Genome-wide characterization of the caspase family genes in different sturgeons: Insights into lineage-specific expansion and immune responses.

Caspases are pivotal executioners of apoptosis and inflammation, playing critical roles in vertebrate immune defense. However, their evolutionary dynamics and functional characteristics in basal ray-finned fish, such as sturgeons, remain largely unexplored. In this study, we performed a genome-wide identification and characterization of the caspase (CASP) gene family in three sturgeons (Acipenser ruthenus, Polyodon spathula, and Acipenser sinensis). Phylogenetic and synteny analyses revealed a lineage-specific expansion of the sturgeon CASPs repertoire, particularly within the CASP8 and CASP3/7 subfamilies. Despite the variation in gene copy number, the core protein domains and motifs remained highly conserved. Expression profiling demonstrated that specific CASPs members exhibit distinct spatial distribution patterns in mucosal immune tissues and validated by qRT-PCR. Notably, inflammatory CASP1 and initiator CASP9 were enriched in the gill and duodenum, whereas effector CASP3 and CASP6 showed preferential expression in the valvular intestine. Furthermore, re-analysis of public transcriptomic datasets revealed that in vivo bacterial infections triggered a robust and systemic upregulation of the caspase network, contrasting with the moderate responses observed in in vitro cell models. Collectively, these findings highlight the evolutionary plasticity of the caspase family in acipenseriforms and underscore their specialized roles in maintaining mucosal homeostasis and combating bacterial pathogens.