Role of neural crest mesenchyme in thymus development and function

描述（由申请方提供）：胸腺为产生适应性免疫应答所必需的自我耐受、自我限制T细胞提供了独特的微环境。鉴于胸腺退化和T细胞输出减少是年龄增长或疾病的后果，因此对旨在恢复胸腺的治疗策略有相当大的兴趣。然而，它是必不可少的，以了解所需的细胞相互作用和分子途径，以产生胸腺从头在个体发育过程中，以制定合理的方法，其再生。本申请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细胞发育的机制。我们的初步数据显示，神经嵴细胞（NCCs）发挥了以前未被认识到的作用，图案第三PP内胚层，并建议，NCCs发挥不同的作用，在早期和晚期阶段的胸腺器官发生。Pax 3Sp/Sp胚胎中的NCC缺陷导致共同的第三囊原基的胸腺和类囊蛋白特异性结构域之间的边界移动。与野生型同窝仔相比，Pax 3Sp/Sp突变体的共享原基具有相对较小的Gcm 2表达结构域和相应较大的Foxnl表达结构域。重要的是，突变体和野生型同窝仔的共有原基中的总体细胞结构相当。与Pax 3 +/+同窝仔相比，在Pax 3Sp/Sp的共享原基中既没有增殖细胞频率的增加，也没有凋亡细胞频率的减少。因此，第三袋内胚层祖细胞的数量增加，致力于胸腺的命运占了意想不到的大，虽然异位，胸腺叶在E12.5 Pax 3Sp/Sp胚胎。虽然这些发现似乎与NCC缺陷导致胸腺发育不全的普遍共识不一致，但对这种矛盾的可能解释是NCC在不同的发育阶段执行不同的功能。最初，NCC衍生的信号是第三囊内胚层的正确图案化所必需的。具体目标1和2关注NCC控制内胚层祖细胞中胸腺与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，浓缩的NC衍生的间充质囊产生Fgf 7和Fgf 10，其促进胸腺原基的生长。NCC是否在晚期胎儿和出生后胸腺中发挥额外的作用仍有待确定。这一问题是具体目标3的核心重点。

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.