Production Of Melanin Pigment Research Articles

Age-related change in melanin-based coloration of Barn owls (Tyto alba): females that become more female-like and males that become more male-like perform better

Ornament expression fluctuates with age in many organisms. Whether these changes are adaptively plastic is poorly known. In order to understand the ultimate function of melanin-based ornaments, we studied their within-individual fluctuations and their covariation with fitness-related traits. In barn owls (Tyto alba), individuals vary from reddish-brown pheomelanic to white, and from immaculate to marked with black eumelanic spots, with males being less reddish and less spotted than females. During the first molt, both sexes became less pheomelanic, females displayed larger spots and males fewer spots, but the extent of these changes was not associated with reproduction. At subsequent molts, intra-individual changes in melanin-based traits covaried with simultaneous reproduction changes. Adult females bred earlier in the season and laid larger eggs when they became scattered with larger spots, whereas adults of both sexes produced larger broods when they became whiter. These results suggest that the production of melanin pigments and fitness-related life-history traits are concomitantly regulated in a sex-specific way. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101, 689‐704.

High diversity of polyketide synthase genes and the melanin biosynthesis gene cluster in Penicillium marneffei

Despite the unique phenotypic properties and clinical importance of Penicillium marneffei, the polyketide synthase genes in its genome have never been characterized. Twenty-three putative polyketide synthase genes and two putative polyketide synthase nonribosomal peptide-synthase hybrid genes were identified in the P. marneffei genome, a diversity much higher than found in other pathogenic thermal dimorphic fungi, such as Histoplasma capsulatum (one polyketide synthase gene) and Coccidioides immitis (10 polyketide synthase genes). These genes were evenly distributed on the phylogenetic tree with polyketide synthase genes of Aspergillus and other fungi, indicating that the high diversity was not a result of lineage-specific gene expansion through recent gene duplication. The melanin-biosynthesis gene cluster had gene order and orientations identical to those in the Talaromyces stipitatus (a teleomorph of Penicillium emmonsii) genome. Phylogenetically, all six genes of the melanin-biosynthesis gene cluster in P. marneffei were also most closely related to those in T. stipitatus, with high bootstrap supports. The polyketide synthase gene of the melanin-biosynthesis gene cluster (alb1) in P. marneffei was knocked down, which was accompanied by loss of melanin pigment production and reduced ornamentation in conidia. The survival of mice challenged with the alb1 knockdown mutant was significantly better than those challenged with wild-type P. marneffei (P < 0.005). The sterilizing doses of hydrogen peroxide, leading to a 50% reduction in survival of conidia, were 11 min for wild-type P. marneffei and 6 min for the alb1 knockdown mutant of P. marneffei, implying that the melanin-biosynthesis gene cluster contributed to virulence through decreased susceptibility to killing by hydrogen peroxide.

Polychlorinated dibenzofurans as a causal agent of fetal Yusho

Polychlorinated dibenzo- p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and dioxin-like polychlorinated biphenyls (dioxin-like PCBs) are highly-toxic environmental pollutants that are still ubiquitous. About 40 years ago, a mass food poisoning, termed “Yusho”, occurred in western Japan, and the causal agent of Yusho was thought to be PCDFs. The preserved umbilical cords of babies who were born to mothers with Yusho 2–5 years after the outbreak of Yusho and diagnosed with fetal Yusho were recently obtained, and the concentrations of PCDDs, PCDFs, dioxin-like PCBs and polychlorinated biphenyls (PCBs) in these preserved umbilical cords were determined. Among babies with fetal Yusho, the pollutant concentrations in umbilical cords were compared between “black babies”, a term that describes the dermatologic abnormality that is classically seen in fetal Yusho, and “non-black babies”. There was almost no difference in the concentrations of 2,3,7,8-tetrachlorodibenzo- p-dioxin (2,3,7,8-TCDD) toxic equivalents (TEQ) concentrations of PCDDs, PCDFs and dioxin-like PCBs found in these two groups of babies. Therefore, the Yusho infants with the dark brown skin pigmentation seemed to have a hypersensitive genetic predisposition to the production of melanin pigment in the skin after the exposure to these toxic compounds. The concentrations of PCDDs, PCDFs, dioxin-like PCBs and PCBs in the preserved umbilical cords of infants diagnosed with fetal Yusho and of healthy babies were also determined and compared. PCDDs, dioxin-like PCBs and PCBs were detected in both groups. PCDFs, however, were found at high concentration only in the babies with fetal Yusho. In 2,3,7,8-TCDD TEQ concentrations, 90% of the total TEQ concentrations were attributable to PCDFs after taking into account the baseline concentrations found in healthy babies. This evidence shows that fetal Yusho is caused by PCDF intoxication.

A developmental analysis of periodic albinism in the amphibian Xenopus laevis

The periodic albino of Xenopus laevis displays a transitory presence of black melanin pigment in the embryo but looses this during tadpole development. This mutation, involving a recessive allele, affects melanogenesis in dermal melanophore pigment cells. It has been suggested that the mutation is intrinsic to the melanophore cell itself or, alternatively, reflects malfunction in the neuroendocrine system that regulates melanophore cell function. This latter system, involving pituitary melanotrope cells which produces α-melanophore stimulating hormone (α-MSH), is responsible for stimulating the production and dispersion of melanin pigment in dermal melanophores. The purpose of the present study was to determine to which degree the albinism is intrinsic to the melanophore or involves neuroendocrine malfunction. Experiments involved transplantation of presumptive melanophores from wild-type to albino embryos, and vice versa, immunocytochemical analysis of the albino neuroendocrine system and the creation of wild-type/albino parabiotic animals to determine if the neuroendocrine system of the albino can support melanotrope cell function. We show that the albino has a functional neuroendocrine system and conclude that the defect in the albino primarily affects the melanophore cell, possibly rendering it incapable of responding to α-MSH. It is also apparent from our results that in later stages of development the cellular environment of the melanotrope cell does become important to its development, but the nature of the critical cellular factors involved remains to be determined.

Glycoprotein nonmetastatic melanoma protein b, a melanocytic cell marker, is a melanosome‐specific and proteolytically released protein

Melanosomes are organelles specialized for the production of melanin pigment and are specifically produced by melanocytic cells. More than 150 pigmentation-related genes have been identified, including glycoprotein nonmetastatic melanoma protein b (GPNMB). A recent proteomics analysis revealed that GPNMB is localized in melanosomes, and GPNMB is a membrane-bound glycoprotein that shows high homology with a well-known melanosomal structural protein, Pmel17/gp100. In this study, we show that GPNMB is expressed in melanocytes of normal human skin, as well as in human melanoma cells. GPNMB is heavily glycosylated and is enriched in mature (stage III and IV) melanosomes in contrast to MART-1 and Pmel17, which are abundant in early (stage I and II) melanosomes. MART-1 and Pmel17 play critical roles in the maturation of early melanosomes; thus, we speculate that GPNMB might be important in the functions of late melanosomes, possibly their transport and/or transfer to keratinocytes. We also demonstrate that a secreted form of GPNMB is released by ectodomain shedding from the largely Golgi-modified form of GPNMB and that the PKC and Ca(2+) intracellular signaling pathways regulate that shedding. We conclude that GPNMB is a melanosomal protein that is released by proteolytic ectodomain shedding and might be a useful and specific histological marker of melanocytic cells.

A fatal case of an adrenal gland melanoma with a mysterious primary lesion

A fatal case of an adrenal gland melanoma with a mysterious primary lesion

Computer-assisted numerical analysis of colour-group data for dereplication of streptomycetes for bioprospecting and ecological purposes

Large numbers of alkaliphilic streptomycetes isolated from a beach and dune sand system were dereplicated manually based on aerial spore mass, colony reverse and diffusible pigment colours formed on oatmeal agar, and on their capacity to produce melanin pigments on peptone-yeast extract-iron agar. The resultant data were converted to their respective red, blue and green shade intensities. The Euclidean distances between each of the colours were calculated by considering red, green and blue shade intensity values as X, Y and Z coordinates in three dimensional space. The clusters of isolates delineated in the dendrogram generated using the distances were found to match those obtained by manual colour-grouping of the isolates. A reasonable linear correlation was found between the colour-group and corresponding rep-PCR data. The implications of the computer-assisted colour-grouping method for bioprospecting and ecological studies are discussed.

Mysteries of salt and pepper

Mysteries of salt and pepper

A 15 YEAR OLD BOY WITH A POSTERIOR FOSSA TUMOR

A 15 year old male presented with hydrocephalus from a tectal mass obstructing the cerebral aqueduct and upper fourth ventricle. The solid-cystic partly enhancing mass proved to be a pigmented pleomorphic xanthoastrocytoma, the third such example reported. The lesion revealed typical features of a PXA with the unusual addition of intracytoplasmic melanin in select lesional cells. Melanin pigment production is uncommon in glial tumors and of uncertain significance. The present case is recurrence-free one year post-operatively.

Standardization of Metal-Based Herbal Medicines

Problem statement: Dermatophytes have developed resistance to the existing antifungal antibiotics. As a part of our continuous search we had isolated, identified and characterized actinomycetes from the halophilic environment having antagonistic activity against the dermatophytes namely Trichophyton, Microsporum and Epidermophyton. Approach: Actinomycetes were isolated from the soil sample collected from the Ennore saltpan region, Chennai, India and screened for antidermatophytic secondary metabolite production by well diffusion method. Four dermatophytes Trichophyton rubrum [MTCC 3272], Trichophyton mentagrophytes [MTCC 7687], Microsporum gypseum [MTCC 2819] and Epidermophyton floccosum [MTCC 7880] were used to study its susceptibility to the isolated actinomycetes. Actinomycetes which showed antidermatophytic activity were subjected to cultural characterization with respect to aerial and substrate mycelia color, diffusible and melanin pigment production and the growth of the organisms on different media. Further the micro morphological characteristics such as spore surface ornamentation and spore chain morphology determined by Scanning Electron Microscopic (SEM) analysis also suggested that the isolates belonged to the genus Streptomyces. The isolates were also tested for utilization of various carbon and nitrogen sources, degradation of complex compounds, sensitivity to antibiotics and inhibitory compounds. Results: All the 3 isolates exhibited different cultural and morphological characteristics. Based on the cultural characters and morphology they were assigned to the genus Streptomyces. The three isolates produced an inhibition zone of 30-31 mm on an average, utilized a wide range of carbon and nitrogen sources, degraded almost all the complex compounds and exhibited a broad spectrum of antibiotic resistance. They were designated as Streptomyces sp. DKDVIT1, Streptomyces sp. DKDVIT2 and Streptomyces sp., DKDVIT3. Conclusion: The Streptomyces sp. isolated from the Ennore saltpan of Bay of Bengal exhibited potential antidermatophytic activity. The extraction and characterization of secondary metabolites from these Streptomyces may be used as a lead compound/therapeutic agent for dermatophytosis.

Inhibitors of melanogenesis increase toxicity of cyclophosphamide and lymphocytes against melanoma cells

High mortality rate for metastatic melanoma is related to its resistant to the current methods of therapy. Melanogenesis is a metabolic pathway characteristic for normal and malignant melanocytes that can affect the behavior of melanoma cells or its surrounding environment. Human melanoma cells in which production of melanin pigment is dependent on tyrosine levels in medium were used for experiments. Peripheral blood mononuclear cells were derived from the buffy coats purchased from Lifeblood Biological Services. Cell pigmentation was evaluated macroscopically, and tyrosinase activity was measured spectrophotometrically. Cell proliferation and viability were measured using lactate dehydrogenase release MTT, [(3)H]-thymidine incorporation and DNA content analyses, and gene expression was measured by real time RT-PCR. Pigmented melanoma cells were significantly less sensitive to cyclophosphamide and to killing action of IL-2-activated peripheral blood lymphocytes. The inhibition of melanogenesis by either blocking tyrosinase catalytic site or chelating copper ions sensitized melanoma cells towards cytotoxic action of cyclophosphamide, and amplified immunotoxic activities of IL-2 activated lymphocytes. Exogenous L-DOPA inhibited lymphocyte proliferation producing the cell cycle arrest in G1/0 and dramatically inhibited the production of IL-1beta, TNF-alpha, IL-6 and IL-10. Thus, the active melanogenesis could not only impair the cytotoxic action of cyclophosphamid but also has potent immunosuppressive properties. This resistance to a chemotherapeutic agent or immunotoxic activity of lymphocytes could be reverted by the action of tyrosinase inhibitors. Thus, the inhibition of melanogenesis might represent a valid therapeutic target for the management of advanced melanotic melanomas.

Synthesis of tyrosinase inhibitory (4-oxo-4 H-pyran-2-yl)acrylic acid ester derivatives

Melanogenesis is a physiological process that results in the production of melanin pigment. However, excessive accumulations of epidermal pigmentation can cause various hyperpigmentary disorders such as, melasma and age spots. Kojic acid and hydroxylated cinnamic acid derivatives are known to inhibit tyrosinase, a key component of melanin biosynthesis. Pyronyl-acrylic acid esters 3a– i, which share structural features of kojic acid and hydroxylated cinnamic acid, were prepared and their abilities to inhibit tyrosinase and melanin production were evaluated. Of the esters synthesized, 3e and 3h, which derived from diethylene glycol moieties were found to inhibit melanin production by ca. 20% at 20 μg/ml, whereas kojic acid at 200 μg/ml inhibited melanin production by 15.8%.

An update on the honesty of melanin‐based color signals in birds

The control mechanisms and information content of melanin-based color signals in birds have generated much recent interest and controversy among evolutionary biologists. Initial experimental studies on this topic manipulated coarse metrics of an individual's condition (i.e. food intake, disease state) and failed to detect significant condition-dependence of melanin ornament expression. However, three new lines of research appear profitable and target specific factors associated with the production of melanin pigments. These include the role of (i) metals, (ii) amino acids, and (iii) testosterone and social interactions in shaping the extent and intensity of melanin-colored plumage patches. Here, I review recent studies of and evidence for these honesty-reinforcing mechanisms.

Melanin as a virulence factor of Paracoccidioides brasiliensis and other dimorphic pathogenic fungi: a minireview.

Melanin pigments are substances produced by a broad variety of pathogenic microorganisms, including bacteria, fungi, and helminths. Microbes predominantly produce melanin pigment via tyrosinases, laccases, catecholases, and the polyketide synthase pathway. In fungi, melanin is deposited in the cell wall and cytoplasm, and melanin particles ("ghosts") can be isolated from these fungi that have the same size and shape of the original cells. Melanin has been reported in several human pathogenic dimorphic fungi including Paracoccidioides brasiliensis, Sporothrix schenckii, Histoplasma capsulatum, Blastomyces dermatitidis, and Coccidioides posadasii. Melanization appears to contribute to virulence by reducing the susceptibility of melanized fungi to host defense mechanisms and antifungal drugs.

Isolation and characterization of melanin pigment from Pleurotus cystidiosus (telomorph of Antromycopsis macrocarpa)

Melanins are enigmatic pigments that are produced by a wide variety of microorganisms including several species of bacteria and fungi. For more than 40 years, fungi have been known to produce pigments called melanins. Melanin pigment production by mushrooms was not intensively studied. The present study was carried out on isolation and characterization of melanin from an edible mushroom Pleurotus cystidiosus var. formosensis. The mushroom produced dark mucous mass of hyaline arthrospores on mycelium. The coremia exclusively produced dikaryotic arthrospores with the remnant of a clamp connection. Continuous cell extension and division in the coremium stipe supplied cells for arthroconidiation at the coremium apex, which is surrounded by a liquid droplet (coremioliquid). The black coloured coremea (conidia) were produced by Antromycopsis macrocarpa (anamorph of P. cystidiosus) when cultured on potato dextrose agar medium. The agar plate was incubated at continuous light illumination for high amount of pigment (coremea) production. The slimy layer of the coremea was extracted and partially purified by alkaline and acid treatment. The black pigment was confirmed as melanin based on UV, IR and EPR spectra apart from chemical analysis. This is the first report on characterization of melanin obtained from Pleurotus cystidiosus var. formosensis.

SLC24A5 Encodes a trans-Golgi Network Protein with Potassium-dependent Sodium-Calcium Exchange Activity That Regulates Human Epidermal Melanogenesis

A non-synonymous single nucleotide polymorphism in the human SLC24A5 gene is associated with natural human skin color variation. Multiple sequence alignments predict that this gene encodes a member of the potassium-dependent sodium-calcium exchanger family denoted NCKX5. In cultured human epidermal melanocytes we show using affinity-purified antisera that native human NCKX5 runs as a triplet of approximately 43 kDa on SDS-PAGE and is partially localized to the trans-Golgi network. Removal of the NCKX5 protein through small interfering RNA-mediated knockdown disrupts melanogenesis in human and murine melanocytes, causing a significant reduction in melanin pigment production. Using a heterologous expression system, we confirm for the first time that NCKX5 possesses the predicted exchanger activity. Site-directed mutagenesis of NCKX5 and NCKX2 in this system reveals that the non-synonymous single nucleotide polymorphism in SLC24A5 alters a residue that is important for NCKX5 and NCKX2 activity. We suggest that NCKX5 directly regulates human epidermal melanogenesis and natural skin color through its intracellular potassium-dependent exchanger activity.

SOX9 and the tanning response: something new under the sun

SOX9 and the tanning response: something new under the sun

Does p53 regulate skin pigmentation by controlling proopiomelanocortin gene transcription?

A recent issue of Cell highlights an intriguing, unexpected role for p53 as the central regulator of pigmentary responses in tanning and pathologic hyperpigmentation (Cui et al., 2007). Furthermore, in claiming to have provided biochemical and genetic evidence that the UV induction of intracutaneous proopiomelanocortin (POMC) (and its enzymatic cleavage products, a-MSH (melanocyte stimulating hormone) and b-endorphin) is directly controlled by p53, the authors propose that UV-induced tanning mainly follows a linear sequence of events that starts with a p53-mediated activation of the POMC promoter (Cui et al., 2007). The potential clinical significance and the biological implications of the reported findings and concepts necessitate further critical discussion of the experimental evidence, and the conclusions drawn from it, in the context of the available information on the subject. First, a significant part of the authors’ conclusion is based on animal experiments performed with C57BL ⁄6 mice (wild-type and p53 null) mice. However, POMCknockout mice on the same C57BL6 background are well known to show normal melanin pigment production (Slominski et al., 2005a). This observation may weaken the authors’ basic concept and also questions the validity of the proposed main regulatory axis for the suntan response and pathological hyperpigmentation (i.e. UV fi p53 fi POMC fi melanin pigmentation). This central issue requires serious explanation, and should have been carefully discussed by the authors. In our view, published evidence supports the hypothesis that it may not be POMC and its products but rather the melanocortin-1 receptor (MC1-R) that is the key regulator of pigmentation (at least in mice) (Slominski et al., 2004, 2005b). Moreover, in the absence of POMC-derived melanocortins, the MC1-R can regulate melanogenesis through an intrinsic, ligand-independent activity, or can be activated by ligands other than melanocortins (Sanchez-Mas et al., 2004; Slominski et al., 2005a,b). Furthermore, the authors do not appear to acknowledge that the regulation of melanocyte behavior, including melanogenesis control, is very heterogeneous and multi-directional; this further underscores the complexity of microenvironment – specific controls in pigmentation, which cannot be satisfactorily explained by an organization consisting of simple linear sequences (Nordlund et al., 2006; Slominski et al., 2004). On this background, we consider it more likely that p53 acts as one important coordinator (among others), but not as the main or sole regulator of pigmentation in the suntan response and pathological hyperpigmentation. Second, the authors provide evidence for direct induction of POMC transcription by p53, yet show only for a moderate increase of POMC precursor immunoreactivity (no evidence is presented that the selected immunoreactive band in their Figures 1 and 2 actually represents POMC). In this context, the surprising, highly unconventional sequence of reported events (e.g. p53 induction by UV is maximal by 3 h, POMC immunoreactivity reportedly peaks at 6 h, but its mRNA transcription at 24 h) requires explanation. Moreover, the authors fail to show conclusive evidence that the detected immunoreactivities (which, again, are rather unconventional: e.g. nuclear location of a-MSH in keratinocytes) indeed represent a-MSH or b-endorphin peptides, as claimed (confirmatory HPLC (high performance liquid chromatography) or mass spectrometry evaluations of representative extracts were not performed). Also, after transcription POMC mRNA is generated by splicing, which then is translated into a protein precursor of approximately 30 kDa. This precursor is further processed in a cell type-specific and tissue microenvironment-specific manner through complex, sequential post-translational modifications (including endoand exopeptidase cleavage, amidation and acetylation), which end with the regulated secretion of the final product (Slominski et al., 2000; Smith and Funder, 1988). The complexity of these events, in fact, renders it rather unlikely that p53 would directly regulate production and release of a-MSH or b-endorphin (however, indirect effects are quite possible).

Dietary mineral content influences the expression of melanin-based ornamental coloration

Many animals develop bold patches of black or brown coloration that are derived from melanin pigments and serve as sexual or social signals. At present, there is much debate among behavioral ecologists over whether melanin-based color signals are costly to produce. Studies that have manipulated crude aspects of nutrition (i.e., total food intake) or health have generally found melanin-based plumage ornaments to be less responsive to such factors than other types of extravagant color (e.g., carotenoid or structural based). However, a recently advanced hypothesis argues that limited minerals in the diet, such as calcium (Ca), zinc (Zn), and iron (Fe), may serve to increase melanin pigment production and maintain signal honesty. Here, I experimentally tested whether variation in the calcium content of the diet affects the color and extent of melanin-based plumage in male zebra finches (Taeniopygia guttata). Calcium supplementation increased the size, but not darkness, of the black breast plumage patch in fledgling and adult males; however, sexually selected, carotenoid-based red beak coloration was not affected by the diet manipulation. These results are the first to support the idea that acquisition of minerals from the diet is a unique, limiting factor for the expression of ornamental melanin coloration in animals. Key words: calcium, honest signaling, plumage pigmentation, Taeniopygia guttata, zebra finch. [Behav Ecol]

The Repeat Domain of the Melanosomal Matrix Protein PMEL17/GP100 Is Required for the Formation of Organellar Fibers

Over 125 pigmentation-related genes have been identified to date. Of those, PMEL17/GP100 has been widely studied as a melanoma-specific antigen as well as a protein required for the formation of fibrils in melanosomes. PMEL17 is synthesized, glycosylated, processed, and delivered to melanosomes, allowing them to mature from amorphous round vesicles to elongated fibrillar structures. In contrast to other melanosomal proteins such as TYR and TYRP1, the processing and sorting of PMEL17 is highly complex. Monoclonal antibody HMB45 is commonly used for melanoma detection, but has the added advantage that it specifically reacts with sialylated PMEL17 in the fibrillar matrix in melanosomes. In this study, we generated mutant forms of PMEL17 to clarify the subdomain of PMEL17 required for formation of the fibrillar matrix, a process critical to pigmentation. The internal proline/serine/threonine-rich repeat domain (called the RPT domain) of PMEL17 undergoes variable proteolytic cleavage. Deletion of the RPT domain abolished its recognition by HMB45 and its capacity to form fibrils. Truncation of the C-terminal domain did not significantly affect the processing or trafficking of PMEL17, but, in contrast, deletion of the N-terminal domain abrogated both. We conclude that the RPT domain is essential for its function in generating the fibrillar matrix of melanosomes and that the luminal domain is necessary for its correct processing and trafficking to those organelles.