DNA synthesis and multinucleation in embryonic stem cell-derived cardiomyocytes.

The proliferative capacity of embryonic stem (ES) cell-derived cardiomyocytes was assessed. Enriched preparations of cardiomyocytes were isolated by microdissection of the cardiogenic regions of cultured embryoid bodies. The identity of the isolated cells was established by immunocytology, and mitotic activity was monitored by [3H]thymidine incorporation and pulse-chase experiments. ES-derived cardiomyocytes were mitotically active and predominantly mononucleated at 11 days after cardiogenic induction. By 21 days postinduction, cardiomyocyte DNA synthesis was markedly decreased, with a concomitant increase in the percentage of multinucleated cells. Interestingly, the duration of active cardiomyocyte reduplication in the ES system appeared to be roughly similar to that observed during normal murine cardiogenesis. Given these observations, as well as the genetic tractability of ES cells, ES-derived cardiogenesis might provide a useful in vitro system with which to assess the molecular regulation of the cardiomyocyte cell cycle.