A toll-like receptor 3 homologue that is up-regulated by poly I:C and DNA virus in turbot Scophthalmus maximus.

In this study, the gene and promoter sequences of turbot Scophthalmus maximus (Sm) toll-like receptor 3 (Tlr3) were cloned and its mRNA tissue distribution and gene expression in response to polyinosinic:polycytidylic acid (poly I:C) and turbot reddish body iridovirus ( TRBIV) challenges were studied in vivo. The smtlr3 gene spans over 4·4 kb with a structure of five exons-four introns and encodes a peptide of 916 amino acids. The putative protein shares the highest sequence identity of 52·8-78·5% with fish Tlr3 and contains a signal peptide sequence, 13 leucine-rich repeat ( LRR) motifs, a transmembrane region and a toll/interleukin-1 receptor ( TIR) domain. Phylogenetic analysis grouped it with other teleost Tlr3s. A number of transcription factor binding sites were identified in the 1538 bp 5′ flanking region of smtlr3, including interferon-stimulated response element ( ISRE) and those for interferon regulatory factors ( IRF) and signal transducer and activator of transcriptions ( STATs) smtlr3 transcripts were expressed ubiquitously with higher levels in the head kidney, heart and digestion organs. They were up-regulated by both poly I:C and TRBIV in immune and non-immune organs, but most strongly in the head kidney. Finally, the smtlr3 exhibited a two-wave induced expression during a five day time course when exposure of S. maximus to poly I:C. These findings provide insights into the role of SmTlr3 in antiviral response. [ABSTRACT FROM AUTHOR]