DNA synthesis and the cell cycle in cultures of normal and mutant ( [formula omitted]) embryonic mouse muscle cells

Abstract

The relationship between cell fusion, DNA synthesis and the cell cycle in cultured embryonic normal and dysgenic ( mdg mdg ) mouse muscle cells has been determined by autoradiography. The experimental evidence shows that the homozygous mutant myotubes form by a process of cell fusion and that nuclei within the myotubes do not synthesize DNA or undergo mitotic or amitotic division. The duration of the total cell cycle and its component phases was statistically the same in 2-day normal and mutant ( mdg mdg ) myogenic cultures with the approximate values: T, 21.5 hr; G 1, 10.5 hr; S, 7.5 hr; and G 2, 2.5 hr. In both kinds of cultures, labeled nuclei appeared in myotubes 15–16 hr after mononucleated cells were exposed to [ 3H]thymidine, and the rate of incorporation of labeled nuclei into multinucleated muscle cells was comparable in control and dysgenic cultures. Thus, homozygous mdg mdg muscle cells in culture are similar to control cells with respect to their mechanism of myotube formation and the coordinate regulation of DNA synthesis and the cell cycle during myogenesis.