Figure 4.

Epigenetic mechanism for islet- and liver-specific silencing of repressed genes. Histone H3 lysine9-acetylation (green bars) and lysine27-trimethylation (red bars) of chromatin around promoter region of repressed genes were compared in adult mouse tissues with and without observed repression. (A,B) For Ldha and Mct1, a high level of H3 lysine27-trimethylation is seen in islets but not in liver, whereas H3 lysine9-acetylation is more extensive in the liver. This difference parallels differences between liver and islets for mRNA expression (see also Fig. 2). (C) Histone modifications during postnatal liver maturation (age 1, 14, and 42 d and adult). Histone H3 trimethylation in the Oxct1 promoter increases during liver development and is significantly higher in adult liver than in adult brain, while acetylation at the lysine9 residue is lower for all liver time points versus brain. (D) Nucleosomes of the beta actin (Actb) promoter, which is active in all tissues, display a high level of histone H3 lysine9 acetylation and a low level of histone 3 lysine 27 trimethylation in islets, brain, and liver. (Black bars) IgG immunoprecipitation control. Data are means ± SEM of three to four QPCRs.