UV GUIDED DENDRITIC GROWTH-PATTERNS AND THE NETWORKING OF MELANOCYTES

Whole skin organ cultures of vitiliginous skin show that the marginal melanocytes are highly sensitive to a pulse of UV exposure (210-380 nm ) during the G(2) phase of the cell cycle, as seen by prominent dendri city. Melanocytes are highly dendritic in the epidermis overlying rapi dly growing tumors, as well as within proliferative lesions such as ba sal cell carcinomas and aggressive seborrheic keratosis. In the organ cultures the dendrites extend towards the source of UV, i.e. the surfa ce, while the main body lies along the basement membrane. The epiderma l melanocytes overlying tumors lie almost vertically, dendrites aligne d towards the underlying tumor on one side and the surface on the othe r. Within tumors dendritic elongation is guided by mitotic and PCNA po sitive (S-phase) tumor cells, which are a source of ultraweak UV emiss ions in the range of 210-330 nm. These observations indicate that ultr aweak biophoton emissions from neighbouring cells can simulate environ mental cues and contribute to the plasticity of networks such as the m elanocytes or the visual pathways.