Cutaneous photobiology. The melanocyte vs. the sun: who will win the final round?

Solar ultraviolet radiation (UV) is a major environmental factor that dramatically alters the homeostasis of the skin as an organ by affecting the survival, proliferation and differentiation of various cutaneous cell types. The effects of UV on the skin include direct damage to DNA, apoptosis, growth arrest, and stimulation of melanogenesis. Long-term effects of UV include photoaging and photocarcinogenesis. Epidermal melanocytes synthesize two main types of melanin: eumelanin and pheomelanin. Melanin, particularly eumelanin, represents the major photoprotective mechanism in the skin. Melanin limits the extent of UV penetration through the epidermal layers, and scavenges reactive oxygen radicals that may lead to oxidative DNA damage. The extent of UV-induced DNA damage and the incidence of skin cancer are inversely correlated with total melanin content of the skin. Given the importance of the melanocyte in guarding against the adverse effects of UV and the fact that the melanocyte has a low self-renewal capacity, it is critical to maintain its survival and genomic integrity in order to prevent malignant transformation to melanoma, the most fatal form of skin cancer. Melanocyte transformation to melanoma involves the activation of certain oncogenes and the inactivation of specific tumor suppressor genes. This review summarizes the current state of knowledge about the role of melanin and the melanocyte in photoprotection, the responses of melanocytes to UV, the signaling pathways that mediate the biological effects of UV on melanocytes, and the most common genetic alterations that lead to melanoma.     

Cutaneous Photobiology. The Melanocyte vs. the Sun: Who Will Win the Final Round?

Solar ultraviolet radiation (UV) is a major environmental factor that dramatically alters the homeostasis of the skin as an organ by affecting the survival, proliferation and differentiation of various cutaneous cell types. The effects of UV on the skin include direct damage to DNA, apoptosis, growth arrest, and stimulation of melanogenesis. Long‐term effects of UV include photoaging and photocarcinogenesis. Epidermal melanocytes synthesize two main types of melanin: eumelanin and pheomelanin. Melanin, particularly eumelanin, represents the major photoprotective mechanism in the skin. Melanin limits the extent of UV penetration through the epidermal layers, and scavenges reactive oxygen radicals that may lead to oxidative DNA damage. The extent of UV‐induced DNA damage and the incidence of skin cancer are inversely correlated with total melanin content of the skin. Given the importance of the melanocyte in guarding against the adverse effects of UV and the fact that the melanocyte has a low self‐renewal capacity, it is critical to maintain its survival and genomic integrity in order to prevent malignant transformation to melanoma, the most fatal form of skin cancer. Melanocyte transformation to melanoma involves the activation of certain oncogenes and the inactivation of specific tumor suppressor genes. This review summarizes the current state of knowledge about the role of melanin and the melanocyte in photoprotection, the responses of melanocytes to UV, the signaling pathways that mediate the biological effects of UV on melanocytes, and the most common genetic alterations that lead to melanoma.     

The lobose amebas: II. A new ameba of the “Proteus” group,polychaos nitidubia N. Sp.

Summary A new ameba of the 'proteus group, Polychaos nitidubia n. sp., is found in lakes, ponds and streams of the State of Florida, United States of America. It resembles both Polychaos dubia (A. A. Schaeffer, 1916) and Amoeba nitida E. Penard, 1902, in certain respects, but it is distinct from either. It resembles P. dubia in its pseudopodal forms and movements and also in the presence of clumped crystals in the cytoplasm. It resembles A. nitida in the form of the nucleus, which is a cup-shaped disc or an invaginated spheriod. It is smaller than A. nitida, but somewhat larger than P. dubia. Polychaos nitidubia n. sp. is found in habitats similar to those where Amoeba proteus and other species of the proteus group occur, and may be present with such species. P. nitidubia n. sp. is 200 to 550 µ long in locomotion; its nucleus is 27 to 35 µ diameter with many submembranellar chromatin granules, but no endosome; cytoplasmic granules are numerous, often in fused groups of 2 to 4 crystals, cytoplasm is clear, viscous; movement is less fluid than that of P. dubia, but resembles it.Resume Une nouvelle amibe du groupe proteus, Polychaos nitidubia spec. nov. a été trouvée dans des lacs, des étangs et des ruisseaux de l'Etat de Florida aux Etats Unis de l'Amerique. Elle ressemble tant à la Polychaos dubia (A. A. Schaeffer, 1916) et à la Amoeba nitida E. Penard, 1902, à certaines égards et en difère à d'autres. Elle ressemble à la Polychaos dubia par rapport à la forme des pseudopodes et leurs mouvements, et aussi par rapport à la présence en cytoplasme des cristaux en groupes. Elle ressemble A. nitida par rapport à la forme du noyau, qui est discoide en forme de tasse, ou spheroide invaginé. C'est une amibe plus petite que l'A. nitida, mais plus grande que P. dubia. La Polychaos nitidubia spec. nov. se trouve dans des habitats pareils à ceux de l'Amoeba proteus et des autres et elle se trouve parfois en même lieu. La Polychaos nitidubia spec. nov. est 200 à 500 µ de long durant la locomotion. Son noyau est de 27 à 35 µ de diamètre, avec de nornbreuses granules chromatines sousmembranelles. L'endosoma est absent. Les cristaux du cytoplasme sont nombreux, dans des groupes de 2 à 4, ou solitaires. Le cytoplasme est claire, visqueux. Le mouvernent est moins coulant que celui de la P. dubia, mais y ressemble.