Whole Transcriptome Profiling of Successful Immune Response to Vibrio Infections in the Oyster Crassostrea gigas by Digital Gene Expression Analysis

Abstract

The cultivated Pacific oyster Crassostrea gigas has suffered for decades large scale summer mortality phenomenon resulting from the interaction between the environment parameters, the oyster physiological and/or genetic status and the presence of pathogenic microorganisms including Vibrio species. To obtain a general picture of the molecular mechanisms implicated in C. gigas immune responsiveness to circumvent Vibrio infections, we have developed the first deep sequencing study of the transcriptome of hemocytes, the immunocompetent cells. Using Digital Gene Expression (DGE), we generated a transcript catalog of up-regulated genes from oysters surviving infection with virulent Vibrio strains (Vibrio splendidus LGP32 and V. aestuarianus LPi 02/41) compared to an avirulent one, V. tasmaniensis LMG 20012T. For that an original experimental infection protocol was developed in which only animals that were able to survive infections were considered for the DGE approach. We report the identification of cellular and immune functions that characterize the oyster capability to survive pathogenic Vibrio infections. Functional annotations highlight genes related to signal transduction of immune response, cell adhesion and communication as well as cellular processes and defence mechanisms of phagocytosis, actin cytosqueleton reorganization, cell trafficking and autophagy, but also antioxidant and anti-apoptotic reactions. In addition, quantitative PCR analysis reveals the first identification of pathogen-specific signatures in oyster gene regulation, which opens the way for in depth molecular studies of oyster-pathogen interaction and pathogenesis. This work is a prerequisite for the identification of those physiological traits controlling oyster capacity to survive a Vibrio infection and, subsequently, for a better understanding of the phenomenon of summer mortality.

Colonization State Influences the Hemocyte Proteome in a Beneficial Squid–Vibrio Symbiosis

“…In addition, this study represents the first combination of iTRAQ and a labelfree proteomic analysis to enhance our understanding of a beneficial symbiosis. Proteomic and gene expression studies in other organisms, including oysters and pigs, have revealed that similar genes and proteins (cathepsins, GM2AP, heat shock protein 22, and cytoskeletal proteins) are altered by both pathogenic and beneficial bacterial colonization (70,71). Few studies have combined both iTRAQ and label-free proteomics; however, label-free methods have been shown to identify a greater number of significantly different proteins than labeling approaches, similar to what was observed in this study (72,73).…”

Finding immune gene expression differences induced by marine bacterial pathogens in the Deep-sea hydrothermal vent mussel <i>Bathymodiolus azoricus</i>

“…In contrast, 12 h and 24 h infections with Flavobacterium induced higher levels of immune lectin receptor 2 transcripts, above the control seawater-incubation expression experiments. In a recent transcriptome profiling study, using the Pacific Crassostrea gigas as a model to address immune responses to the virulent Vibrio splendidus and Vibrio aestuarianus bacteria, several immune genes were characterised in relation to the oyster capability to survive pathogenic Vibrio infections, including the Rhamnose-binding lectin, C-type lectin 2 and Metallothionein IV whose expression were up-regulated in surviving oysters (De Lorgeril et al, 2011). Xue et al (2010) also evidenced the involvement of a new lysozyme in the oyster Crassostrea virginica which also agrees with the finding that B. azoricus lysozyme is up-regulated in Flavobacterium infections.…”

The new insights into the oyster antimicrobial defense: Cellular, molecular and genetic view

“…Lysozyme expression has been detected and localized in digestive cells of digestive tubules, gills and mantle [56,58,60,61]. However, CGL-1 was shown to be differentially expressed in hemocytes following C. gigas infection with the pathogenic V. tasmaniensis LGP32 compared to a non-virulent one [62]. Besides, lysozyme activity has been shown to increase in hemolymph following a co-stimulation of LPS and an oyster recombinant tumor necrosis factor, rCg-TNF1 [63].…”