Polymorphism distribution and structural conservation in RNA-sensing Toll-like receptors 3, 7, and 8 in pigs

Background: Viral genomic RNA-both single-stranded (ss) and double-stranded (ds)-is recognized by RNA-sensing Toll-like receptors (TLRs), notably TLR3 (dsRNA), TLR7 (ssRNA). and TLR8 (ssRNA). However. our knowledge of the roles of porcine TLR3, 7, and 8 in antiviral immunity is inadequate. Methods: From information on exon-intron boundaries obtained through comparisons of the genomic and cDNA sequences, polymorphisms in the coding sequences of each gene were detected in 84 male pigs of 11 breeds. Results: Genomic structures are conserved between pigs and humans. The RNA-sensing TLR genes had fewer polymorphisms causing amino acid alterations than did the cell-surface TLR genes, but the alterations were distributed with a similar bias toward ectodomains. Conclusions: The low level of diversity of substitutive polymorphisms in RNA-sensing TLRs than cell-surface ones implies that polymorphisms severely affecting function have been eliminated by selection pressure during longstanding pig breeding. General significance: Recognition of virus-derived RNA is critical in host defense against infection. These results should provide a useful clue to analysis of the association between polymorphisms in RNA-sensing TLRs and disease resistance. (C) 2009 Elsevier B.V. All rights reserved.