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• Sp TIA-1 is overexpressed during WSSV infection in mud crab. • Sp TIA-1 suppresses WSSV infection via apoptosis promotion. • Sp TIA-1 can activate caspase signaling in mud crab. • Sp TIA-1 can modulate MMP (⊿ψm) by regulating ROS levels. TIA-1 (T cell restricted intracellular antigen-1) is a kind of RNA-binding protein which serves as the downstream of CED-9 (a BCL2 homolog) and induces apoptosis under stress conditions. So far, the function of apoptosis mediated by TIA-1 has been extensively studied in higher animals, and apoptosis happens to be related to biological immune defense. However, the involvement of TIA-1 in the study of immune function during viral infection has not been clearly studied, especially in marine invertebrates. In the study, Sp TIA-1 in mud crab (Scylla paramamosain) was specifically identified. The Open Reading Frame (ORF) of Sp TIA-1 was consisted of 1116 nucleotide bases and encoded 372 amino acids. Besides, the results showed that the expression of Sp TIA-1 was obviously up-regulated during WSSV (White Spot Syndrome Virus) infection in hemocytes of mud crab. Furthermore, through RNAi approach, we found that Sp TIA-1 could activate Caspase-3 signaling and increase ROS levels to reduce mitochondrial membrane potential, resulting in the increase of apoptosis rate in hemocytes, which eventually suppressed WSSV multiplication in mud crab. The current study therefore improves the knowledge of antiviral immunity in mud crab and provides new insights into the innate immunity of marine crustaceans. [ABSTRACT FROM AUTHOR]

ICAD is the inhibitor of caspase-activated deoxyribonuclease and has been widely investigated for its apoptotic regulatory function in higher animals, whereas apoptosis is tightly relevant to immune defense. However, the involvement of ICAD during virus infection has not been addressed in invertebrates. In this study, Sp ICAD identified in mud crab (Scylla paramamosain) was characterized, we found that the expression of Sp ICAD was upregulated during WSSV (White Spot Syndrome Virus) infection in mud crab, then, the role of Sp ICAD in immunoregulation was further explored via RNAi approach, the data revealed that Sp ICAD could inhibit caspase signaling and mitochondrial membrane potential (⊿ψm) and thus suppress apoptosis process. Moreover, our results showed that virus infection could activate Sp ICAD to reduce the apoptosis rate of hemocyte, which eventually contribute to WSSV replication in mud crab. The current study therefore provides novel insights into the anti-viral immune response of mud crabs. • Sp ICAD identified in mud crab (Scylla paramamosain) was characterized. • The expression of Sp ICAD was upregulated in mud crab during WSSV infection. • Sp ICAD contributes to virus infection via suppressing apoptosis. • Sp ICAD could inhibit caspase signaling and mitochondrial membrane potential. [ABSTRACT FROM AUTHOR]

The Toll pathway is crucial for innate immune responses in organisms (including Drosophila and mammals). The Spätzle protein outside of cells acts as a ligand for Toll receptors, enabling the transfer of signals from outside the cell to the inside. However, the function of Spätzle in the immune system of mud crab (Scylla paramamosain) remains unclear. This research discovered a novel Spätzle gene (Sp -Spz) in mud crab, which showed extensive expression in all the tissues that were examined. The RNA interference exhibited the correlation between Sp -Spz and the anti-lipopolysaccharide factors (ALFs). Knockdown of Sp -Spz decreased the expression of Sp -Toll2 but not Sp -Toll1. In Drosophila Schneider 2 cells, Sp -Spz was found interacted with Sp -Toll2. Moreover, the depletion of Sp -Spz caused the separation of hepatic lobules from the basement membrane, resulting in the disruption of the structural coherence of hepatopancreatic cells. Additionally, the knockdown of Sp -Spz resulted in changes to the composition of the hemolymph microbiota, specifically affecting the proportions of different phylum and family levels. The findings indicated that Sp -Spz may promote the synthesis of ALFs via Sp -Toll2, thereby influencing the homeostasis of microbiota in the hemolymph. In this study, novel insights into mud crab immunity are provided. • Full-length of Sp -Spz with 996 bp was cloned from mud crab. • Sp -Spz promoted bacteria clearance and up-regulating the expression of ALFs. • Sp -Spz can regulate the expression of ALFs through Sp -Toll2. • Sp -Spz knockdown altered the relative abundance of the hemolymph microbiota at the phylum and family levels. [ABSTRACT FROM AUTHOR]