Department of Immunology, Duke University Medical Center, Durham, NC 27710, USA.
J Immunol. 2011 Sep 1;187(5):2484-91. doi: 10.4049/jimmunol.1100468. Epub 2011 Jul 22.
Murine Tcra and Tcrd gene segments are organized into a single genetic locus (Tcra/Tcrd locus) that undergoes V(D)J recombination in CD4(-)CD8(-) double-negative (DN) thymocytes to assemble Tcrd genes and in CD4(+)CD8(+) double-positive thymocytes to assemble Tcra genes. Recombination events are regulated by two developmental stage-specific enhancers, E(δ) and E(α). Effects of E(α) on Trca/Tcrd locus chromatin have been well documented, but effects of E(δ) have not. In this regard, E(α) acts over long distances to activate many V(α) and J(α) segments for recombination in double-positive thymocytes. However, in DN thymocytes, it is unclear whether E(δ) functions over long distances to regulate V(δ) gene segments or functions only locally to regulate D(δ) and J(δ) gene segments. In this study, we analyzed germline transcription, histone modifications, and recombination on wild-type and E(δ)-deficient alleles in adult and fetal thymocytes. We found that E(δ) functions as a local enhancer whose influence is limited to no more than ∼10 kb in either direction (including D(δ), J(δ), and TRDV5 gene segments) in adult DN thymocytes. However, we identified a unique long-distance role for E(δ) promoting accessibility and recombination of fetal V(δ) gene segment TRDV4, over a distance of 55 kb, in fetal thymocytes. TRDV4 recombination is specifically repressed in adult thymocytes. We found that this repression is enforced by a developmentally regulated loss of histone acetylation. Constitutively high levels of a suppressive modification, histone H3 lysine 9 dimethylation, may contribute to repression as well.
鼠 TCRa 和 TCRd 基因片段组织在一个单一的遗传基因座（TCRa/TCRd 基因座）中，该基因座在 CD4(-)CD8(-)双阴性（DN）胸腺细胞中经历 V(D)J 重组，以组装 TCRd 基因，在 CD4(+)CD8(+)双阳性胸腺细胞中组装 TCRa 基因。重组事件受两个发育阶段特异性增强子 E(δ)和 E(α)调控。E(α)对 Trca/Tcrd 基因座染色质的影响已有详细记录，但 E(δ)的影响尚未确定。在这方面，E(α)通过长距离作用激活许多 V(α)和 J(α)片段，以在双阳性胸腺细胞中进行重组。然而，在 DN 胸腺细胞中，尚不清楚 E(δ)是否通过长距离作用来调节 V(δ)基因片段，还是仅在局部作用来调节 D(δ)和 J(δ)基因片段。在这项研究中，我们分析了野生型和 E(δ)缺陷型等位基因在成年和胎儿胸腺细胞中的原始转录、组蛋白修饰和重组。我们发现，E(δ)作为一个局部增强子发挥作用，其影响在成年 DN 胸腺细胞中不超过 10kb（包括 D(δ)、J(δ)和 TRDV5 基因片段）。然而，我们发现 E(δ)在胎儿胸腺细胞中具有独特的长距离作用，可促进胎儿 V(δ)基因片段 TRDV4 的可及性和重组，距离为 55kb。TRDV4 重组在成年胸腺细胞中特异性受到抑制。我们发现这种抑制是通过发育调节的组蛋白乙酰化丢失来执行的。组成性高抑制修饰，组蛋白 H3 赖氨酸 9 二甲基化，也可能有助于抑制。
