Identification of a novel C1q complement component in razor clam Sinonovacula constricta and its role in antibacterial activity.

The serum complement component C1q mediates a variety of immune regulatory functions. Herein, we identified a globular head C1q (ghC1q) gene in razor clam Sinonovacula constricta. The complete Sc-ghC1q gene was 872 bp long included an 81 bp 5'-untranslated region (UTR), a 95 bp 3'-UTR with a poly(A) tail, and an open reading frame (ORF) of 696 bp. The mRNA expression of Sc-ghC1q was upregulated in hepatopancreas and hemocytes. After Staphylococcus aureus or Vibrio anguillarum challenge, Sc-ghC1q mRNA transcript abundance was significantly upregulated in hemolymph. Recombinant Sc-ghC1q protein could bind lipopolysaccharide (LPS) and lipoteichoic acid (LTA), and it could agglutinate both Gram-positive and Gram-negative bacteria. Additionally, flow cytometry revealed that Sc-ghC1q strongly promoted phagocytosis in hemocytes. Together, these results demonstrated that Sc-ghC1q played an important role in innate immunity in S. constricta.