Hirobe T. Structure and function of melanocytes: Microscopic morphology and cell biology of mouse melanocytes in the epidermis and hair follicle. Histol Histopathol10: 223-237
Division of Biology, National Institute of Radiological Sciences, Chiba, Japan. Histology and histopathology
(Impact Factor: 2.1).
Melanocytes characterized by their tyrosinase activity, melanosomes and dendrites locate in the basal layer of epidermis and hair bulb in the skin of mice. Melanocytes differentiate from undifferentiated melanoblasts derived from embryonic neural crest. Melanocyte-stimulating hormone plays an important role in the regulation of the differentiation of mouse melanocytes in the epidermis and hair bulb by inducing tyrosinase activity, melanosome formation, transfer of melanosomes and increased dendritogenesis. The proliferative activity of differentiating epidermal melanocytes of newborn mice during the healing of skin wounds is regulated by semidominant genes, suggesting that the genes are involved in regulating the proliferative activity of epidermal melanocytes during differentiation. The morphology and differentiated functions of mouse melanocytes are shown to be influenced by environmental factors such as ultraviolet and ionizing radiations. From the results of serum-free culture of mouse epidermal melanoblasts, basic fibroblast growth factor is shown to stimulate the sustained proliferation of melanoblasts in the presence of dibutyryl adenosine 3',5'-cyclic monophosphate and keratinocytes. In contrast, melanocyte differentiation in serum-free culture is induced by melanocyte-stimulating hormone in the presence of keratinocytes. These results suggest that the structure and function of mouse melanocytes in the epidermis and hair bulb are controlled by both genetic factors and local tissue environment, such as hormones and growth factors.
Available from: Amadi O Ihunwo
- "In mammals, skin or coat colour is essentially determined by melanocytes either situated in the epidermis or the hair bulb. These specialised cells synthesize melanin in membrane-bound organelles termed melanosomes, which are transferred through dendritic processes to their final destination [8, 12, 13, 29]. Melanocytes are specialised cells found between the stratum basale cells and in hair follicles [8–10, 12–14], although their precise distribution in mammalian skin is different from one species to another . "
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ABSTRACT: The four-striped mouse has a grey to brown coloured coat with four characteristic dark stripes interspersed with three lighter stripes running along its back. The histological differences in the skin of the juvenile and adult mouse were investigated by Haematoxylin and Eosin and Masson Trichrome staining, while melanocytes in the skin were studied through melanin-specific Ferro-ferricyanide staining. The ultrastructure of the juvenile skin, hair follicles, and melanocytes was also explored. In both the juvenile and adult four-striped mouse, pigment-containing cells were observed in the dermis and were homogeneously dispersed throughout this layer. Apart from these cells, the histology of the skin of the adult four-striped mouse was similar to normal mammalian skin. In the juvenile four-striped mouse, abundant hair follicles of varying sizes were observed in the dermis and hypodermis, while hair follicles of similar size were only present in the dermis of adult four-striped mouse. Ultrastructural analysis of juvenile hair follicles revealed that the arrangement and differentiation of cellular layers were typical of a mammal. This study therefore provides unique transition pattern in the four-striped mouse skin morphology different from the textbook description of the normal mammalian skin.
Available from: Yohei Hirai
- "Melanocytes are scattered about basal layer of skin epidermis and the hair matrix in hair bulbs. They produce melanin granules and transfer the granule-containing melanosomes to adjacent keratinocytes, thus inducing epidermal/hair pigmentation (Hirobe, 1995; Kondo and Hearing, 2011). In the melanocyte cytoplasm, melanin exerts an intrinsically cohesive effect which gives rise to the large granules in a lysosome-related organelle melanosome. "
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ABSTRACT: The melanin granules are synthesized in melanocytes in the epidermal basal layer and the hair matrix. For the effective passage of melanin granules to the adjacent keratinocytes, melanocytes utilize unique cytoplasmic delivery system in which cytoskeletal network is prominently involved. Here, we show that the t-SNARE protein syntaxin3, a member of a family of key mediators of the cytoplasmic vesicle fusion and potent modulators of cytoskeletal dynamics, dramatically affects melanocyte cell behavior. Although plasmalemmal syntaxin3 has been detected also on the melanosomes of normal human melanocytes, we noticed that mouse melanoma B16 cells had completely lost endogenous syntaxin3. In response to the forcible expression of syntaxin3, B16 cells formed well-developed dendritic filopodia and accumulated melanin granules in the cytoplasm. We found that exogenous syntaxin3 was not expressed at the plasma membrane, but rather, localized with non-fibrous F-actin and melanin-packed melanosomes in the cytoplasm, by which the assembly/polymerization of actin was dramatically impacted and the melanosome secretion was severely suppressed. The syntaxin3-triggered phenotypic changes were also induced by a syntaxin3 mutant lacking SNARE and transmembrane domains, and they were completely reverted by the subsequent knockdown of exogenous syntaxin3. This t-SNARE protein may act as a regulator of the actin dynamics, rather than a direct vesicle fusion mediator, to determine the fundamental properties of melanocytes.
Available from: Tomohisa Hirobe
- "In addition, the so-called bystander effect or the interaction between melanoblasts/melanocytes and keratinocytes or fibroblasts may be relevant here. The mouse epidermis consists mostly of keratinocytes (approximately 98%) and a few melanoblasts/melanocytes (approximately 2%), and the dermis is composed predominantly of fibroblasts, in addition to melanoblasts/melanocytes, endothelial cells and blood cells . Hair follicles are made up of melanoblasts/melanocytes, keratinocytes and fibroblasts. "
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ABSTRACT: The effects of prenatal low-dose irradiation with heavy ions on embryonic development in mice and on melanocyte differentiation are not well understood. We performed whole-body irradiation of pregnant C57BL/10J mice at embryonic Day 9 (E9) with a single dose of γ-rays, silicon, argon or iron ions. The number of living embryos and embryonic body weight at E18 decreased after exposure to heavy ions at high doses. Malformations such as small eyes and limb anomalies were observed in heavy-ion-treated embryos, but not in γ-ray-treated embryos. The frequency of abnormally curved tails was increased by exposure to γ-rays and argon and iron ions even at a dose of 0.1 Gy (P < 0.05). In contrast, a dose-dependent decrease in the number of epidermal melanoblasts/melanocytes and hair bulb melanocytes was observed after 0.1 Gy irradiation with γ-rays or heavy ions (P < 0.01). The decrease in the number of dorsal hair bulb melanocytes, dorsal and ventral epidermal melanoblasts/melanocytes and ventral hair bulb melanocytes was not necessarily correlated with the linear energy transfer of the radiation tested. Moreover, the effects of heavy ions were larger on the ventral skin than on the dorsal skin, indicating that the sensitivity of melanocytes to heavy ions differs between the dorsal and ventral skin. Taken together, these results suggest that the effects of the low-dose heavy ions differ between cell types and tissues, and the effects on the prenatal development of mice and melanocyte development are not necessarily greater than those of γ-rays.
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