Fig. 1.

Fetal and adult human cardiomyocyte cell cycle patterns and sarcomere structure. While fetal human cardiomyocytes maintain their proliferative capacity as they progress through the stages of the cell cycle, adult cardiomyocytes lose their proliferative capacity and exit the cell cycle prior to completion of mitosis or cytokinesis (top panel). It has been proposed that the sarcomere inhibits proliferation because sarcomeres in the adult heart cannot be disassembled (middle panel). Alternative mechanisms may connect the sarcomere to cell cycle regulation such as contraction-induced metabolic and signaling alterations that promote cell cycle arrest (bottom panel)