Willys K. Silvers, Ph.D. 



TACTICS in PIGMENT-CELL RESEARCHt 



The phenomena of genie action and interaction are so clearly presented by the 

 permanent record which results from the elaboration of melanin granules in the hair 

 matrices and their incorporation in the hair shaft, that the elucidation of the genetic 

 aspects of melanogenesis greatly preceded a true understanding of the anatomical 

 basis and biochemistry of pigment formation. Indeed, it was not until about 1940 

 that the extraepidermal origin of the pigment cell was unequivocally demonstrated in 

 the classic experiments of Rawles. 1040, 1041 We now are aware that pigment formation 

 in mammalian skin and hair is restricted to specialized branched or dendritic cells — 

 melanocytes — of neural crest origin, usually located in the basal layer of the superficial 

 epidermis, in the case of skin pigmentation, and in the hair bulbs for hair pigmentation. 



Once it had been established that the many coat-color patterns found in mammals 

 resulted from genie mutations and genie interactions, geneticists became interested in 

 studying particular coat-color phenotypes, since it was evident that such phenotypes 

 reflected or expressed, rather directly, the end results of specific gene-controlled pro- 

 cesses. Interest in coat color was intensified when it was realized that only a single 

 genie change was necessary to alter the phenotype drastically. Thus any study of 

 mammalian coat color could not help but be concerned with the final results of a 

 dynamic interplay of genie actions and interactions originating within the boundaries 

 of a single type of cell, the melanocyte, and its milieu. Moreover, the fact that the entire 

 genetically controlled sequence of chemical reactions in the synthesis of melanin from 

 precursor tyrosine was restricted to the cytoplasm of the melanocyte, and could 



f Some of the work referred to in this paper was supported by a grant (C-3577) from 

 the National Institutes of Health, U.S. Public Health Service. 



323 



