Developmental expression of immune-associated secreted novel AID/APOBEC-like deaminases (SNAD1s) in common carp (Cyprinus carpio).

Early developmental stages of teleost fish represent vulnerable phases of the life cycle, characterized by exposure to fluctuating abiotic and biotic environmental conditions. Immune system maturation is gradual, beginning with reliance on maternally transferred immune factors, followed by activation of the innate immune system and culminating in the establishment of adaptive immunity. Recent studies in common carp (Cyprinus carpio) have identified a novel family of cytidine deaminases termed Secreted Novel AID/APOBEC-like Deaminases (SNAD1s). Although their biological functions remain unknown, preliminary evidence suggests that snad1 genes may participate in immune- and stress-related processes. In the present study, we analyzed the expression of 13 snad1 genes during embryonic and early larval development of common carp. Twelve of the thirteen genes (excluding snad_506) exhibited significant stage-dependent variation in expression and formed four distinct temporal expression patterns. Four paralogous genes (snad_318, snad_800, snad_835, and snad_810) were maternally expressed, suggesting deposition in the oocyte and potential involvement in early developmental regulation. In contrast, snad_409, snad_208, and snad_962 displayed delayed post-zygotic activation, with increased expression observed during later developmental stages coinciding with post-hatching maturation of immune-related physiological processes and establishment of host defense mechanisms. Comparative analysis of publicly available RNA-seq datasets confirmed conserved snad1 expression dynamics across independent studies and methodological approaches. This study provides the first comprehensive overview of developmental snad1 gene expression during vertebrate ontogeny. The dynamic and stage-dependent expression of snad1 genes reveals distinct developmental regulation patterns and highlights substantial heterogeneity within the carp snad1 gene family during ontogeny.