Figure 4: Expression levels of intermediate cell cycle regulators during postnatal maturation of cardiomyocytes. Western blots show the upregulation of cell cycle repressor p53, but down-regulation of transcription activator di-methylated Histone 3 at lysine 4 (H3K4m2) and telomerase (Telom) in postnatal myocytes as compared to new born cells (1d). vs 1d.