Melanin containing organelles in cells of the human gingiva I. Epithelial Melanocytes

Biopsies of the marginal gingiva obtained from 21 caucasoid subjects (average age of 25 years) served for the electron microscopic examination of epithelial melanocytes and their organelles. In 60 to 70 per cent of the subjects, melanin producing dendritic melanocytes could be observed within the stratum basale and the suprabasal stratum spinosum. Electron microscopically, 2 types of structurally different melanocytes could be distinguished: inactive, and actively premelanosomes producing and melanin synthesizing cells. The number of premelanosomes and melanosomes per cytoplasmic unit area of melanocyte projections increased towards their peripheral termination. The developmental stages of possibly two structurally different premelanosomes are described to be comparable to those of the human skin. Fully melanized ovoid melanosomes were measured to be 0.27±0.06 micron long and 0.10±0.04 micron wide. Striated bars inside premelanosomes are suggested to represent a tightly coiled spiral possibly reflecting the molecular arrangement of tyrosinase. The findings are discussed with reference to the knowledge of melanocytes, premelanosomes and melanosomes in human skin, hair bulbs and melanomatous tissues.