Cloning and Analysis of Gene Expression of Two Toll Receptors in Freshwater Pearl Mussel Hyriopsis cumingii

Characterization of a novel toll-like receptor and activation NF-κB signal pathway in triangle sail mussel Hyriopsis cumingii

Toll-like receptor (TLR) family plays an important role in innate immunity for detection of and defense against microbial pathogens. In this study, a novel toll-like receptor (HcTLRn) was characterized from freshwater pearl mussel H. cumingii. The complete sequence of HcTLRn was 3725 bp, and the open reading frame (ORF) encoded 718 amino acid residues. Predicted HcTLRn protein possessed seven atypical leucine-rich repeat (LRR) domains, two typical LRR subfamily domains, a C-terminal domain LRR, a transmembrane domain and an intracellular Toll/interleukin-1 (IL-1) receptor domain. Transcripts of HcTLRn were constitutive expressed in the tissues of healthy mussels and were markedly induced in hepatopancreas and gills after lipopolysaccharide (LPS), peptidoglycan (PGN) and polyinosinic polycytidylic acid (ploy I: C) stimulation. Knockdown of HcTLRn in vivo significantly decreased the mRNA levels of TLR pathway transcription factors p65 and p105 as well as antimicrobial peptides (AMPs) including lysozyme (HcLys), theromacin (HcTher), whey acidic protein (HcWAP), LPS-binding protein/bactericidal permeability increasing protein (HcLBP/BPI) 1 and 2 after mussels challenged by LPS. In situ hybridization results showed that HcTLRn mRNA was significantly increased in hemocytes after LPS, PGN and poly I:C stimulation. HcTLRn protein was mainly expressed in hepatopancreas and gills and was significantly increased after LPS stimulation. Moreover, recombinant extracellular domain of HcTLRn (HcTLRn-ECD) proteins could bind to a variety of bacterial and pathogen-associated molecular patterns such as LPS, PGN, and poly I:C in vitro. Subcellular localization results showed that HcTLRn was mainly distributed near the cell membrane and in cytoplasm. Over-expression of HcTLRn activated the NF-κB luciferase reporter in HEK293T cells. Collectively, these results suggested that HcTLRn was a TLR family member that might play an important role in activation of NF-κB signal pathway in Mollusca.

Molecular Characterization of Two Toll Receptors in Hyriopsis cumingii and Their Potential Roles in Antibacterial Response

Tolls/Toll-like receptors (TLRs) play a key role in innate immunity by detecting the invading microbes and subsequently activating downstream signaling cascades. In this study, two new molluscan Toll members (designed as HcToll6 and HcToll7) were identified from triangle-shell pearl mussel (Hyriopsis cumingii). The obtained HcToll6 full-length cDNA was 3207 bp consisting of a 2223 bp open reading frame (ORF) that encoded a peptide of 740 amino acids. HcToll7 cDNA is a 3216 bp molecule that contains an ORF of 2139 bp encoding a protein of 712 amino acids. The deduced HcToll6 and HcToll7 proteins share two common structures: extracellular leucine-rich repeat (LRR) domains and intracellular Toll/interleukin-1 receptor (TIR) domain. Quantitative real-time PCR results showed that HcToll6 and HcToll7 were mainly expressed in the hepatopancreas and the gills, and they responded rapidly to bacterial stimulation. RNA interference by dsRNA results revealed that HcToll6 and HcToll7 RNAi strongly decreased the expression of lysozyme (HcLyso) and defensin (HcDef) in the gills of RNAi-treated mussels with Vibrio parahaemolyticus challenge. As a pattern recognition receptor, the prokaryotic expressed the recombinant LRR domains of HcToll6 and HcToll7 (rHcToll6-LRR and rHcToll7-LRR) could bind to Gram-positive and Gram-negative bacteria and had a strong tendency to recognize lipopolysaccharide (LPS) and peptidoglycan (PNG). rHcToll6-LRR and rHcToll7-LRR exhibited a significant in vitro bactericidal activity against V. parahaemolyticus and Staphylococcus aureus. These findings provide useful information to characterize Tolls in mussels.

Cloning and Characterization of Two Toll Receptors (PcToll5 and PcToll6) in Response to White Spot Syndrome Virus in the Red Swamp Crayfish Procambarus clarkii

Toll/Toll-like receptors are key components in the innate immune responses of invertebrates. In this study, we identified two novel Toll receptors (PcToll5 and PcToll6) from the red swamp crayfish Procambarus clarkii. The complete cDNA sequence of PcToll5 is 4247 bp, encoding a 1293 amino acid polypeptide. The full-length 4688 bp PcToll6 encodes a putative protein of 1195 amino acids. Quantitative RT-PCR analysis indicated that PcToll5 and PcToll6 were constitutively expressed in all tissues studied. The highest expression levels of PcToll5 and PcToll6 were found in the intestine and gills, respectively, and were significantly upregulated from 24 to 48 h during white spot syndrome virus (WSSV) challenge. siRNA-mediated RNA interference results showed that PcToll5 and PcToll6 might regulate the expression of anti-lipopolysaccharide factors (PcALF2 and PcALF3) in vivo. Overexpression of PcToll5 and PcToll6 in Drosophila Schneider 2 (S2) cells activated the transcription of Drosophila antimicrobial peptides, including drosomycin (Drs), metchnikowin (Mtk), and attacin A (AttA), and shrimp Penaeidin-4 (Pen4). These findings provide significant information that PcToll5 and PcToll6 may contribute to host immune defense against WSSV in P. clarkii.