FOXO is involved in antimicrobial peptides expression during WSSV infection in Exopalaemon carinicauda.

The forkhead box transcription factor O family protein (FOXO) acts as a transcription factor that regulates biological processes regarding DNA repair, immunity, cell cycle regulation, and other biological processes. In this study, EcFOXO was identified from the ridgetail white prawn, Exopalaemon carinicauda. EcFOXO protein contains multiple low-complexity regions and a forkhead (FH) domain. Phylogenetic tree showed that EcFOXO is clustered with crustacean FOXOs. The amino acid sequences of its FH domain are highly similar to the FH domain of FOXOs from other crustaceans. The expression of EcFOXO is altered after white spot syndrome virus (WSSV) stimulation in hepatopancreas and gills. The relationship between EcFOXO and EcRelish was explored by RNA interference (RNAi). Results showed that EcFOXO and EcRelish could positively regulate each other's expression. The expression levels of various antimicrobial peptides (AMPs) significantly reduced after interfering with EcFOXO or EcRelish. These results suggest a positive regulatory loop between EcFOXO and EcRelish, which participates in the innate immunity of ridgetail white prawn by regulating the expression of AMPs during WSSV infection. This study enriches the knowledge about the regulatory mechanism of FOXO in the innate immunity of crustaceans.

Duox mediated ROS production inhibited WSSV replication in Eriocheir sinensis under short-term nitrite stress.

Nitrite stress and white spot syndrome virus (WSSV) infection are major problems threatening the sustainable and healthy development of Eriocheir sinensis. Some studies have found that nitrite stress can lead to the production of reactive oxygen species (ROS), whereas synthetic ROS plays a vital role in the signaling pathway. However, whether nitrite stress influences the infection of crabs by WSSV remains unclear. NADPH oxidases, including NOX1-5 and Duox1-2, are important for ROS production. In the present study, a novel Duox gene (designated as EsDuox) was identified from E. sinensis. The studies found that nitrite stress could increase the expression of EsDuox during WSSV infection and decrease the transcription of the WSSV envelope protein VP28. Moreover, nitrite stress could increase the production of ROS, and the synthesis of ROS relied on EsDuox. These results indicated a potential "nitrite stress-Duox activation-ROS production" pathway that plays a negative role in WSSV infection in E. sinensis. Further studies found that nitrite stress and EsDuox could promote the expression of EsDorsal transcriptional factor and antimicrobial peptides (AMPs) during WSSV infection. Moreover, the synthesis of AMPs was positively regulated by EsDorsal in the process of WSSV infection under nitrite stress. Furthermore, EsDorsal played an inhibitory role in the replication of WSSV under nitrite stress. Our study reveals a new pathway for "nitrite stress-Duox activation-ROS production-Dorsal activation-AMP synthesis" that is involved in the defense against WSSV infection in E. sinensis during short-term nitrite stress.

Glutathione S-transferase gene diversity and their regulation by Nrf2 in Chinese mitten crab (Eriocheir sinensis) during nitrite stress.

Eriocheir sinensis is one of the most important economic aquatic products in China. However, nitrite pollution has become a serious threat to the healthy culture of E. sinensis. Glutathione S-transferase (GST) is an important phase II detoxification enzyme, which plays a leading role in the cellular detoxification of exogenous substances. In this study, we obtained 15 GST genes (designated as EsGST1-15) from E. sinensis, and their expression and regulation in E. sinensis under nitrite stress were studied. EsGST1-15 belonged to different GST subclasses. EsGST1, EsGST2, EsGST3, EsGST4, and EsGST5 belonged to Delta-class GSTs; EsGST6 and EsGST7 are Theta-class GSTs; EsGST8 is a mGST-3-class GST; EsGST9 belonged to mGST-1-class GSTs; EsGST10 and EsGST11 belonged to Sigma-class GSTs; EsGST12, EsGST13, and EsGST14 are Mu-class GSTs; EsGST15 is a Kappa-class GST. Tissue distribution experiments showed that EsGSTs were widely distributed in all detected tissues. The expression level of EsGST1-15 was significantly increased in the hepatopancreas under nitrite stress, indicating that EsGSTs were involved in the detoxification of E. sinensis under nitrite stress. Nuclear factor-erythroid 2 related factor 2 (Nrf2) is a transcription factor that can activate the expression of detoxification enzyme. We detected the expression of EsGST1-15 after interfering with EsNrf2 in the hepatopancreas of E. sinensis with or without nitrite stress. Results showed that EsGST1-15 were all regulated by EsNrf2 with or without nitrite stress. Our study provides new information about the diversity, expression, and regulation of GSTs in E. sinensis under nitrite stress.