An “immunome” gene panel for transcriptomic analysis of immune defence activities in the teleost sea bass (Dicentrarchus labrax L.): a review.
E. RANDELLI, F. BUONOCORE, D. CASANI, A. M. FAUSTO & G. SCAPIGLIATI*
Dipartimento di Scienze Ambientali, Università della Tuscia, 01100 Viterbo, Italy.
*Corresponding author: Giuseppe Scapigliati, Dipartimento di Scienze Ambientali, Università della Tuscia, Largo dell'Università, 01100Viterbo, Italy
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ABSTRACT
Teleost fish are the oldest living vertebrates displaying a morphological and functional immune system conserved until mammals, thus representing a useful model for evolutionary studies. Teleosts are increasingly employed as experimental animal species for studies on physiological activities of vertebrates, and are widely used in the aquaculture industry. Due to its importance as high quality food, the sea bass is, at present, one of the most important farmed species in the Mediterranean sea and many studies reported on the morphological and functional organisation of immune defences with the aim of controlling its health in farming conditions. From these studies, a panel of genes coding for main immunomodulatory peptides of innate and acquired defences is available and constituted, at present, by genes coding for innate defences, for acquired defences, and for other immune-related activities. In this review all these genes are collected and defined as the sea bass “immunome”, that is analysed in an evolutionary context.
Keywords: Sea bass, Dicentrarchus labrax, immune system, transcriptome, immunome.
INTRODUCTION
Survival of an organism depends upon an effective defence against foreign invaders. In all species living today, the defence mechanisms have evolved into an effective machine that has enabled their successful survival and their adaptive radiation. Most micro-organisms such as bacteria, parasites, fungi and viruses have represented an enormous source of aggressors during the evolution of metazoans, usually responsible either directly or indirectly for multiple causes of infection.
Since their appearance, micro-organisms and metazoans have been and are still engaged in a never ending arms race, which has led to the evolution of protection mechanisms in vertebrates and pathogenicity mechanisms in microbes. It has been suggested that the diverse evasive strategies of micro-organisms to their host have acted as inducers of vertebrate defence evolution (Castro and Gonzalez, 2001).
Higher Metazoa are represented by Vertebrates, which can be considered at present as the group of species in which evolution reached its maximum. Living vertebrates are around 40.000 species, half of which are bony fish. Bony fish are in full adaptive radiation and are present in every aquatic environment ranging from warm tropical freshwaters, to polar seas, to abyssal depths.
It should be noted that in all environmental conditions animal species must fight invading microbes. Hence, the immune defence is an indispensible feature under the control of genes which can mutate and evolve under selective pressures, but which must leave immune defences fully functional. Therefore, studies on the evolution of immune responses among vertebrates will be a valuable tool for the understanding of conserved responses, conserved genes, conserved molecules, and conserved conformational epitopes.
In addition, teleost fish represent an indispensible two-in-one model for studies in the function of immune activities, since have a larval stage during which they must rely solely on innate activities, and more mature stages where both innate and acquired defences are functional.
Due to its importance for aquaculture, sea bass rearing is continuously improving mostly in southern European countries. Much work is performed on the prevention of the main bacterial and viral pathologies that affect this species in aquaculture. The current status of knowledge on sea bass immune system has been recently reported (Scapigliati et al. 2006). Sea bass may represent a reference animal model for studies on the immune system of vertebrates, since it is, at present, the only marine species for which are available several cellular and molecular markers represented by monoclonal antibodies for B- and T- lymphocytes, and nucleotide probes for several immunomodulatory molecules. In addition, the conditions for culturing of leucocytes are known for this species, and this allowed studies on “in vitro” reactions of leucocytes to particular stimulation.
In recent years, with the increasing knowledge on gene cloning technologies, many genes coding for immunoregulatory molecules and homologous to their mammalian counterparts have been discovered in teleost fish, including sea bass, and this review summarizes the knowledge in this species (Table 1). The selected genes code for molecules endowed with pivotal immune defence activities, and this panel will be henceforth defined as the Dicentrarchus labrax immunome.