Deciphering the transcriptional regulatory networks of FOX genes in nitrite-induced spleen injury in largemouth bass

Nitrite accumulation in aquatic habitats can induce toxicity and cause spleen injury in fish. This study identified forkhead box (FOX) transcription factors involved in the splenic response to nitrite stress in largemouth bass through transcriptomic analysis. Phylogenetic analysis classified 93 FOX genes into 17 subgroups, with FOXN, FOXP and FOXO showing significant upregulation after nitrite treatment. Further analysis identified msFOX_29, msFOX_81, msFOX_89 and msFOX_7 as key FOX transcriptional regulators mediating spleen injury. Co-expression network analysis revealed that these FOX transcription factors may regulate downstream targets involved in pathways such as apoptosis (CASP8), immune cell infiltration (CD34), protein synthesis (UBA52, FARSB), signal transduction (PPP2CB), and metabolism (GUK1). These targets contained FOX binding sites in promoter regions and were upregulated under nitrite stress. Additionally, FOX expression was found correlated with changes in immune cell infiltration. Cross-species analyses revealed phylogenetic conservation and functional importance of FOXN, FOXP and FOXO subgroups in the splenic responses more fish species. Our study delineates the FOX transcriptional regulatory networks mediating nitrite-induced spleen injury in largemouth bass and provides insights into nitrite toxicity mechanisms in fish.