Current observations/claims for CTCF in insulation potency and chromatin interactionΒΆ
Chromatin interactions are possibly formed by convergent CTCF pairs, although there are tandom CTCF pairs. But the chances of a loop with convergent pair is 3 times higher than a tandem pair.
In terms of insulation potency, the number of CTCF sites is important, more sites means more insulation power. But these observation is tested using core TAD boundary CTCF sequences.
Replacing TAD boundary CTCF sequences with non-TAD boundary CTCF sequences significantly reduced insulation power. And it seems the +/- 20bp flanking sequences of the 19bp CTCF motif is the key. One known motif is the CTCF-upstream motif, which binds to a Znic-Finger protein.
Disruption of the CTCF-upstream motif did not affect CTCF binding.
Reference:
[Loop competition and extrusion model predicts CTCF interaction specificity](https://www.nature.com/articles/s41467-021-21368-0)
[Many facades of CTCF unified by its coding for three-dimensional genome architecture](https://www.sciencedirect.com/science/article/pii/S1673852720301284)
[Promoter-proximal CTCF binding promotes distal enhancer-dependent gene activation](https://www.nature.com/articles/s41594-020-00539-5?utm_source=other&utm_medium=other&utm_content=null&utm_campaign=JRCN_1_DD01_CN_NatureRJ_article_paid_XMOL)
[CTCF mediates dosage- and sequence-context-dependent transcriptional insulation by forming local chromatin domains](https://www.nature.com/articles/s41588-021-00863-6?proof=t)