无义介导的mRNA衰变(NMD)是真核细胞中高度保守的转录后基因表达调控机制。NMD消除了具有过早终止密码子的异常mRNA,以掩盖转录组完整性。此外,NMD通过使具有特定NMD特征的RNA不稳定来微调基因表达。因此,通过控制转录组的质量和数量,NMD在哺乳动物发育中起着至关重要的作用,应激反应,和肿瘤发生。NMD因子的缺乏导致早期胚胎致死,而潜在的机制却知之甚少。SMG5是NMD的关键因素。在这项研究中,我们建立了一个Smg5条件性敲除小鼠模型,发现Smg5-null导致E13.5之前的早期胚胎致死性。此外,我们产生了Smg5敲除小鼠胚胎干细胞(mESC)的多个品系,并发现mESC中Smg5的缺失不会损害细胞活力。Smg5-null延迟mESC的分化。机械上,我们的研究表明,c-MYC蛋白,但不是c-MycmRNA,在SMG5缺陷型mESC中上调。c-MYC蛋白的过量产生可能是由SMG5丢失后的蛋白合成增强引起的。此外,SMG5缺失导致多种干细胞分化调节剂上的选择性剪接失调。总的来说,我们的发现强调了SMG5-NMD在调节mESC细胞状态转换中的重要性.
Nonsense-mediated mRNA decay (NMD) is a highly conserved post-transcriptional gene expression regulatory mechanism in eukaryotic cells. NMD eliminates aberrant mRNAs with premature termination codons to surveil transcriptome integrity. Furthermore, NMD fine-tunes gene expression by destabilizing RNAs with specific NMD features. Thus, by controlling the quality and quantity of the transcriptome, NMD plays a vital role in mammalian development, stress response, and tumorigenesis. Deficiencies of NMD factors result in early embryonic lethality, while the underlying mechanisms are poorly understood. SMG5 is a key NMD factor. In this study, we generated an Smg5 conditional knockout mouse model and found that Smg5-null results in early embryonic lethality before E13.5. Furthermore, we produced multiple lines of Smg5 knockout mouse embryonic stem cells (mESCs) and found that the deletion of Smg5 in mESCs does not compromise cell viability. Smg5-null delays differentiation of mESCs. Mechanistically, our study reveals that the c-MYC protein, but not c-Myc mRNA, is upregulated in SMG5-deficient mESCs. The overproduction of c-MYC protein could be caused by enhanced protein synthesis upon SMG5 loss. Furthermore, SMG5-null results in dysregulation of alternative splicing on multiple stem cell differentiation regulators. Overall, our findings underscore the importance of SMG5-NMD in regulating mESC cell-state transition.