Nature：调控干细胞自我更新的新分子

　　

生物通报道  近日来自美国洛克菲勒大学的研究人员通过一项大规模的功能性RNA干扰筛选来鉴别了可能调控上皮干细胞长期自我更新的因素，并识别出了转录因子TBX1在长期再生中所发挥的一个新功能。相关研究论文发布在5月4日的《自然》（Nature）杂志上。

领导这一研究的是杰出女科学家、洛克菲勒大学教授Elaine Fuchs，其长期从事小鼠上皮干细胞和人上皮干细胞研究。其实验室涉及多个研究领域，包括分子、细胞、发育生物学和遗传学。因其在皮肤生物学和皮肤干细胞研究中的成就曾获得美国总统奥巴马颁发的2009国家科学奖章，以及2010年欧莱雅-联合国教科文组织生命科学奖。

成人干细胞在动物体的整个生命周期中维持组织维护和再生。这些细胞通常位于特异的信号微环境中基于组织再生的需要调控干细胞在静息状态与细胞周期之间的平衡。然而对于这些干细胞如何维持自我更新能力的机制目前仍不是很清楚。

在这篇文章中，研究人员利用功能性RNA干扰筛查技术作为强有力的方法鉴别了了调控干细胞自我更新能力和再生潜力的转录调控因子。由于毛囊具有有力的组织再生能力，因此是探究成人干细胞自我更新机制的一个理想模型。研究人员从小鼠体内天然的微环境中纯化出毛囊干细胞并确定了它们的特征。与快速分裂的子细胞相比，分离的干细胞能够在体外长期维持和传代。通过比较分析毛囊干细胞与子细胞的核蛋白和/或转录因子，研究人员筛查出了约2000个在体外对干细胞自我更新具有长期效应的短发夹RNAs。

为了揭示研究发现的生理相关性，研究人员从中选择出了一个候选因子：TBX1。这一转录因子表达于多种组织中，然而一直以来未有研究过它在干细胞生物学中的作用。通过在小鼠体内条件性敲除Tbx1，研究人员证实可导致组织再生发生明显延迟。在经历数次再生循环后，研究人员发现Tbx1缺陷干细胞微环境逐渐耗竭。在进一步的机制研究中，研究人员证实TBX1是通过微调对于BMP信号的反应来调控干细胞的增殖的。

新研究揭示出了一个在组织再生过程中对毛囊干细胞自我更新起关键性作用的调控因子及分子机制。并验证了RNA干扰筛查方法在干细胞机制研究中的巨大潜力，表明这一方法在其他大量发育系统中也许还会有广泛的用途。

（生物通：何嫱）

生物通推荐原文摘要：

An RNA interference screen uncovers a new molecule in stem cell self-renewal and long-term regeneration

Adult stem cells sustain tissue maintenance and regeneration throughout the lifetime of an animal1, 2. These cells often reside in specific signalling niches that orchestrate the stem cell’s balancing act between quiescence and cell-cycle re-entry based on the demand for tissue regeneration2, 3, 4. How stem cells maintain their capacity to replenish themselves after tissue regeneration is poorly understood. Here we use RNA-interference-based loss-of-function screening as a powerful approach to uncover transcriptional regulators that govern the self-renewal capacity and regenerative potential of stem cells. Hair follicle stem cells provide an ideal model. These cells have been purified and characterized from their native niche in vivo and, in contrast to their rapidly dividing progeny, they can be maintained and passaged long-term in vitro5, 6, 7. Focusing on the nuclear proteins and/or transcription factors that are enriched in stem cells compared with their progeny5, 6, we screened ~2,000 short hairpin RNAs for their effect on long-term, but not short-term, stem cell self-renewal in vitro. To address the physiological relevance of our findings, we selected one candidate that was uncovered in the screen: TBX1. This transcription factor is expressed in many tissues but has not been studied in the context of stem cell biology. By conditionally ablating Tbx1 in vivo, we showed that during homeostasis, tissue regeneration occurs normally but is markedly delayed. We then devised an in vivo assay for stem cell replenishment and found that when challenged with repetitive rounds of regeneration, the Tbx1-deficient stem cell niche becomes progressively depleted. Addressing the mechanism of TBX1 action, we discovered that TBX1 acts as an intrinsic rheostat of BMP signalling: it is a gatekeeper that governs the transition between stem cell quiescence and proliferation in hair follicles. Our results validate the RNA interference screen and underscore its power in unearthing new molecules that govern stem cell self-renewal and tissue-regenerative potential.