Figure 5.

Models for epigenetic regulation of polyadenylation at H13. Maternal alleles are shown in red, and paternal are in blue. Filled circles represent CpG methylation (5mC), and Pol II represents the RNA polymerase II initiation complex. pF denotes a hypothetical polyadenylation factor(s). (A) Methylation-sensitive formation of transcriptional initiation complexes at the Mcts2 promoter results in transcriptional interference specifically on paternally derived alleles. In this model, transcription factors bound at the Mcts2 promoter act indirectly as polyadenylation factors. (B) Methylation-sensitive binding of transcriptional initiation complexes and distinct polyadenylation factors within the DMR. In this model, allele-specific utilization of the H13d + e polyA sites and Mcts2 transcription occur independently and do not require common factors. (C) Methylation prevents the binding of polyadenylation factors on maternally derived alleles, and the elongation of H13 transcripts through the maternal Mcts2 promoter brings about silencing by promoter occlusion (Shearwin et al. 2005).