The Development of Dopa Oxidase Activity in the Skin and in the Hair Cycle

The development of melanocytes and of their dopa oxidase activity was followed in mice embryos and was compared with the regeneration of melanocytes and their dopa oxidase activity during anagen I to IV.2. Melanocytes with dopa-negative “propigment granules” were already present in 10-day-old embryos in the loosely-knit mesenchymal tissue of the skin. These premature melanocytes were round to oval and sometimes dendritic. Dopa oxidase activity first became apparent in the dermal melanocytes and in those of tactile hair bulbs in 14-day-old embryos. The enzyme reaction gradually increased in intensity as the melanocytes enlarged and became more dendritic. Melanocytes began to inoculate melanin granules into tactile hairs in the 18-day-old embryo, and into coat hairs in the new-born mouse.3. The number of melanocytes lying free in the dermis increased until about the 16 th day of gestation. Thereafter, their number gradually decreased as the melanocytes tended to congregate in the hair bulbs, in the upper dermis and around the upper portion of tactile hairs. In the adult mouse the number of free dermal melanocytes was small.4. In the hair papilla of the plucked coat hair some dopa-reactive melanocytes remained present in a shrunken form. Regeneration of melanocytes and of their enzymatic activity began 4 days after plucking (anagen III) ; and a burst of melanocyte regeneration accompanied by intense enzyme activity occurred 6 days after plucking (anagen IV). The speed of regeneration of the coat hair, of its melanocytes and of the dopa oxidase activity in the melanocytes was approximately twice as fast as observed during the embryonic development.