Insights into the innate immunity of the Mediterranean mussel Mytilus galloprovincialis

Abstract

BackgroundSessile bivalves of the genus Mytilus are suspension feeders relatively tolerant to a wide range of environmental changes, used as sentinels in ecotoxicological investigations and marketed worldwide as seafood. Mortality events caused by infective agents and parasites apparently occur less in mussels than in other bivalves but the molecular basis of such evidence is unknown. The arrangement of Mytibase, interactive catalogue of 7,112 transcripts of M. galloprovincialis, offered us the opportunity to look for gene sequences relevant to the host defences, in particular the innate immunity related genes.ResultsWe have explored and described the Mytibase sequence clusters and singletons having a putative role in recognition, intracellular signalling, and neutralization of potential pathogens in M. galloprovincialis. Automatically assisted searches of protein signatures and manually cured sequence analysis confirmed the molecular diversity of recognition/effector molecules such as the antimicrobial peptides and many carbohydrate binding proteins. Molecular motifs identifying complement C1q, C-type lectins and fibrinogen-like transcripts emerged as the most abundant in the Mytibase collection whereas, conversely, sequence motifs denoting the regulatory cytokine MIF and cytokine-related transcripts represent singular and unexpected findings. Using a cross-search strategy, 1,820 putatively immune-related sequences were selected to design oligonucleotide probes and define a species-specific Immunochip (DNA microarray). The Immunochip performance was tested with hemolymph RNAs from mussels injected with Vibrio splendidus at 3 and 48 hours post-treatment. A total of 143 and 262 differentially expressed genes exemplify the early and late hemocyte response of the Vibrio-challenged mussels, respectively, with AMP trends confirmed by qPCR and clear modulation of interrelated signalling pathways.ConclusionsThe Mytibase collection is rich in gene transcripts modulated in response to antigenic stimuli and represents an interesting window for looking at the mussel immunome (transcriptomes mediating the mussel response to non-self or abnormal antigens). On this basis, we have defined a new microarray platform, a mussel Immunochip, as a flexible tool for the experimental validation of immune-candidate sequences, and tested its performance on Vibrio-activated mussel hemocytes. The microarray platform and related expression data can be regarded as a step forward in the study of the adaptive response of the Mytilus species to an evolving microbial world.

Toll signal transduction pathway in bivalves: Complete cds of intermediate elements and related gene transcription levels in hemocytes of immune stimulated Mytilus galloprovincialis

“…Although only some transcripts have been evidenced, several hypothetical schemes have been constructed in bivalves by analogy with Drosophila and mammals, i.e. in the Pacific oyster, C. gigas (Montagnani et al, 2004), the mussels, M. galloprovincialis (Venier et al, 2011) and M. edulis (Philipp et al, 2012), and the Manila clam, Ruditapes philippinarum (Moreira et al, 2012). The 454 reads from M. edulis (Philipp et al, 2012) together with new Illumina assembly reads that we have obtained from M. galloprovincialis and C. gigas allowed us a more complete investigation of the bivalve transcriptomes.…”

“…Similarly, the temporal control of NF-jB activation in mammals is coordinated by degradation and synthesis of IjB proteins which are responsible for the strong negative regulation allowing a fast turn-off of the NF-jB response (Hoffmann et al, 2002). On the opposite, up-and down-regulation of the various AMP genes in M. galloprovincialis was reported by several laboratories using different techniques (Costa et al, 2009b;Li et al, 2010;Mitta et al, 2000a;Pallavicini et al, 2008;Venier et al, 2011) and appears somehow conflicting. Details related to the experimental challenges (e.g.…”

“…By contrast, the IMD pathway is similar to the tumor-necrosis-factor (TNF) receptor pathway of mammals (Ferrandon et al, 2007;Hoffmann, 2003). After AMPs were discovered in bivalves (reviewed by , regulation of their transcription levels in response to experimental immune stimulation was reported in the Mediterranean mussel, Mytilus galloprovincialis (Mitta et al, 1999a(Mitta et al, ,b, 2000bSonthi et al, 2012;Venier et al, 2011), the deep-sea hydrothermal vent mussel, Bathymodiolus azoricus (Bettencourt et al, 2007), the Pacific oyster, Crassostrea gigas (Gonzalez et al, 2007;Gueguen et al, 2006;Schmitt et al, 2012), the carpet-shell clam, Ruditapes decussatus (Gestal et al, 2007), the hard clam, Mercenaria mercenaria (Perrigault et al, 2009), the triangle-shell pearl mussel, Hyriopsis cumingii (Ren et al, 2011) and the blue mussel, Mytilus edulis (Tanguy et al, 2013).…”

Cell tracking and velocimetric parameters analysis as an approach to assess activity of mussel (Mytilus edulis) hemocytes in vitro

“…These animals, living in complex estuarine and intertidal environments, experience major fluctuations of physico-chemical parameters in coastal areas (GauthierClerc et al 2013;Malagoli et al 2007). In addition to those abiotic stressors, mussels house a variety of endoparasites and microbial organisms (Venier et al 2011). To control host-pathogen interactions and to respond immediately to invaders, mussels as others invertebrates, rely on innate immunity.…”

“…To be effective in host-defense, hemocytes do not require prior exposure to antigens but can express a vast repertoire of immune-related genes, over-represented in bivalves, as revealed by recent reports on sequencing of oyster genome (Zhang et al 2012) and analyses of mussel transcriptomes after biotic and abiotic stress challenges (Craft et al 2010;Philipp et al 2012;Venier et al 2011).…”