CHROMOSOME CONDENSATION IN CHICK MYOTUBES IN CULTURE BY EXTRACELLULARLY APPLIED β-GLYCEROPHOSPHATE

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Chromosome condensation and nuclear membrane breakdown were induced in cultured chick myotubes by exposure to a solution containing 50 mM β-glycerophosphate. These changes were effectively induced only when the Ca²⁺ concentration in the solution was reduced below several micromolar level. The chromosome condensation proceeded in the presence of cycloheximide (1 mg/ml), but was partially inhibited by ethidium bromide (10 μg/ml). Mononucleated cells in the myogenic culture also underwent the chromosome condensation when exposed to the solution containing β-glycerophosphate. Thus, the chromosome condensation in multinucleated skeletal muscle cells was chemically induced for the first time. The results suggest that the chromosomecondensing mechanism is preserved, but is not functioning in myotubes, which never enter the mitotic state under the physiological condition. A possible mechanism of the β-glycerophosphate-induced chromosome codensation was discussed.