Identification and transcriptional analysis of eight C1q genes in Takifugu obscurus during bacterial infection.

As an initiating molecule of the classical complement pathway, C1q performs diverse biological functions. In this study, eight C1q genes were identified in Takifugu obscurus and designated as ToC1q1-ToC1q8. Bioinformatics analysis revealed that the proteins encoded by these cDNAs consist of 197-261 amino acids, with varying molecular weights and isoelectric points. SMART domain analysis indicated that all ToC1q proteins contain a signal peptide and a C1q domain, one of which also contains a collagen-like domain. Sequence alignment and phylogenetic analysis showed low sequence similarity among the eight genes, although they exhibited high similarity with their orthologs in T. rubripes and T. flavidus. Pathway analysis revealed that they may be involved in complement-related pathways and may play a role in defense against pathogens. Tissue distribution profiling revealed distinct expression patterns for each gene across different tissues, suggesting potential tissue-specific immune roles. Furthermore, expression pattern analysis following bacterial challenge indicated that the eight genes responded differentially depending on the infection time and bacterial species, with most of them showing significant upregulation upon infection. Collectively, these findings suggest that ToC1q1-ToC1q8 may play important roles in the innate immunity of T. obscurus, participating in the host response to pathogens and sustaining immune function post-infection.