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Background: Toll-like receptors (TLRs) play an important role in detecting pathogen-associated molecular patterns (PAMPs). Among the TLRs, TLR3 is involved in the recognition of double-stranded RNA. This study was designed to explore the relationship between duTLR3 and duck reovirus (DRV) infection. Methods: In this study, we cloned and performed a molecular characterization of the complete sequence of Peking duck TLR3 (duTLR3). The expression level of duTLR3 was also determined, along with the relative levels of Mx and IFN-α mRNA after DRV infection. Results: The duTLR3 gene is 2776-bp long and encodes an 895-amino-acid-long protein. Sequence analysis of the product revealed the complete transcript of Peking duck TLR3, including the 88-bp 5'UTR, the 2688-bp coding sequence (ORF), and the 76-bp 3'UTR and poly(A) tail. DuTLR3 was found to share a high amino acid sequence similarity with TLR3 from Jing ding duck (99.6 %), Muscovy duck (97.1 %) and chicken (86.3 %). Additionally, the tissue distribution of duTLR3 suggested that it was abundantly expressed in various tissues, especially in the trachea, esophagus and pancreatic gland. Duck reovirus (DRV) infection resulted in high mRNA expression levels of duTLR3 in the spleen, liver, lung and brain. Conclusion: These results suggest that duTLR3 may play an important role in anti-viral defense mechanisms. [ABSTRACT FROM AUTHOR]

Duck hepatitis virus (DHV-1) is a worldwide distributed picornavirus that causes acute and fatal disease in young ducklings. Recently, the complete genome of DHV-1 has been determined and comparative sequence analysis has shown that possesses the typical picornavirus organization but exhibits several unique features. For the first time, we provide evidence that the 626-nucleotide-long 5'-UTR of the DHV-1 genome contains an internal ribosome entry site (IRES) element that functions efficiently both in vitro and in mammalian cells. The prediction of the secondary structure of the DHV-1 IRES shows significant similarity to the hepatitis C virus (HCV) IRES. Moreover, similarly to HCV IRES, DHV-1 IRES can direct translation initiation in the absence of a functional eIF4F complex. We also demonstrate that the activity of the DHV-1 IRES is modulated by a viral coding sequence located downstream of the DHV-1 5'-UTR, which enhances DHV-1 IRES activity both in vitro and in vivo. Furthermore, mutational analysis of the predicted pseudo-knot structures at the 3'-end of the putative DHV-1 IRES supported the presence of conserved domains II and III and, as it has been previously described for other picornaviruses, these structures are essential for keeping the normal internal initiation of translation of DHV-1. [ABSTRACT FROM AUTHOR]