Biochemical Adaptation Laboratory, Department of Zoology, North-Eastern Hill University, Shillong 793022, India.
Molecular Endocrinology Laboratory, Centre for Advanced Studies in Zoology, Visva-Bharati University, Santiniketan 731235, India.
Gene. 2019 Jun 30;703:35-49. doi: 10.1016/j.gene.2019.04.009. Epub 2019 Apr 3.
The facultative air-breathing magur catfish (Clarias magur) frequently face different environmental challenges, such as hyper-ammonia, and desiccation stresses in their natural habitats. All these stresses lead to higher accumulation of body ammonia, thereby causing various harmful effects to the fish due to its toxicity. Nonetheless, the mechanisms underlying ammonia-induced toxicity is yet not clear. In the present study, we used RNA sequencing and utilized a modified method for de novo assembly of the transcriptome to provide an exhaustive study on the transcriptomic alterations of magur catfish in response to high environmental ammonia (HEA; 25 mM NHCl). The final contig assembly produced a total of 311,076 unique transcripts (termed as unigenes) with a GC content of 48.3% and the average length of 599 bp. A considerable number of SSR marker associated with these unigenes were also detected. A total of 279,156 transcripts were successfully annotated by using various databases. Comparative transcriptomic analysis revealed a total of 3453 and 19,455 genes were differentially expressed in the liver and brain tissues, respectively, in ammonia-treated fish compared to the control. Enrichment analysis of the differentially expressed genes (DEGs) showed that several GO and KEGG pathway terms were significantly over-represented. Functional analysis of significantly elevated DEGs demonstrated that ammonia stress tolerance of the magur catfish was associated with quite a few pathways related to immune response, oxidative stress, and apoptosis, as well as few transporter proteins involved with ammonia and urea transport. Both liver and brain tissues showed HEA-mediated oxidative damage with consequent activation of antioxidant machinery. However, elevated ROS levels led to an activation of inflammatory cytokines and thus innate immune response in the liver. Conversely, in the brain ROS-mediated irreversible cell damages activated apoptosis via both p53-Bax-Bcl2 and caspase-mediated pathways. The present study provides a novel understanding of the molecular responses of this air-breathing catfish against the ammonia-induced stressors, which could elucidate the underlying mechanisms of adaptation of this facultative air-breather living under various environmental constraints.
兼性空气呼吸的湄公河巨鲶（Clarias magur）在其自然栖息地经常面临各种环境挑战，如高氨、干燥胁迫。所有这些压力都会导致体内氨的积累增加，从而对鱼类造成各种有害影响，因为氨具有毒性。然而，氨诱导毒性的机制尚不清楚。在本研究中，我们使用 RNA 测序，并利用一种改良的从头转录组组装方法，对巨鲶鱼对高环境氨（HEA；25 mM NHCl）的转录组变化进行了详尽的研究。最终的连续体组装共产生了 311,076 个独特的转录本（称为基因），GC 含量为 48.3%，平均长度为 599bp。还检测到了与这些基因相关的大量 SSR 标记。通过各种数据库，成功注释了总共 279,156 个转录本。比较转录组分析显示，与对照组相比，氨处理鱼的肝脏和脑组织中分别有 3453 个和 19,455 个基因差异表达。差异表达基因（DEGs）的富集分析显示，GO 和 KEGG 途径术语中有几个显著过表达。显著上调 DEGs 的功能分析表明，巨鲶对氨胁迫的耐受性与许多与免疫反应、氧化应激和细胞凋亡相关的途径以及一些与氨和尿素转运相关的转运蛋白有关。肝脏和脑组织均显示出 HEA 介导的氧化损伤，随后激活抗氧化机制。然而，ROS 水平的升高导致肝脏中炎症细胞因子的激活和先天免疫反应。相反，在大脑中，ROS 介导的不可逆细胞损伤通过 p53-Bax-Bcl2 和 caspase 介导的途径激活细胞凋亡。本研究为这种空气呼吸鱼类对氨诱导应激的分子反应提供了新的认识，这可以阐明这种兼性空气呼吸鱼在各种环境限制下适应的潜在机制。
