Ontogeny and tissue specific expression profiles of recombination activating genes (RAGs) during development in Nile tilapia, Oreochromis niloticus

Recombination activating genes (RAGs) mediates the process of rearrangement and somatic recombination (V(D)J) to generate different antibody repertoire. Studies on the expression pattern of adaptive immune genes during ontogenic development are crucial for the formulation of fish immunization strategy. In the present study, Nile tilapia was taken to explore the relative expression profile of RAG genes during their developmental stages. The developmental stages of Nile tilapia, i.e., unfertilized egg, 0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28 and 30 days post-hatch (dph) and kidney, blood, gill, liver and spleen tissues from adult fish were collected and the cDNA synthesis was carried out. Gene specific primers for RAG-1 and RAG-2 of Nile tilapia were designed and their annealing temperature (Tm) was optimized by gradient PCR. Consequently, PCR was performed to confirm the specific amplification of RAG-1 and RAG-2 genes. Quantitative real-time PCR (qRT-PCR) gene expression of RAG-1 and RAG-2 were noticed in all the developmental stages; however, a significant increase was observed after 12 dph and peaked at 24 dph, followed by a gradual decrease until 30 dph. Tissue-specific gene expression profiling revealed that the highest expression of RAG-1 and RAG-2 was observed in the kidney, followed by spleen, gill, liver and blood. The findings of the study explored the suitable timing of lymphoid maturation that could be technically used for the adoption of strategies to improve disease resistance of fish larvae for mitigating larval mortality.