Actively transcribed genes insulate Polycomb domains in Drosophila

Drosophila genome is organized into topological domains. The functional relationship between these domains and genes present within these domains is under investigation. In this report, using genetic and genomic tools, we show that for Polycomb [PcG] domains, flanking ubiquitously transcribed genes, transcribed towards the PcG domain can act as boundaries and stop the spreading of H3K27me3, the PcG chromatin mark. Early transcription termination of boundary genes results in extension of the PcG domain over the flanking genes.