Role of neural crest mesenchyme in thymus development and function

描述（由申请人提供）：胸腺为产生自我耐受、自我限制的T细胞提供了一个独特的微环境，这是适应性免疫反应不可或缺的。鉴于胸腺退化和T细胞输出减少是年龄增长或疾病的结果，针对胸腺恢复的治疗策略有相当大的兴趣。然而，为了设计出合理的胸腺再生方法，有必要了解在个体发育过程中产生胸腺新生所需的细胞相互作用和分子途径。本应用程序的重点是在胸腺器官发生过程中，神经嵴来源的间充质细胞调节上皮和造血室发育的机制。我们的初步数据显示，神经嵴细胞（NCCs）在第三PP内胚层的模式中发挥了以前未被认识到的作用，并表明NCCs在胸腺器官发生的早期和晚期发挥了不同的作用。Pax3Sp/Sp胚胎的NCC缺陷导致第三育袋原基胸腺和甲状旁腺特异性结构域之间的边界转移。与野生型幼崽相比，Pax3Sp/Sp突变体的共享原基具有相对较小的Gcm2表达域和相应较大的Foxnl表达域。重要的是，在突变型和野生型幼崽共有的原基中，整体细胞结构是相似的。与Pax3+/+幼崽相比，Pax3Sp/Sp共享原基中增殖细胞的频率没有增加，凋亡细胞的频率也没有减少。因此，致力于胸腺命运的第三育儿袋内胚层祖细胞数量的增加解释了E12.5 Pax3Sp/Sp胚胎中出乎意料的大（尽管异位）胸腺叶。尽管这一发现似乎与NCC缺乏导致胸腺发育不全的普遍共识不一致，但对这一悖论的可能解释是，NCC在不同的发育阶段发挥着不同的功能。最初，ncc衍生的信号是第三育儿袋内胚层的正确模式所必需的。具体目标1和2集中于NCCs控制内胚层祖细胞胸腺和甲状旁腺命运决定的分子机制。在胸腺器官发生的稍晚阶段，凝聚的nc来源的间充质囊产生促进胸腺雏形生长的Fgf7和FgflO。NCCs是否在胎儿晚期和出生后胸腺中发挥其他作用仍有待确定。这个问题是具体目标3的中心焦点。

DESCRIPTION (provided by applicant): The thymus provides a unique microenvironment for the generation of self-tolerant, self-restricted T cells that are indispensable for the adaptive immune response. Given that thymus involution and reduced T cell output are consequences of advancing age or disease, there is considerable interest in therapeutic strategies aimed at thymus restoration. However, it is essential to understand the cellular interactions and molecular pathways that are required to generate the thymus de novo during ontogeny in order to devise rational approaches for its regeneration. This application focuses on the mechanisms by which neural crest-derived mesenchymal cells regulate development of the epithelial and hematopoietic compartments during thymus organogenesis. Our preliminary data reveal that neural crest cells (NCCs) play a previously unrecognized role in patterning 3rd PP endoderm and suggest that NCCs play distinct roles during early and late stages of thymus organogenesis. The NCC defect in Pax3Sp/Sp embryos results in a boundary shift between thymus and parathryoid specific domains of the common third pouch primordia. In comparison to wild-type littermates, the shared primordia of Pax3Sp/Sp mutants have a relatively smaller Gcm2 expressing domain and a correspondingly larger Foxnl expressing domain. Importantly, overall cellularity is comparable in the shared primordia of mutant and wild-type littermates. There is neither an increase in the frequency of proliferating cells, nor a decrease in the frequency of apoptotic cells in the shared primordia of Pax3Sp/Sp compared to Pax3+/+ littermates. Therefore, the increased number of third pouch endodermal progenitors that are committed to a thymus fate accounts for the unexpectedly large, albeit ectopic, thymic lobes in E12.5 Pax3Sp/Sp embryos. Although the findings appear to be at odds with the general consensus that NCC deficiencies result in thymus hypoplasia, the likely explanation for this paradox is that NCCs perform distinct functions at different developmental stages. Initially, NCC-derived signals are required for correct patterning of the third pouch endoderm. Specific Aims 1 and 2 focus on the molecular mechanisms by which NCCs control thymus versus parathyroid fate decisions in endodermal progenitors. At a slightly later stage of thymus organogenesis, the condensing NC-derived mesenchymal capsule produces Fgf7 and FgflO that promote-outgrowth of the thymus rudiment. It remains to be determined whether NCCs play additional roles in the late fetal and postnatal thymus. This issue is the central focus of Specific Aim 3.