Genome‐wide analysis of the caspase gene family in common carp ( C yprinus carpio ) and their transcriptional responses to nitrate exposure

Caspases are a family of cysteine proteases that play essential roles in apoptosis, inflammation and cellular homeostasis. Despite their biological importance, the genomic organization and stress-related functions of the caspase gene family remain insufficiently characterized in many teleost fish species. In the present study, a comprehensive genome-wide analysis of the caspase gene family was conducted in common carp (Cyprinus carpio), and the transcriptional responses of selected caspase genes to nitrate-induced stress were investigated. A total of 37 caspase genes were identified and classified into initiator, executioner and inflammatory groups based on phylogenetic relationships, conserved domain architecture and motif composition. Comparative genomic analyses revealed extensive gene family expansion associated with the allotetraploid genome structure of common carp, while synteny and duplication analyses supported the evolutionary conservation of caspase genes among teleosts. Structural characterization demonstrated the preservation of the conserved caspase catalytic domain and typical caspase protein architecture. Functional enrichment analyses indicated that Cc_CASP proteins are predominantly involved in apoptosis, programmed cell death, immune regulation and stress-response pathways. Gene expression analyses further revealed tissue-specific transcriptional responses to nitrate exposure, with several caspase genes showing significant differential expression in liver and brain tissues. These findings provide new insights into the evolution, structural diversity and functional roles of the caspase gene family in common carp and suggest that selected caspase genes may serve as potential molecular biomarkers for assessing environmental stress in freshwater ecosystems.