EMBRYONIC DEVELOPMENT OF MELANOCYTES IN HUMAN HAIR AND EPIDERMIS - THEIR CELLULAR DIFFERENTIATION AND MELANOGENIC ACTIVITY

[摘要] Ammoniated silver nitrate reaction for premelanin and the dopa reaction was used in this study. Dopa-and premelanin-positive melanocytes appear in embryonic hair from the earliest pre-germ stage to the end of the hair peg stage without any specific localization or higher concentration. In the bulbous peg stage before 6 mo. fetal age melanocytes are mostly localized in the peripheral layer of the outer root sheath of the infundibulum, the lower bulb and the pigment matrix although a few premelaninpositive melanocytes are seen in the inner cell layers of the infundibulum and in the middle portion and upper bulb. After 6 mo. fetal age the bulbous peg exhibits complete localization of melanocytes in the peripheral layer of the outer root sheath of the infundibulum, the lower bulb and pigment matrix. The epidermal melanocyte manifests a random distribution in the early differentiating epidermis from its time of epidermal entry up to 6 mo. fetal age although there appears a definite tendency for junctional localization at 5 mo. fetal age. After 6 mo. fetal age epidermal melanocytes assume their permanent junctional distribution. Embryonic human hair melanocytes and epidermal melanocytes undergo an essentially parallel process of differentiation and distribution. The genesis and fate of high-level dopa and premelanin positive fetal melanocytes are discussed in relation to Langerhans cells. Premelanin positive melanocytes greatly exceed dopa positive cells in number. It is suggested that in the process of fetal melanocyte differentiation the melanosome formation by the Golgi apparatus and active tyrosinase synthesized by ribosomes can occur separately with the former preceding the latter.