College of Life Science, Henan Normal University, Xinxiang, 453007, China.
College of Life Science, Henan Normal University, Xinxiang, 453007, China.
Vet Parasitol. 2020 May;281:109097. doi: 10.1016/j.vetpar.2020.109097. Epub 2020 Apr 3.
Cylicocyclus spp. are common parasites in the intestine of equine animals. Hosts infected by these strongylid nematodes might face emaciation, anemia, and even death, all of which lead to significant economic losses. In the present study, the complete mitochondrial genome (mitogenome) of Cylicocyclus radiatus, the type species of the genus Cylicocyclus, was sequenced and characterized for the first time using next-generation sequencing technology. Results show that the mitogenome of C. radiatus is a double-stranded 13,836 bp circular molecule, containing 12 protein-coding genes, 22 tRNA genes, two rRNA genes, and two non-coding regions. Moreover, it has a clear bias in nucleotide composition and codon preference towards protein-coding genes with elevated AT content. All protein-coding genes are initiated by ATT and TTG codons, and almost all of them end with complete TAA and TAG termination codons; only the COШ gene harbors the incomplete T termination codon. All tRNA genes fold into an atypical clover-leaf secondary structure. The tRNA-Ser genes possess a TΨC arm and variable loop, but lack the dihydrouridine arm and loop. Twenty tRNAs contain the dihydrouridine arm and loop, in which the variable TΨC arm and loop are replaced by a "TV-replacement loop". Most tRNA gene secondary structures contain G-U, U-U, and A-G mismatches. Phylogenetic analysis based on nucleotide sequences of the 12 protein-coding genes using maximum likelihood and Bayesian inference indicated that C. radiatus is related more closely to Cylicocyclus nassatus than to Cylicocyclus insigne. In summary, this study provides the first annotated sequence of the mitogenome of C. radiatus, paving the way for further research on species classification and the molecular evolution of strongylid nematodes.
Cylicocyclus spp. 是马属动物肠道内常见的寄生虫。感染这些 Strongylid 线虫的宿主可能会出现消瘦、贫血，甚至死亡，这一切都会导致重大的经济损失。在本研究中，首次使用下一代测序技术对 Cylicocyclus radiatus 的完整线粒体基因组（mitogenome）进行了测序和特征描述。结果表明，C. radiatus 的线粒体基因组是一个双链 13836bp 圆形分子，包含 12 个蛋白质编码基因、22 个 tRNA 基因、2 个 rRNA 基因和 2 个非编码区。此外，它在核苷酸组成和密码子偏好方面存在明显的偏向性，对蛋白质编码基因的 AT 含量要求较高。所有蛋白质编码基因均以 ATT 和 TTG 密码子起始，几乎所有基因都以完整的 TAA 和 TAG 终止密码子终止；只有 COШ 基因含有不完整的 T 终止密码子。所有 tRNA 基因都折叠成非典型的三叶草二级结构。tRNA-Ser 基因具有 TΨC 臂和可变环，但缺乏二氢尿嘧啶臂和环。20 个 tRNA 包含二氢尿嘧啶臂和环，其中可变 TΨC 臂和环被“TV-替换环”取代。大多数 tRNA 基因二级结构包含 G-U、U-U 和 A-G 错配。基于最大似然法和贝叶斯推断的 12 个蛋白质编码基因核苷酸序列的系统发育分析表明，C. radiatus 与 Cylicocyclus nassatus 的亲缘关系比与 Cylicocyclus insigne 的更近。总之，本研究提供了 C. radiatus 线粒体基因组的第一个注释序列，为进一步研究 Strongylid 线虫的物种分类和分子进化奠定了基础。
