Apostichopus japonicus matrix metalloproteinase-16 might act as a pattern recognition receptor

The selective regulation of immune responses by matrix metalloproteinase MMP14 in Ostrinia furnacalis

Matrix metalloproteinases (MMPs) are crucial for tissue remodeling and immune responses in insects, yet it remains unclear how MMPs affect the various immune processes against pathogenic infections and whether the responses vary among insects. In this study, we used the lepidopteran pest Ostrinia furnacalis larvae to address these questions by examining the changes of immune-related gene expression and antimicrobial activity after the knockdown of MMP14 and bacterial infections. We identified MMP14 in O. furnacalis using the rapid amplification of complementary DNA ends (RACE), and found that it was conserved and belonged to the MMP1 subfamily. Our functional investigations revealed that MMP14 is an infection-responsive gene, and its knockdown reduces phenoloxidase (PO) activity and Cecropin expression, while the expressions of Lysozyme, Attacin, Gloverin, and Moricin are enhanced after MMP14 knockdown. Further PO and lysozyme activity determinations showed consistent results with gene expression of these immune-related genes. Finally, the knockdown of MMP14 decreased larvae survival to bacterial infections. Taken together, our data indicate that MMP14 selectively regulates the immune responses, and is required to defend against bacterial infections in O. furnacalis larvae. Conserved MMPs may serve as a potential target for pest control using a combination of double-stranded RNA and bacterial infection.

Functions of lysin motif (LysM)-containing protein in antibacterial responses of sea cucumbers, Apostichopus japonicus

The lysin motif (LysM)-containing protein is one of widespread pattern-recognition receptors in prokaryotes and eukaryotes. Numerous LysM-containing gene sequences are present in gene databases; however, few have been well characterized, especially in echinoderms. In this study, the full-length cDNA of a novel LysM-containing gene was obtained from the sea cucumber Apostichopus japonicus, named AjLysM-1, using polymerase chain reaction (PCR) combined with rapid amplification of cDNA ends. We prepared and expressed recombinant AjLysM-1 protein (rAjLysM-1) and determined its pathogen-recognition ability by enzyme-linked immunosorbent and immunofluorescence assays. We also analyzed the tissue expression pattern and response to immune challenges of AjLysM-1 using quantitative real-time reverse transcription-PCR and in situ hybridization. The AjLysM-1 protein was predicted to be an intracellular non-secreted LysM-containing protein, highly homologous to the same protein in other marine echinoderms. AjLysM-1 transcripts were highest expressed in coelomocytes and were strikingly induced by challenge with representative bacterial and fungal polysaccharides. rAjLysM-1 showed weak binding to mannan, Pseudoalteromonas nigrifaciens, and Shewanella baltica, implying that AjLysM-1 might provide inadequate defense against Gram-negative bacteria and fungi. Notably, rAjLysM-1 also interacted with tyrosine protein kinase and filamin-B, indicating that it could be involved in focal adhesion in A. japonicus. These findings improve our understanding of the functions of LysM-containing proteins in marine echinoderms.