X-chromosome dynamics revealed by the RNA interactome and chromosomal binding of CTCF

CTCF is a master regulator that plays a role in genome architecture and gene expression. A key aspect of CTCF’s mechanism involves bringing together distant genetic elements for intra- and inter-chromosomal interactions. Evidence from epigenetic processes, such as X-chromosome inactivation (XCI), suggests that CTCF may carry out its functions through interacting RNAs. Using genome-wide approaches to investigate the relationship between CTCF’s RNA interactome and its epigenomic landscape, here we report that CTCF interacts with thousands of transcripts in mouse embryonic stem cells (mESC), many in close proximity to CTCF’s genomic binding sites. Biochemical analysis demonstrates that CTCF is a high-affinity RNA binding protein that contacts RNA directly and specifically. In the XCI model, CTCF binds the active and inactive X-chromosomes allele-specifically. At the X-inactivation center, Tsix RNA binds CTCF and targets CTCF to a region associated with X-chromosome pairing. Our work implicates CTCF-RNA interactions in long-range chromosomal interactions in trans and adds a new layer of complexity to CTCF regulation. The genome-wide datasets reported here will provide a useful resource for further study of CTCF-mediated epigenomic regulation. CTCF RNA interactome was identified by UV-crosslinking and immunoprecipitation followed by high-throughput sequencing (CLIP-seq), and was compared to CTCF's epigenomic landscape as obtained by chromatin immunoprecipitation (ChIP-seq).