The generation of a diverse antibody repertoire is essential for humoral immunity and requires the participation of all V genes in V(D)J recombination, which depends on the Pax5-regulated contraction of the 2.8-Mb long immunoglobulin heavy-chain (Igh) locus. How Pax5 controls Igh contraction in pro-B cells is, however, not known. Here, we demonstrate that locus contraction is caused by cohesin-mediated chromatin loop extrusion across the entire Igh locus. Notably, expression of the cohesin-release factor Wapl is repressed by Pax5 specifically in pro-B and pre-B cells, which facilitates extended loop extrusion by increasing the residence time of cohesin on chromatin. Pax5 mediates the transcriptional repression of Wapl through a single Pax5-binding site by recruiting the Polycomb repressive complex 2 to induce bivalent chromatin at the Wapl promoter. Reduced Wapl expression causes global alterations of the three-dimensional chromatin architecture, indicating that the potential to recombine all V genes entails structural changes of the entire genome in pro-B cells. SOURCE: Meinrad Busslinger (meinrad.busslinger@imp.ac.at) - Busslinger IMP

Pluto Bioinformatics

GSE140975: Wapl repression by Pax5 promotes loop extrusion and V gene recombination at the Igh locus