Transcriptomic Response of Mussel Gills After a Vibrio splendidus Infection Demonstrates Their Role in the Immune Response

Abstract

Mussels (Mytilus galloprovincialis) are filter feeder bivalves that are constantly in contact with a wide range of microorganisms, some of which are potentially pathogenic. How mussels recognize and respond to pathogens has not been fully elucidated to date; therefore, we investigated the immune mechanisms that these animals employ in response to a bacterial bath infection from the surrounding water, mimicking the response that mussels mount under natural conditions. After the bath infection, mussels were able to remove the bacteria from their bodies and from the water tank. Accordingly, antibacterial activity was detected in gill extracts, demonstrating that this tissue plays a central role in removing and clearing potential pathogens. A transcriptomic study performed after a bath infection with Vibrio splendidus identified a total of 1,156 differentially expressed genes. The expression levels of genes contributing to a number of biological processes, such as immune response activation pathways and their regulation with cytokines, cell recognition, adhesion and apoptosis, were significantly modulated after infection, suggesting that the gills play important roles in pathogen recognition, as well as being activators and regulators of the mussel innate immune response. In addition to RNA-seq analysis, long non-coding RNAs and their neighboring genes were also analyzed and exhibited modulation after the bacterial challenge. The response of gills against bath infection was compared with the findings of a previous transcriptomic study on hemocytes responding to systemic infection, demonstrating the different and specific functions of gills. The results of this study indicate that recognition processes occur in the gill, thereby activating the effector agents of the immune response to overcome bacterial infection.

The Evolution and Diversity of Interleukin-17 Highlight an Expansion in Marine Invertebrates and Its Conserved Role in Mucosal Immunity

“…Another isoform was induced in adult immune cells, representing evidence of functional diversification of the repertoire (31). In mussels, an upregulation of IL-17 in the gills in response to a waterborne infection from the surrounding water has been reported (48). In situ hybridization with the most highly expressed isoform (IL17-3) suggested that these interleukins may be expressed in hemocytes and in the epithelial cells of gills.…”

“…Transcriptomic data were recovered from two different experiments performed with individual Mytilus galloprovincialis mussels, including a gill transcriptome obtained after 24 h of waterborne exposure to an infection with Vibrio splendidus (48) and a transcriptome obtained from hemocytes 24 h after injection with the same bacteria, with the goal of establishing a systemic infection (49). Assemblies were constructed as explained in Saco et al (48) and in Rey-Campos et al (49), and reads from each transcriptome are accessible through PRJNA638821 and PRJNA466718, respectively. IL-17 and IL-17R protein sequences from the isoforms of the reference genome were used in a tblastn search against those assemblies.…”

“…IL-17 expression retrieved from transcriptomic data of mussels subjected to bacterial infections differed among isoforms. Two transcriptomic experiments were analyzed: a bath or waterborne infection (24 h) sampled in gills (48) and a systemic infection (24h) sampled in hemocytes (49). As displayed in Figures 6A, B, the set of isoforms expressed was stimulus-specific and conditioned by the route of infection.…”

“…IL-17 inflammatory triggering functions seemed to be of importance in the mussel immune response in gills after the recognition of a bath bacterial infection (48). IL-17 genes were modulated in gills against the incoming infection, while there was no modulation in the defensive cells (the hemocytes), against a systemic infection with the same bacteria (48,49).…”

Understanding Pathogen-host Interplay by Expression Profiles of LncRNA and mRNA in the Liver of Echinococcus Multilocularis-infected Mice

“…Long non-coding RNAs (lncRNAs) have received increased attention lately as a newly discovered class of regulatory molecules [6][7][8]. Studies have shown that the expression pro le of lncRNA in the host can be altered during viral, bacterial, or parasitic infection, suggesting the potential role of lncRNAs in regulating host-pathogen interactions [9][10][11][12]. Moreover, a growing body of evidence showed that some dysregulated lncRNAs of the host could participate in the pathophysiological process of various diseases by affecting the host immune mechanisms [13][14][15].…”