The Distal VH Gene Cluster of the Igh Locus Contains Distinct Regulatory Elements with Pax5 Transcription Factor-Dependent Activity in Pro-B Cells

V-H-DJ(H) recombination of the immunoglobulin heavy chain (Igh) locus is temporally and spatially controlled during early B cell development, and yet no regulatory elements other than the V-H gene promoters have been identified throughout the entire VH gene cluster. Here, we discovered regulatory sequences that are interspersed in the distal VH gene region. These conserved repeat elements were characterized by the presence of Rax5 transcription factor-dependent active chromatin by binding of the regulators Pax5, E2A, CTCF, and Rad21, as well as by Pax5-dependent antisense transcription in pro-B cells. The Pax5-activated intergenic repeat (PAIR) elements were no longer bound by Pax5 in pre-B and B cells consistent with the loss of antisense transcription, whereas E2A and CTCF interacted with PAIR elements throughout early B cell development. The pro-B cell-specific and Pax5-dependent activity of the PAIR elements suggests that they are involved in the regulation of distal V-H-DJ(H) recombination at the Igh locus.