DNA synthesis, mitosis and fusion of myocardial cells

Abstract

Myocardial cells obtained from embryonic chick ventricles have been used to investigate (1) whether differentiated cells can undergo DNA synthesis and mitosis and, (2) whether heart cells when grown in culture can fuse with each other and with chick skeletal myoblasts to form heterokaryon myotubes. Electron microscopic observations have shown that myocardial cells of day 3 and day 20 chick embryos did contain myofibrils with defined sarcomeres; these cells have been observed i n mitosis. Cells obtained by tryptic digestion of day 12 chick ventricles when grown in culture continued to replicate their IjNA as shown by thymidine-SH radioautography with DNase controls and were observed in all stages of mitosis. Electron microscopy showed that myofibrils were present i n some of the cultured cells.Bi-, tri-and tetranucleate cells were observed in the cultures. Thymidine-SH radioautography showed that these cells were formed by karyokinesis without cytokinesis and by the fusion of uninucleate cells. Since the heart cells could fuse with each other, we tested the possibility that they could fuse with skeletal myoblasts to form heterokaryon myotubes. This was accomplished by co-culturing thymidine-"H labeled ventricular cells and unlabeled skeletal myoblasts. Radioautography with DNase controls showed that some of the myotubes consisted of unlabeled skeletal muscle nuclei and labeled heart nuclei i n varied proportions. The factors initiating the not been elucidated.

Regulation of proliferation of the fetal myocardium

“…3). Consistent with previous reports (Przybylski and Chlebowski, 1972;Chacko, 1973;Polinger, 1973;Bogenmann and Eppenberger, 1980;Clark and Fischman, 1983;Claycomb and Bradshaw, 1983;Ueno et al, 1988;Kardami, 1990), monolayercultured cardiomyocytes did show a modest fraction of (Table 5A), but the fraction was unaffected by the addition of these growth factors to the medium. The difference in responsiveness of cardiomyocyte tissue (myocyte spheroids) and monolayers is significant.…”

Heterogeneous proliferative potential in regenerative adult newt cardiomyocytes

“…4B). The fact that more cells in this experiment became multinucleate, as compared to those in the time lapse experiment described above, could be because of the longer incubation time or the unavoidable inclusion of putative fusion events (Przybylski and Chlebowski, 1972) or membrane overlapping events in this category.…”

DNA Synthesis and Mitosis in Well-Differentiated Mammalian Cardiocytes

“…36, 717 (1966 Unlike skeletal muscle, embryonic cardiac cells synthesize DNA and divide after myofibrils have appeared (4)(5)(6)(7)(8). With autoradiography, DNA synthesis has been demonstrated in differentiating cardiac cells of chick embryos (4,5). Mitotic figures have been observed in electron micrographs of chick heart cells containing a few myofibrils (6, 7).…”