Enhancers of the PAIR4 regulatory module promote distal VH gene recombination at the Igh locus

While extended loop extrusion across the entire Igh locus controls VH-DJH recombination, local regulatory sequences, such as the PAIR elements, may also activate VH gene recombination in pro-B-cells. Here we show that PAIR-associated VH8 genes contain a conserved putative regulatory element (V8E) in their downstream sequences. To investigate the function of PAIR4 and its V8.7E, we deleted all 14 PAIRs in the Igh 5'-region, which reduced distal VH gene recombination over a 100-kb distance on either side of the 890-kb deletion. Reconstitution by insertion of PAIR4-V8.7E strongly activated distal VH gene recombination. PAIR4 alone resulted in lower induction of recombination, indicating that PAIR4 and V8.7E function as one regulatory unit. The pro-B-cell-specific activity of PAIR4 depends on CTCF, as mutation of its CTCF-binding site led to sustained PAIR4 activity in pre-B and immature B-cells and in PAIR4 activation in T-cells. Notably, insertion of V8.8E was sufficient to activate VH gene recombination. Hence, enhancers of the PAIR4-V8.7E module and V8.8E element activate distal VH gene recombination and thus contribute to the diversification of the BCR repertoire in addition to loop extrusion. Overall design: VDJ-Seq: Nine experimental conditions, with three biological replicates each, associated with control samples (Igh(+/+)). RNA-Seq: two control (Igh(_delta_890/+) and two experimental (Igh(P4V/P4V)) samples. total RNA-Seq: two control samples. ChIP-Seq: Four control samples, single replcates.