Rb/p130 is dispensable for Suv39h1-mediated H3K9me3. (A) Rb/p130 deletion did not affect methyltransferase activity of Suv39h1 on H3K9. Comparable reduction of H3K9me3 was detected after depletion of Suv39h1 by siRNA in ACMs isolated from control and IDKO mice hearts 4 wk after TAM treatment. siNS, NS siRNA. (B) Semiquantitative RT-PCR demonstrating increased expression of cdc2 and PLK1 after Suv39h1 is depleted in ACMs with siRNA. CBP, cAMP response element-binding–binding protein. (C) A schematic model depicting Rb/p130-dependent epigenetic modifications associated with cell cycle gene regulation in embryonic cardiac myocytes and ACMs and Rb/p130-dependent heterochromatin formation in ACMs based on our results and published data (Roth et al., 2001; Daniel et al., 2005; Grewal and Jia, 2007; Jin et al., 2011). CM, cardiac myocyte; PCAF, P300/cAMP response element-binding CBP–associated factor.