A hemocyte gene expression signature correlated with predictive capacity of oysters to survive Vibrio infections

Abstract

BackgroundThe complex balance between environmental and host factors is an important determinant of susceptibility to infection. Disturbances of this equilibrium may result in multifactorial diseases as illustrated by the summer mortality syndrome, a worldwide and complex phenomenon that affects the oysters, Crassostrea gigas. The summer mortality syndrome reveals a physiological intolerance making this oyster species susceptible to diseases. Exploration of genetic basis governing the oyster resistance or susceptibility to infections is thus a major goal for understanding field mortality events. In this context, we used high-throughput genomic approaches to identify genetic traits that may characterize inherent survival capacities in C. gigas.ResultsUsing digital gene expression (DGE), we analyzed the transcriptomes of hemocytes (immunocompetent cells) of oysters able or not able to survive infections by Vibrio species shown to be involved in summer mortalities. Hemocytes were nonlethally collected from oysters before Vibrio experimental infection, and two DGE libraries were generated from individuals that survived or did not survive. Exploration of DGE data and microfluidic qPCR analyses at individual level showed an extraordinary polymorphism in gene expressions, but also a set of hemocyte-expressed genes whose basal mRNA levels discriminate oyster capacity to survive infections by the pathogenic V. splendidus LGP32. Finally, we identified a signature of 14 genes that predicted oyster survival capacity. Their expressions are likely driven by distinct transcriptional regulation processes associated or not associated to gene copy number variation (CNV).ConclusionsWe provide here for the first time in oyster a gene expression survival signature that represents a useful tool for understanding mortality events and for assessing genetic traits of interest for disease resistance selection programs.

Comparative analysis of oyster (Crassostrea gigas) immune responses under challenge by differentVibriostrains and conditions

“…This is consistent with previous studies. Also, in previous studies, the haemocyte gene expression was able to predict the capacity of oysters to survive infections by the pathogenic Vibrio strains (Rosa et al 2012). From our results, we can put forward a hypothesis that the oyster antioxidant enzyme gene expressions may be used to evaluate long-term mortalities.…”

“…Emails: lili@qdio.ac.cn; gfzhang@qdio.ac.cn to be associated with large-scale summer mortalities in oysters (Garnier et al 2007) and are widely used for experimental oyster infection (Gay et al 2004b;Garnier et al 2008). Transcriptomic and genomic approaches have also been used for the characterization of the oyster defence mechanisms in response to infection by these two strains (de Lorgeril et al 2011;Rosa et al 2012). Vibrio tubiashii (Hada et al 1984) has been found to be responsible for serious disease in North American hatchery-reared C. gigas (Estes et al 2004;Elston et al 2008).…”

“…It was used in oyster challenge experiments, combined with other stress effectors including heat shock and heavy metal exposure, indicating that this strain induced significant oyster immune responses under stress conditions (Taris et al 2009;Metzger et al 2012). Vibrio (Listonella) anguillarum (Bergman 1909), isolated as a pathogen from the oyster spat, has also been used for experimental challenge to study immune-related gene expression Rosa et al 2012). In addition, Vibrio vulnificus (Reichelt et al 1976), Vibrio harveyi (Johnson and Shunk 1936) and Vibrio parahaemolyticus (Fujino et al 1951) have been used for experimental oyster infection Froelich and Oliver 2013;Parveen et al 2013).…”

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

“…On the one hand, the first sequencing of C. gigas genome [78] and various transcriptomic studies allowed to identify a vast range of potential effectors and key actors of oyster immunity [62,94,125e127]. On the other hand, the development of genomic technologies such as high throughput RT-qPCR analyses allowed to explore the expression of numerous immune-related genes at the individual levels revealing an extraordinary polymorphism in basal expression of some of them in this species [128]. Indubitably, analyses performed at individual level may give new light on the genetic bases of oyster immune response and reveal its diversity and complexity.…”

The use of -omic tools in the study of disease processes in marine bivalve mollusks

“…Another disease of adult bivalves associated with exposure 640 to pathogens (including vibrios) combined with environmental 641 stress is summer mortality (Barbosa et al, this issue). A few tran-642 scriptomic studies have looked at the responses of Pacific oysters 643 to challenge with vibrio species associated with summer mortality, 644with the goal of determining potential mechanisms of resistance to 645 summer mortality(de Lorgeril et al, 2011;Rosa et al, 2012). All 646 these transcriptomic studies have led to the identification of genes 647 and molecular processes potentially involved in resistance to bac-648 terial diseases in bivalves.…”