Genomic organization, evolution and functional characterization of soluble toll-like receptor 5 (TLR5S) in miiuy croaker (Miichthys miiuy)

Toll-like receptors (TLRs) play the key role in host defense of invasion of pathogens, not only in the innate immunity, but also in adaptive immunity. There are significant varieties and distinct features in fish TLRs, the TLR5 subfamily have two members (TLR5M and TLR5S). However, the exact role of TLR5 was lack of research in fish. In this study, a soluble form of TLR5 (TLR5S) was identified in miiuy croaker. The bioinformatics analysis showed that miiuy croaker TLR5S lacked the transmembrane domain and TIR domain. In other words, mmiTLR5S only has leucine-rich repeats (LRRs) domain, it is one of differences between TLR5M and TLR5S. Comparative genomic analysis showed that TLR5S might have happened an evolution between species. Expression analysis showed that mmiTLR5S was expressed in all tested miiuy croaker tissues and the mmiTLR5S expressions were significantly upregulated at 12 h in liver and kidney after Vibrio harveyi infection. Further functional experiments showed that NF-кB can be actived by mmiTLR5S, TLR5S might be an indispensable role in organism immune response. In short, the study of mmiTLR5S enriches the information of TLR5S and lays the foundation for future research on teleost TLRs system.