Expression analysis of heat shock protein genes during Aeromonas hydrophila infection in rohu, Labeo rohita, with special reference to molecular characterization of Grp78.

Heat shock protein (Hsp) genes are stress-related genes that activate the host immune system during infection. Hsp genes expression in fish, studied during bacterial infections, is mostly confined to Hsp70 and Hsp90. The present study is an expression analysis of seven Hsp genes: Apg2, Hsp90, Hsp70, glucose-regulated protein 78 (Grp78), heat shock cognate 70 (Hsc70), Grp75, and Hsp30 during Aeromonas hydrophila infection in rohu, Labeo rohita. Forty-eight rohu juveniles were challenged with 3 × 10(7) cfu bacteria per 20 g of body weight intraperitoneally. The expression of these genes was studied in infected liver, anterior kidney, and spleen tissues of rohu at different time periods: 0, 1, 3, 6, 12, 24, 48, 72 h, 7, and 15 days post-infection by qPCR. The Hsp gene modulation was greater in liver as compared to spleen and kidney tissues. Induced expression of Apg2, Hsp90, Grp78, Grp75, and Hsc70 was noticed during peak periods (3 to 24 h post-challenge) of bacterial infectivity. Hsp70 was found to be down-regulated during the process of infection. In contrast to the other six genes, Hsp30 showed a variable expression pattern in all three tissues. Grp78 was found to be the most highly (1,587-fold) expressed gene in liver at 12 h post-challenge. Further, molecular characterization of Grp78 revealed it to be a highly conserved Hsp gene, essential not only during infection but also during early developmental stages of rohu, and its expression was noticed in all organs studied except in gill tissues, which indicated its potential immune regulatory role during infection process.