Gene Dosage Dependence of Pigment Synthesis in Melanoma x Fibroblast Hybrids

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Abstract
Hybrids between Syrian hamster melanoma cells and mouse fibroblasts, containing one genome (1s) of each parent, produce neither melanin nor DOPA-oxidase ("extinction"). Attempts to induce loss of the fibroblast chromosomes by irradiation of the fibroblasts before fusion with melanoma cells resulted in the formation of colonies comprising pigmented hybrid cells, which contained 2s melanoma and 1s fibroblast chromosome-complements suggesting that extinction or re-expression of melanogenesis is a function of genic balance. This interpretation was confirmed by crosses between 2s melanoma cells with unirradiated 1s fibroblasts, which produced both pigmented and unpigmented hybrids. No correlation has thus far been established between karyotype and phenotype of the hybrid cells, but analysis of the karyological data suggests that the fibroblast chromosomes responsible for extinction cannot be numerous.