Gorbushin Alexander M
Sechenov Institute of Evolutionary Physiology and Biochemistry (IEPhB RAS), Saint-Petersburg, Russia.
Dev Comp Immunol. 2018 Jul;84:250-263. doi: 10.1016/j.dci.2018.02.018. Epub 2018 Feb 28.
The evolution of complement system in invertebrates is poorly investigated. While the repertoire of complement genes in several Ecdysozoa lineages is found substantially different from that of Deuterostomia, the composition and function of the complement in the second protostome lineage, Lophotrochozoa, remains unclear. Here we report the general description of new transcriptomic data on the common periwinkle, Littorina littorea, and trace the evolutionary trajectories of the ancestral proto-complement repertoire. The repertoire is defined as immune cascade providing the minimum set of C3-associated molecules required for C3b amplification, opsonization of the targets and their phagocytosis: thioester protein (TEP) C3, serine protease C2/factor B (Bf) and complement receptors (CR). The reference transcriptome of L. littorea was built from the dual-species RNA-seq experiment with the periwinkle and its tissue digenean parasite Himasthla elongata. Five TEPs, including the ortholog of the C3, are found expressed in the in the mollusk's inflamed tissues. The homolog of the complement receptors CR1/CR2 is also expressed, however the ortholog of Bf is not. The extensive phylogenetic analysis showed that the C3 ortholog and the complement receptors are retained in all key lophotrochozoan taxa: Mollusca, Annelida and Brachiopoda. However, the Bf ortholog was lost at least three times independently in different lineages: i) Cephalopoda, ii) a common ancestor of all Gastropoda and iii) one of the Annelida lineage, Clitellata. Both C3 and Bf molecules were retained in bivalve species, brachiopods and annelid worms from the Polychaeta lineage. Hypothetically, the function of the lost Bf in these animals can be compensated by Factor L (Lf) - the serine protease first found in L. littorea and homologous to both, the Bf and the arthropod factor C (Cf). The contrast differences in proto-complement repertoire between the sister mollusk' taxa, Bivalvia and Gastropoda (the conserved and modified sets, respectively), can underlie differences in their susceptibility to digenean infection.
无脊椎动物补体系统的进化研究较少。虽然已发现几种蜕皮动物谱系中的补体基因库与后口动物的有很大不同，但第二个原口动物谱系——冠轮动物门中补体的组成和功能仍不清楚。在此，我们报告了关于滨螺（Littorina littorea）的新转录组数据的总体描述，并追踪了原始补体基因库的进化轨迹。该基因库被定义为免疫级联反应，提供C3b扩增、靶标调理作用及其吞噬作用所需的最小C3相关分子集：硫酯蛋白（TEP）C3、丝氨酸蛋白酶C2/因子B（Bf）和补体受体（CR）。滨螺的参考转录组是通过滨螺及其组织复殖吸虫寄生虫长形希马斯吸虫（Himasthla elongata）的双物种RNA测序实验构建的。在软体动物的炎症组织中发现了包括C3直系同源物在内的5种TEP表达。补体受体CR1/CR2的同源物也有表达，但Bf的直系同源物没有。广泛的系统发育分析表明，C3直系同源物和补体受体在所有关键的冠轮动物门类中都得以保留：软体动物门、环节动物门和腕足动物门。然而，Bf直系同源物在不同谱系中至少独立丢失了三次：i）头足纲，ii）所有腹足纲的共同祖先，iii）环节动物谱系之一的寡毛纲。双壳贝类物种、腕足动物和多毛纲环节动物中同时保留了C3和Bf分子。据推测，这些动物中丢失的Bf的功能可能由因子L（Lf）补偿——因子L是首次在滨螺中发现的丝氨酸蛋白酶，与Bf和节肢动物因子C（Cf）都同源。姐妹软体动物类群双壳纲和腹足纲（分别为保守集和修饰集）之间原始补体基因库的显著差异，可能是它们对复殖吸虫感染易感性差异的基础。
