Transcription factor network involved in maintenance and regeneration of epithelial progenitor cells in the thymus

大多数上皮组织保留干细胞/祖细胞以维持成年组织的动态平衡；然而，胸腺上皮细胞(TEC)前体细胞的存在能够维持出生后胸腺的动态平衡仍不清楚。在这里，我们显示高水平表达MEIS1的TEC群体，MEIS1是一种同源结构域转录因子，在未分裂的静止细胞中富含未成熟的细胞表型。出生后MEIS1在TECs中的失活导致未成熟的MEIS1高TECs耗竭，并促进其进入细胞周期，最终导致胸腺过早消失。Meis1高TEC人群的比例随着年龄的增长而降低，这也可能与胸腺退缩有关。这些发现表明，在出生后的胸腺中，Meis1的高水平表达标志着一个独特的具有祖细胞活性的TEC群体，其中Meis1的功能是维持出生后胸腺的动态平衡所需的未分化状态。

Most epithelial tissues retain stem/progenitor cells to maintain homeostasis of the adult tissues ; however, the existence of a thymic epithelial cell(TEC) progenitor capable of maintaining homeostasis of the postnatal thymus remains unclear. Here we show that a TEC population expressing high levels of Meis1, a homedodomain transcription factor, is enriched in non-dividing quiescent cells with an immature cellular phenotype. Postnatal inactivation of Meis1 in TECs caused exhaustion of the immature Meis1high TECs and promoted their cell cycle entry, which ultimately lead to premature disappearance of the thymus. There was an age-associated reduction in the proportion of the Meis1high TEC population, which may also relate to thymic involution. These findings indicate that in the postnatal thymus the high level expression of Meis1 marks a unique population of TECs with progenitor activity, in which Meis1 functions to maintain the undifferentiated state that is required for homeostasis of the postnatal thymus.