Fish Hereditary Melanoma Cell Lines of Different Degrees of Cell Differentiation

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Abstract
Four cell lines including 2 sublines were established from hereditary melanomas in interspecific hybrids between platyfish (Xiphophorus maculatus) carrying the Sp gene and swordtails (X. helleri) and maintained in vitro for > 34 mo. Cells in each cell line grew randomly across each other with an apparent lack of contact inhibition of growth and at a population doubling time of 50-72 h. They retained the characteristics of young pigment cells in regard to ultrastructure, tyrosinase activity, the dopa and combined dopa-premelanin reactions. In the degree of differentiation, the cells of the 3 cell lines seemed comparable to early melanocytes close to melanoblasts, and those of the remaining one cell line seemed comparable to young melanocytes but were in a more differentiated state than the early melanocytes. Colony forming ability on plastic plates was at a level of 10% in the 3 cell lines but only 1% in the 1 cell line. All 4 cell lines failed to form colonies in soft agar. Chromosome analysis revealed that these 4 cell lines were heteroploid with many abnormal figures of chromosomes and double minute chromosomes. None of the cell lines showed transplantability to fish.