Ell3 Enhances Differentiation of Mouse Embryonic Stem Cells by Regulating Epithelial-Mesenchymal Transition and Apoptosis

Ell3 is a testis-specific RNA polymerase II elongation factor whose cellular function is not clear. The present study shows that Ell3 is activated during the differentiation of mouse embryonic stem cells (mESCs). Furthermore, Ell3 plays a critical role in stimulating lineage differentiation of mESCs by promoting epithelial-mesenchymal transition (EMT) and suppressing apoptosis. Mouse ESCs engineered to stably express Ell3 were rapidly differentiated compared with control cells either under spontaneous differentiation or neural lineage-specific differentiation conditions. Gene expression profile and quantitative RT-PCR analysis showed that the expression of EMT markers, such as Zeb1 and Zeb2, two major genes that regulate EMT, was upregulated in Ell3-overexpressing mESCs. Remarkably, knockdown of Zeb1 attenuated the enhanced differentiation capacity of Ell3-overexpressing mESCs, which indicates that Ell3 plays a role in the induction of mESC differentiation by inducing EMT. In contrast to Ell3-overexpressing mESCs, Ell3-knock down mESCs could not differentiate under differentiation conditions and, instead, underwent caspase-dependent apoptosis. In addition, apoptosis of differentiating Ell3-knock out mESCs was associated with enhanced expression of p53. The present results suggest that Ell3 promotes the differentiation of mESCs by activating the expression of EMT-related genes and by suppressing p53 expression.

Ell3是一种睾丸特异性RNA聚合酶II延伸因子，其细胞功能尚未明确。本研究发现，Ell3在小鼠胚胎干细胞（mouse embryonic stem cells，mESCs）的分化进程中被激活。此外，Ell3通过促进上皮间质转化（epithelial-mesenchymal transition，EMT）并抑制细胞凋亡，在促进小鼠胚胎干细胞谱系分化方面发挥关键作用。在自发分化或神经谱系特异性分化诱导条件下，稳定过表达Ell3的小鼠胚胎干细胞的分化进程均显著快于对照细胞。基因表达谱与定量逆转录聚合酶链反应（quantitative RT-PCR）分析结果显示，在过表达Ell3的mESCs中，调控EMT的两个关键基因Zeb1与Zeb2等EMT标志物的表达均出现上调。值得注意的是，敲低Zeb1会减弱过表达Ell3的mESCs的增强分化能力，这表明Ell3通过诱导EMT来促进mESC的分化。与过表达Ell3的mESCs相反，Ell3基因敲低的mESCs在分化条件下无法完成分化，反而发生了半胱天冬酶依赖型细胞凋亡。此外，在分化中的Ell3基因敲除mESCs中，细胞凋亡与p53的表达上调密切相关。本研究结果表明，Ell3通过激活EMT相关基因的表达并抑制p53的表达，促进小鼠胚胎干细胞的分化。