Überlebenszeitanalyse: Der Log-Rang-Test

A C-type lectin (LvCTL4) from Litopenaeus vannamei is a downstream molecule of the NF-κB signaling pathway and participates in antibacterial immune response

C-type lectins (CTLs) play multiple roles in innate immune defense against invading pathogens in both vertebrates and invertebrates. In this study, a new C-type lectin gene from pacific white shrimp Litopenaeus vannamei (designated as LvCTL4) was cloned by rapid amplification of the cDNA ends (RACE) method. The full-length cDNA of LvCTL4 was 563 bp with open reading frame (ORF) of 471 bp encoding a polypeptide of 156 amino acids, including a putative signal sequence and a single C-type lectin-like domain (CTLD). The CTLD of 137 amino acid residues contained a mutated 'EPA' (Glu(121)-Pro(122)-Ala(123)) motif in the calcium-binding site 2 and three conserved disulfide bonds involved in structure maintenance. Tissue expression analysis showed LvCTL4 was ubiquitously distributed with high levels in gill, intestine, epithelium and hepatopancreas. The expression of LvCTL4 in gill was up-regulated in response to Vibrio parahaemolyticus challenge. RNAi knock-down of the LvCTL4 gene significantly increased mortality after V. parahaemolyticus infection. A 103 bp 5' flanking promoter sequence was obtained using the genome walking method and it contained a conserved NF-κB binding motif. Dual-Luciferase assay showed both LvDorsal and LvRelish could up regulate the promoter activity of LvCTL4. This is the first report that a shrimp C-type lectin can be regulated by both LvDorsal and LvRelish. These findings provided novel insights into the regulation of shrimp CTLs expression.

Identification and functional analysis of a Hemolin like protein from Litopenaeus vannamei

Hemolin is a specific immune protein belonging to immunoglobulin superfamily and firstly identified in insects. Growing evidences suggest that Hemolin can be activated by bacterial and viral infections and may play an important role in antimicrobial immunity. In this paper, we firstly identified a Hemolin-like protein from Litopenaeus vannamei (LvHemolin). Sequence analysis showed that LvHemolin shares high similarity with insect Hemolins and is mainly composed of seven immunoglobulin (Ig) domains which form a 'horseshoe' tertiary structure. Tissue distribution analysis demonstrated that LvHemolin mainly expressed in stomach, gill, epithelium and pyloric cecum of L. vannamei. After challenge with pathogens or stimulants, expression of LvHemolin was significantly up-regulated in both gill and stomach. Agglutination analysis demonstrated that recombinant LvHemolin protein purified from Escherichia coli could accelerate the agglutination of Vibrio parahaemolyticus, E. coli, Staphylococcus aureus, and Bacillus subtilis in the presence of Ca(2+). To verify the immune function of LvHemolin in vivo, shrimps were injected with gene-specific dsRNA, followed by challenge with white spot syndrome virus (WSSV) or V. parahaemolyticus. The results revealed that silence of LvHemolin could increase the cumulative mortalities of shrimps challenged by pathogens and increase the WSSV copies in shrimp tissues. These suggested that Hemolin could play an important role in shrimp innate immune defense against bacterial and viral infections.

Presence of Tube isoforms in Litopenaeus vannamei suggests various regulatory patterns of signal transduction in invertebrate NF-κB pathway

The toll-like receptor (TLR)/NF-κB signaling pathways play critical roles in the innate immune system. The intracellular signal transduction of most TLR pathways in invertebrate cells is triggered by formation of a heterotrimeric complex composed of MyD88, Tube and Pelle. In this study, we identified a Litopenaeus vannamei Pelle (LvPelle) and an isoform of L. vannamei Tube (LvTube) designated as LvTube-1. The interactions among LvPelle, LvTube/LvTube-1 and LvMyD88/LvMyD88-1 were elucidated and their functions during pathogen infections were investigated. Knockdowns of LvPelle and LvTube/LvTube-1 using RNAi strategy led to higher mortalities of shrimps during Vibrio parahemolyticus infection, and could reduce the genome copy number of white spot syndrome virus (WSSV) in the infected muscle tissue but did not affect the mortality caused by WSSV infection. The effects of LvPelle and LvTube/LvTube-1 on promoters containing NF-κB binding motifs were analyzed by dual-luciferase reporter assays and the results demonstrated that LvTube-1 could activate the NF-κB activity to significantly higher level than LvTube did. Moreover, tissue distributions of LvTube and LvTube-1 mRNAs and their expression profiles during pathogen and immune stimulant challenges were different, indicating that they could play different roles in immune responses. This is the first report of Tube isoforms in invertebrates. Together with our previous study on LvMyD88 isoforms, our results suggest that various isoforms of adaptor components may be involved in various regulatory patterns of signal transduction in invertebrate TLR/NF-κB pathway and this could be a strategy adopted by invertebrates to modulate immune responses.