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Melanin
Kinds of Melanin Terms modified by Melanin Selected AbstractsMacrophage aggregates in gilthead sea bream fed copper, iron and zinc enriched dietsJOURNAL OF FISH BIOLOGY, Issue 2 2000M. Manera Gilthead sea bream Sparus aurata from consecutive year classes (0+ and 1+) and from the same parent stock were fed four diets, three of which were fortified with copper, iron and zinc. Concentrations of these elements were little affected by the diet. Hepatic, renal and splenic tissues sections were examined to detect the influence of the diet on the number and morphology of macrophage aggregates (MAs); in particular their structure was examined in the spleen. Three different types of MAs were detected: (1) unstructured, (2) partially structured and scarcely defined and (3) fully structured and well defined. Melanin was the most abundant pigment in the pigmented macrophages which form MAs and the amount of this pigment was influenced by season. Ferritin, in contrast with previous data obtained in other fish species, was more abundant in renal than in splenic MAs. Significant differences in splenic MA numbers among fish fed different diets and among different periods of the year were detected. The results suggest that a polyfactorial regulation could act on the splenic MA number in gilthead sea bream. [source] Cold adaptation in Arctic and Antarctic fungiNEW PHYTOLOGIST, Issue 2 2001Clare H. Robinson Summary Growth and activity at low temperatures and possible physiological and ecological mechanisms underlying survival of fungi isolated from the cold Arctic and Antarctic are reviewed here. Physiological mechanisms conferring cold tolerance in fungi are complex; they include increases in intracellular trehalose and polyol concentrations and unsaturated membrane lipids as well as secretion of antifreeze proteins and enzymes active at low temperatures. A combination of these mechanisms is necessary for the psychrotroph or psychrophile to function. Ecological mechanisms for survival might include cold avoidance; fungal spores may germinate annually in spring and summer, so avoiding the coldest months. Whether spores survive over winter or are dispersed from elsewhere is unknown. There are also few data on persistence of basidiomycete vs microfungal mycelia and on the relationship between low temperatures and the predominance of sterile mycelia in tundra soils. Acclimation of mycelia is a physiological adaptation to subzero temperatures; however, the extent to which this occurs in the natural environment is unclear. Melanin in dark septate hyphae, which predominate in polar soils, could protect hyphae from extreme temperatures and play a significant role in their persistence from year to year. [source] Photoprotection by Porcine Eumelanin Against Singlet Oxygen Production,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 3 2008Alice Wang Melanin, a major pigment found in retinal pigment epithelium (RPE) cells, is considered to function in dual roles, one protective and one destructive. By quenching free radical species and reactive oxygen species (ROS) melanin counteracts harmful redox stress. However, melanin is also thought to be capable of creating ROS. In this destructive role, melanin increases redox strain in the cell. This study uses readily available eumelanin extracted from porcine RPE cells as a more authentic model than synthetic melanin to determine specific mechanisms of melanin activity with regard to singlet oxygen in the presence and absence of rose bengal, a singlet-oxygen photosensitizer. Optical detection of singlet-oxygen was determined by monitoring the bleaching of p -nitrosodimethylaniline in the presence of histidine. Production of singlet oxygen in aqueous oxygen-saturated solutions of rose bengal without eumelanin was readily accomplished. In contrast, detection of singlet oxygen in oxygen-saturated solutions of eumelanin without rose bengal failed, consistent with results of others. However, a significant decrease in singlet oxygen production by rose bengal was observed in the presence of eumelanin. After correction for light absorption and chemical bleaching of eumelanin, the results show that eumelanin also provides a photoprotective mode arising from chemistry, that is, not just the physical process of light absorption followed by energy dissipation as heat. [source] Ascorbate Enhances Photogeneration of Hydrogen Peroxide Mediated by the Iris Melanin,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 3 2008Albert R. Wielgus The iris in the human eye is exposed to UV and visible light transmitted by the cornea. This pigmented tissue is bathed with the aqueous humor (AqH), which contains high concentration of ascorbate. It has been postulated that the presence of ascorbate in AqH can contribute to increased photoproduction of H2O2 mediated by the iris melanin. In this study, we monitored generation of H2O2 induced by UV,VIS irradiation of bovine irides, bovine and human iris homogenates and iris melanin. Our data show that exogenous ascorbate significantly amplified the rate of H2O2 photoformation in all melanotic samples. Deactivation of endogenous catalase with NaN3 in bovine irides increased the level of the accumulated H2O2 in the bathing solution following sample irradiation. Photoformation of H2O2 in samples with exogenous ascorbate was accompanied by its photo-oxidation. Both photoprocesses exhibited significant wavelength dependence. EPR spectroscopy measurements showed that ascorbyl radical is an intermediate product of the ascorbate photo-oxidation. The photoproduction of H2O2 and photo-oxidation of ascorbate appear to be stoichiometric processes. No significant differences in the photoreactivity of iridial melanin from donors of different age and iris color was found. We postulate that also in vivo ascorbate increases the rate of iris melanin-mediated photoformation of H2O2 and its steady state concentration in AqH. [source] Photobleaching of Melanosomes from Retinal Pigment Epithelium: I. Effects on Protein OxidationPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2007Janice M. Burke ABSTRACT Melanin in the long-lived melanosomes of the retinal pigment epithelium (RPE) may undergo photobleaching with aging, which appears to diminish the antioxidant function of melanin and could make photobleached melanosomes less efficient in protecting biomolecules from oxidative modification. Here we analyzed whether photobleaching of melanosomes affects their ability to modify the oxidation state of nearby protein. As conventional methods developed to study soluble antioxidants are not well suited for analysis of granules such as melanosomes, we developed a new analytic method to focus on particle surfaces that involves experimentally coating granules with the cytoskeletal protein ,-actin to serve as a reporter for local protein oxidation. Isolated porcine RPE melanosomes were photobleached with visible light to simulate aging, then photobleached melanosomes, untreated melanosomes and control particles (black latex beads) were actin coated and illuminated in a photosensitized cell free system. Protein was re-stripped from particles and analyzed for carbonylation by Western blotting. Quantitative densitometry showed no reproducible differences for protein associated with untreated melanosomes when compared with control particles. Melanin has both anti- and pro-oxidant functions when light irradiated, but neither of these functions predominated in the protein oxidation assay when untreated melanosomes were used. However, protein extracted from photobleached melanosomes showed markedly increased carbonylation, both of associated actin and of endogenous melanosomal protein(s), and the effect increased with extent of granule photobleaching. Photobleaching of RPE melanosomes therefore changes the oxidation state of protein endogenous to the organelle and reduces the ability of the granule to modify the oxidation of exogenous protein near the particle surface. The results support the growing body of evidence that photobleaching of RPE melanosomes, which is believed to occur with aging, changes the physicochemical properties of the organelle and reduces the likelihood that the granules perform an antioxidant function. [source] Structural Studies of Bleached Melanin by Synchrotron Small-angle X-ray Scattering,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 2 2003Kenneth C. Littrell ABSTRACT Small-angle X-ray scattering was used to measure the effects of chemical bleaching on the size and morphology of tyrosine-derived synthetic melanin dispersed in aqueous media. The average size as measured by the radius of gyration of the melanin particles in solution, at neutral to mildly basic pH, decreases from 16.5 to 12.5 Å with increased bleaching. The melanin particles exhibit scattering characteristic of sheet-like structures with a thickness of approximately 11 Å at all but the highest levels of bleaching. The scattering data are well described by the form factor for scattering from a pancake-like circular cylinder. These data are consistent with the hypothesis that unbleached melanin, at neutral to mildly basic pH, is a planar aggregate of 6- to 10-nm-sized melanin protomolecules, hydrogen bonded through their quinone and phenolic perimeters. The observed decrease in melanin particle size with increased bleaching is interpreted as evidence for deaggregation, most probably the result of oxidative disruption of hydrogen bonds and an increase in the number of charged, carboxylic acid groups, whereby the melanin aggregates disassociate into units composed of decreasing numbers of protomolecules. [source] The Chemical Structure of MelaninPIGMENT CELL & MELANOMA RESEARCH, Issue 4 2004William L. Cheun First page of article [source] Melanin as a Target for Melanoma Chemotherapy: Pro-oxidant Effect of Oxygen and Metals on Melanoma ViabilityPIGMENT CELL & MELANOMA RESEARCH, Issue 3 2003Patrick J. Farmer Melanoma cells have a poor ability to mediate oxidative stress, which may be attributed to constitutive abnormalities in their melanosomes. We hypothesize that disorganization of the melanosomes will allow chemical targeting of the melanin within. Chemical studies show that under oxidative conditions, synthetic melanins demonstrate increased metal affinity and a susceptibility to redox cycling with oxygen to form reactive oxygen species. The electron paramagnetic resonance (EPR)-active 5,5,-dimethyl-pyrollidine N-oxide spin adduct was used to show that binding of divalent Zn or Cu to melanin induces a pro-oxidant response under oxygen, generating superoxide and hydroxyl radicals. A similar pro-oxidant behaviour is seen in melanoma cell lines under external peroxide stress. Melanoma cultures grown under 95% O2/5% CO2 atmospheres show markedly reduced viability as compared with normal melanocytes. Cu- and Zn-dithiocarbamate complexes, which induce passive uptake of the metal ions into cells, show significant antimelanoma activity. The antimelanoma effect of metal- and oxygen-induced stress appears additive rather than synergistic; both treatments are shown to be significantly less toxic to melanocytes. [source] The Effect of Preparation Procedures on the Morphology of Melanin from the Ink Sac of Sepia officinalisPIGMENT CELL & MELANOMA RESEARCH, Issue 1 2003Yan Liu The structure of melanin extracted from the ink sac of the cuttlefish Sepia officinalis was examined for different methods of isolation and purification of the pigment. Scanning electron microscopy (SEM) images of Sepia eumelanin prepared by different procedures establish that multi-,m-sized aggregates reported by previous workers are generated by their sample preparation, and that the dominant constituents of Sepia melanin are ,150 nm spherical granules. Brunauer-Emmett-Teller (BET) measurements reveal that Sepia eumelanin from Sigma (prepared by spray drying the pigment) has a surface area of 14.3 m2/g. Pigment extracted directly from the fresh ink sac and then freeze-dried has a surface area of 21.5 m2/g, while CO2 -supercritically dried has a surface area of 37.5 m2/g. This is consistent with SEM images showing that the process of freeze-drying produces aggregates, but to a lesser extent than spray drying. Supercritical drying of the sample produces suspensions of the individual ,150 nm granule, which is more reflective of the natural pigment. Brunauer-Emmett-Teller surface area analysis and Barrett-Joyner-Halenda (BJH) pore volume analysis indicate that the surface of the granules is not smooth and the interior of the granules is not porous, but rather the aggregates of granules are porous. Ultra-high resolution SEM and atomic force microscopy (AFM) images show the granules are easily deformed and are comprised of smaller constituents. De-aggregation of the granules by sonication and ultra-filtration reveal a range of structures depending on the pore size of the membrane used. The implications of these results on quantifying photochemical properties and kinetic reaction rate constants of melanin are discussed. [source] Comparative Biochemistry of Eumelanogenesis and the Protective Roles of Phenoloxidase and Melanin in InsectsPIGMENT CELL & MELANOMA RESEARCH, Issue 1 2002Manickam Sugumaran The phenolic biopolymer eumelanin is an important skin pigment found throughout the animal kingdom. The enzyme, tyrosinase, initiates melanogenesis in mammals. The biogenesis is assisted by a number of mammalian protein factors including dopachrome tautomerase and 5,6-dihydroxyindole-2-carboxylate oxidase. Invertebrates, such as insects, employ phenoloxidase and dopachrome (decarboxylating) isomerase for melanin biosynthesis. Recently generated molecular biological and biochemical data indicate that tyrosinase and phenoloxidase are distinctly different enzymes in spite of possessing both monophenol monooxygenase activity as well as o -diphenoloxidase activity. Similarly, insect dopachrome isomerase also differs significantly from its mammalian counterpart in several of its properties including the nature of the enzymatic reaction. In addition, there are considerable differences in the eumelanogenic pathways of these two animal groups that include the utility of substrates, use of dihydroxyindoles and the nature of eumelanin pigment. Thus, the biochemistry and molecular biology of melanogenesis in mammals and insects are significantly different. The advantages of generating different eumelanin pigments and intermediates by the insects are discussed. [source] Black and white , does melanin change the bulk carbon and nitrogen isotope values of feathers?RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 7 2010Andreas Michalik Bird feathers are employed in a wide range of carbon and nitrogen isotope studies relating to diet and migration. Feathers are chemically inert with respect to carbon and nitrogen, after synthesis. It has always been assumed that feathers show isotope values characteristic of keratin, a fibrous structural protein from which they are formed. Little attention has been paid to other components of feathers such as melanin or carotenoids. Melanin is synthesized from tyrosine, which is depleted in both 13C and 15N. We compared isotope values of coeval black and white feathers in four different species. Black feather parts were in all cases significantly depleted in 13C relative to white feather parts but in most species no clear trend was discernable for 15N. We suggest that additional evaluation may be required to characterize the carbon and nitrogen isotope contribution of feather pigments like carotenoids. Care should be taken in future stable isotope studies when comparing differently coloured feathers. Copyright © 2010 John Wiley & Sons, Ltd. [source] Introduction to the Symposium-in-Print on MelaninsPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 3 2008John D. Simon No abstract is available for this article. [source] Ultrafast Energy Transfer from Bound Tetra(4- N,N,N,N -trimethylanilinium)porphyrin to Synthetic Dopa and Cysteinyldopa Melanins,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2003Tong Ye ABSTRACT The binding of tetra(4- N,N,N,N -trimethylanilinium)porphyrin (TAP) to melanins quenches the porphyrin emission. Time-resolved femtosecond absorption spectroscopy reveals that the mechanism behind this quenching is ultrafast nonradiative energy transfer (,ET < 100 fs) from electronically excited TAP to melanin. Similar dynamics are observed for both dopa and cysteinyldopa melanins. Steady-state emission studies demonstrate that the emission from melanin increases upon excitation of bound TAP, thereby confirming that rapid energy transfer occurs. These results are consistent with previous photoacoustic studies, which revealed that the TAP,melanin complex behaves like a supermolecular system liberating heat as a whole. [source] Treatment of Idiopathic Cutaneous Hyperchromia of the Orbital Region (ICHOR) with Intense Pulsed LightDERMATOLOGIC SURGERY, Issue 6 2006NATALIA CYMROT CYMBALISTA MD BACKGROUND Idiopathic cutaneous hyperchromia of the orbital region (ICHOR) does not have a clear etiopathogenesis. Genetic factors, increased melanin, prominent vasculature, and eyelid skin slackness seem to be involved. OBJECTIVE To evaluate individuals with ICHOR clinically and histologically, before and after treatment with high-energy pulsed light (HEPL), considering epidermal and dermal melanin, in order to evaluate HEPL efficacy in clearing away ICHOR, and 1 month and 1 year later to check whether improvement was maintained. METHODS Twelve individuals with ICHOR underwent clinical and histological evaluation before and after HEPL application, with photographic comparison. They underwent one to four HEPL sessions on the lower eyelid at approximately 30-day intervals. Melanin quantification by area, before and after treatment was performed by digital image morphometry. RESULTS Eyelid skin was significantly lightened (p=.24), and was maintained 1 year later with no ICHOR reincidence. All individuals (100%) showed postinflammatory hyperchromia (average 6-month duration), while 58.33% presented hypochromia (7-month duration). There was significantly decreased epidermal and dermal melanin after treatment. CONCLUSION HEPL was shown to be useful in clearing up ICHOR. This was maintained after 1 year. Epidermal and dermal histopathology showed decreased melanin following treatment. Longer follow-up is needed to evaluate possible later recurrence of ICHOR. [source] Review of Photorejuvenation: Devices, Cosmeceuticals, or Both?DERMATOLOGIC SURGERY, Issue 2005Cameron K. Rokhsar MD Background:. Both the public and the medical profession have placed a lot of attention on reversal of signs of aging and photodamage, resulting in numerous cosmeceutical products and nonablative laser techniques designed to achieve these results. Objective:. The purpose of this report is to briefly review both the cosmeceutical products and nonablative laser techniques that appear to be most promising based on published studies. After this review, recommendations for potential enhancement of benefits by combining cosmeceuticals and laser treatments will be explored. Results. Pulsed dye lasers targeting microvessels, intense pulsed light targeting both melanin and microvessels, and midinfrared lasers targeting dermal water and collagen all appear to have some ability to improve skin texture, color, and wrinkling. Retinoids, vitamin C, alpha-hydroxy acids, and topical growth factors may also stimulate repair mechanisms that result in similar improvements in photodamaged skin. Conclusion:. Although supported only by theoretic considerations and anecdotal reports, it seems logical that the concurrent use of appropriate cosmeceuticals with nonablative laser photorejuvenation should result in enhanced benefits. [source] The Effect of Full-Face Broadband Light Treatments Alone and in Combination With Bilateral Crow's Feet Botulinum Toxin Type A ChemodenervationDERMATOLOGIC SURGERY, Issue 3 2004Jean Carruthers MD Background. Broadband light (BBL; Intense Pulsed Light; Lumenis Ltd., Yokneam, Israel) is a powerful, nonablative, light-based technology that targets melanin and hemoglobin and stimulates the formation of collagen and elastin. Botulinum toxin type A (BTX-A; BOTOX; Allergan Inc., Irvine, CA) treatment of the lateral periocular region relaxes the vertical fibers of the orbicularis oculi and results in softening of the lateral orbital crow's feet rhytides and widening of the palpebral aperture. Objective. To compare the effects of full-face BBL in combination with BTX-A and BBL alone in female subjects with Fitzpatrick I,III skin types, Glogau II,III rhytides, and significant associated facial lentigines and telangiectasia. Methods. This was a prospective, randomized study of 30 women with moderate to severe crow's feet rhytides. Half of the subjects were treated with BTX-A and BBL and the other half with BBL alone. Their response was assessed clinically and photographically. Skin biopsies of the temporal skin were taken from two subjects in each group and were stained with Masson trichrome. Results. Patients treated with a combination of BTX-A and BBL experienced a better response to treatment, both at rest and on maximum smile, as well as a slightly improved response in associated lentigines, telangiectasia, pore size, and facial skin texture compared with patients who received BBL treatment alone. Skin biopsies showed an increase in dermal collagen in each group. Conclusions. The patients in this study benefited from both treatments. Although BBL led to a remarkable improvement in full-face telangiectasias, lentigines, and skin texture, the improvement increased in all categories with combination therapy. In addition, an added improvement in the full-face aesthetic with both BTX-A and BBL therapy combined was obvious. These results suggest that both treatments,although evidently complementary,may also act synergistically to produce optimal clinical effects, revolutionizing the treatment of facial aging. [source] Combined Therapy Using Q-Switched Ruby Laser and Bleaching Treatment With Tretinoin and Hydroquinone for Acquired Dermal MelanocytosisDERMATOLOGIC SURGERY, Issue 10 2003Akira Momosawa MD Background and objective. Acquired dermal melanocytosis (ADM; acquired bilateral nevus of Ota-like macules) is known for its recalcitrance compared with Nevus of Ota, and we assume that one of the reasons is a higher rate and degree of postinflammatory hyperpigmentation (PIH) seen after laser treatments. Methods. Topical bleaching treatment with 0.1% tretinoin aqueous gel and 5% hydroquinone ointment containing 7% lactic acid was initially performed (4 to 6 weeks) to discharge epidermal melanin. Subsequently, Q-switched ruby (QSR) laser was irradiated to eliminate dermal pigmentation. Both steps were repeated two to three times until patient satisfaction was obtained (usually at a 2-month interval for laser sessions). This treatment was performed in 19 patients with ADM. Skin biopsy was performed in six cases at baseline, after the bleaching pretreatment, and at the end of treatment. Results. All patients showed good to excellent clearing after two to three sessions of QSR laser treatments. The total treatment period ranged from 3 to 13 (mean of 8.3) months. PIH was observed in 10.5% of the cases. Histologically, epidermal hyperpigmentation was observed in all specimens and was dramatically improved by the topical bleaching pretreatment. Conclusion. QSR laser combined with the topical bleaching pretreatment appeared to treat ADM consistently with a low occurrence rate of PIH and lessen the number of laser sessions and total treatment period and may also be applied to any other lesions with both epidermal and dermal pigmentation. [source] Clinical pathologic correlations for diagnosis and treatment of nail disordersDERMATOLOGIC THERAPY, Issue 1 2007Olympia I. Kovich ABSTRACT:, Clinicopathologic correlation is crucial to the correct diagnosis of disorders of the nail unit. This chapter will explore four common clinical scenarios and how pathology can help differentiate between their various etiologies. These include: dark spot on the nail plate (melanin versus heme), subungual hyperkeratosis (onychomycosis versus psoriasis), longitudinal melanonychia (benign versus malignant), and verrucous papule (verruca versus squamous cell carcinoma). Consideration must be given to both when to perform a biopsy and the location of the biopsy site, which must be based on an understanding of the origin of the changes. An overarching principle is that lesions within the same differential diagnosis may be present concomitantly, such as malignant melanoma of the nail unit associated with hemorrhage. Therefore, even with a biopsy-proven diagnosis, the clinician must always monitor lesions of the nail unit for appropriate response to treatment and consider an additional biopsy for recalcitrant lesions. [source] Diagnosis of melanoma aspirates on ThinPrep®: The University of Michigan experienceDIAGNOSTIC CYTOPATHOLOGY, Issue 5 2002Güliz Akdas Barkan M.D. Abstract The purpose of this study was to compare the cytologic features of melanoma fine-needle aspirates (FNAs) prepared by ThinPrep® (TP) with those in conventional smears (CS) and to identify any diagnostic pitfalls. Fifty-one aspirates diagnosed as melanoma were obtained, 36 of which were prepared by both TP and CS. The preparations were evaluated for cellularity, cell aggregates, cellular appearance, melanin pigment, cytoplasmic, and nuclear features. Categorical data were analyzed by the chi-square test and continuous data by the Wilcoxin-signed rank test. Correlation was determined by Spearman's test for bivariate correlations (rho). Good correlation between the two methods was identified for the following features: cellularity, cell type, bi/multinucleated cells, cytoplasmic features, NC ratio, and presence of macronucleoli. TP exhibits coarser chromatin compared to CS (P = 0.005). Six of 36 CS contained large cellular groups; none of the TP contained them (P = 0.018). Twenty-five of 36 CS contained intranuclear inclusions as opposed to 12/36 TP (P < 0.001). The number of inclusions was significantly reduced on TP. The amount of intracellular melanin was the same with both techniques. Background melanin was markedly reduced on TP except when either trapped by fibrin or attached to cellular clusters (P = 0.006). Background blood was also markedly reduced on TP (P < 0.005). In summary, the cytological features of TP and CS for FNA evaluation of melanoma correlate well; however, one needs to be aware of the cytologic alterations introduced by TP. TP is a sufficient preparation method in the diagnosis of melanoma FNA aspirates when performed by clinicians. It is also a useful adjunct in bloody or low-cellular aspirates, where it tends to reduce the background blood and concentrate the cells. Diagn. Cytopathol. 2002;26:334,339. © 2002 Wiley-Liss, Inc. [source] Incubation Feeding and Nest Attentiveness in a Socially Monogamous Songbird: Role of Feather Colouration, Territory Quality and Ambient EnvironmentETHOLOGY, Issue 7 2010Beata Matysioková Parental investment and environmental conditions determine reproductive success in wild-ranging animals. Parental effort during incubation, and consequently factors driving it, has profound consequences for reproductive success in birds. The female nutrition hypothesis states that high male feeding enables the incubating female to spend more time on eggs, which can lead to higher hatching success. Moreover, both male and female parental investment during incubation might be signalled by plumage colouration. To test these hypotheses, we investigated relationships between male and female incubation behaviour and carotenoid and melanin-based plumage colouration, territory quality and ambient temperature in the Great Tit Parus major. We also studied the effect of female incubation behaviour on hatching success. Intensity of male incubation feeding increased with lower temperatures and was higher in territories with more food supply, but only in poor years with low overall food supply. Female nest attentiveness increased with lower temperatures. Plumage colouration did not predict incubation behaviour of either parent. Thus, incubation behaviour of both parents was related mainly to environmental conditions. Moreover, there was no relationship between male incubation feeding, female nest attentiveness and hatching success. Consequently, our data were not consistent with the female nutrition hypothesis. [source] The role of melanin- and carotenoid-based plumage coloration in nest defence in the Great TitETHOLOGY, Issue 7 2007Javier Quesada Although plumage coloration is recognized to convey valuable information about the bearer's parental abilities, few studies have explored the relationship between coloration and nest defence. In this study in Great Tit Parus major, we analysed the relationship between nest defence and melanin- as well as carotenoid-based plumage coloration, after controlling for ecological variables known to influence nest defence. A principal components analysis was applied to classify birds according to how vigorously they defended the nest, and the intensity of nest defence was tested against plumage coloration. Males with a large black tie defended their nests more vigorously, but no such effect was found for yellow breast coloration. This suggests that melanin-based coloration in the Great Tit is associated with aggression, including both dominance-aggression and nest defence, whereas carotenoid-based coloration is not. The challenge in future studies will be to demonstrate whether females use this trait as an ornament to assess male quality and whether they trade off between the different ornaments a male may exhibit. [source] Age-related changes in the dynamics of human albino visual pathwaysEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 7 2003Magella M. Neveu Abstract A deficiency of melanin in the retinal pigment epithelium, which regulates the development of neural retina, leads to chiasmal misrouting such that the uncrossed pathway (to the ipsilateral hemisphere) is reduced relative to the crossed pathway (to the contralateral hemisphere). This study examines age-related changes in the flash and pattern appearance visual evoked potentials (VEP) of human albinos. Scalp recorded cortical VEPs to flash (FVEP) and pattern appearance stimulation were recorded in 58 albino (8 months to 60 years) and 34 normal subjects (4,55 years). VEPs were analysed by amplitude and latency. The contralateral hemisphere FVEP amplitude decreased with age in albino subjects, as in both hemispheres in normals. However, the ipsilateral hemisphere FVEP amplitude was significantly lower in young albino subjects, initially giving a marked interhemispheric asymmetry, but this normalized with age. Significant interhemispheric FVEP latency asymmetries were not observed. The contralateral pattern appearance VEP latency in albino subjects decreased with age, as in both hemispheres in normals; the ipsilateral latency increased significantly with age. Significant interhemispheric pattern appearance VEP amplitude asymmetries were not observed. These novel and unexpected observations indicate significant age-related changes in the retinocortical pathways of the human albino. These changes have implications for our understanding of development and plasticity of the central visual pathways. [source] THE COST OF MELANIZATION: BUTTERFLY WING COLORATION UNDERENVIRONMENTAL STRESSEVOLUTION, Issue 2 2004W. Talloen Abstract Evolutionary studies typically focus on adaptations to particular environmental conditions, thereby often ignoring the role of possible constraints. Here we focus on the case of variation in dorsal wing melanization in a satyrine butterfly Pararge aegeria. Because melanin is a complex polymer, its synthesis may be constrained if ambient conditions limit the resource budget. This hypothesis was tested by comparing melanization among butterflies that fed as larvae on host grasses experiencing different drought-stress treatments. Treatment differences were validated both at the level of the host plant (nitrogen, carbonate, and water content) and of the butterfly (life-history traits: survival, development time, and size at maturity). Melanization rate was measured as average gray value of the basal dorsal wing area. This area, close to the thorax, is known to be functionally significant for basking in order to thermoregulate. Individuals reared on drought-stressed host plants developed paler wings, and development of darker individuals was slower and less stable as estimated by their level of fluctuating asymmetry. These results provide evidence that melanin is indeed costly to synthesize, and that differences in environmental quality can induce phenotypic variation in wing melanization. Therefore, studies dealing with spatial and/or temporal patterns of variation in wing melanization should not focus on adaptive explanations alone, but rather on a cost-benefit balance under particular sets of environmental conditions. [source] Why do melanomas get so dark?EXPERIMENTAL DERMATOLOGY, Issue 11 2009Rossitza Lazova Abstract:, Cutaneous malignant melanomas often exhibit pigmented regions that are darker than the surrounding skin. While melanoma cells are the original source of the melanin, keratinocytes and melanophages also contribute to the tumor colour because they contain melanin obtained from melanoma cells. However, little is known of the origin of darkly pigmented melanoma cells or of the molecular pathways regulating their melanin production. Here we discuss observations that dark melanoma cells emerge from within populations of melanoma in situ and that, in addition to producing abundant dark pigment, they appear to be undergoing autophagy. Moreover, autophagy appears to be a common trait of invasive melanoma cells in the dermis. The underlying cause of this phenomenon may stem from aberrant production of glycosylation structures known as ,1,6-branched oligosaccharides. Our studies of dark cutaneous melanomas were prompted by analyses of experimental mouse macrophage-melanoma hybrids fused in the laboratory. Like melanoma cells in cutaneous malignant melanoma, experimental hybrids also displayed abundant dark pigment and autophagy, and had high levels of ,1,6-branched oligosaccharides. Whether or not darkly pigmented malignant melanoma cells originate from fusion with macrophages in vivo remains to be determined. In any event, pigmentation in melanoma, long considered as a secondary aspect of the malignancy, may be a visible warning that the cells have gained competence for invasion and metastasis. [source] Antimelanogenesis effect of Tunisian herb Thymelaea hirsuta extract on B16 murine melanoma cellsEXPERIMENTAL DERMATOLOGY, Issue 12 2007Mitsuko Kawano Abstract:, Skin pigmentation is the result of melanogenesis that occurs in melanocytes and/or melanoma cells. Although melanogenesis is necessary for the prevention of DNA damage and cancer caused by UV irradiation, excessive accumulation of melanin can also cause melanoma. Thus, we focused on the antimelanogenesis effect of an extract from Thymelaea hirsuta, a Tunisian herb. Murine melanoma B16 cells were treated with T. hirsuta extract, and then cell viability and synthesized melanin content were measured. We found that the T. hirsuta extract decreased the synthesized melanin content in B16 cells without cytotoxicity. Tyrosinase is a key enzyme of melanogenesis and extracellular signal-regulated kinase (ERK)-1/2 phosphorylation is known to be related to melanogenesis inhibition. To clarify its mechanism, we also determined ERK1/2 phosphorylation and tyrosinase expression level. ERK1/2 was immediately phosphorylated in cells just after treatment with the extract. The tyrosinase expression was inhibited after 24 h of stimulation with the extract. The T. hirsuta extract was fractionated, and we found that one fraction considerably decreased the melanin synthesis in B16 cells and that this fraction contains daphnanes as the main component. This indicates that our findings might be attributable to daphnanes. [source] Immunohistochemistry and in situ hybridization in the study of human skin melanocytesEXPERIMENTAL DERMATOLOGY, Issue 3 2007Thierry Passeron Abstract: Although keratinocytes are the most numerous type of cell in the skin, melanocytes are also key players as they produce and distribute melanin that protects the skin from ultraviolet (UV) radiation. In vitro experiments on melanocytic cell lines are useful to study melanogenesis and their progression towards melanoma. However, interactions of melanocytes with keratinocytes and with other types of cells in the skin, such as fibroblasts and Langerhans cells, are also crucial. We describe two techniques, immunohistochemistry (IHC) and tissue in situ hybridization (TISH), that can be used to identify and study melanocytes in the skin and their responses to UV or other stimuli in situ. We describe a practical method to localize melanocytic antigens on formalin-fixed, paraffin-embedded tissue sections and in frozen sections using indirect immunofluorescence with conjugated secondary antibodies. In addition, we detail the use of TISH and its combination with IHC to study mRNA levels of genes expressed in the skin at cellular resolution. This methodology, along with relevant tips and troubleshooting items, are important tools to identify and study melanocytes in the skin. [source] Carotenoid and melanin-based ornaments signal similar aspects of male quality in two populations of the common yellowthroatFUNCTIONAL ECOLOGY, Issue 1 2010Peter O. Dunn Summary 1.,Female preferences for particular male ornaments may shift between populations as a consequence of ecological differences that change the reliability and detectability of the ornament, but few studies have examined how ornaments function in different populations. 2.,We examined the signalling function of male plumage ornaments in a warbler, the common yellowthroat (Geothlypis trichas), breeding in New York (NY) and Wisconsin (WI), USA. Males have two prominent ornaments: a black facial mask pigmented with melanin and a yellow bib pigmented by carotenoids. Previous studies in WI indicate that the size of the mask, and not the bib, is primarily related to female choice and male reproductive success. In NY, however, the pattern is reversed and attributes of the bib (size and colour), and not the mask, are the target of sexual selection. 3.,We found that brightness of the yellow bib was the best signal of humoral immunity (immunoglobulin G) in NY and mask size was the best signal in WI, after controlling for breeding experience and capture date. Thus, similar aspects of male quality appeared to be signalled by different ornaments in different populations. 4.,There was no difference between populations in the level of plasma carotenoids or the prevalence of malarial parasites, which may affect the costs and benefits of choosing males with particular ornaments in each location. 5.,Even though females in different populations prefer different ornaments produced by different types of pigments, these ornaments appear to be signalling similar aspects of male quality. Our results caution against inferring the function of particular ornaments based simply on their type of pigment. [source] Role of dopachrome conversion enzyme in the melanization of filarial worms in mosquitoesINSECT MOLECULAR BIOLOGY, Issue 6 2005C.-Y. Huang Abstract Melanization is an effective defence reaction of mosquito hosts against invading parasites. In mosquitoes, the biosynthesis of melanin is initiated by the hydroxylation of tyrosine to DOPA by phenoloxidase (PO). DOPA is a branch point of the melanization reaction; it may be oxidized to dopaquinone by PO or be decarboxylated to dopamine by dopa decarboxylase. Further oxidation of dopaquinone by PO produces dopachrome. Dopachrome is then converted to 5, 6-dihydroxyindole by dopachrome conversion enzyme (DCE) to produce melanin. The conversion of dopachrome is a rate-limiting step of the melanization reaction, and the presence of PO and DCE significantly accelerates melanization reactions. In this study, a cDNA encoding DCE was cloned from the mosquito Armigeres subalbatus. Real-time PCR analysis revealed increased transcripts from haemocytes in microfilariae (mf)-inoculated mosquitoes. Gene silencing using double-stranded RNA was used to elucidate the role of DCE in the melanization reaction of parasites in Ar. subalbatus. The levels of both DCE transcripts and protein in gene knockdown mosquitoes were dramatically reduced. Compared with controls, the degree of melanization of mf in DCE-knockdown mosquitoes was significantly decreased. These results suggest that DCE is a critical enzyme that is required for effective melanization immune responses. [source] Molecular characterization of a prophenoloxidase cDNA from the malaria mosquito Anopheles stephensiINSECT MOLECULAR BIOLOGY, Issue 2 2000L. Cui Abstract Some refractory anopheline mosquitoes are capable of killing Plasmodium, the causative agent of malaria, by melanotic encapsulation of invading ookinetes. Phenoloxidase (PO) appears to be involved in the formation of melanin and toxic metabolites in the surrounding capsule. A cDNA encoding Anopheles stephensi prophenoloxidase (Ans-proPO) was isolated from a cDNA library screened with an amplimer produced by reverse transcriptase polymerase chain reaction (RT-PCR) with degenerate primers designed against conserved proPO sequences. The 2.4-kb-long cDNA has a 2058 bp open reading frame encoding Ans-proPO of 686 amino acids. The deduced amino acid sequence shows significant homology to other insect proPO sequences especially at the two putative copper-binding domains. In A. stephensi, Ans-proPO expression was detected in larval, pupal and adult stages. The Ans-proPO mRNA was detected by RT-PCR and in situ hybridization in haemocytes, fat body and epidermis of adult female mosquitoes. A low level of expression was detected in the ovaries, whereas no expression was detected in the midguts. Semi-quantitative RT-PCR analysis of Ans-proPO mRNA showed that its expression was similar in adult female heads, thoraxes and abdomens. No change in the level of Ans-proPO expression was found in adult females after blood feeding, bacterial challenge or Plasmodium berghei infection. However, elevated PO activity was detected in P. berghei -infected mosquitoes, suggesting that in non-selected permissive mosquitoes PO may be involved in limiting parasite infection. Genomic Southern blot and immunoblots suggest the presence of more than one proPO gene in the A. stephensi genome, which is consistent with the findings in other Diptera and Lepidoptera species. The greatest similarity in sequence and expression profile between Ans-proPO and A. gambiae proPO6 suggests that they might be homologues. Our results demonstrate that Ans-proPO is constitutively expressed through different developmental stages and under different physiological conditions, implying that other factors in the proPO activation cascade regulate melanotic encapsulation. [source] Testing the effect of individual color morphology on immune response in bush-cricketsINSECT SCIENCE, Issue 5 2010Åsa Berggren Abstract, Despite the growing interest in how an individual's immune response is correlated to morphological and ecological factors, little empirical data has been available from wild insect populations. Many insects have different color morphs and exhibit differences in immune responses. Links are expected to exist between body colors and immune function in insects, because the same biochemical precursors involved in the immune response are responsible for melanin-based color markings. In this study, I assay the immune response of two different color morphs of 377 wild-caught bush-crickets, Metrioptera roeseli, from 20 populations by measuring individual encapsulation responses to a surgically implanted nylon monofilament. There was no difference between green and brown bush-cricket morphs (low melanin vs high melanin investment in cuticula color respectively) and their ability to mount an immune response to the implant. Further study is needed on the relationship between color morphology and immune response in wild insects, and whether trade-offs occur between factors during an insect's development phase and long-term health. [source] | |||||||||||||||||||||||||||||||