Functional divergence and epigenetic regulation of Caspase-3a and Caspase-8a in Apoptosis-Inflammation crosstalk during Streptococcus iniae infection in golden pompano (Trachinotus ovatus).

Golden pompano (Trachinotus ovatus) is an economically important marine aquaculture species, but its production is frequently threatened by bacterial diseases, particularly infection by Streptococcus iniae. Caspases are central regulators of apoptosis and inflammatory signaling, yet their functional diversification and regulatory mechanisms in T. ovatus remain poorly understood. In this study, we systematically characterized the caspase gene family in T. ovatus and selected Tovcasp3a and Tovcasp8a for further investigation based on their infection-responsive and phenotype-associated expression patterns. Expression analyses showed that Tovcasp3a was associated with modulation of intrinsic apoptotic signaling, whereas Tovcasp8a was linked to activation of RIPK1/FADD/NF-κB-related inflammatory responses. In situ hybridization further localized both transcripts predominantly to hepatic vascular wall cells. Promoter dissection and CpG methylation analyses indicated that upstream cis-regulatory elements and DNA methylation contribute to the differential expression of these two genes. Collectively, these results support a coordinated regulatory model in which apoptosis and inflammatory signaling are balanced during host defense against S. iniae. This study provides new insight into the molecular basis of antibacterial immunity in golden pompano and identifies candidate regulatory targets for future disease-resistance research.