Initiation of a differentiated function (hyaluronic acid synthesis) by hybrid formation in culture

Abstract

Gene expression in mammalian cells was investigated by the use of somatic cell hybridization technique in culture. 1. 1. One clonal line, B-6, among hybrids derived from the fusion of mouse and Chinese hamster cell lines was demonstrated to synthesize and secrete hyaluronic acid into medium. 2. 2. Although B-6 line comprised floating, round and single cells, they had a highly differentiated function, characteristic of only a few fibroblastic lines in culture. 3. 3. This property was barely present in either both the parental or the other three hybrid lines obtained, suggesting that the hybridization event initiated the expression of genes responsible for hyaluronic acid synthesis in the B-6 line alone. 4. 4. A kinetic study of the mucopolysaccharide production revealed that the function of the B-6 line in question operated only during the actively growing phase of the cells, stopping completely in the stationary phase. This suggests the existence of an intimate coordination between active cell growth and hyaluronic acid synthesis. 5. 5. Treatment of B-6 cells with either actinomycin D or cycloheximide which are potent inhibitors of RNA and protein synthesis, respectively, inhibited cell growth and hyaluronic acid synthesis to the same degree, whereas in the presence of hydroxyurea, an inhibitor of DNA synthesis, hyaluronic acid continued to be produced by the cells in spite of the absence of multiplication.