Vogeler Susanne, Carboni Stefano, Li Xiaoxu, Joyce Alyssa
Department of Marine Science, University of Gothenburg, Carl Skottbergsgata 22 B, 41319, Gothenburg, Sweden.
Institute of Aquaculture, University of Stirling, Stirling, Scotland, FK9 4LA, UK.
BMC Genomics. 2021 Jan 25;22(1):80. doi: 10.1186/s12864-021-07380-0.
Apoptosis is an important process for an organism's innate immune system to respond to pathogens, while also allowing for cell differentiation and other essential life functions. Caspases are one of the key protease enzymes involved in the apoptotic process, however there is currently a very limited understanding of bivalve caspase diversity and function.
In this work, we investigated the presence of caspase homologues using a combination of bioinformatics and phylogenetic analyses. We blasted the Crassostrea gigas genome for caspase homologues and identified 35 potential homologues in the addition to the already cloned 23 bivalve caspases. As such, we present information about the phylogenetic relationship of all identified bivalve caspases in relation to their homology to well-established vertebrate and invertebrate caspases. Our results reveal unexpected novelty and complexity in the bivalve caspase family. Notably, we were unable to identify direct homologues to the initiator caspase-9, a key-caspase in the vertebrate apoptotic pathway, inflammatory caspases (caspase-1, - 4 or - 5) or executioner caspases-3, - 6, - 7. We also explored the fact that bivalves appear to possess several unique homologues to the initiator caspase groups - 2 and - 8. Large expansions of caspase-3 like homologues (caspase-3A-C), caspase-3/7 group and caspase-3/7-like homologues were also identified, suggesting unusual roles of caspases with direct implications for our understanding of immune response in relation to common bivalve diseases. Furthermore, we assessed the gene expression of two initiator (Cg2A, Cg8B) and four executioner caspases (Cg3A, Cg3B, Cg3C, Cg3/7) in C. gigas late-larval development and during metamorphosis, indicating that caspase expression varies across the different developmental stages.
Our analysis provides the first overview of caspases across different bivalve species with essential new insights into caspase diversity, knowledge that can be used for further investigations into immune response to pathogens or regulation of developmental processes.
细胞凋亡是生物体先天免疫系统应对病原体的重要过程，同时也参与细胞分化和其他基本生命功能。半胱天冬酶是参与细胞凋亡过程的关键蛋白酶之一，然而目前对双壳贝类半胱天冬酶的多样性和功能了解非常有限。
在这项工作中，我们结合生物信息学和系统发育分析研究了半胱天冬酶同源物的存在情况。我们在太平洋牡蛎基因组中搜索半胱天冬酶同源物，除了已克隆的23种双壳贝类半胱天冬酶外，还鉴定出35种潜在的同源物。因此，我们提供了所有已鉴定的双壳贝类半胱天冬酶与已明确的脊椎动物和无脊椎动物半胱天冬酶同源性相关的系统发育关系信息。我们的结果揭示了双壳贝类半胱天冬酶家族出人意料的新颖性和复杂性。值得注意的是，我们未能鉴定出与脊椎动物凋亡途径中的关键半胱天冬酶起始半胱天冬酶-9、炎性半胱天冬酶（半胱天冬酶-1、-4或-5）或执行半胱天冬酶-3、-6、-7的直接同源物。我们还探讨了双壳贝类似乎拥有与起始半胱天冬酶组-2和-8的几种独特同源物这一事实。还鉴定出了半胱天冬酶-3样同源物（半胱天冬酶-3A-C）、半胱天冬酶-3/7组和半胱天冬酶-3/7样同源物的大量扩增，这表明半胱天冬酶具有不同寻常的作用，这对于我们理解与双壳贝类常见疾病相关的免疫反应具有直接意义。此外，我们评估了两种起始半胱天冬酶（Cg2A、Cg8B）和四种执行半胱天冬酶（Cg3A、Cg3B、Cg3C、Cg3/7）在太平洋牡蛎后期幼虫发育和变态过程中的基因表达，表明半胱天冬酶表达在不同发育阶段有所变化。
我们的分析首次概述了不同双壳贝类物种中的半胱天冬酶，为半胱天冬酶多样性提供了重要的新见解，这些知识可用于进一步研究对病原体的免疫反应或发育过程的调控。
