Control of Lineage Commitment in Developing Thymocytes

描述（由申请人提供）：迄今为止，ThPOK在T细胞发育中的表达被认为仅限于ab T细胞谱系，特别是胸腺和周围的移行性CD4+8lo胸腺细胞和SP CD4细胞。我们现在表明，gdTCR+胸腺细胞的一个子集也表达ThPOK，并且ThPOK的表达与激活标记物CD44的表达密切相关。此外，ThPOK在KN6 gdTCR转基因小鼠中表达时存在高亲和力配体，而不存在低亲和力配体。这些观察结果表明ThPOK在gd胸腺细胞中被诱导以响应强TCR信号。值得注意的是，缺乏功能性ThPOK的HD-/-小鼠在成熟gd胸腺细胞的发育中表现出严重缺陷，而组成性表达ThPOK的小鼠则表现出显著的增加，这表明ThPOK在gd细胞的成熟和/或谱系承诺中发挥了重要作用。鉴于TCR信号传导和选择对gd发育的重要性仍然存在高度争议，确定ThPOK在这些过程中的关键作用将是一项重大进展。因此，在本提案的目标1和目标2中，我们提出解决ThPOK在gd胸腺细胞中的诱导是否由TCR信号直接调节，以及ThPOK是否控制gd胸腺细胞的阳性/阴性选择和/或对gd谱系的承诺。有趣的是，虽然ThPOK似乎是正常gd发育所必需的，但其在表达precr的DN胸腺细胞中的表达导致胸腺淋巴瘤的高发。在Aim 3中，我们提出确定淋巴瘤发生起始的细胞类型和个体发生阶段，并测试gdTCR表达或gd承诺是否足以保护DN胸腺细胞免受thpok介导的淋巴瘤发生。

DESCRIPTION (provided by applicant): Hitherto, the expression of ThPOK in T cell development was believed to be restricted to the ab T cell lineage, in particular to transitional CD4+8lo thymocytes and SP CD4 cells in the thymus and periphery. We now show that a subset of gdTCR+ thymocytes also expresses ThPOK, and that ThPOK expression correlates largely with expression of the activation marker CD44. Furthermore, ThPOK is expressed in KN6 gdTCR transgenic mice in the presence of high but not low affinity ligands. These observations suggest that ThPOK is induced in gd thymocytes in response to strong TCR signals. Significantly, HD-/- mice, which lack functional ThPOK, show a severe defect in development of mature gd thymocytes, while mice expressing ThPOK constitutively show a striking increase, establishing an important role for ThPOK in maturation and/or lineage commitment of gd cells. Given that the importance of TCR signaling and selection for gd development remains highly controversial, establishing a critical role for ThPOK in these processes would represent a significant advance. Hence in Aims 1 and 2 of the current proposal, we propose to address whether ThPOK induction in gd thymocytes is directly regulated by TCR signaling, and whether ThPOK controls positive/negative selection of gd thymocytes and/or commitment to the gd lineage. Interestingly, while ThPOK appears to be required for normal gd development, its expression in preTCR-expressing DN thymocytes leads to a high incidence of thymic lymphomas. In Aim 3 we propose to identify the cell type and stage in ontogeny at which lymphomagenesis is initiated, and test whether gdTCR expression or gd commitment are sufficient to protect DN thymocytes against ThPOK-mediated lymphomagenesis. PUBLIC HEALTH RELEVANCE: The current proposal deals with the process by which T cells develop to the distinct gd lineage, which we show is controlled by a key transcription factor called ThPOK. How ThPOK controls this process is unknown and the subject of this proposal. Unregulated expression of ThPOK causes blood cell cancer, so that understanding its function is of direct relevance to health.