In mammals, the melanin pigment is produced in two cell types of distinct developmental origins. The melanocytes of the skin originate form the neural crest whereas the retinal pigment epithelium (RPE) of the eye originates from the optic cup. The genetic programs governing these two cell types are thus quite different but have evolved to allow the expression of pigment cell-specific genes such as the three members of the tyrosinase-related family. Tyrosinase, Tyrp1 and Dct promoters contain a motif termed E-box which is bound by the transcription factor Mitf. These E-boxes are also found in the promoters of the corresponding fish genes, thus highlighting the pivotal role of Mitf in pigment cell-specific gene regulation. Mitf, which displays cell type-specific isoforms, transactivates the promoters of the tyrosinase gene family in both pigment cell lineages. However, specific DNA motifs have been found in these promoters, and they correspond to binding sites for RPE-specific factors such as Otx2 or for melanocyte-specific factors such as Sox10 or Pax3. The regulation of pigment cell-specific expression is also controlled by genetic elements located outside of the promoter, such as the tyrosinase distal regulatory element located at -15 kb which acts as a melanocyte-specific enhancer but also protects from spreading of condensed chromatin. Thus, by using the tyrosinase gene family as a model, it is possible to define the transcription factor networks that govern pigment production in either melanocytes or RPE.
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"The members of the tyrosinase-related family (tyrosinase and tyrosinase-related proteins TRP-1 (DHICAoxidase) and TRP-2, DOPAchrome tautomerase (Del Marmol and Beermann 1996) are also involved in the process of melanogenesis leading to the production of either eumelanin (brown-black) or pheomelanin (yellow-red). This difference in colour development in cell-specific pigment is regulated by MITF through transactivation of the promoters of the tyrosinase gene family (Murisier and Beermann 2006). The overall production of melanin is orchestrated by the pituitary through secretion of melanocyte-stimulating hormone and other cleavage products of a large precursor peptide proopiomelanocortin (Pritchard et al. 2002). "
[Show abstract][Hide abstract]ABSTRACT: The pigments found in plants, animals and humic substances are well described and classified. In humans considerable progress has been made with the main pigment melanin in defining its biochemistry, the different types and function. However, analytical techniques to show these differences in vivo are still not readily available. NMR and IR spectroscopy are relatively insensitive and reveal only major structural differences. Techniques utilising MS are useful in determining elemental content but require further studies to optimise conditions for accurate mass analysis. How the components may be structurally organised seems to be the most problematic with scanning TEM and the improved FTIR of use in this respect. As regards understanding the nature of the pigment related to HGA seen in patients with Alkaptonuria (AKU), it is still thought of as a melaninlike pigment simply because of its colour and likewise thought to be a polymer of undetermined size. It is important that detailed analysis be carried out to define more accurately this pigment. However, observations suggest it to be the same as the HGA-derived pigment, pyomelanin, produced by bacteria and containing both quinone and phenolic groups. The interesting developments in alkaptonuria will be to understand how such a polymer can cause such profound collagen and connective tissue damage and how best to reverse this process.
"Contrary, animals not exposed to light are often colorless, such as cavefish and nematodes (Singh and Nüsslein Volhard, 2015). Three members of the tyrosinase-related family (tyrosinase, tyrosinase-related protein-1 (Tyrp1), and dopachrome tautomerase (dct or Tyrp2)) are involved in melanogenesis, leading to the production of either eumelanin (brownblack ) or pheomelanin (yellow-red), which are both derived from L-tyrosine (Murisier and Beermann, 2006; Krauss et al., 2014). The synthesis of both melanin forms occurs within unique melanocyte organelles -the melanosomes. "
[Show abstract][Hide abstract]ABSTRACT: Retinoic acid (RA) signaling exerts several important functions during vertebrate development. Several cell types derived from neural crest cells (NCC) have been shown to require balanced RA levels for their development. The neural crest is a transient, multipotent embryonic tissue, which also gives rise to melanophores and other pigment cell types. Here, I examined whether RA signaling is involved in NCC-derived melanophore development.
My results indicate that enhanced RA levels cause hyperpigmentation in zebrafish larvae by increasing the melanoblast population, most likely by interfering with NCC development. I suggest that RA acts on NCCs, through either enhancing NCC induction, promoting proliferation, or inhibiting NCC apoptosis. It remains to be shown whether RA exerts additional functions within the melanophore lineage or, if the observations are primarily caused by RA´s well known function within NCC development.
"Ultraviolet radiation triggers the activation of p53 gene through DNA damage in the nucleus of keratinocytes (Lin and Fisher, 2007).This increases the modulation of gene encoding the propiomelanocortin (POMC) (Abdel et al., 2001). Posttranscriptional modification of POMC stimulates the production of melanocyte stimulating hormone (MSH) and β-endorphin (Biossy, 1988 and Rouzand et al., 2005).MSH is transported to the melanocytes where it binds to the melanocortin 1 receptor (MCR1) which activates cAMP response element binding protein (CREB) through downstream stimulation of cAMP (Storm and Elder, 2006 and Murisier and Beermann, 2006). The melanocyte master regulator MITF is activated further channelizing the transcription and modification of melanogenic enzymes with tyrosinase, thereby inducing the production of melanin pigment which is actively transported from the melanocytes in the dermis to the keratinocytes located in the epidermis where the pigment vesicles accumulate over the photo exposed surface of the nucleus subsequently causing tanning as a consequence (Thody and Graham, 1998). "
[Show abstract][Hide abstract]ABSTRACT: Human phenotype including skin colour patterns is associated with genetic, evolutional as well as cultural aspects which rely on production of melanin. Melasma is crucial disorder related to the skin that affects the population. The aim of this study was to evaluate the various contributing circulating biochemical markers that could be responsible for melasma. Fifty (50) patients suffering from melasma and twenty (20) clinically healthy individuals were selected for this study. Lipid profile as well as oxidative and anti-oxidative profiles was estimated in patients and healthy individuals. HDL was decreased in patients (1.39±0.10∗) as compared to control (1.73±0.17) group. On contrary, TCh (5.48±0.92∗), Tg (2.59±0.53∗), and LDL (2.48±0.23∗) were raised in patients. Alterations in lipid profile were statistically significant (P<0.05). Malondialdehyde (MDA) was elevated (5.44±1.14∗) in patients while anti-oxidative parameters were decreased in patients and all were statistically significant (P<0.05). It can be concluded that not only the melanin but also other circulating biomarkers like cholesterol, Tg, HDL and LDL may be the contributing factors for the progression of melasma. Moreover, oxidative stress markers may also be used in disease prognosis and diagnosis.
Full-text · Article · Jan 2015 · Pakistan Journal of Medical and Health Sciences