Research Techniques Made Simple: Cell Biology Methods for the Analysis of Pigmentation (original) (raw)
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Melanin Transfer and Fate within Keratinocytes in Human Skin Pigmentation
Integrative and Comparative Biology, 2021
Synopsis Human skin and hair pigmentation play important roles in social behavior but also in photoprotection from the harmful effects of ultraviolet light. The main pigments in mammalian skin, the melanins, are synthesized within specialized organelles called melanosomes in melanocytes, which sit at the basal layer of the epidermis and the hair bulb. The melanins are then transferred from melanocytes to keratinocytes, where they accumulate perinuclearly in membrane-bound organelles as a “cap” above the nucleus. The mechanism of transfer, the nature of the pigmented organelles within keratinocytes, and the mechanism governing their intracellular positioning are all debated and poorly understood, but likely play an important role in the photoprotective properties of melanin in the skin. Here, we detail our current understanding of these processes and present a guideline for future experimentation in this area.
Melanocyte biology and skin pigmentation
Nature, 2007
Melanocytes can absorb ultraviolet radiation (UVR) and survive considerable genotoxic stress. The skin is the main barrier to the external environment, and relies on melanocytes to provide, among other things, photoprotection and thermoregulation by producing melanin. The degree of pigment production manifests as skin 'phototype' (skin colour and ease of tanning) 1 and is the most useful predictor of human skin cancer risk in the general population. The colours we see in feathers, fur and skin are largely determined by melanocytes. In addition to carotenoids and haemoglobin, melanin is the main contributor to pigmentation. There are two main types of melanin-red/yellow pheomelanin and brown/black eumelanin. Melanincontaining granules are known as melanosomes and are exported from melanocytes to adjacent keratinocytes, where most pigment is found. As a result, pigmentation differences can arise from variation in the number, size, composition and distribution of melanosomes, whereas melanocyte numbers typically remain relatively constant (Fig. 1a, b). Mutations affecting pigmentation have been identified in many species because they are easily recognizable. Such mutants can be categorized into four groups: hypopigmentation and hyperpigmentation, with or without altered melanocyte number. These phenotypic distinctions have afforded the opportunity to easily classify genes affecting the melanocyte lineage, with respect to viability or differentiation (or both). Some of these mutants function in non-cell-autonomous manner, thereby further revealing cellcell communication pathways of physiological importance. Collectively, pigmentation or coat colour mutants have become an invaluable resource for the analysis of melanocyte differentiation and as a model for the broader fields of neural-crest development and mammalian genetics. There are two discrete melanocytic populations in hair follicles: melanocyte stem cells and their differentiated progeny, which reside in geographically distinct locations to comprise a follicular unit that is tightly linked to the surrounding keratinocyte population. Hair follicle melanocyte stem cells have important roles in both normal hair pigmentation and senile hair greying, and specific genetic defects have shed further light on the survival properties of this cell population. This review summarizes how pigmentation is regulated at the molecular level and how the tanning response provides protection against damage and skin cancer. We discuss recent advances in our knowledge of the genes involved in these processes and how they affect skin and hair colour. We also cover the developmental origin of melanocytes and how they are maintained by melanoblast stem cells, whose eventual depletion may contribute to hair greying. Finally, we detail some questions that research into melanocyte biology hopes to address in the future.
Muscle Cell and Tissue, 2015
Melanocytes are specialized dendritic melanin producing pigment cells, which have originated from the pluripotent embryonic cells and are termed as neural crest cells (NCC). The primary locations of these cells are basal layer of epidermis and hair follicles. Besides this, they are also found in the inner ear, nervous system, and heart with spatial specific functions. There are other cells able to produce melanin but of different embryonic origin (pigmented epithelium of retina, some neurons, and adipocytes). Melanocytes of the epidermis and hair are cells which share some common structural features but in general they form biologically different populations living in unique niches of the skin. Ultra structurally, melanocytes differ from each other on the basis of their locations and function. Principal function of epidermal melanocytes is photoprotection and thermoregulation by packaging melanin pigment into melanosomes and delivering them to neighboring keratinocytes. It is unfair to think that melanocytes reap all the glory for their role in pigmenting the skin and providing it critical protection against UV damage. They probably play a significant role in diverse physiological functions and their particular functions in all target places are much wider than the melanin synthesis only. Alternation in any structure and function of these pigmentary cells affects the process of pigmentation/melanogenesis which leads to pigmentary disorders like hyperpigmentation or hypopigmentation.
Human hair melanins: what we have learned and have not learned from mouse coat color pigmentation
Pigment Cell & Melanoma Research, 2011
Hair pigmentation is one of the most conspicuous phenotypes in humans. Melanocytes produce two distinct types of melanin pigment: brown to black, indolic eumelanin and yellow to reddish brown, sulfur-containing pheomelanin. Biochemically, the precursor tyrosine and the key enzyme tyrosinase and the tyrosinase-related proteins are involved in eumelanogenesis, while only the additional presence of cysteine is necessary for pheomelanogenesis. Other important proteins involved in melanogenesis include P protein, MATP protein, a-MSH, agouti signaling protein (ASIP), MC1R (the receptor for MSH and ASIP), and SLC7A11, a cystine transporter. Many studies have examined the effects of loss-of-function mutations of those proteins on mouse coat color pigmentation. In contrast, much less is known regarding the effects of mutations of the corresponding proteins on human hair pigmentation except for MC1R polymorphisms that lead to pheomelanogenesis. This perspective will discuss what we have ⁄ have not learned from mouse coat color pigmentation, with special emphasis on the significant roles of pH and the level of cysteine in melanosomes in controlling melanogenesis. Based on these data, a hypothesis is proposed to explain the diversity of human hair pigmentation.
Melanin Transfer in the Epidermis: The Pursuit of Skin Pigmentation Control Mechanisms
International Journal of Molecular Sciences, 2021
The mechanisms by which the pigment melanin is transferred from melanocytes and processed within keratinocytes to achieve skin pigmentation remain ill-characterized. Nevertheless, several models have emerged in the past decades to explain the transfer process. Here, we review the proposed models for melanin transfer in the skin epidermis, the available evidence supporting each one, and the recent observations in favor of the exo/phagocytosis and shed vesicles models. In order to reconcile the transfer models, we propose that different mechanisms could co-exist to sustain skin pigmentation under different conditions. We also discuss the limited knowledge about melanin processing within keratinocytes. Finally, we pinpoint new questions that ought to be addressed to solve the long-lasting quest for the understanding of how basal skin pigmentation is controlled. This knowledge will allow the emergence of new strategies to treat pigmentary disorders that cause a significant socio-economi...
Epidermal Keratinocytes from Light vs. Dark Skin Exhibit Differential Degradation of Melanosomes
Journal of Investigative Dermatology, 2011
Modification of skin complexion coloration has traditionally been accomplished by interruption or attenuation of melanogenesis and/or melanosome transfer. Post-transfer modification of pigmented melanosomes provides an attractive and distinct avenue of modulating skin pigmentation. The processing of melanosomes during keratinocyte (KC) terminal differentiation and the degradative variability observed between light and dark skin (LS and DS) remains enigmatic. To evaluate this, we developed a model system to investigate the loss of fluorescently labeled and isolated melanosomes by cultured human KCs. The extent of melanosome loss has been qualitatively assessed using transmission electron microscopy and indirect immunofluorescence with confocal microscopy, and quantitatively assessed using flow cytometry analysis. Results show that melanosomes are incorporated into the cytoplasm of both light and dark keratinocytes (LKCs and DKCs) and trafficked to a perinuclear region. Within 48 hours, confocal microscopy images suggest that LKCs display accelerated melanosome loss. This time-dependent decrease in carboxyfluorescein diacetate (CFDA) fluorescence was then quantitatively analyzed using flow cytometry. Consistent with the results of the confocal analysis, over a 48-hour time frame, LKCs appear to lose melanosomes more efficiently than DKCs. These experiments show that melanosomes are more rapidly lost in KCs derived from LS as opposed to DS. Abbreviations: CFDA, carboxyfluorescein diacetate; DKC, dark keratinocyte; DS, dark skin; KC, keratinocyte; LKC, light keratinocyte; LS, light skin; Md X, median X; PE, R-phycoerythrin; TEM, transmission electron microscopy Yoshida Y, Hachiya A, Sriwiriyanont P et al. (2007) Functional analysis of keratinocytes in skin color using a human skin substitute model composed of cells derived from different skin pigmentation types.
Melanins and melanogenesis: methods, standards, protocols
Pigment Cell & Melanoma Research, 2013
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Physiological factors that regulate skin pigmentation
BioFactors, 2009
More than 150 genes have been identified that affect skin color either directly or indirectly, and we review current understanding of physiological factors that regulate skin pigmentation. We focus on melanosome biogenesis, transport and transfer, melanogenic regulators in melanocytes, and factors derived from keratinocytes, fibroblasts, endothelial cells, hormones, inflammatory cells, and nerves. Enzymatic components of melanosomes include tyrosinase, tyrosinase‐related protein 1, and dopachrome tautomerase, which depend on the functions of OA1, P, MATP, ATP7A, and BLOC‐1 to synthesize eumelanins and pheomelanins. The main structural component of melanosomes is Pmel17/gp100/Silv, whose sorting involves adaptor protein 1A (AP1A), AP1B, AP2, and spectrin, as well as a chaperone‐like component, MART‐1. During their maturation, melanosomes move from the perinuclear area toward the plasma membrane. Microtubules, dynein, kinesin, actin filaments, Rab27a, melanophilin, myosin Va, and Slp2...
Chemical and biochemical control of skin pigmentation with special emphasis on mixed melanogenesis
Pigment Cell & Melanoma Research, 2021
Melanin pigments, widely distributed in vertebrates, are composed of insoluble brown to black pigments termed eumelanin (EM) and alkalisoluble yellow to reddish-brown pigments termed pheomelanin (PM) (Ito & Wakamatsu, 2003, 2008). Melanin pigments in vertebrates are produced in melanocytes within membrane-bound organelles termed melanosomes; thereafter, the melanosomes in the hair follicle and epidermal melanocytes are transferred to the surrounding keratinocytes leading to a diverse range of hair and skin colors (Del