Position-Dependent Silencing of Germline V beta Segments on TCR beta Alleles Containing Preassembled V beta DJ beta C beta 1 Genes

Abstract

The genomic organization of TCRβ loci enables Vβ-to-DJβ2 rearrangements on alleles with assembled VβDJβCβ1 genes, which could have deleterious physiologic consequences. To determine whether such Vβ rearrangements occur and, if so, how they might be regulated, we analyzed mice with TCRβ alleles containing preassembled functional VβDJβCβ1 genes. Vβ10 segments were transcribed, rearranged, and expressed in thymocytes when located immediately upstream of a Vβ1DJβCβ1 gene, but not on alleles with a Vβ14DJβCβ1 gene. Germline Vβ10 transcription was silenced in mature αβ T cells. This allele-dependent and developmental stage-specific silencing of Vβ10 correlated with increased CpG methylation and decreased histone acetylation over the Vβ10 promoter and coding region. Transcription, rearrangement, and expression of the Vβ4 and Vβ16 segments located upstream of Vβ10 were silenced on alleles containing either VβDJβCβ1 gene; sequences within Vβ4, Vβ16, and the Vβ4/Vβ16-Vβ10 intergenic region exhibited constitutive high CpG methylation and low histone acetylation. Collectively, our data indicate that the position of Vβ segments relative to assembled VβDJβCβ1 genes influences their rearrangement and suggest that DNA sequences between Vβ segments may form boundaries between active and inactive Vβ chromatin domains upstream of VβDJβCβ genes.