3D GENOME ARCHITECTURE IN DIVERSE SPECIES (Page 17)

; [What is the biological function of TADs?]

TADs generate a local compartment within which regulatory elements are more likely to 'randomly' contact each other. Enhancer-promoter contacts generally occur within TADs.

; [What happens across TAD boundaries?]

CTCF and Cohesin mediated spatial boundaries prevent enhancer-promoter contacts across TADs.

; [How do TADs relate to transcriptional activity?]

TADs generally function as transcriptional units with similar transcriptional patterns within TADs (active A compartments) while neighbouring TADs may have different transcriptional activity (repressed B compartments).

; [Are TADs found in all organisms?]

No. TADs are animal specific.

; [What do other species have instead of TADs?]

Other species have sub-chromosomal mechanisms of organisation that are reminiscent of mammalian A and B 'compartments'. These are not considered TADs and do not require CTCF.

; [Is CTCF found in all organisms?]

No. CTCF is a Bilateria-specific gene.  ; [Why don't single-cell organisms have TADs?]