Cell transformation in isolated striated muscle of hydromedusae independent of DNA synthesis

Monotypical isolated and cultivated striated muscle was demonstrated to change (metaplasia) into a cell type possessing flagellae and other characteristics of smooth muscle cells [4]. In situ and within the first 48 h following isolation, no DNA synthesis is observed in striated muscle tissue. However, between the 2nd and 3rd day in culture, approximately one day prior to the formation of flagellae, a dramatic burst of DNA synthesis is observed. In the presence of low concentrations of mitomycin-C which inhibited DNA synthesis, the transformation process from striated to smooth muscle was virtually unaffected. Increasingly higher concentrations of mitomycin-C, which completely inhibited DNA synthesis yet inhibited flagellae formation when administered immediately following isolation, had only a graduated effect on flagellae formation which was inversely proportional to the length of time in culture before treatment, and the concentration employed. The results represent the first clear case of transformation of a differentiated cell type to another distinct type without going through the S phase of the cell cycle.