How to Confirm a TAD Boundary Is Functional

A boundary is functional when perturbing the boundary itself changes contact and changes expression in the predicted direction. The standard design is a CTCF-motif inversion (or small motif deletion) at the boundary, followed by locus-specific contact measurement and expression of the flanking genes, with a non-targeting edit and a second boundary edit as controls.

Deleting the whole boundary region, or showing that a boundary correlates with insulation, does neither.

• • Call the boundary from contact data at a stated resolution, and report the insulation score and the caller used.
• • Locate the CTCF motif at the boundary and confirm its orientation; convergent motif pairs matter, and a single motif is often one of several.
• • Confirm CTCF occupancy at the site in your cell type by ChIP or CUT&RUN.
• • Define the two flanking regions and the gene(s) on each side that you will measure.

A boundary with several CTCF sites is not one element. Decide which site you will perturb and say so.

Three perturbation classes, in order of interpretability:

Motif inversion is preferred because it preserves the DNA, the spacing, and the local chromatin while abolishing the orientation that CTCF binding requires. It is the cleanest available test of "this site, this function".

Whichever is used, confirm the edit by sequencing and check that CTCF occupancy falls at the edited site.

Locus-specific methods are required; genome-wide Hi-C is usually too shallow to resolve a single boundary change convincingly.

• • Capture-C or Micro-Capture-C at the locus, with probes on both flanking regions and on the candidate enhancers.
• • Compare contact profiles between edited and control clones, at matched sequencing depth.
• • Report the change quantitatively: not only "contact decreased" but by how much, over what interval, and with what replicate variability.

A change in contact that is smaller than the between-clone variability of control clones is not a result.

The functional claim rests on the expression consequence, and it needs the same care as any regulatory experiment:

• • Measure genes on both sides of the boundary, not only the gene you expect to change.
• • Include genes distal to the boundary that should not change, as specificity controls.
• • Use at least two independent edited clones per genotype.
• • Report effect sizes with intervals, and state the detectable range.

A contact change without an expression change supports "this site contributes to architecture" — which may still be publishable, but is a different claim.

• • Non-targeting edit processed through the same pipeline.
• • Second boundary motif, elsewhere in the locus, edited the same way — if only your site produces the effect, specificity is supported.
• • Motif-swap control: replace the CTCF motif with a different factor's motif, preserving binding but not CTCF identity.
• • Acute cohesin depletion as an orthogonal perturbation: if loop architecture is required for the effect, acute loss should reproduce part of the phenotype.
• • Rescue: re-invert the motif, or re-insert the site, and show the phenotype reverses.

The rescue step is what most boundary papers lack, and it is the first thing a careful reviewer will ask for.

The third row is where most credible papers sit. The fourth is what distinguishes a mechanistically complete study.

EDITGENE builds CTCF motif inversion and deletion lines with sequenced edits, confirmed occupancy loss, matched non-targeting clones, and rescue derivatives — designed for Capture-C readout at matched depth.

Send us the boundary coordinates and the genes you intend to measure. Contact EDITGENE to request a project consultation or quote.

Boundary calls depend on resolution and normalization, and a single motif is often one of several contributing sites; an effect at one site does not establish that the boundary as a whole is required.

Contact measurements are population averages and should be interpreted alongside, not instead of, expression and occupancy data.

• • Lupiáñez DG, et al. Disruptions of topological chromatin domains cause pathogenic rewiring of gene–enhancer interactions. Cell. 2015;161:1012–1025.
• • Hnisz D, et al. Activation of proto-oncogenes by disruption of chromosome neighborhoods. Science. 2016;351:1454–1458.
• • Rao SSP, et al. Cohesin loss eliminates all loop domains. Cell. 2017;171:305–320.
• • Nora EP, et al. Targeted degradation of CTCF decouples local insulation of chromosome domains from genomic compartmentalization. Cell. 2017;169:930–944.