Ontogenic expression of adaptive immune genes in Rohu, Labeo rohita (Hamilton-Buchanan, 1822)

The ontogenic expression of selected adaptive immune genes in Labeo rohita was studied using semi-quantitative RT-PCR and quantitative real-time PCR. Adaptive immune genes, viz., Ikaros, MHC-II and Rag-1 were cloned and sequenced using self-designed primers. The partial nucleotide sequences of L. rohita Ikaros gene (510 bp), MHC-II gene (310 bp) and Rag-1 gene (142 bp) showed 94%, 93% and 99% homology with the sequences of Danio rerio, Barbus intermedius-and Catla catla, respectively. Total RNA extracted from fertilized eggs and larvae at 1, 3, 7, 10, 14, 17, 21, 24, 28, 35 and 42 days post-hatch (dph) was subjected to real-time PCR using self-designed real-time primers to amplify the adaptive immune genes, viz., IgM heavy chain gene, Ikaros, Rag-1 and MHC-II. The expressions of IgM heavy chain gene, Rag-1 and were first detected at 1 dph and thereafter increased gradually, and the onset of statistically significant (P < 0.05) increase in expression was observed from 24 dph (18.6 fold), 17 dph (16.7 fold) and 28 dph (10.7 fold), respectively, whereas, Ikaros gene expression was observed even at the fertilized egg stage and significant (P < 0.05) increase in expression was observed from 28 dph (7.1 fold) onwards. The findings of the present study suggest that the initial development of immunocompetence may occur by 3-4 weeks post-hatch in L. rohita.