An ectopic CTCF-dependent transcriptional insulator influences the choice of Vβ gene segments for VDJ recombination at TCRβ locus

Insulators regulate transcription as they modulate the interactions between enhancers and promoters by organizing the chromatin into distinct domains. To gain better understanding of the nature of chromatin domains defined by insulators, we analyzed the ability of an insulator to interfere in VDJ recombination, a process that is critically dependent on long-range interactions between diverse types of cis-acting DNA elements. A well-established CTCF-dependent transcriptional insulator, H19 imprint control region (H19-ICR), was inserted in the mouse TCRβ locus by genetic manipulation. Analysis of the mutant mice demonstrated that the insulator retains its CTCF and position-dependent enhancer-blocking potential in this heterologous context in vivo. Remarkably, the inserted H19-ICR appears to have the ability to modulate cis-DNA interactions between recombination signal sequence elements of the TCRβ locus leading to a dramatically altered usage of Vβ segments for Vβ-to-DβJβ recombination in the mutant mice. This reveals a novel ability of CTCF to govern long range cis-DNA interactions other than enhancer–promoter interactions and suggests that CTCF-dependent insulators may play a diverse and complex role in genome organization beyond transcriptional control. Our functional analysis of mutated TCRβ locus supports the emerging role of CTCF in governing VDJ recombination.