Fish Hereditary Melanoma Cell Lines of Different Degrees of Cell Differentiation: (fish/hereditary Melanoma/melanoma Cell Line/pigment Cell Differentiation)

Four cell lines including two 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 more than 34 months. 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 to 72 hr. 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 three 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 three cell lines but only 1% in the one cell line. All four cell lines failed to form colonies in soft agar. Chromosome analysis revealed that these four cell lines were heteroploid with many abnormal figures of chromosomes and double minute chromosomes. None of the cell lines showed transplantability to fish.