Figure 4. Chromatin activation in the absence of Rb occurs at the level of E2f. qRT-PCR analysis of the PCNA and CycA2 promoters in GFP, Cre or Cre/ DP1_Δ103–126 infected cortical neurons (Rb^Flox/Flox) at 6DIV from chromatin immunoprecipitated DNA. (A) Western blot analysis of total protein extracted from control (GFP), Rb-deficient (Cre) and Rb-deficient/dominant negative DP1 (Cre and DP1_Δ103–126) cortical neurons at 6 DIV. (B) Chromatin was immunoprecipitated with an antibody directed toward acetylated histone 3 (Acetyl-H3). (C) Chromatin was immunoprecipitated using an antibody that recognizes tri-methylated lysine 9 on histone 3 (H3K9me3). Error bars represent SEM (n = 3, where n represents a ChIP performed on neurons isolated from a unique embryo); statistical significance was determined using a one-way ANOVA, where *p < 0.05 was considered statistically significant.