Abstract
Upon encountering a virus, fish initiate an innate immune response, guided by IFNs. Foxo3 plays a part in the body's immune response; however, its specific role in the IFN-guided immune response in fish is yet to be clarified. In this study, we characterized foxo3 in Japanese medaka (Oryzias latipes) and examined its role in the IFN-dependent immune response upon infection with the RGNNV. The results show that the coding region of the medaka foxo3 gene is 2007 base pairs long, encoding 668 amino acids, and possesses a typical forkhead protein family structural domain. The product of this gene shares high homology with foxo3 in other fish species and is widely expressed, especially in the brain, eyes, testes, and heart. Upon RGNNV infection, foxo3-/- mutant larvae showed a lower mortality rate, and adults exhibited a significant reduction in virus replication. Moreover, the absence of foxo3 expression led to an increase in the expression of irf3, and a decrease in the expression of other IFN-related genes such as tbk1 and mapk9, implying that foxo3 may function as a negative regulator in the antiviral signaling pathway. These findings provide crucial insights for disease-resistant breeding in the aquaculture industry.