Dissecting the functional roles of CTCF and CTCF-s in human embryonic stem cells

CTCF is a highly conserved zinc finger protein that plays critical roles in transcriptional regulation and three-dimensional (3D) genome organization. An alternative splice isoform of CTCF (CTCF-s), lacking the N-terminal domain and 2.5 zinc fingers, competes with CTCF for genomic occupancy and reduces CTCF-mediated chromatin interactions. However, the functional differences between CTCF and CTCF-s remain unclear. In this study, by using an auxin-inducible degron (AID2) system with doxycycline-inducible transgene expression, we systematically investigate the roles of CTCF and CTCF-s in human embryonic stem cells (hESCs). Acute degradation of endogenous CTCF and CTCF-s, followed by isoform-specific rescue, reveals that CTCF is essential for cell morphology and proliferation, whereas CTCF-s exerts much weaker effects. Genome-wide ChIP-seq and Hi-C analysis uncover distinct binding landscapes for CTCF and CTCF-s, as well as their differential contributions to chromatin conformation. Notably, our data indicate that CTCF-s, like CTCF, could either act as a boundary insulator or bind to gene promoters to modulate expression of a fraction of genes. Overall, our study reveals that CTCF is dominant in regulating chromatin boundary stability and gene regulation, while CTCF-s contributes to a lesser degree.