

We present a molecular model of a chromatophore vesicle from Rhodobacter sphaeroides. These vesicles are ideal benchmark systems for molecular and systemic simulations, because they have been well studied, they are small, and they are naturally separated from their cellular environment. To set up a photosynthetic chain working under steady-state conditions, we compiled from the experimental literature the specific activities and geometries that have been determined for their constituents. This data then allowed defining the stoichiometries for all membrane proteins. This article contains the kinetic part of the reconstructed model, while the spatial reconstruction is presented in a companion article. By considering the transport properties of the Cytochrome c(2) and ubiquinone pools, we show that their size and oxidation states allow for an efficient buffering of the statistical fluctuations that arise from the small size of the vesicles. Stoichiometric and kinetic considerations indicate that a typical chromatophore vesicle of Rb. sphaeroides with a diameter of 45 nm should contain approximately five bc(1) monomers.

The photosynthetic apparatus of purple bacteria is generally considered a well-studied and understood system. However, recent atomic force microscopy images of flattened chromatophore vesicles from Rhodobacter sphaeroides restarted a debate about the stoichiometry and positions of the membrane proteins, with the interpretations of the observed images only partly being in agreement with earlier models. The most puzzling observation from the recent images is that the Cytochrome bc(1) complex, which is a central part of the photosynthetic apparatus, seems to be missing on the chromatophore vesicles, even when these were extracted from photosynthetically grown bacteria. From the available information on the geometry of the vesicle and of the proteins we reconstructed here a three-dimensional model vesicle at molecular resolution. Its central feature, also determining its diameter of approximately 45 nm, is an equatorial array of LH1 dimers, lined by a region of LH2 rings. This naturally puts the Cytochrome bc(1) complexes and the ATPase at the vesicle's poles. This spatial model may explain why the vesicle's endcaps with the bc(1) complexes are lost during the preparatory steps of the imaging process together with the ATPase and are therefore absent from the available images.

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.

Melanophores, xanthophores, and iridophores from the skins of the two Antarctic fish species Pagothenia borchgrevinki and Trematomus bernacchii were tested immunocytochemically for the presence of a variety of muscle proteins. Actin, myosin, and calmodulin, not surprisingly, were confirmed for all three chromatophore types of the two fishes, but the presence of caldesmon and calponin, both characteristic proteins of smooth muscle fibers, represents a new discovery. It is not known at this stage whether these proteins occur also in the chromatophores of other fishes and are not restricted to Antarctic species. Since, however, motility control of particles in fish chromatophores and the regulation of smooth muscle tension both involve the sympathetic nervous system, the presence of similar target proteins should not come as a surprise. The fact that none of the chromatophores tested positive for troponin shows that there is no close relationship between pigment cells and striated muscle. The lack of alpha-actinin in iridophores, but its presence in melanophores and xanthrophores, is thought to be a reflection of the considerably greater pigment translocations within the latter two types of chromatophore cells.

To investigate the possible photoprotective role of chromatophores in fish, the absorbances of four types of intact chromatophores in adult and larval Japanese medaka were analyzed using microspectrophotometric techniques. The absorbance spectrum of each chromatophore class was obtained from 300 to 550 nm. The absorbance spectra of intact leucophores, melanophores and xanthophores were very similar to the published absorbance spectra of the isolated pure pigments contained in each chromatophore type, pteridines, melanin and carotenoids or pteridines, respectively. Based on these absorbance spectra, leucophores and melanophores should provide the most ultraviolet (UV) photoprotection to fish since the compounds they contain, pteridines and melanin, correspondingly, have strong absorbances in the UV region of the spectrum. Xanthophores containing carotenoids are not likely to provide much protection to fish from UV-induced damage since carotenoids have low absorbances in the UV range. Xanthophores containing colored pteridines, however, may provide somewhat greater UV protection to fish, since pteridines absorb more light than carotenoids in the UV portion of the spectrum. The relative frequency, coverage and thickness of these two types of xanthophores should determine how much protection xanthophores as a chromatophore type would provide against UV-induced damage.

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

We analyze the adsorption of the fluorescent monoamine 9-aminoacridine to the membrane phase of photosynthetic chromatophores, in the physiological interval of pH values ranging from 5.5 to 8.5 and at ionic strengths of 0.005 and 0.150 M. The interaction of the probe with the membrane phase is described with S-shaped isotherms of the Hill type and is modulated by electrostatic effects as modelled with the Gouy-Chapman-Boltzman theory. This description is consistent with different values of the surface change density of the chromatophore membranes decreasing from about 1.3 x 10(-3) to about 0.5 x 10(-3) e-/A2, on changing the pH from 8.5/7.5 to 6.5/5.5, respectively. Furthermore we show that, when the free concentrations of the probe in the inner and outer vesicle compartments are computed from the adsorbing isotherms at the proper pH values, the model considering the equilibrium distribution of the neutral monoamine following the onset of a delta pH is sufficient to describe the dependence of the artificially induced transmembrane delta pH values on the observed quenching of the probe fluorescence.

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.

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.

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.

Melanocytes and melanin granules have been studied by electron microscopy in normal human and cat skin, and in hyperplastic human skin lesions. The melanocytes have always been found as free cells within the epidermis,i.e., on the epidermal side of the dermal membrane. Melanocytes frequently rest on the dermal membrane or bulge towards the dermis. In such cases the uninterrupted dermal membrane is uniformly thin and smooth in appearance, in contrast with the regions alongside Malpighian cells, where it appears appreciably thicker and seemingly anchored to the basal cell layer. Two types of melanin granules have been distinguished according to their location in the melanocytes and to morphological characteristics which may only express different stages in the maturation of the granules: (a) light melanin granules in which a structure resembling a fine network is apparent; (b) dense melanin granules which, in osmium-fixed preparations, appear as uniformly dense masses surrounded by a coarsely granular, intensely osmiophilic shell. Treatment of sections of osmium-fixed tissues with potassium permanganate has revealed within the dense granules the existence of an organized framework in the form of a regular, crystalline-like lattice. It is suggested that this basic structure is protein in nature and may include the enzymatic system capable of producing melanin. The existence is reported of fine filaments located in the cytoplasm of melanocytes and morphologically distinct from the tonofilaments found in Malpighian cells.