Insertion of an Imprinted Insulator into the IgH Locus Reveals Developmentally Regulated, Transcription-Dependent Control of V(D)J Recombination

Abstract

? 2015, American Society for Microbiology.The assembly of antigen receptor loci requires a developmentally regulated and lineage-specific recombination between variable (V), diversity (D), and joining (J) segments through V(D)J recombination. The process is regulated by accessibility control elements, including promoters, insulators, and enhancers. The IgH locus undergoes two recombination steps, D-JH and then VH-DJH, but it is unclear how the availability of the DJH substrate could influence the subsequent VH-DJH recombination step. The E? enhancer plays a critical role in V(D)J recombination and controls a set of sense and antisense transcripts. We epigenetically perturbed the early events at the IgH locus by inserting the imprinting control region (ICR) of the Igf2/H19 locus or a transcriptional insulator devoid of the imprinting function upstream of the E? enhancer. The insertions recapitulated the main epigenetic features of their endogenous counterparts, including differential DNA methylation and binding of CTCF/cohesins. Whereas the D-JH recombination step was unaffected, both the insulator insertions led to a severe impairment of VH-DJH recombination. Strikingly, the inhibition of VH-DJH recombination correlated consistently with a strong reduction of DJH transcription and incomplete demethylation. Thus, developmentally regulated transcription following D-JH recombination emerges as an important mechanism through which the E? enhancer controls VH-DJH recombination.