INSERM, Unité U955, Créteil, France.
PLoS Genet. 2010 Oct 7;6(10):e1001153. doi: 10.1371/journal.pgen.1001153.
Approximately 30% of alleles causing genetic disorders generate premature termination codons (PTCs), which are usually associated with severe phenotypes. However, bypassing the deleterious stop codon can lead to a mild disease outcome. Splicing at NAGNAG tandem splice sites has been reported to result in insertion or deletion (indel) of three nucleotides. We identified such a mechanism as the origin of the mild to asymptomatic phenotype observed in cystic fibrosis patients homozygous for the E831X mutation (2623G>T) in the CFTR gene. Analyses performed on nasal epithelial cell mRNA detected three distinct isoforms, a considerably more complex situation than expected for a single nucleotide substitution. Structure-function studies and in silico analyses provided the first experimental evidence of an indel of a stop codon by alternative splicing at a NAGNAG acceptor site. In addition to contributing to proteome plasticity, alternative splicing at a NAGNAG tandem site can thus remove a disease-causing UAG stop codon. This molecular study reveals a naturally occurring mechanism where the effect of either modifier genes or epigenetic factors could be suspected. This finding is of importance for genetic counseling as well as for deciding appropriate therapeutic strategies.
大约 30%的导致遗传疾病的等位基因产生过早终止密码子（PTCs），通常与严重的表型相关。然而，绕过有害的终止密码子可能导致轻度疾病结果。已经报道了在 NAGNAG 串联剪接位点进行剪接会导致三个核苷酸的插入或缺失（indel）。我们发现这种机制是囊性纤维化患者中 CFTR 基因 E831X 突变（2623G>T）纯合子观察到的轻度至无症状表型的起源。对鼻上皮细胞 mRNA 的分析检测到三种不同的异构体，这比预期的单个核苷酸取代复杂得多。结构-功能研究和计算机分析提供了第一个通过 NAGNAG 受体位点的选择性剪接导致终止密码子插入缺失的实验证据。除了有助于蛋白质组可塑性外，NAGNAG 串联位点的选择性剪接还可以去除致病的 UAG 终止密码子。这项分子研究揭示了一种自然发生的机制，其中修饰基因或表观遗传因素的影响可能受到怀疑。这一发现对于遗传咨询以及决定适当的治疗策略都非常重要。
