Li Hui, Wang Beibei, Yang Acong, Lu Rui, Wang Weicheng, Zhou Yang, Shi Guilai, Kwon Sung Won, Zhao Yingming, Jin Ying
Shanghai Stem Cell Institute, Institute of Medical Sciences, Shanghai Jiao Tong University School of Medicine, Shanghai, China.
Stem Cells. 2009 Jun;27(6):1244-54. doi: 10.1002/stem.55.
Embryonic stem cells (ESCs) possess the capacity to self-renew and differentiate into all cell types of an organism. It is essential to understand how these properties are controlled for the potential usage of their derivatives in clinical settings and reprogramming of differentiated somatic cells. Although transcriptional factors, such as Oct4, Sox2, and Nanog, have been considered as a part of the core regulatory circuitry, a growing body of evidence suggests that additional factors exist and contribute to the control of ESC self-renewal and differentiation. Here, we report that Ly-1 antibody reactive clone (LYAR), a zinc finger nucleolar protein highly expressed in undifferentiated ESCs, plays a critical role in maintaining ESC identity. Its downregulation significantly reduces the rate of ESC growth and increases their apoptosis. Moreover, reduced expression of LYAR in ESCs impairs their differentiation capacity, failing to rapidly silence pluripotency markers and to activate differentiation genes upon differentiation. Mechanistically, LYAR forms a complex with another nucleolar protein, nucleolin, and prevents its self-cleavage, maintaining a normal steady-state level of nucleolin protein in undifferentiated ESCs. Interestingly, the downregulation of nucleolin is detrimental to the growth of ESCs and increases the rate of apoptosis, similarly to the knockdown of LYAR. Thus, our data emphasize the fact that other genes besides Oct4 and Nanog are uniquely required for ESC self-renewal and differentiation and demonstrate that LYAR functions to control the stability of nucleolin protein, which in turn is essential for maintaining the self-renewal of ESCs.
胚胎干细胞（ESCs）具有自我更新和分化为生物体所有细胞类型的能力。了解这些特性是如何被调控的，对于其衍生物在临床应用以及分化体细胞的重编程中的潜在用途至关重要。尽管转录因子，如Oct4、Sox2和Nanog，被认为是核心调控回路的一部分，但越来越多的证据表明还存在其他因素，它们有助于控制胚胎干细胞的自我更新和分化。在此，我们报道Ly-1抗体反应性克隆（LYAR），一种在未分化胚胎干细胞中高度表达的锌指核仁蛋白，在维持胚胎干细胞特性方面发挥着关键作用。其下调显著降低了胚胎干细胞的生长速率并增加了它们的凋亡。此外，胚胎干细胞中LYAR表达的降低损害了它们的分化能力，在分化时无法迅速沉默多能性标记物并激活分化基因。从机制上讲，LYAR与另一种核仁蛋白核仁素形成复合物，并阻止其自我切割，从而在未分化胚胎干细胞中维持核仁素蛋白的正常稳态水平。有趣的是，核仁素的下调对胚胎干细胞的生长有害，并增加凋亡速率，这与LYAR的敲低类似。因此，我们的数据强调了这样一个事实，即除了Oct4和Nanog之外，其他基因对于胚胎干细胞的自我更新和分化也是独特必需的，并证明LYAR的功能是控制核仁素蛋白的稳定性，而这反过来对于维持胚胎干细胞的自我更新至关重要。
