Nonsense-mediated mRNA decay (NMD) is originally identified as a widespread mRNA surveillance machinery in degrading 'aberrant' mRNA species with premature termination codons (PTCs) rapidly, which protects the cells from the accumulation of truncated proteins. Recent studies show that NMD can also regulate the degradation of normal gene transcripts, which execute important cellular and physiological functions. Therefore, NMD is considered as a highly conserved post-transcriptional regulatory mechanism in eukaryotes. NMD modulates 3% to 20% of the transcriptome from yeast to human directly or indirectly, which is essential for various physiological processes, such as cell homeostasis, stress response, proliferation, and differentiation. NMD can regulate the level of transcripts that involves in development, and single knockout of most NMD factors has an embryonic lethal effect. NMD plays an important role in the self-renewal, differentiation of embryonic stem cells and is critical during embryonic development. In this review, we summarized the latest advances in the roles and mechanisms of NMD in embryonic development, in order to provide new ideas for the research on embryonic development and the treatment of embryonic development related diseases.
Codon, Nonsense ; Embryonic Development ; Humans ; Nonsense Mediated mRNA Decay ; RNA, Messenger ; Transcriptome

无义介导的信使RNA（mRNA）降解途径（nonsense-mediated mRNA decay，简称为NMD)是真核生物细胞内一种重要的基因转录后表达调控机制，它积极参与一系列细胞生理和生化过程，控制细胞命运和生命体的组织稳态。NMD的缺陷会导致人类疾病，如神经发育障碍、肿瘤发生和自身免疫疾病等。UPF3 (Up-frameshift protein 3)是一个核心的NMD因子，它最早在酵母中被发现。UPF3A和UPF3B是UPF3在生物进化到脊椎动物阶段出现的两个旁系同源物，在NMD中具有激活或抑制的作用。以往研究发现，UPF3B蛋白几乎在所有哺乳动物器官中均有表达，而UPF3A蛋白在除睾丸外的大多数哺乳动物组织中难以被检测到。解释这一现象的假说为：在NMD途径中，UPF3B具有比UPF3A更高的竞争性结合UPF2的能力，UPF3B和UPF2的结合促使UPF3A成为游离状态，而游离的UPF3A蛋白不稳定且易被降解。此假说提示UPF3A和UPF3B在NMD中存在拮抗作用。在本研究中，我们重新定量评估了UPF3A和UPF3B在野生型成年雄性和雌性小鼠的9个主要组织和生殖器官中的mRNA和蛋白表达，结果证实UPF3A在雄性生殖细胞中表达量最高。令人惊讶的是，我们发现在包括大脑和胸腺在内的大多数组织中，UPF3A与UPF3B的蛋白水平相当，而在小鼠脾、肺组织中，UPF3A表达高于UPF3B。公共基因表达数据进一步支持了上述发现。因此，我们的研究表明了UPF3A是小鼠组织中普遍表达的NMD因子。同时，该研究结果推测：在生理条件下，UPF3A和UPF3B蛋白之间不存在竞争抑制，且UPF3A在多种哺乳动物组织的稳态中发挥重要作用。
Animals ; Humans ; Mice ; HeLa Cells ; Nonsense Mediated mRNA Decay ; RNA-Binding Proteins/genetics*

BACKGROUNDMutations in fumarylacetoacetate hydrolase (FAH) gene can lead to tyrosinemia type 1 (HT1), a relatively rare autosomal recessive disorder. To date, no molecular genetic defects of HT1 in China have been described. We investigated a Chinese family with a HT1 child to identify mutations in FAH.

METHODSDNA sequencing was used for mutations screening in FAH gene. Real-time polymerase chain reaction (PCR) was performed to determine the FAH gene expression level. To confirm the presence of degradation by the nonsense-mediated mRNA decay pathway (NMD), the fragments containing R237X mutations were analyzed by primer introduced restriction analysis-polymerase chain reaction (PIRA-PCR) and cDNA sequencing. Finally, the effects of the mutations reported in this study were predicted by online softwares.

RESULTSA boy aged 3 years and 8 months was diagnosed clinically with HT1 based on his manifestations and biochemical abnormalities. Screening of FAH gene revealed two heterozygous mutations R237X and L375P transmitted from his mother and father respectively. In this pedigree, the amount of FAH mRNA relative to a healthy control was 0.44 for the patient, 0.77 for his mother and 1.07 for his father. Moreover, both PIRA-PCR and cDNA sequencing showed significant reduction of the FAH mRNA with R237X nonsense mutation. The missense mutation of L375P was not reported previously and prediction software showed that this mutation decreased the stability of protein structure and affected protein function.

CONCLUSIONSThis is the first case of HT1 analyzed by molecular genetics in China. The R237X mutation in FAH down- regulates the FAH gene expression, and the L375P mutation perhaps interrupts the secondary structure of FAH protein.

Child, Preschool ; China ; Humans ; Hydrolases ; genetics ; Male ; Molecular Sequence Data ; Mutation ; Mutation, Missense ; genetics ; Nonsense Mediated mRNA Decay ; genetics ; Real-Time Polymerase Chain Reaction ; Tyrosinemias ; genetics

In this study, we used next-generation sequencing methods to screen 300 individuals for BRCA1 and BRCA2. A novel mutation (c.849dupT) in BRCA2 was identified in a female patient and her unaffected brothers. This mutation leads to the truncation of BRCA2 functional domains. Moreover, BRCA2 mRNA expression levels in mutation carriers are significantly reduced compared to noncarriers. Immunofluorescence and western blot assays showed that this mutation resulted in reduced BRCA2 protein expression. Thus, we identified a novel mutation that damaged the function and expression of BRCA2 in a family with breast cancer history. The pedigree analysis suggested that this mutation is strongly associated with familial breast cancer. Genetic counsellors suggest that mutation carriers in this family undergo routine screening for breast cancer, as well as other malignancies, such as prostate and ovarian cancer. The effects of this BRCA2 mutation on drug resistance should be taken into consideration during treatment.
Blotting, Western ; BRCA2 Protein ; Breast Neoplasms* ; Breast* ; Drug Resistance ; Female ; Fluorescent Antibody Technique ; Genes, BRCA2 ; High-Throughput Nucleotide Sequencing ; Humans ; Mass Screening ; Nonsense Mediated mRNA Decay* ; Ovarian Neoplasms ; Pedigree ; Prostate ; RNA, Messenger ; Siblings

Cytoplasmic processing bodies, termed P bodies, are involved in diverse post-transcriptional processes including mRNA decay, nonsense-mediated RNA decay (NMD), RNAi, miRNA-mediated translational repression and storage of translationally silenced mRNAs. Regulation of the formation of P bodies in the context of multicellular organisms is poorly understood. Here we describe a systematic RNAi screen in C. elegans that identified 224 genes with diverse cellular functions whose inactivations result in a dramatic increase in the number of P bodies. 83 of these genes form a complex functional interaction network regulating NMD. We demonstrate that NMD interfaces with many cellular processes including translation, ubiquitin-mediated protein degradation, intracellular trafficking and cytoskeleton structure.We also uncover an extensive link between translation and RNAi, with different steps in protein synthesis appearing to have distinct effects on RNAi efficiency. Moreover, the intracellular vesicular trafficking network plays an important role in the regulation of RNAi. A subset of genes enhancing P body formation also regulate the formation of stress granules in C. elegans. Our study offers insights into the cellular mechanisms that regulate the formation of P bodies and also provides a framework for system-level understanding of NMD and RNAi in the context of the development of multicellular organisms.
Animals ; Animals, Genetically Modified ; Caenorhabditis elegans ; genetics ; Cytoplasmic Structures ; Gene Expression Regulation ; Genes, Helminth ; Genome, Helminth ; genetics ; MicroRNAs ; genetics ; Nonsense Mediated mRNA Decay ; physiology ; RNA Interference ; RNA, Helminth ; genetics ; Reverse Transcriptase Polymerase Chain Reaction