Submitted to: Fish and Shellfish Immunology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 4, 2010
Publication Date: April 23, 2010
Citation: Palti, Y., Rodriguez, M., Gahr, S.A., Purcell, M., Rexroad III, C.E., Wiens, G.D. 2010. Identification, characterization and genetic mapping of the TLR1 gene in rainbow trout (Oncorhynchus mykiss). Fish and Shellfish Immunology. 28:918-926. Interpretive Summary: The U.S. salmonid aquaculture industry suffers severe economic loss to diseases. Every year, viral and bacterial epidemics in farmed Atlantic salmon and rainbow trout have resulted in production losses accounting for millions of dollars of lost revenue. Toll-like receptors (TLRs) are a family of transmembrane proteins that recognize specific pathogen molecules to induce innate immune response. In vertebrates, TLRs can also distinguish among classes of pathogens and serve an important role in orchestrating the appropriate adaptive immune responses. Detailed mapping and gene annotation of TLR genes in rainbow trout and the development of genetic markers for the different TLR genes will provide useful tools for genetic improvement of disease resistance in rainbow trout and other salmonids.
Technical Abstract: Induction of innate immune pathways is critical for early antimicrobial defense but there is limited understanding of how teleosts recognize microbial molecules and activate these pathways. In mammals, Toll-like receptors (TLR) 1 and 2 form a heterodimer involved in recognizing peptidoglycans and lipoproteins of microbial origin. Herein, we identify and describe the rainbow trout (Oncorhynchus mykiss) TLR1 gene ortholog and its mRNA expression. Two TLR1 loci were identified from a rainbow trout bacterial artificial chromosome (BAC) library using DNA sequencing and genetic linkage analyses. Full length cDNA clone and direct sequencing of four BACs revealed an intact omTLR1 open reading frame (ORF) located on chromosome 14 and a second locus on chromosome 25 that contains a TLR1 pseudogene. The duplicated trout loci exhibit conserved synteny with other fish genomes that extends beyond the TLR1 gene sequences. The omTLR1 gene includes a single large coding exon similar to all other described TLR1 genes, but unlike other teleosts it also has a 5' UTR exon and intron preceding the large coding exon. The omTLR1 ORF is predicted to encode an 808 amino-acid protein with 69% similarity to the Fugu TLR1 and a conserved pattern of predicted leucine-rich repeats (LRR). Phylogenetic analysis grouped omTLR1 with other fish TLR1 genes on a separate branch from the avian TLR1 and mammalian TLR1, 6 and 10. omTLR1 expression levels in rainbow trout anterior kidney leukocytes were not affected by the human TLR2/6 and TLR2/1 agonists diacylated lipoprotein (Pam2CSK4) and triacylated lipoprotein (Pam3CSK4). However, due to the lack of TLR6 and 10 genes in teleost genomes and upregulation of TLR1 mRNA in response to LPS and bacterial infection in other fish species we hypothesize an important role for omTLR1 in antimicrobial immunity. Therefore, the identification of a TLR2 ortholog in rainbow trout and the development of assays to measure ligand binding and downstream signaling are critical for future elucidation of omTLR1 functions.