Ultrastructure and cell biology of pigment cells. Intracellular dynamics and the fine structure of melanocytes with special reference to the effects of MSH and cyclic AMP on microtubules and 10-nm filaments.

Four functions characterize the melanocyte: the synthesis of melanin granules; the growth and maintenance of dendrites; the translocation of melanin granules within the cytoplasm in response to hormones or neurotransmitters; the transfer of melanin granules to adjacent cells that have phagocytic capacities. The melanocyte of the amphibian epidermis exhibits all of these functions and thus is ideal for study. Other melanocytes may express one or the other of these functions less apparently. The mammalian epidermal melanocyte, for example, does not translocate melanin granules so rapidly; the dermal melanocyte does not transfer melanin granules; the albino melanocyte synthesizes little or no melanin; some melanoma cells do not form dendrites. The melanoma cell, on the other hand, after transplantation or growth in cell culture, has an additional capability that it shares with certain other tumor cells: it synthesizes particles that are assumed to be RNA tumor viruses. In this report we will correlate the functions of the vertebrate melanocyte with its appearance by transmission electron microscopy. Unless specifically indicated, all electron micrographs shown are of cells fixed at room temperature in a solution consisting of 3% glutaraldehyde, 0.1 M sodium cacodylate buffer (pH 7.2), and 0.1% calcium chloride. The cells were refixed in 1% buffered osmium tetroxide, dehydrated in ethanol, and embedded in Epon 812 or, especially in the case of frog skin, in the less viscous epoxy mixture of Spurr (1). Thin sections were cut on an LKB Ultrotome III equipped with a diamond knife. They were counter-stained with uranyl acetate and lead citrate and examined in a Hitachi HU-1 lB electron microscope.