AUTHOR=Xu Kexin , Wang Yinghui , Lian Shanshan , Hu Naina , Chen Xiaomei , Dai Xiaoting , Zhang Lingling , Wang Shi , Hu Jingjie , Hu Xiaoli , Bao Zhenmin 

TITLE=Expansion of C1Q Genes in Zhikong Scallop and Their Expression Profiling After Exposure to the Toxic Dinoflagellates

JOURNAL=Frontiers in Marine Science

VOLUME=8

YEAR=2021

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2021.640425

DOI=10.3389/fmars.2021.640425

ISSN=2296-7745

ABSTRACT=<p>C1Q (Complement 1Q) is an important recognition molecule in the immunological complement system, which could also be putatively involved in the stress responses induced by endotoxins or exotoxins, potentially through detoxification processes. Marine bivalves are well adapted to highly complex aquatic environments with various stressors. As filter feeders, they have to cope with highly potent microalgae-derived neurotoxins, such as paralytic shellfish toxin (PSTs). Zhikong scallops, <italic>Chlamys farreri</italic>, are commercially important bivalve with the remarkable ability to accumulate PSTs. Exploring the <italic>C1Q</italic>s related to PST accumulation in <italic>C. farreri</italic> could benefit our understanding of the adaptations of bivalve species. In the present study, we systematically analyzed <italic>C1Q</italic> genes in <italic>C. farreri</italic>. In total, 97 <italic>CfC1Q</italic> genes mainly from the expanded C1Q-B subfamily were identified, from which the <italic>C1QL</italic>, <italic>C1QTNF</italic>, and <italic>C1QDC1</italic> members in <italic>C. farreri</italic> were revealed to be under positive selection. Spatiotemporal expression analysis revealed that most <italic>CfC1QL</italic>s and <italic>CfC1QDC1</italic>s were highly expressed during the post-umbo stage and in hepatopancreas, while most <italic>CfC1QTNF</italic> members were highly expressed after the creeping larva stage and in mantle. The hepatopancreas and kidney in <italic>C. farreri</italic> are two toxin-rich organs with the highest concentrations of PSTs, acting as major “centers” for toxin accumulation and transformation, respectively. Therefore, after feeding the scallops with PST-producing dinoflagellates <italic>Alexandrium minutum</italic> and <italic>Alexandrium catenella</italic>, we determined the expression patterns of <italic>CfC1Q</italic>s in these two organs. In kidney, more than 85% of <italic>CfC1QL</italic>s and <italic>CfC1QDC1</italic>s showed drastic up-regulation with both diets. However, among these members with significant induction, a different response manner was detected after feeding with <italic>A. minutum</italic> and <italic>A. catenella</italic>, respectively as acute and chronic response patterns. In comparison, far fewer <italic>CfC1Q</italic>s showing significant up-regulation in hepatopancreas with both toxic diets and only mild regulation pattern could be found. This organ-, toxin-, and time-dependent genetic regulation of <italic>CfC1Q</italic>s may contribute to the virulence difference on account of the tissue-specific or dinoflagellate-specific different toxin analogs composition, implying the possible involvement of <italic>CfC1Q</italic>s in PST transport and homeostasis. Our findings imply the functional diversity of scallop <italic>C1Q</italic> genes in coping with PST accumulation, which might be developed as potential molecular indicators for monitoring toxin accumulation in edible mollusks or provide insight into the lineage-specific adaptation of scallops for dealing with microalgal toxin challenges.</p>