Jak/Stat-regulated Esftz-f1 negatively regulates the antibacterial immunity of Eriocheir sinensis against Vibrio parahaemolyticus

With the growing global demand for premium aquatic products, the expanding international market presence of Eriocheir sinensis has led to a continuous appreciation of its economic value. However, E. sinensis is threatened by various diseases during its breeding, among which bacterial diseases seriously affect its immune function and impede its growth. Ftz-f1, an orphan nuclear receptor, plays a vital role in the embryonic development, molting process, gonadal development, and immune regulation of invertebrates. This study aims to identify the ftz-f1 homolog, called Esftz-f1, in E. sinensis. The Esftz-f1 ORF spans 1770 bp, encoding a 589-amino acid protein that shares 87.84 % sequence similarity with the Litopenaeus vannamei homolog and this protein contains two conserved functional domains. It is widely expressed in the multiple tissues of E. sinensis, with particularly high expression in the hepatopancreas. Subcellular localization analysis revealed nuclear localization of EsFtz-f1. The expression level of Esftz-f1 changes significantly upon stimulation by V. parahaemolyticus. When Jak and Stat are silenced or inhibited, the expression levels of Esftz-f1 are significantly downregulated. After Esftz-f1 is silenced, the expression levels of antimicrobial peptides, the phagocytic ability of hemocytes, bacterial clearance rate and the survival rate of crabs are significantly upregulated, suggesting that EsFtz-f1 plays a negative regulatory role in the resistance of E. sinensis to V. parahaemolyticus infection. We believe our study will help broaden the research scope of orphan nuclear receptors. It may also provide useful insights that aid further study of the immune mechanism of E. sinensis and provided references for the prevention of diseases during its breeding.