Clonal heterogeneity in physiological properties of melanized cells induced from goldfish erythrophoroma cell lines.

Cells of the uncloned goldfish erythrophoroma lines, GEM-81 and GEM-218, have been induced to melanize by cultivation in autologous serum. The melanized cells continue to proliferate and exhibit clonal heterogeneity in terms of morphology, growth rates, contact behavior and pigment content, and distribution and translocation in response to hormones. Based on these characteristics and those of their normal counterparts, the melanized tumor cells have been categorized as type-I and type-II melanocytomas, and melanophoromas. The melanophoroma cells are capable of pigment translocation in response to epinephrine, melatonin, and/or MSH, whereas melanocytoma cells are not. The distinguishing characteristics of each type are apparent at the first appearance of melanized cells and appear to be stable except in some type-II melanocytoma clones which contain cells capable of differentiating into melanophoroma cells in long-term cultures. It appears that the parent erythrophoroma lines contain stem cells, melanoblastomas, which are capable of melanogenesis. These stem cells may themselves be a heterogeneous population with respect to the characteristics of the melanized cells to which they give rise.