Laboratory for Lymphocyte Development, RIKEN Research Centre for Allergy and Immunology, Yokohama, Japan.
Mol Immunol. 2010 Feb;47(5):1106-13. doi: 10.1016/j.molimm.2009.10.034. Epub 2009 Nov 27.
Thymic epithelial cells (TECs), derived from polarized two-dimensional (2D) oriented endodermal cells, are distinguished from other epithelial cells by their unique three-dimensional (3D) phenotype. However, some polarized epithelial cells remain present in the normal thymus, forming thymic cysts at the cortico-medullary junction. Here, we analyse the dynamics, origin and phenotype of such thymic cysts. In time-course experiments, we show a reverse correlation between thymic cyst expansion and the presence of thymocytes, suggesting a default pathway for the development of TECs in the absence of thymocytes. By transplanting isolated TEC populations into E15 fetal thymic lobes, we provide evidence that medullary thymic epithelial cells (mTECs), rather than cortical thymic epithelial cells (cTECs) contribute to the formation of thymic cysts. Finally, thymi of reporter mice reveal that the cysts originate from epithelia committed to a thymic fate, as indicated by the expression of Foxn1. The 2D-phenotype of cyst-lining TECs is not caused by a downregulation of Foxn1 expression, since a significant proportion of these cells in the embryonic and adult thymus continues to express Foxn1 at the protein level.
胸腺上皮细胞（TEC）来源于极化的二维（2D）内胚层细胞，其独特的三维（3D）表型将其与其他上皮细胞区分开来。然而，在正常胸腺中仍存在一些极化的上皮细胞，在皮质-髓质交界处形成胸腺小囊。在这里，我们分析了这些胸腺小囊的动力学、起源和表型。在时间过程实验中，我们发现胸腺小囊扩张与胸腺细胞的存在之间呈反向相关，这表明在没有胸腺细胞的情况下，TEC 的发育存在默认途径。通过将分离的 TEC 群体移植到 E15 胎胸腺小叶中，我们提供的证据表明，参与胸腺小囊形成的是髓质胸腺上皮细胞（mTEC），而不是皮质胸腺上皮细胞（cTEC）。最后，报告小鼠的胸腺表明，这些小囊起源于已经决定向胸腺命运发展的上皮细胞，这一点可以通过 Foxn1 的表达来指示。囊壁衬里 TEC 的 2D 表型不是由 Foxn1 表达下调引起的，因为在胚胎和成年胸腺中，这些细胞中有相当一部分仍在蛋白质水平上表达 Foxn1。
