HISTOGENESIS OF THE INTRADERMAL MELANOCYTIC TUMOR IN BDF1 MICE INDUCED BY TOPICAL APPLICATION OF 9, 10-DIMETHYL-1, 2-BENZANTHRACENE (DMBA) AND 12–0-TETRADECANOYLPHORBOL-13-ACETATE (TPA)

The histogenesis of the intradermal melanocytic tumor induced in the skin of 88 female BDF₁ mice by DMBA and TPA is studied light-and electron-micro-scopically. Four types of melanocytes were found in the mouse skin. 1] The epidermal melanocytes transiently appeared several days after topical application of DMBA. 2] Hair follicles turned into anagen phase and follicular melanocytes became apparent by week 3. 3] After week 3, intradermal melanocytes of the perifollicular melanocytic networks (PFM), which were scattered in untreated mouse skin, proliferated to form the intradermal melanocytic tumors, and 267 tumors, composed of oval melanocytes in medullary growth, were induced in all of the 19 treated mice by week 32. 4] Large dendritic melanocytes located deep in the reticular dermis, which did not participate in the formation of the tumor. Only 3 papillomas were induced in 2 of the 19. Light-and electron-microscopically, there was no evidence of migration of epidermal and hair follicular melanocytes into the dermis. Additionally, melanin-producing activity in the cytoplasm of Schwann cell and perineural epithelium was observed. The histogenesis of the intradermal melanocytic tumor was closely related to the melanocytes of the perifollicular melanocytic network (PFM).