Ontogeny and expression analysis of tube (interleukin-1 receptor-associated kinase-4 homolog) from Penaeus monodon in response to white spot syndrome virus infection and on exposure to ligands

Tube, an IRAK- 4 (Interleukin-1 receptor-associated kinase-4) homolog, is a key component in the Toll signalling pathway that has diverse role in the innate immunity of organisms including the ontogenic development. In the present study, Tube from Penaeus monodon (PmIRAK-4) was studied in response to infection with white spot syndrome virus (WSSV) and on exposure to various ligands. The ontogenic expression pattern of PmIRAK-4 in different developmental stages of P. monodon showed that the gene was constitutively expressed in all the stages tested with the maximum expression detected in egg. Immune-modulation of PmIRAK-4 in response to WSSV was studied in post-larvae, juveniles and adult P. monodon in vivo, and in primary haemocyte cultures at different time-points post-infection in vitro. PmIRAK-4 displayed significant up-regulation in haemocytes, gill, lymphoid organ and stomach at all time-points in vivo as well as in primary haemocyte cultures in vitro. To understand the post-injection stress on the immune-modulation, we have compared the expression level of PmIRAK-4 using zero hour (un-injected) and phosphate buffered saline (PBS)-injected controls, wherein the trend in expression was found to be similar. Following in vitro stimulation with ligands such as lipopolysaccharide and peptidoglycan, significant up-regulation of the gene could be observed at all time-points. However, poly I:C induction resulted in down-regulation of the same at early time-points. The ubiquitous expression of PmIRAK-4 in different larval and post-larval stages implies the involvement of the gene in defense mechanism during early developmental stages of P. monodon. Further, the modulation of expression of PmIRAK-4 in response to WSSV and different ligands indicates its possible role in immune responses in shrimp.