Insights into the transcriptional and translational mechanisms of linear organellar chromosomes in the box jellyfish <i>Alatina alata</i> (Cnidaria: Medusozoa: Cubozoa)
收藏资源简介：
Background: In most animals, the mitochondrial genome is characterized by its small size, organization into a single circular molecule, and a relative conservation of the number of encoded genes. In box jellyfish (Cubozoa, Cnidaria), the mitochondrial genome is organized into 8 linear mito-chromosomes harboring between one and 4 genes each, including 2 extra protein-coding genes: <i>mt-polB</i> and <i>orf314</i>. Such an organization challenges the traditional view of mitochondrial DNA (mtDNA) expression in animals. In this study, we investigate the pattern of mitochondrial gene expression in the box jellyfish <i>Alatina alata</i>, as well as several key nuclear-encoded molecular pathways involved in the processing of mitochondrial gene transcription. Results: Read coverage of DNA-seq data is relatively uniform for all 8 mito-chromosomes, suggesting that each mito-chromosome is present in equimolar proportion in the mitochondrion. Comparison of DNA and RNA-seq based assemblies indicates that mito-chromosomes are transcribed into individual transcripts in which the beginning and ending are highly conserved. Expression levels for <i>mt-polB</i> and <i>orf314</i> are similar to those of other mitochondrial-encoded genes, which provides further evidence for them having functional roles in the mitochondrion. Survey of the transcriptome suggests recognition of the mitochondrial tRNA-Met by the cytoplasmic aminoacyl-tRNA synthetase counterpart and C-to-U editing of the cytoplasmic tRNA-Trp after import into the mitochondrion. Moreover, several mitochondrial ribosomal proteins appear to be lost. Conclusions: This study represents the first survey of mitochondrial gene expression of the linear multi-chromosomal mtDNA in box jellyfish (Cubozoa). Future exploration of small RNAs and the proteome of the mitochondrion will test the hypotheses presented herein.
背景：在绝大多数动物中，线粒体基因组（mitochondrial genome）以其分子量小巧、组装为单条环状分子以及编码基因数量相对保守为典型特征。在箱形水母（立方水母纲Cubozoa、刺胞动物门Cnidaria）中，其线粒体基因组组装为8条线性线粒体染色体（mito-chromosome），每条染色体携带1至4个编码基因，其中包含2个额外的蛋白质编码基因：mt-polB与orf314。这种基因组结构颠覆了学界对动物线粒体DNA（mitochondrial DNA, mtDNA）表达模式的传统认知。本研究以箱形水母*Alatina alata*的线粒体基因表达模式，以及参与线粒体基因转录加工的若干关键核编码分子通路展开探究。 结果：DNA-seq（DNA测序）数据的读段覆盖度在8条线粒体染色体上均相对均匀，表明每个线粒体染色体在线粒体中以等摩尔比例存在。对比DNA测序与RNA-seq（RNA测序）的组装结果可知，线粒体染色体被转录为独立的转录本，其首尾序列高度保守。mt-polB与orf314的表达水平与其他线粒体编码基因相近，进一步证明二者在线粒体中具有功能性作用。转录组（transcriptome）分析显示，细胞质中的氨酰-tRNA合成酶（aminoacyl-tRNA synthetase）可识别线粒体tRNA-Met，且细胞质tRNA-Trp在被转运至线粒体后会发生C到U的编辑。此外，若干线粒体核糖体蛋白似乎发生了丢失。 结论：本研究首次针对箱形水母（立方水母纲Cubozoa）的线性多染色体线粒体DNA的线粒体基因表达展开调研。未来可通过探究小RNA与线粒体蛋白质组（proteome），对本研究提出的假说进行验证。
