The role of myosin-9 in Scylla paramamosain against Vibrio alginolyticus and white spot syndrome virus infection

Abstract

Myosin-9 is an important component of myofibrillar filament which is widely distributed in the various tissues and organs of animals. In this research we studied the role of the Scylla paramamosain myosin-9 gene in the immune process against white spot syndrome virus (WSSV) or Vibrio alginolyticus infection. The myosin-9 gene with a total length of 2735 bp, including a 2145 bp ORF encoding a 715aa protein, was cloned from S. paramamosain. The expression of myosin-9 in muscle was the highest and decreased in crab hemocytes after challenges with WSSV or V. alginolyticus. After myosin-9 knockdown by double-stranded RNA (myosin-9-dsRNA), the expression of c-type-lectin, Toll-like-receptor, and crustin antimicrobial peptide was increased significantly, and the expression of JAK, STAT, and prophenoloxidase was decreased significantly. An immune activity test showed that the total number of hemocytes decreased significantly and the activity of phenoloxidase (PO) and superoxide dismutase (SOD) were decreased after myosin-9 knockdown. After myosin-9 knockdown and WSSV infection, the phagocytosis rate of hemocytes was significantly decreased but the apoptosis rate of hemocytes was increased, and the copy number of virus and the mortality rate of crabs were significantly increased compared with that of control. These results indicated that myosin-9 may participate in the antiviral immune process of S. paramamosain against WSSV infection. After myosin-9 knockdown and V. alginolyticus infection, the phagocytosis rate of hemocytes was significantly reduced, the apoptosis rate of hemocytes was significantly increased, and the mortality rate of crabs was significantly increased compared with that of control. It was revealed that myosin-9 may play a positive role in the immune response to V. alginolyticus through increasing the phagocytosis rate of hemocytes. This study interpreted the role of myosin-9 in the innate immunity of S. paramamosain, and provided strong support for the prevention and treatment of diseases in S. paramamosain culture.