Molecular characterization and expression analysis of Tf_TLR4 and Tf_TRIL in yellow catfish Tachysurus fulvidraco responding to Edwardsiella ictaluri challenge.

ABSTRACT

Toll-like receptors play significant roles in defensing against pathogen invasion. In this study, TLR4 and TRIL from Yellow catfish Tachysurus fulvidraco (Tf), were identified and characterized. The open reading frames of the Tf_TLR4 and Tf_TRIL genes were 2466 bp and 1827 bp in length, encoding 821 and 608 amino acids, respectively. The Tf_TLR4 consists of LRRs, a transmembrane domain and a TIR domain, and Tf_TRIL only contains LRRs and TIR domain. Homologous identity revealed that both Tf_TLR4 and Tf_TRIL have high protein sequence similarity with that of channel catfish Ictalurus punctatus. Both the Tf_TLR4 and Tf_TRIL genes were highly expressed in head kidney and brain, respectively. The mRNA expression levels of Tf_TLR4 and Tf_TRIL genes were up-regulated in intestine and immune-related tissues after challenge of Edwardsiella ictaluri. The microscopic observation of the gut showed that the pathological changes in midgut and hindgut are more obvious than that in foregut after challenged with E. ictaluri. These results indicate that these two genes play potential roles in the host defense against E. ictaluri invasion. This study will provide valuable information to better understand the synergistic roles of TLR4 and TRIL in the innate immune system of yellow catfish and other fish.