Cloning, characterization and ontogenetic expression profile of RAG-2 and IgM in angelfish (Pterophyllum scalare).

Early larval developmental stages of fish are highly susceptible to opportunistic pathogens until the complete maturation of the lymphoid organs. Knowledge of the expression pattern of important markers of adaptive immune system during the ontogenetic development is essential before vaccinating the fish. In the present study, Pterophyllum scalare (angelfish) was taken to explore the relative expression profile of developmental markers of adaptive immunity, recombination activating gene-2 (RAG-2) and immunoglobulin M (IgM). The fishes were bred and early developmental stages (0-45 days post-hatched) were used to assess the expression profile. The genes, RAG-2 and IgM were cloned and sequenced with the base pair lengths of 1958 bp and 225 bp respectively. The mRNA expression of RAG-2 appeared at insignificant level at the first day of hatching, but the expression was significantly increased from 24 dph (days post-hatching) onwards and reached its peak at 27 dph. The results proved that the maturation of lymphoid organs was completed at 27 dph as the respective protein is involved in the V(D)J recombination, important for the maturation of lymphoid organs. A similar trend was also observed in the mRNA transcript levels of IgM gene and a significantly high expression was detected from 27 dph onwards. The present study suggested that the suitable time for vaccination in P. scalare could be taken at 27 dph, as the maturation and development of lymphoid organs is completed thus helps in stimulating the adaptive response of immunity against any pathogen.