The novel six LIM and one PET domain-containing protein Lmpt is involved in the immune response through activation of the NF-κB signalling pathway in the crustacean, Macrobrachium nipponense.

The four-and-a-half LIM-only protein family of transcription co-factors participates in various cellular processes, such as cell proliferation, cell differentiation, apoptosis, cell adhesion, migration, transcription and signal transduction. However, the knowledge of the structural characteristics and immune functions of its ancestor Lmpt, which contains six LIM domains at the C-terminus and a PET domain at the N-terminus, is limited in invertebrates, especially in crustaceans. In the present study, a novel Lmpt from oriental river prawn (Macrobrachium nipponense) was identified, and its role in the immune response was investigated. Its full-length cDNA sequence was 6407 bp, which contained a 2595 bp ORF encoding 865 amino acids, exhibiting high similarity to the structure of Lmpt derived from other invertebrates. Tissue distribution analysis revealed that MnLmpt was widely expressed in all examined tissues, and high expression levels were observed in muscle, heart and intestine in M. nipponense. After experimental challenges with bacteria and virus, the transcription levels of MnLmpt significantly fluctuated in gill and hepatopancreas, indicating that it might play a role in the innate immune response in M. nipponense. Silencing of MnLmpt by dsRNA injection in vivo could promote bacterial growth, suggesting that MnLmpt exerted an antibacterial immune function in prawn. Immunocytochemistry assay results demonstrated that MnLmpt was able to translocate from the cytoplasm to the nucleus after being stimulated with pathogens. The expression levels of NF-κB signalling cascade members, such as dorsal, relish, TAK1, TAB1, Ikkβ, and Ikkε, and AMPs, including ALF4, Cru1, and Cru2, exhibited significant downregulation in the MnLmpt silenced group. Similarly, dual-luciferase reporter assays also demonstrated that MnLmpt could stimulate an NF-κB signalling cascade. Meanwhile, all of the LIM domains of MnLmpt could trigger NF-κB signalling; however, their cumulative effect on NF-κB promoter activation was hardly observed. These results showed that MnLmpt might play a crucial role in the innate immune response in M. nipponense, and these findings paved the way for a better understanding of the immune system in crustacean species.