Aging of Melanocytes

Choroidal melanocytes of the eyes of postnatal animals are classified as postmitotic terminally differentiated cells. They have specific granules, the melanosomes, which undergo changes qualitatively and quantitatively correlated to the animal's increasing age. Epidermal melanocytes, which normally divide only on demand or by stimulation, are classified as intermittent mitotic cells. During their development, lentigines and nevi of the skin show progressive ultrastructural and cytochemical changes similar to those in the choroidal cells, and thus may be considered as aging populations of skin melanocytes. These facts have led to the conclusion that choroidal melanocytes may be used advantageously as a model for studying changes in cells from maturation to senescence

The Effect Of Msh On Thymidine Incorporation By Keratinocytes In The Epidermal Melanin Unit

Epidermal melanocytes were observed in the black but not in the white skin of black-and-white spotted guinea pigs. In experiments designed to determine whether melanocyte-stimulating hormone (MSH) affects the incorporation of thymidine by keratinocyte nuclei of the epidermal melanin unit, the labeling index was the same in all skin before MSH administration. After MSH injections, the level of [3H]thymidine incorporation in keratinocytes increased significantly in black skin but not in white. We suggest that through the mediation of melanocytes MSH indirectly affects keratinocytes in the epidermal melanin unit

Hybrid Hierarchical Collision Detection Based on Data Reuse

To improve the efficiency of collision detection between rigid bodies in complex scenes, this paper proposes a method based on hybrid bounding volume hierarchies for collision detection. In order to improve the simulation performance, the method is based on weighted oriented bounding box and makes dense sampling on the convex hulls of the geometric models. The hierarchical bounding volume tree is composed of many layers. The uppermost layer adopts a cubic bounding box, while lower layers employ weighted oriented bounding box. In the meantime, the data of weighted oriented bounding box is reused for triangle intersection check. We test the method using two scenes. The first scene contains two Buddha models with totally 361,690 triangle facets. The second scene is composed of 200 models with totally 115, 200 triangle facets. The experiments verify the effectiveness of the proposed method

Theophylline and Melanocyte-Stimulating Hormone Effects on Gamma-Glutamyl Transpeptidase and DOPA Reactions in Cultured Melanoma Cells

Gamma-glutamyl transpeptidase (GGT), an enzyme of the γ-glutamyl cycle, was demonstrated in 3 of 6 cell lines derived from a single B16 murine melanoma. Its activity in these cells varied a great deal, appeared to be correlated with the developmental cycle of the cells, and was greatest in young, actively melanogenic cells. Generally, the activity seemed parallel to that of tyrosinase, an enzyme specific for melanin synthesis. The levels of both enzymes tended to decline with prolonged in vitro cultivation, but could be readily renewed after one animal passage. The 3 cell lines that were GGT-negative were nonpigniented and DOPA-negative; so was a nonmelanogenic and nonmelanocytic rhesus cell line. Melanocyte-stimulating hormone (MSH) and theophylline both enhanced pigmentation in murine melanoma cells. The mechanisms of their action apparently differed. We found that theophylline increased both DOPA- and GGT- reactive cells, whereas MSH only increased DOPA-reactive cells. All 3 GGT-positive lines were tumorigenic, and 2 GGT-negative lines were not tumorigenic. Our observations suggest that GGT plays a role in the melanin biosynthetic pathway and that its activity is greater in melanoma cells that are tumorigenic