Cutting Edge: Developmental Stage-Specific Recruitment of Cohesin to CTCF Sites throughout Immunoglobulin Loci during B Lymphocyte Development

Abstract

Contraction of the large Igh and Igκ loci brings all V genes, spanning >2.5 Mb in each locus, in proximity to DJH or Jκ genes. CCCTC-binding factor (CTCF) is a transcription factor that regulates gene expression by long-range chromosomal looping. We therefore hypothesized that CTCF may be crucial for the contraction of the Ig loci, but no CTCF sites have been described in any V loci. Using ChIP-chip, we demonstrated many CTCF sites in the VH and Vκ regions. However, CTCF enrichment in the Igh locus, but not the Igκ locus, was largely unchanged throughout differentiation, suggesting that CTCF binding alone cannot be responsible for stage-specific looping. Because cohesin can colocalize with CTCF, we performed chromatin immunoprecipitation for the cohesin subunit Rad21 and found lineage and stage-specific Rad21 recruitment to CTCF in all Ig loci. The differential binding of cohesin to CTCF sites may promote multiple loop formation and thus effective V(D)J recombination.