Thymic epithelial cells induce formation of mesenchymal network structure after abrogation of thymic crosstalk

In the earliest step of thymic organogenesis, mesenchymal cells support the growth of thymic epithelial cells (TECs). It is established that TECs and thymocytes influence each other for their growth/differentiation, a process called thymic crosstalk. However, little is known about the influence of developing thymocytes or TECs on mesenchymal cells. Here, we show that during normal thymus development fibroblast ingrowth occurs towards hypoxic areas. Similar overgrowth of mesenchymal cells is seen in a fetal thymic organ culture system under low oxygen conditions. However, when thymocytes were depleted by deoxyguanosine treatment, mesenchymal cells were also induced, precluding the direct effect of hypoxia. In the fetal thymus of hCD3eTg mice, which lack T lineage cells, an overgrowth of mesenchymal cells can be seen at a very early stage of thymic organogenesis. The growth of the mesenchymal cells is due to extensive proliferation and not mere enrichment. With RNA sequencing analysis comparing hCD3eTg with wild type TECs, we identified candidate factors that could be involved in mesenchymal network formation. Overall design: Comparison of thymic epithelial cells of different in vivo situations; one in presence of thymocytes, the other in the absence of thymocytes

在胸腺器官发生的最早阶段，间充质细胞可支持胸腺上皮细胞（thymic epithelial cells, TECs）的生长。已有研究证实，胸腺上皮细胞与胸腺细胞可通过相互作用调控彼此的生长与分化，这一过程被称为胸腺串扰（thymic crosstalk）。然而，目前对于发育中的胸腺细胞或胸腺上皮细胞如何影响间充质细胞的机制仍知之甚少。本研究发现，在正常胸腺发育过程中，成纤维细胞会向缺氧区域浸润生长。在低氧培养条件下的胎儿胸腺器官体外培养体系中，同样可观察到间充质细胞的过度增殖。但当通过脱氧鸟苷（deoxyguanosine）处理清除胸腺细胞后，间充质细胞的增殖同样被诱导，这排除了缺氧直接发挥作用的可能性。在缺乏T细胞系的hCD3eTg转基因小鼠的胎儿胸腺中，在胸腺器官发生的极早期阶段即可观察到间充质细胞的过度增殖。该间充质细胞群体的扩增源于细胞的广泛增殖，而非单纯的细胞富集。通过对hCD3eTg小鼠与野生型小鼠的胸腺上皮细胞进行RNA测序（RNA sequencing）比对分析，本研究筛选出了可能参与间充质网络形成的候选因子。实验整体设计：对比两种体内环境下的胸腺上皮细胞——一组存在胸腺细胞，另一组缺失胸腺细胞