title: A Rac1 GTPase is a critical factor in the immune response of shrimp (Litopenaeus vannamei) to Vibrio alginolyticus infection.
abstract: The small GTPase Rac1 acts as a molecular switch for signal transduction that regulates various cellular functions. However, its functions in crustaceans remain unclear. In this study, a cDNA encoding a RAS GTPase (LvRac1) in the Pacific white shrimp (L. vannamei) was identified and characterized. A recombinant variant of this GTPase, rLvRac1, was expressed in the model organism P. pastoris and its expression was confirmed by mass spectrometry. Biochemical assays indicated that the recombinant protein retained GTPase activity and was expressed in all of the organism's tested tissues. Injection of the bacterium V. alginolyticus into L. vannamei induced hepatopancreatic upregulation of LvRac1 expression. Moreover, knocking down LvRac1 in vivo significantly reduced the expression of the L. vannamei p53 and Cu/Zn superoxide dismutase genes (Lvp53 and LvCu/Zn SOD, respectively) while increasing that of the galectin gene (Lvgal). Hemolymph samples from control and LvRac1-silenced L. vannamei individuals were analyzed by flow cytometry, revealing that the latter exhibited significantly reduced respiratory burst activity and total hemocyte counts. Cumulative mortality in shrimp lacking LvRac1 was significantly greater than in control groups following V. alginolyticus challenge. The silencing of LvRac1 by double-stranded RNA injection thus increased the V. alginolyticus challenge sensitivity of L. vannamei and weakened its bacterial clearance ability in vivo. Suppressing LvRac1 also promoted the upregulation of Lvp53, LvCu/ZnSOD, and Lvgal following V. alginolyticus injection. Taken together, these results suggest that LvRac1 is important in the innate immune response of shrimp to V. alginolyticus infection.
authors.affiliation: Key Laboratory of Ecology and Environmental Science in Guangdong Higher Education, Guangdong Provincial Key Laboratory for Healthy and Safe Aquaculture, College of Life Science, South China Normal University, Guangzhou 510631, China.
authors.forename: Gui-Hong
authors.initials: GH
authors.lastname: Cha
authors.affiliation: Key Laboratory of Ecology and Environmental Science in Guangdong Higher Education, Guangdong Provincial Key Laboratory for Healthy and Safe Aquaculture, College of Life Science, South China Normal University, Guangzhou 510631, China. Electronic address: wangwn@scnu.edu.cn.
authors.forename: Wei-Na
authors.initials: WN
authors.lastname: Wang
authors.affiliation: Key Laboratory of Ecology and Environmental Science in Guangdong Higher Education, Guangdong Provincial Key Laboratory for Healthy and Safe Aquaculture, College of Life Science, South China Normal University, Guangzhou 510631, China.
authors.forename: Ting
authors.initials: T
authors.lastname: Peng
authors.affiliation: Key Laboratory of Ecology and Environmental Science in Guangdong Higher Education, Guangdong Provincial Key Laboratory for Healthy and Safe Aquaculture, College of Life Science, South China Normal University, Guangzhou 510631, China.
authors.forename: Ming-Zhu
authors.initials: MZ
authors.lastname: Huang
authors.affiliation: Key Laboratory of Ecology and Environmental Science in Guangdong Higher Education, Guangdong Provincial Key Laboratory for Healthy and Safe Aquaculture, College of Life Science, South China Normal University, Guangzhou 510631, China.
authors.forename: Yuan
authors.initials: Y
authors.lastname: Liu
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D037161:Galectins / Q000235:genetics / Q000378:metabolism; D006434:Hemocytes / Q000502:physiology*; D043143:Hepatopancreas / Q000276:immunology*; D007113:Immunity, Innate / Q000235:genetics; D033561:Penaeidae / Q000276:immunology*; D034741:RNA, Small Interfering / Q000235:genetics; D013482:Superoxide Dismutase / Q000235:genetics / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism; D015854:Up-Regulation; D014733:Vibrio / Q000276:immunology*; D014735:Vibrio Infections / Q000276:immunology*; D020830:rac1 GTP-Binding Protein / Q000235:genetics / Q000378:metabolism*
chemical_list: D037161:Galectins; D034741:RNA, Small Interfering; D016159:Tumor Suppressor Protein p53; D013482:Superoxide Dismutase; D020830:rac1 GTP-Binding Protein
keywords: Litopenaeus vannamei; LvRac1; RNAi; Shrimp innate immunity; Vibrio alginolyticus