Abstract
Toll receptors are involved in innate immunity of invertebrates. In this study, we identify and characterize two Toll genes (named HcToll4 and HcToll5) from triangle sail mussel Hyriopsis cumingii. HcToll4 has complete cDNA sequence of 3,162 bp and encodes a protein of 909 amino acids. HcToll5 cDNA is 4,501 bp in length and encodes a protein of 924 amino acids. Both deduced HcToll4 and HcToll5 protein contain signal peptide, extracellular leucine rich repeats (LRRs), and intracellular Toll/interleukin-1 (IL-1) receptor domains. Quantitative real-time PCR analysis revealed that HcToll4 and HcToll5 were largely distributed in the hepatopancreas and could be detected in the gills and mantle. HcToll4 and HcToll5 expression could respond to Staphylococcus aureus, Vibrio parahaemolyticus, White spot syndrome virus (WSSV) or Poly I:C challenge. RNA interference by siRNA results showed that HcToll4 and HcToll5 were involved in the regulation of theromacin (HcThe) and whey acidic protein (HcWAP) expression. Based on these results, HcToll4 and HcToll5 might play pivotal function in H. cumingii innate immune response.
Highlights
Innate immune system is the first line of host defense against inevitably encounter pathogens and is conserved throughout evolution
This study aims to (1) identify new Toll genes in H. cumingii, (2) clone their complete nucleotide sequences, (3) investigate their phylogenic relationships, (4) measure their constitutive tissue-specific expression, (5) quantify their expression level following in vivo challenges with bacteria or virus, and (6) investigate their involvement in innate immune response by exploring their possible relationship with downstream immune related genes
Two expressed sequence tag sequences similar to the Toll genes were identified after analyzing the transcriptome data of the hepatopancreas from H. cumingii and were used to clone the full length of Toll cDNAs by Rapid Amplification of cDNA Ends (RACE) method using gene-specific primers (Table 1)
Summary
Innate immune system is the first line of host defense against inevitably encounter pathogens and is conserved throughout evolution. The activation of innate immune response requires the recognition of pathogen-associated molecular patterns (PAMPs) by pathogen-recognition receptors (PRRs), such as Tolls/Toll-like receptors (TLRs), Nod-like receptors (NLRs), and RIGlike receptors (RLRs) (Bilak et al, 2003; Carty and Bowie, 2010). These PRRs can recognize the unique patterns of PAMPs as conserved molecular motifs on the surface of invading microbes (Imler and Zheng, 2004; Kawai and Akira, 2010) and subsequently trigger a series of rapid and effective immune responses, including the release of molecules and circulating humoral and cellular components (Medzhitov, 2007). After Toll pathway activation, Dorsal or Dif translocates into the nucleus, leading to the expression of several AMP genes (Belvin and Anderson, 1996; Lemaitre and Hoffmann, 2007; Valanne et al, 2011)
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