Analysis of Bcl11b function during thymocyte Differentiation

研究表明，任何选择后的DP胸腺细胞在表达ThPOK时都会分化为CD4系细胞，而在没有ThPOK的情况下，它们会分化为CD8系细胞。因此，了解ThPOK基因的辅助谱系特异性表达是如何调控的是至关重要的。我们在ThPOK基因中发现了一个ThPOK沉默因子，它在MHC-I类细胞向细胞毒株分化的过程中抑制ThPOK基因的表达。为了揭示ThPOK沉默因子活性的调节，我们用功能较短的沉默因子序列进行了下拉亲和纯化。通过对上述方法获得的几个候选基因进行分子和生物学筛选，Bcl11b转录因子似乎在激活ThPOK沉默方面发挥了重要作用。对Bcl11b条件性基因敲除小鼠的遗传分析表明，ThPOK在预选胸腺细胞和MHC I类选择细胞中均被下调，导致MHC I类选择细胞向CD4~+辅助系细胞转化。这些结果表明，Bcl11b是通过调节ThPOK沉默分子的活性来调节淋巴细胞的辅助/细胞毒性谱系决定的中心。

It has been shown that any post-selection DP thymocytes differentiate into CD4-lineage upon expression of ThPOK, whereas they become CD8-linage cells in the absence of ThPOK. Therefore it is crucial to understand how helper-lineage specific expression of ThPOK gene is regulated. We have identified a ThPOK silencer in the ThPOK gene that is essential to repress ThPOK gene during differentiation of MHC class I selected cells toward the cytotoxic-lineage.In order to reveal regulation of ThPOK silencer activity, we performed pull down affinity purification with the functional shorter silencer sequences. After molecular and biological screening of several candidates obtained by the above approach, Bcl11b transcription factor appeared to play an essential role in activating ThPOK silencer. Genetic analysis of Bcl11b conditional knock-out mice showed that de-repression of ThPOK in both pre-selection thymocyte and in MHC class I selected cells, resulting in cell fate conversion of MHC class I selected cells to CD4^+helper lineage cells. These results suggested that Bcl11b is central to regulate helper/cytotoxic lineage decision by lymphocytes via regulation of ThPOK silencer activity.