Incomplete nonsense-mediated mRNA decay in Giardia lamblia
Incomplete nonsense-mediated mRNA decay in Giardia lamblia
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DOI：
10.1016/j.ijpara.2008.02.006
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发表时间：
2008-09-01
影响因子：
4
通讯作者：
Sun, Chin-Hung
中科院分区：
文献类型：
--
作者：
Chen, Yi-Hsiu;Su, Li-Hsin;Sun, Chin-Hung
含有过早翻译终止密码子的信使rna被无义介导的mRNA衰变（NMD）系统降解。NMD通路存在于酵母、植物和哺乳动物中，被认为通过快速降解突变mrna来保护细胞不产生无功能蛋白。对真核生物起源的生物学，特别是NMD途径的了解很少。使用BLAST程序的搜索显示，原生动物贾第鞭毛虫只有NMD途径的一些成分。我们开发了一个带无义突变的荧光素酶报告系统来监测贾第鞭毛虫的NMD。无义突变引发了荧光素酶mRNA水平和稳定性的下降，表明贾第鞭毛虫可能存在NMD现象。我们还发现另一个含有贾第鞭毛虫自身的囊壁蛋白3基因的无义突变的系统的mRNA水平显著降低。然而，在这两个系统中观察到的减少水平低于晚期分支真核生物，这表明贾第鞭毛虫的NMD系统可能功能较差。有趣的是，G418在贾第鞭毛虫中促进无义突变的解读和抑制NMD的作用与在晚期分支真核生物中的作用相似。我们还鉴定了保守的NMD因子UPF1的贲门同源物。免疫荧光分析显示，与酵母UPF1一样，心包UPF1在细胞质中表达，而不在细胞核中表达。此外，UPF1的过表达导致无义转录物水平的降低和无义密码子翻译终止的增强。这些结果提示贾第鞭毛虫可能有一个不完整的NMD通路，而贾第鞭毛虫的UPF1可能在功能上保守，参与NMD和防止无义抑制。(C) 2008澳大利亚寄生虫学学会Elsevier Ltd.出版。版权所有。
Messenger RNAs containing premature translation stop codons are degraded by a nonsense-mediated mRNA decay (NMD) system. The NMD pathway is present in yeast, plants and mammals and is thought to protect cells from production of nonfunctional proteins by rapidly degrading mutant mRNAs. There is little understanding of the biology of the origins of eukaryotes, particularly of the NMD pathway. Searches using the BLAST program revealed that the protozoan Giardia lamblia has only some of the components of the NMD pathway. We developed a luciferase reporter system with a nonsense mutation to monitor NMD in Giardia. The nonsense mutation triggered a decrease in luciferase mRNA levels and stability, suggesting that the NMD phenomenon could be present in Giardia. We also found a significant reduction of the mRNA levels of another system containing Giardia its own cyst wall protein 3 gene with a nonsense mutation. However, the reduction levels observed in these two systems are lower than that in late-branching eukaryotes, suggesting that the NMD system in Giardia may be less functional. Interestingly, the effect of G418 in promoting read-through of the nonsense mutation and inhibiting NMD in Giardia is similar to that in late-branching eukaryotes. We also characterised the giardial homologue of a conserved NMD factor, UPF1. Immunofluorescence assays revealed that giardial UPF1, like yeast UPF1, is expressed in the cytoplasm, but not in the nucleus. In addition, overexpression of UPF1 resulted in a reduction of the levels of nonsense-containing transcripts and enhanced translation termination at a nonsense codon. These results suggest that Giardia may have an incomplete NMD pathway and giardial UPF1 may be functionally conserved, involved in NMD and in preventing nonsense suppression. (C) 2008 Australian Society for Parasitology Inc. Published by Elsevier Ltd. All rights reserved.