Project description:we combined Assay for Transposase-Accessible Chromatin and lattice light-sheet PALM microscopy (3D ATAC-PALM) to selectively image key features of the 3D accessible genome in single cells. We found that accessible chromatin domains (ACDs) form spatially segregated clusters in the nucleus. Rapid depletion of CTCF or Cohesin (RAD21 subunit) induced extensive 3D spatial mixing of ACD clusters and reduced physical separation between ACDs within chromosomes. Experimental perturbations and modeling suggest that both weak, multivalent, dynamic protein-protein interactions together with loop extrusion influence ACD organization. Live-cell studies suggest that ACD clustering regulates transcription factor binding site distribution, target search kinetics and binding dynamics. Here we report the ATAC-seq results from Tn5 PA549 and nextera Tn5 upon various chemical and genetic perturbations.
Project description:To dissect Cohesin-independent mechanisms that compartmentalize the mammalian genome, we combined super-resolution imaging and high-resolution chromatin interactome, chromatin binding and accessibility and RNA sequencing analysis. We found that the bromodomain and extra-terminal domain (BET) family protein BRD2 is one key regulator to promote compartmental interactions in the absence of Cohesin. We also identified competitive, rather than cooperative relationship between BET family proteins in shaping the 3D genome organization. This study uncovers new mechanisitc insights on the 3D organization of the mammalian genome.
Project description:CTCF is present at the anchors of thousands of loops likely formed via cohesin-mediated loop extrusion in mammalian cells. Interaction domains present in D. melanogaster chromosomes form via the segregation of active and inactive chromatin in the absence of CTCF looping, but the role of transcription versus other architectural proteins in chromatin organization is unclear. Here we find that positioning of RNAPII via transcription elongation is essential in the formation of gene loops, which in turn interact to form compartmental domains. Inhibition of transcription elongation or depletion of cohesin decreases gene looping and formation of active compartmental domains. In contrast, depletion of condensin II, which also localizes to active chromatin, results in increased gene looping, formation of compartmental domains, and stronger intra-chromosomal compartmental interactions. Condensin II has a similar role in maintaining inter-chromosomal interactions responsible for pairing between homologous chromosomes, whereas inhibition of transcription elongation or cohesin depletion has little effect on homolog pairing. The results suggest distinct roles for cohesin and condensin II in the establishment of 3D nuclear organization in Drosophila.
Project description:Spatial genome organization is essential to direct fundamental DNA-templated biological processes (e.g. transcription, replication, and repair), but the 3D in situ nanometer-scale structure of accessible cis-regulatory DNA elements within the crowded nuclear environment remains elusive. Here, we combined the recently developed Assay for Transposase-Accessible Chromatin with visualization (ATAC-see), PALM super-resolution imaging and lattice light-sheet microscope (a method termed 3D ATAC-PALM) to selectively image and quantitatively analyze key features of the 3D accessible genome in single cells. 3D ATAC-PALM reveals that accessible chromatin are non-homogeneously organized into spatially segregated clusters or accessible chromatin domains (ACDs). To directly link imaging and genomic data, we optimized multiplexed imaging of 3D ATAC-PALM with Oligopaint DNA-FISH, RNA-FISH and protein fluorescence. We found that ACDs colocalize with active chromatin and enclose transcribed genes. By applying these methods to analyze genetically purterbed cells, we demonstrated that genome architectural protein CTCF prevents excessive clustering of accessible chromatin and decompacts ACDs. These results highlight the 3D ATAC-PALM as a useful tool to probe the structure and organizing mechanism of the genome.
Project description:The 3D architecture that the genome is folded into is regulated by CTCF, which determines domain borders, and cohesin, which generates interactions within domains. However, organisms lacking CTCF have been reported to still have cohesin-mediated 3D structures with strong borders. How this can be achieved and precisely regulated are yet unknown. Using in situ Hi-C, we found that 3’-end RNA processing factors coupled with proper transcription termination are a cis-acting determinant that regulates the localization and dynamics of cohesin on the chromosome arms. Loss of RNA processing factors, including nuclear exosome and Pfs2, destabilizes cohesin from the 3'-ends of convergent genes and results in decreased cohesin-mediated domain boundaries. We observed the co-localization between Rad21 and a wide range of 3'end RNA processing/termination factors. Further, deletion of Rrp6 leads to cohesin redistribution to facultative heterochromatin, resulting in improper domain boundaries. Importantly, we observed that knockdown of Rrp6Exosc10 caused a defect in cohesin binding and loss of local topologically associating domains (TADs) interactions in mouse embryonic stem cells. Based on these findings, we propose a novel function of the RNA surveillance pathway in 3D genome organization via cohesin complex, which provides the molecular basis underlying the dynamics of cohesin function.
Project description:One bottleneck in understanding the principles of 3D chromatin structures is caused by the paucity of known regulators. Cohesin is essential for 3D chromatin organization, and its interacting partners are candidate regulators. Here, we performed proteomic profiling of the Cohesin in chromatin and identified transcription factors, RNA-binding proteins, and chromatin regulators associated with Cohesin. Acute protein degradation followed by time-series genomic binding quantitation and BAT Hi-C analysis were conducted, and the results showed that the transcription factor ZBTB21 contributes to Cohesin chromatin binding, 3D chromatin interactions and transcriptional repression. Strikingly, multiomic analyses revealed that the other four ZBTB factors interacted with Cohesin, and double degradation of ZBTB21 and ZBTB7B led to a further decrease in Cohesin chromatin occupancy. We propose that multiple ZBTB transcription factors orchestrate the chromatin binding of Cohesin to regulate chromatin interactions, and we provide a catalog of many additional proteins associated with Cohesin that warrant further investigation.
Project description:One bottleneck in understanding the principles of 3D chromatin structures is caused by the paucity of known regulators. Cohesin is essential for 3D chromatin organization, and its interacting partners are candidate regulators. Here, we performed proteomic profiling of the Cohesin in chromatin and identified transcription factors, RNA-binding proteins, and chromatin regulators associated with Cohesin. Acute protein degradation followed by time-series genomic binding quantitation and BAT Hi-C analysis were conducted, and the results showed that the transcription factor ZBTB21 contributes to Cohesin chromatin binding, 3D chromatin interactions and transcriptional repression. Strikingly, multiomic analyses revealed that the other four ZBTB factors interacted with Cohesin, and double degradation of ZBTB21 and ZBTB7B led to a further decrease in Cohesin chromatin occupancy. We propose that multiple ZBTB transcription factors orchestrate the chromatin binding of Cohesin to regulate chromatin interactions, and we provide a catalog of many additional proteins associated with Cohesin that warrant further investigation.
Project description:One bottleneck in understanding the principles of 3D chromatin structures is caused by the paucity of known regulators. Cohesin is essential for 3D chromatin organization, and its interacting partners are candidate regulators. Here, we performed proteomic profiling of the Cohesin in chromatin and identified transcription factors, RNA-binding proteins, and chromatin regulators associated with Cohesin. Acute protein degradation followed by time-series genomic binding quantitation and BAT Hi-C analysis were conducted, and the results showed that the transcription factor ZBTB21 contributes to Cohesin chromatin binding, 3D chromatin interactions and transcriptional repression. Strikingly, multiomic analyses revealed that the other four ZBTB factors interacted with Cohesin, and double degradation of ZBTB21 and ZBTB7B led to a further decrease in Cohesin chromatin occupancy. We propose that multiple ZBTB transcription factors orchestrate the chromatin binding of Cohesin to regulate chromatin interactions, and we provide a catalog of many additional proteins associated with Cohesin that warrant further investigation.