Rb/p130-dependent recruitment of HP1-γ to E2F-responsive promoters is essential for irreversible silencing of proliferation-associated genes in ACMs. (A) HP1-γ bound to G2/M and cytokinesis genes in an Rb/p130-dependent manner as shown by ChIP using chromatin extracts from purified ACMs. (B) Quantitation of HP1-γ enrichment at the indicated promoters by real-time PCR. Error bars represent the SEM from three replicates. *, P = 0.018; **, P = 0.003. (C) A Western blot showing HP1-α, -β, and -γ expression in ventricles from mice with the indicated genotypes. (D) HP1-γ colocalized with heterochromatin in control ACM. IDKO ACM lost heterochromatin, and HP1-γ staining is diffused. TnC, troponin C. Bar, 5 µm.