The involvement of VEGF and VEGFR in bacterial recognition and regulation of antimicrobial peptides in Eriocheir sinensis.

Vascular endothelial growth factor (VEGF) and VEGF reporter (VEGFR) are essential molecules in VEGF signalling pathway. Although the functions of VEGF and VEGFR have been well reported in vertebrates, their functions are still poorly understood in invertebrates. In this study, the open reading frame sequences of EsVEGF1 and EsVEGFR4 were cloned from Eriocheir sinensis, and their corresponding proteins shared typical structure characteristics with their counterparts in other species. EsVEGF1 were predominantly expressed in hepatopancreas and muscle while EsVEGFR4 mainly expressed in hemocytes and intestine. The expression levels of EsVEGF1 in hemocytes were rapidly induced by Staphylococcus aureus and Vibrio parahaemolyticus, and it also increased rapidly in hepatopancreas after being challenged with V. parahaemolyticus. The expression levels of EsVEGFR4 only increased in hepatopancreas of crabs injected with S. aureus. The extracellular immunoglobulin domain of EsVEGFR4 could bind with Gram-negative and Gram-positive bacteria as well as lipopolysaccharide and peptidoglycan. EsVEGF1 could act as the ligand for EsVEGFR4 and Toll-like receptor and regulate the expression of crustins and lysozyme with a tissue-specific manner, while have no regulatory function on that of anti-lipopolysaccharide factors. This study will provide new insights into the immune defense mechanisms mediated by VEGF and VEGFR in crustaceans.

Spätzle, a signaling molecule that interacts with pathogen-associated molecules and Toll-like receptor in Portunus trituberculatus.

Spätzle is a crucial ligand for Toll-like receptor (TLR) that triggers the activation of TLR signal pathway in insects. In this study, open reading frames (ORFs) of two spätzles were cloned from Portunus trituberculatus (PtSpz1 and PtSpz2). Both of PtSpzs contained the typical cystine-knot domain of spätzle. Tissue distribution analysis showed that both of PtSpzs were predominantly expressed in the gills. Transcriptional levels of the two PtSpzs in hemocytes and gill rapidly increased at 3 h and 6 h post Vibrio alginolyticus challenge, respectively. The two PtSpzs could bind to several pathogen-associated molecules including lipopolysaccharide (LPS), peptidoglycan (PGN) and envelope proteins of white spot syndrome virus (WSSV). Moreover, the two PtSpzs could directly interact with the extracellular leucine-rich repeats (LRR) domain of TLR. This study revealed that spätzle could interact with pathogen-associated molecules and TLR of host, which may be two important steps for spätzle to deliver signals into host cells.