The Occurrence and Morphogenesis of Melanocytes in the Connective Tissues

MAMMALS, as a rule, are described as having melanocytes of neural crest origin confined almost entirely to the skin. Of the organs other than skin which have been described as possessing melanocytes are portions of the gonado-genital apparatus of the Opossum (Burns, 1939), and, in the house mouse, tissues of the nictitans, the meninges of the brain, the parathyroids, the thymus and harderian glands (Markert & Silvers, 1956), and the parathyroids of C58 mice (Dunn, 1949). The present investigation has been made in a strain of mice in which melanocytes are found in the connective tissues throughout much of the body. This strain originated several years ago in the Department of Genetics, Medical College of Virginia, from a cross between inbred C3H and black mice of unknown breed obtained from a local pet shop. Because of the latter circumstance, the line-bred progeny have been termed the PET/MCV strain. Upon the discovery by the authors (Reams & Nichols, 1959) of melanocytes in the serosae of new-born PET/MCV mice, a stock was developed for investigation. The presence of melanocytes in the coelomic lining of the chick and other fowl has been known for years (Willier & Yuh, 1928; Eastlick, 1939; and Rawles, 1940, 1945). Recently, Reams (1956) has shown that peritoneal pigment cells are excellent subjects for the study of the ontogeny of cell form since they are easily obtained for experimentation, and since the changes which they undergo in their morphogenesis are readily apparent due to the onset of melanogenesis prior to the development of their definitive shape. The melanocytes within the connective tissues of the PET/MCV mouse similarly lend themselves to analysis by experimental techniques.