Abstract:The immune system of teleost, similar to mammals, is divided into two subsystems: Innate immune system and acquired immune system. Acting as the first line of defense against invading pathogens and pathogenicity factors, the innate immune system can be activated by the pattern recognition receptor (PRRs) which can recognize the pathogen-associated molecular pattern (PAMPs) and activate the downstream inflammatory response accordingly. MAPK(mitogen-activated protein kinase) signaling pathway is an important signal transduction system in eukaryote cells, which can mediate extracellular signaling into the cell and participate in various cellular processes such as cell proliferation, apoptosis, and immune response. JNK (c-Jun N-terminal kinase) signal pathway is an important branch of MAPK signal pathway. JNK have been extensively studied in mammals, but not adequately in the teleost. In this research, we designed experiments to study the role of JNK2 genes in the antimicrobial reaction of Japanese flounder and their effects on the downstream of the pathway in order to provide a theoretical basis for the study of JNK signaling pathway in fish. In this study, the JNK2 gene sequences of Japanese flounder were obtained from the transcription database of flounder and named after PoJNK2. The PoJNK2 ORF region encodes is 1263 bp and encodes 420 amino acids. The domains of PoJNK2 genes were predicted by SMART server. The results showed that the JNK2 gene had a typical serine-threonine protein kinase domain S_TKc. The expression levels of PoJNK2 genes in different tissues of flounder were analyzed by the qRT-PCR technique. It was found that PoJNK2 were widely expressed in the immune tissue of Japanese flounder. Therefore, it was preliminarily speculated that PoJNK2 played a major role in the immune response of Japanese flounder. We designed an infection experiment of Edwardsiella tarda in vivo and immune stimulatory cell experiments in vitro to investigate the role of PoJNK2 in the immune response of Japanese flounder. The expression of PoJNK2 was up-regulated in the spleen, kidney, and gill of Japanese flounder after injecting E. tarda in vivo. At the same time, the gill cells of flounder (FG) were stimulated by E. tarda, Poly I:C and TNF-α. The expression of PoJNK2 was up-regulated at different time points. In addition, we overexpressed PoJNK2 in FG by cell transfection and it was found that PoJNK2 had significant regulatory effects on the regulation of downstream pro-inflammatory cytokines and transcription factor AP-1. The role of PoJNK2 in regulating the immune response of Japanese flounder was further clarified.
