Project description:Polycomb-mediated chromatin repression modulates gene expression during development in metazoans. Binding of multiple sequence-specific factors at discrete Polycomb Response Elements (PREs) is thought to recruit repressive complexes that spread across an extended chromatin domain. To dissect the structure of PREs, we applied high-resolution mapping of non-histone chromatin proteins in native chromatin of Drosophila cells. Analysis of occupied sites reveal cooperative interactions between transcription factors that stabilize Polycomb anchoring to DNA, and implicate the general transcription factor Adf1 as a novel PRE component. By comparing two Drosophila cell lines with differential chromatin states, we provide evidence that repression is accomplished at multiple steps in transcription, including inactivation of distant enhancers, enhanced Polycomb recruitment to PREs and target promoters, and elevated stalling of RNAPII in repressed genes. These results suggest that the stability of complexes bridging promoters, enhancers, and PREs is a crucial aspect of developmentally regulated gene expression. Native chromatin immunoprecipitation of histones, transcription factors and Polycomb protein in Drosophila cell lines.
Project description:Interphase chromatin is organized into topologically associating domains (TADs). Within TADs, chromatin looping interactions are formed between DNA regulatory elements, but their functional importance for the establishment of the 3D genome organization and gene regulation during development is unclear. Using high-resolution Hi-C experiments, we analyze higher order 3D chromatin organization during Drosophila embryogenesis and identify active and repressive chromatin loops that are established with different kinetics and depend on distinct factors: Zelda-dependent active loops are formed before the midblastula transition between transcribed genes over long distances. Repressive loops within polycomb domains are formed after the midblastula transition between polycomb response elements by the action of GAGA factor and polycomb proteins. Perturbation of PRE function by CRISPR/Cas9 genome engineering affects polycomb domain formation and destabilizes polycomb-mediated silencing. Preventing loop formation without removal of polycomb components also decreases silencing efficiency, suggesting that chromatin architecture can play instructive roles in gene regulation during development.
Project description:We use deep-sequencing of Hi-C libraries to identify topological boundaries at high resolution and show that boundaries, insulators, and polytene interbands converge on the same short genomic elements.
Project description:Polycomb-mediated chromatin repression modulates gene expression during development in metazoans. Binding of multiple sequence-specific factors at discrete Polycomb Response Elements (PREs) is thought to recruit repressive complexes that spread across an extended chromatin domain. To dissect the structure of PREs, we applied high-resolution mapping of non-histone chromatin proteins in native chromatin of Drosophila cells. Analysis of occupied sites reveal cooperative interactions between transcription factors that stabilize Polycomb anchoring to DNA, and implicate the general transcription factor Adf1 as a novel PRE component. By comparing two Drosophila cell lines with differential chromatin states, we provide evidence that repression is accomplished at multiple steps in transcription, including inactivation of distant enhancers, enhanced Polycomb recruitment to PREs and target promoters, and elevated stalling of RNAPII in repressed genes. These results suggest that the stability of complexes bridging promoters, enhancers, and PREs is a crucial aspect of developmentally regulated gene expression.