Role of neural crest mesenchyme in thymus development and function

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， 对于适应性免疫反应来说是不可或缺的。鉴于胸腺退化和T细胞输出量减少 是年龄增长或疾病的后果，人们对治疗策略有相当大的兴趣 旨在恢复胸腺。然而，了解细胞间的相互作用和分子机制是必要的。 在个体发育过程中产生胸腺新生所需的途径，以便设计出合理的 它的再生途径。这个应用着重于神经脊派生的机制。 间充质细胞调节胸腺上皮和造血室的发育 器官发生。我们的初步数据显示，神经脊细胞(NCC)扮演着以前未被认识到的角色 在第三PP内胚层构型中的作用，并提示NCC在早期和晚期发挥着不同的作用 胸腺器官发生。Pax3Sp/Sp胚胎NCC缺陷导致胸腺边界移位 和甲状旁腺特异区的共同第三袋原基。与通配型相比 Pax3Sp/Sp突变体的共有原基具有相对较小的Gcm2表达结构域和 相应较大的Foxn1表达结构域。重要的是，整体细胞密度在 突变型和野生型的共同原基。既没有增加频率，也没有增加 Pax3Sp/Sp共有原基中细胞增殖，也不降低细胞凋亡率 与Pax3+/+窝产仔相比。因此，第三袋内皮祖细胞数量的增加 致力于胸腺命运的人解释了胸腺叶出人意料地大，尽管是异位的 E12.5Pax3Sp/Sp胚胎。 尽管这些发现似乎与普遍的共识不符，即NCC缺陷导致 胸腺发育不良，这一矛盾的可能解释是NCC在不同的 发育阶段。最初，第三袋的正确图案需要NCC导出的信号 内胚层。特异性目标1和2集中在NCC控制胸腺的分子机制上 甲状旁腺决定内皮祖细胞的命运。在胸腺器官发生的稍晚阶段， 凝聚NC来源的间充质胶囊产生Fgf7和FgflO，促进细胞生长 胸腺雏形。NCC是否在胎儿晚期和晚期是否发挥了额外的作用仍有待确定 出生后的胸腺。这个问题是具体目标3的中心焦点。

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 wildtype 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 wildtype 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.