GSE128014
DamC reveals principles of chromatin folding in vivo without crosslinking and ligation [4C]
Mammalian chromosomes are folded into an intricate hierarchy of structural domains, within which topologically associating domains (TADs) and CTCF-associated loops partition the physical interactions between regulatory sequences. Current understanding of chromosome folding largely relies on chromosome conformation capture (3C)-based experiments, where chromosomal interactions are detected as ligation products after crosslinking of chromatin. To measure chromosome structure in vivo, quantitatively and without relying on crosslinking and ligation, we have implemented a new method named damC. DamC combines DNA-methylation based detection of chromosomal interactions with next-generation sequencing and a biophysical model of methylation kinetics. DamC performed in mouse embryonic stem cells provides the first in vivo validation of the existence of TADs and CTCF loops, confirms 3C-based measurements of the scaling of contact probabilities within TADs, and provides evidence that mammalian chromatin in vivo is essentially rigid below 5 kilobases. Combining damC with transposon-mediated genomic engineering shows that new loops can be formed between ectopically introduced and endogenous CTCF sites, which alters the partitioning of physical interactions within TADs. This establishes damC as a crosslinking- and ligation-free framework to measure and modify chromosome interactions combined with a solid theoretical background for rigorous data interpretation. This orthogonal approach to 3C validates the existence of key structural features of mammalian chromosomes and provides novel insights into how chromosome structure within TADs can be manipulated. Overall design: 4C-seq was performed on a range of viewpoints in embryonic stem cells carrying TetO arrays at diverse chromosomal integrations. In order to determine the chromosome structure at the TetO arrays, a single viewpoint (VP1) was designed on top of the TetO sequence allowing the identification of chromosomal interactions from every integrated platform. The other viewpoints, CTCF and reverse CTCF (VP21 and VP22; respectively) were designed on the mouse genome. Please note that the processed data generated from both replicates is linked to the corresponding 'replicate 1' sample records as indicated in the REAME.txt.