Mitochondrial mRNA fragments are circularized in a human HEK cell line
Mitochondrial mRNA fragments are circularized in a human HEK cell line
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DOI：
10.1016/j.mito.2019.11.002
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发表时间：
2020-03-01
期刊：
影响因子：
4.4
通讯作者：
Cahoon, A. Bruce
中科院分区：
文献类型：
--
作者：
Mance, Landon G.;Mawla, Ishaat;Cahoon, A. Bruce
近年来，人们对人类细胞核中环状RNA（circRNA）的广泛存在和丰富程度的关注，引发了人们对它们的存在及其在细胞基因表达和生理学中可能作用的浓厚兴趣。然而，哺乳动物线粒体中circRNA的存在尚未得到充分研究。线粒体mRNA不同于由核基因产生的那些，因为它们缺乏内含子并且被转录为多顺反子转录物，所述多顺反子转录物被内切核酸裂解，留下具有非常小的5'和3' UTR的转录物。环状RNA已经在单细胞生物和植物的半自主细胞器中被鉴定，但它们的目的尚未明确证明。我们的项目的目标是测试这一假设，加工的mRNA在脊椎动物线粒体中被环化，作为翻译前必要的RNA加工步骤。从人细胞系HEK 293中分离线粒体mRNA，并通过用RNAse-R处理RNA，然后扩增推定的3 '-S'连接位点来寻找环化的证据。测序结果表明，在线粒体基因组的每个编码区的mRNA环化的发生。然而，在大多数情况下，circRNA携带被截短的编码区，这表明它们是不可翻译的。对mRNA的环化形式的定量显示它们占总mRNA的一小部分（类似于10%）。这些发现表明，mRNA环化发生在哺乳动物线粒体，但它似乎没有发挥作用，使可翻译的mRNA。
The relatively recent focus on the widespread occurrence and abundance of circular RNAs (circRNA) in the human cell nucleus has sparked an intensive interest in their existence and possible roles in cell gene expression and physiology. The presence of circRNAs in mammalian mitochondria, however, has been under-explored. Mitochondrial mRNAs differ from those produced from nuclear genes because they lack introns and are transcribed as poly-cistronic transcripts that are endonucleolytically cleaved, leaving transcripts with very small 5' and 3' UTRs. Circular RNAs have been identified in the semi-autonomous organelles of single-celled organisms and plants but their purpose has not been clearly demonstrated. The goal of our project was to test the hypothesis, processed mRNAs are circularized in vertebrate mitochondria as a necessary RNA processing step prior to translation. Mitochondrial mRNAs were isolated from the human cell line HEK293 and evidence of circularization sought by treating RNA with RNAse-R and then amplifying putative 3'-S' junction sites. Sequence results demonstrated the occurrence of mRNA circularization within each coding region of the mitochondrial genome. However, in most cases the circRNAs carried coding regions that had been truncated, suggesting they were not translatable. Quantification of the circularized versions of the mRNAs revealed they comprise a small portion (similar to 10%) of the total mRNA. These findings demonstrate that mRNA circularization occurs in mammalian mitochondria but it does not appear to play a role in making translatable mRNAs.