Department of Pathology and Laboratory Medicine, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA.
J Immunol. 2010 Feb 1;184(3):1369-78. doi: 10.4049/jimmunol.0900723. Epub 2009 Dec 30.
Ag receptor allelic exclusion is thought to occur through monoallelic initiation and subsequent feedback inhibition of recombinational accessibility. However, our previous analysis of mice containing a V(D)J recombination reporter inserted into Vbeta14 (Vbeta14(Rep)) indicated that Vbeta14 chromatin accessibility is biallelic. To determine whether Vbeta14 recombinational accessibility is subject to feedback inhibition, we analyzed TCRbeta rearrangements in Vbeta14(Rep) mice containing a preassembled in-frame transgenic Vbeta8.2Dbeta1Jbeta1.1 or an endogenous Vbeta14Dbeta1Jbeta1.4 rearrangement on the homologous chromosome. Expression of either preassembled VbetaDJbetaC beta-chain accelerated thymocyte development because of enhanced cellular selection, demonstrating that the rate-limiting step in early alphabeta T cell development is the assembly of an in-frame VbetaDJbeta rearrangement. Expression of these preassembled VbetaDJbeta rearrangements inhibited endogenous Vbeta14-to-DJbeta rearrangements as expected. However, in contrast to results predicted by the accepted model of TCRbeta feedback inhibition, we found that expression of these preassembled TCR beta-chains did not downregulate recombinational accessibility of Vbeta14 chromatin. Our findings suggest that TCRbeta-mediated feedback inhibition of Vbeta14 rearrangements depends on inherent properties of Vbeta14, Dbeta, and Jbeta recombination signal sequences.
Ag 受体等位基因排斥被认为是通过单等位基因起始和随后的重组可及性反馈抑制来发生的。然而，我们之前对含有插入 Vbeta14 的 V(D)J 重组报告基因的小鼠（Vbeta14(Rep)）的分析表明，Vbeta14 染色质的可及性是双等位基因的。为了确定 Vbeta14 重组可及性是否受到反馈抑制，我们分析了含有预组装的框架内转基因 Vbeta8.2Dbeta1Jbeta1.1 或同源染色体上内源性 Vbeta14Dbeta1Jbeta1.4 重排的 Vbeta14(Rep) 小鼠中的 TCRbeta 重排。预组装的 VbetaDJbetaC β链的表达由于增强的细胞选择而加速了胸腺细胞的发育，这表明早期αβ T 细胞发育的限速步骤是形成框架内的 VbetaDJbeta 重排。这些预组装的 VbetaDJbeta 重排的表达如预期的那样抑制了内源性 Vbeta14 到 DJbeta 的重排。然而，与 TCRbeta 反馈抑制的公认模型的预测结果相反，我们发现这些预组装的 TCRβ 链的表达并没有下调 Vbeta14 染色质的重组可及性。我们的研究结果表明，TCRbeta 介导的 Vbeta14 重排的反馈抑制取决于 Vbeta14、Dbeta 和 Jbeta 重组信号序列的固有特性。
