The I N D U C T I O N of Melanization in Goldfish Scales with Acth, I N Vitro

The induction of melanization in xanthic goldfish scales with ACTH in vitro has been studied by light and electron microscopy utilizing ammoniated silver nitrate staining of premelanin and melanin. The melanized cells (melanophores and melanocytes) and the yellow pigmented cells (lipophores and the newly described lipocytes) were found to possess many similarities at the levels of cellular and subcellular structure. The latter cells contain characteristic cytoplasmic bodies which react positively to the premelanin stain. Changes accompanying ACTH stimulation of goldfish scales in tissue culture suggest that these bodies in the lipocytes and lipophores can become melanized. Electron micrographs illustrate the intermediate staining of newly formed melanin granules in an induced melanocyte and the appearance of a transitional melanolipophore. It is postulated that ACTH can promote the association of the enzyme tyrosinase with the preformed structure of unmelanized granules. I N T R O D U C T I O N Thc studies of Dalton (1) and Birbeck, Mercer, and Barnicot (2) showed that melanin granules are derived from small vesicles of low density in the Golgi region of pigrncnt cells. Wellings and Sicgel (3) have described a progressive increase in the size and density of the vcsicles as stages in the development of melanin granules in human malignant melanoma cells. Recently, thc name "melanosome" has been proposed to apply to the precursor organellc of melanin granules (4). Birbeck and Barnicot (5), investigating the amclanotic melanocytes from hair bulbs of human albinos, found "ghost" granules, vesicles with low interior density having a size and distribution comparablc to those of the dense mature melanin granulcs of the normal hair melanocyte. Thus, in the growth of melanin granules the formation of a characteristic cytoplasmic structure and the deposition of melanin within it seem to be independent but normally coordinated processes. A number of stimuli will cause the appearance in vivo of melanized cells in xanthic (amelanotic) goldfish scales where no such cells were previously found (6-9). Furthermore, Hu and Chavin (10) have demonstrated a similar induction of melanization in vitro in pieces of xanthic goldfish fin incubated in tissue culture with adrenocorticotropic hormone (ACTH). The present investigation was undertaken to identify the precursor cell in which melanization is initiated by ACTH. In these experiments there are two groups of pigment cells which occur in the goldfish integument: (a) those containing melanin granules, the melanocytes and melanophores, and (b) those wi th an agranular 181 on Jne 8, 2017 D ow nladed fom Published July 1, 1963