Bioorganic Research Institute, Suntory Foundation for Life Sciences, Kyoto, Japan.
PLoS One. 2021 Sep 24;16(9):e0254308. doi: 10.1371/journal.pone.0254308. eCollection 2021.
Tissue/organ-specific genes (TSGs) are important not only for understanding organ development and function, but also for investigating the evolutionary lineages of organs in animals. Here, we investigate the TSGs of 9 adult tissues of an ascidian, Ciona intestinalis Type A (Ciona robusta), which lies in the important position of being the sister group of vertebrates. RNA-seq and qRT-PCR identified the Ciona TSGs in each tissue, and BLAST searches identified their homologs in zebrafish and mice. Tissue distributions of the vertebrate homologs were analyzed and clustered using public RNA-seq data for 12 zebrafish and 30 mouse tissues. Among the vertebrate homologs of the Ciona TSGs in the neural complex, 48% and 63% showed high expression in the zebrafish and mouse brain, respectively, suggesting that the central nervous system is evolutionarily conserved in chordates. In contrast, vertebrate homologs of Ciona TSGs in the ovary, pharynx, and intestine were not consistently highly expressed in the corresponding tissues of vertebrates, suggesting that these organs have evolved in Ciona-specific lineages. Intriguingly, more TSG homologs of the Ciona stomach were highly expressed in the vertebrate liver (17-29%) and intestine (22-33%) than in the mouse stomach (5%). Expression profiles for these genes suggest that the biological roles of the Ciona stomach are distinct from those of their vertebrate counterparts. Collectively, Ciona tissues were categorized into 3 groups: i) high similarity to the corresponding vertebrate tissues (neural complex and heart), ii) low similarity to the corresponding vertebrate tissues (ovary, pharynx, and intestine), and iii) low similarity to the corresponding vertebrate tissues, but high similarity to other vertebrate tissues (stomach, endostyle, and siphons). The present study provides transcriptomic catalogs of adult ascidian tissues and significant insights into the evolutionary lineages of the brain, heart, and digestive tract of chordates.
组织/器官特异性基因（TSGs）不仅对于理解器官的发育和功能很重要，而且对于研究动物器官的进化谱系也很重要。在这里，我们研究了 9 种成年组织的 TSGs，这些组织来自于尾索动物海鞘属 A 型（Ciona robusta），它处于脊椎动物姐妹群的重要地位。RNA-seq 和 qRT-PCR 鉴定了每种组织中的海鞘 TSGs，并通过 BLAST 搜索鉴定了其在斑马鱼和小鼠中的同源物。使用 12 种斑马鱼和 30 种小鼠组织的公共 RNA-seq 数据，分析和聚类了脊椎动物同源物的组织分布。在神经复合体的海鞘 TSGs 的脊椎动物同源物中，48%和 63%分别在斑马鱼和小鼠大脑中表达较高，表明在脊索动物中中枢神经系统是进化保守的。相比之下，海鞘卵巢、咽和肠的 TSGs 的脊椎动物同源物在脊椎动物相应组织中没有一致的高表达，表明这些器官在海鞘中进化出了特有的谱系。有趣的是，更多的海鞘胃 TSG 同源物在脊椎动物肝脏（17-29%）和肠道（22-33%）中高度表达，而在小鼠胃（5%）中表达较低。这些基因的表达谱表明，海鞘胃的生物学功能与它们的脊椎动物对应物不同。总的来说，海鞘组织可分为 3 组：i）与相应的脊椎动物组织高度相似（神经复合体和心脏），ii）与相应的脊椎动物组织相似性低（卵巢、咽和肠），iii）与相应的脊椎动物组织相似性低，但与其他脊椎动物组织（胃、内柱和虹吸管）相似性高。本研究提供了成年海鞘组织的转录组目录，并深入了解了脊索动物的大脑、心脏和消化道的进化谱系。
