Spatial organisation of the X inactivation center

We report the application of Chromosome Conformation Capture Carbon-copy (5C) to a 4.5 Mb stretch of the mouse X chromosome encompassing the X inactivation center locus. We uncover a series of discrete 200kb-1Mb topologically associating domains (TADs). These align with several domain-wide epigenomic features as well as co-regulated gene clusters. 5C analysis in EED and G9A mutants reveal that this segmental organisation in TADs does not relie on the underlying H3K27me3 or H3K9me2 blocks. Deletion of a boundary between two TADs leads to ectopic chromosomal contacts between them. Analysis of mESCs, mNPCs and MEFs suggest that the positioning of TADs on the chromosome is stable during cell differentiation though their internal organisation changes. Comparison of male (XY) and female (XX) differentiated cells highlights that the long-range chromosomal contacts within TADs are dampened on the inactive X compared to the active X. Overall design: 5C oligonucleotides were designed around HindIII restriction site following an alternative scheme