title: Dopa oxidase expression in fibroblast x melanoma fusions. Extinction in heterokaryons and maintenance in non-dividing cybrids.
abstract: Pigmented B-16 mouse melanoma cells were fused with chick embryo fibroblasts or fibroblast cytoplasts and maintained as heterokaryons or non-dividing cybrids, respectively. These single cells were examined ultrastructurally for evidence or pigment gene expression using a cytochemical test for dopa oxidase, the initial enzyme in the conversion of dopa to melanin. Heterokaryons showed significantly less enzyme activity than control cells, whereas non-dividing cybrids showed no significant difference. Therefore, the presence of the intact nuclear membranes in the heterokaryons did not serve as a barrier to the interactions resulting in extinction of differentiated function(s). However, the presence of the fibroblast nucleus was necessary to elicit continued response.
mesh_terms: D000818:Animals; D004156:Catechol Oxidase / Q000096:biosynthesis*; D002467:Cell Nucleus / Q000502:physiology*; D002642:Chick Embryo; D003593:Cytoplasm / Q000502:physiology*; D005347:Fibroblasts; D005786:Gene Expression Regulation; D006651:Histocytochemistry; D006822:Hybrid Cells; D008545:Melanoma; D051379:Mice; D014442:Monophenol Monooxygenase / Q000096:biosynthesis*; D009374:Neoplasms, Experimental
chemical_list: D004156:Catechol Oxidase; D014442:Monophenol Monooxygenase