Proliferation in vivo and in culture of differentiated adult atrial cardiomyocytes from transgenic mice.

Transgenic mice expressing atrial natriuretic factor-SV40 T-antigen fusion genes (ANF-TAG) developed unilateral right atrial tumors composed of differentiated dividing cardiomyocytes. The atrial tumors could be propagated as transplantable tumor lineages in syngeneic animals. Cardiomyocytes derived from ANF-TAG atrial tumors did not proliferate in tissue culture. However, cardiomyocytes derived from the transplantable tumor lines proliferated in culture, and these proliferating cardiomyocytes could be passaged in culture and recovered from frozen stocks. Cardiomyocytes from either tumor source were highly differentiated as determined by diverse functional and structural criteria. The cells continued to express numerous cardiac-specific proteins and retained ultrastructural features characteristic of cardiomyocytes including well-formed myofibrils, transverse tubules, and intercalated disks. In addition, the cultured cells displayed spontaneous electrical and contractile activities. These atrial tumor cardiomyocytes are a novel experimental resource for the identification of genes regulating the cardiomyocyte cell cycle.