Disease relevance of Melanophores

• When melanophores express the small t antigen of SV-40 virus, a specific inhibitor of protein phosphatase 2A (PP2A), aggregation is completely prevented [1].
• Synthesis and structure-function studies of melanocyte stimulating hormone analogues modified in the 2 and 4(7) positions: comparison of activities on frog skin melanophores and melanoma adenylate cyclase [2].
• In Xenopus melanophores, melatonin induces a rapid perinuclear aggregation of intracellular pigment which is associated with a pertussis toxin-sensitive inhibition of cAMP [3].
• Toxicity of 0.3 ppm (96 h LC50 value) and 0.03 ppm of mercuric chloride on the melanophores of the skin at different time intervals has been studied [4].

High impact information on Melanophores

• It is well established that the melanotropins alpha- and beta-MSH are responsible for pigment dispersion in the integumentary melanophore of lower vertebrates and that these molecules are derived from a common precursor protein, proopiocortin, by specific processing within the intermediate lobe [5].
• In melanophores, Agouti protein has no effect in the absence of alpha-MSH, but its action cannot be explained solely by inhibition of alpha-MSH binding [6].
• We have used a sensitive bioassay based on Xenopus melanophores to characterize pharmacologic properties of recombinant Agouti protein, and have directly measured its cell-surface binding to mammalian cells by use of an epitope-tagged form (HA-Agouti) that retains biologic activity [6].
• Melatonin was first isolated from bovine pineal extracts in 1958 by Lerner and his colleagues (2), who used as a marker the capacity of the hormone to aggregate the pigment granules in amphibian melanophores around the cell nucleus [7].
• We find that cytoplasmic dynein, dynactin, and kinesin II remain on pigment granules during aggregation and dispersion in melanophores, indicating that control of direction is not mediated by a cyclic association of motors with these organelles [8].

Chemical compound and disease context of Melanophores

• In this report we show that both pertussis toxin and dibutyryl-adenosine-3',5'-monophosphate block the ability of light to cause photoaggregation of pigment in cultured tail-fin melanophores, whereas dibutyryl-guanosine-3',5'-monophosphate is without effect [9].
• Pertussis toxin (PT) has been found to block noradrenaline-induced pigment aggregation in fish melanophores, and, based on this, a rapid and highly sensitive assay for PT was developed [10].
• MSH stimulates (1) rapid translocation of melanosomes (melanin granules) in dermal melanophores to effect rapid colour change and (2) melanogenesis in normal and abnormal (melanoma) epidermal melanocytes [11].

Biological context of Melanophores

• Down-regulation of melanocortin receptor signaling mediated by the amino terminus of Agouti protein in Xenopus melanophores [12].
• A cDNA encoding for ETcR was isolated by a polymerase chain reaction-mediated DNA amplification strategy using degenerate oligonucleotides prepared based on conserved regions of other known G-protein-coupled receptor sequences and by the subsequent screening of a frog melanophore cDNA library [13].
• The effects of ap-2alpha MO injected into heterozygous and homozygous c-kit mutants support the notion that Ap-2alpha works through C-kit and additional target genes to mediate melanophore cell number and migration [14].
• Transient transfection of NPY1, NPY2, NPY4, CXCR4, and CCR5 cDNA produced increased light transmittance through melanophores (consistent with G(i)-protein activation) [15].
• These results indicate that although receptor density does decline on prolonged treatment, this is not responsible for the diminishing melatonin potency, which is entirely due to degradation of melatonin by deacetylation and subsequent deamination in melanophores [16].

Anatomical context of Melanophores

• Iontophoretic release of cyclic AMP and dispersion of melanosomes within a single melanophore [17].
• Regulation of organelle movement in melanophores by protein kinase A (PKA), protein kinase C (PKC), and protein phosphatase 2A (PP2A) [1].
• We investigate how the combined system of myosin-V motors plus actin filaments is used to transport pigment granules in Xenopus melanophores [18].
• These results demonstrate that melanophore development in fish and mammals shares a dependence on the nacre/Mitf transcription factor, but that proper development of the retinal pigment epithelium in the fish is not nacre-dependent, suggesting an evolutionary divergence in the function of this gene [19].
• Therefore, teleost melanophores possess a developed radial system of vimentin intermediate filaments [20].

Associations of Melanophores with chemical compounds

• Gentle lysis of the melanophores resulted in a permeabilized cell model, which, in the absence of exogenous ATP, could undergo multiple rounds of pigment granule aggregation and dispersion when sequentially challenged with epinephrine and cAMP [21].
• Previous studies suggest that melanophores regulate the direction of pigment movements via changes in intracellular cAMP (Rozdzial and Haimo, 1986a; Sammak et al., 1992), whereas erythrophores may use calcium- (Ca(2+)-) based regulation (Luby-Phelps and Porter, 1982; McNiven and Ward, 1988) [22].
• In addition, no changes were observed for injections of 5'-AMP or cyclic guanosine monophosphate (GMP) through electrodes positioned inside or adjacent to melanophores [17].
• In the zebrafish D. rerio, alternating light and dark horizontal stripes develop, in part, owing to interactions between melanophores and cells of the xanthophore lineage that depend on the fms receptor tyrosine kinase; zebrafish fms mutants lack xanthophores and have disrupted melanophore stripes [23].
• In contrast, neural-crest-derived melanophores were abundant even in aneural larvae [24].

Gene context of Melanophores

• These findings show that the essential function of sox10 in melanophore development is limited to transcriptional regulation of mitfa [25].
• This rescue of melanophores in sox10(-/-) embryos is quantitatively indistinguishable from rescue in mitfa(-/-) embryos [25].
• Cloning and characterization of an endothelin-3 specific receptor (ETC receptor) from Xenopus laevis dermal melanophores [13].
• We use epistasis analyses to show that puma promotes the development of both early-appearing metamorphic melanophores that depend on the kit receptor tyrosine kinase, as well as late-appearing metamorphic melanophores that depend on both the G-protein-coupled endothelin receptor b1 (ednrb1) and the kit-related fms receptor tyrosine kinase [26].
• Melanin-concentrating hormone (MCH) is a neuropeptide occurring in all vertebrates and some invertebrates and is now known to stimulate pigment aggregation in teleost melanophores and food-intake in mammals [27].

Analytical, diagnostic and therapeutic context of Melanophores

• Selective dispersion of melanosomes was often observed after iontophoretic injection of cyclic adenosine monophosphate (AMP) from a glass microelectrode positioned in a target melanophore in frog skin (as viewed from above through a microscope), with other melanophores in the field serving as controls [17].
• In situ hybridization studies using probes derived from these retinal opsins, together with parapinopsin, reveal no expression of retinal opsins in pineal and parapineal organ and no expression of any opsin tested in the "deep brain," iris, or dermal melanophores [28].
• Immunoblotting experiments showed the presence of the intermediate filament protein vimentin in melanophore lysates [20].
• Stereo high voltage electron microscopy of melanophores. Matrix transformations during pigment movements and the effects of cold and colchicine [29].
• We demonstrate that the differentiation of xanthophores is enhanced, while that of the melanophores are inhibited in guanosine-supplemented neural crest cell cultures [30].

References