Abstract
MyD88 and TRAF6 play an essential role in the innate immune response in most animals. This study reports the full-length MaMyD88 and MaTRAF6 genes identified from the blunt snout bream (Megalobrama amblycephala) transcriptome profile. MaMyD88 is 2501 base pairs (bp) long, encoding a putative protein of 284 amino acids (aa), including the N-terminal DEATH domain of 78 aa and the C-terminal TIR domain of 138 aa. MaTRAF6 is 2252 bp long, encoding a putative protein of 542 aa, including the N-terminal low-complexity region, RING domain (40 aa), a coiled-coil region (64 aa) and C-terminal MATH domain (147 aa). Coding regions of MaMyD88 and MaTRAF6 genomic sequences consisted of five and six exons, respectively. Physicochemical and functional characteristics of the proteins were analysed. Alpha helices were dominant in the secondary structure of the proteins. Homology models of the MaMyD88 and MaTRAF6 domains were constructed applying the comparative modelling method. RT-qPCR was used to analyse the expression of MaMyD88 and MaTRAF6 mRNA transcripts in response to Aeromonas hydrophila challenge. Both genes were highly upregulated in the liver, spleen and kidney during the first 24 h after the challenge. While MyD88 and TRAF6 have been reported in various aquatic species, this is the first report and characterisation of these genes in blunt snout bream. This research also provides evidence of the important roles of these two genes in the blunt snout bream innate immune system.
Highlights
The immune system protects an organism against diseases by identifying and eliminating the pathogen [1]
The innate immune response is triggered by germline-encoded pattern recognition receptors (PRRs) that are responsible for recognising conserved pathogen-associated molecular patterns of foreign stimuli, such as lipopolysaccharide or peptidoglycan of bacterial cell walls, β-1,3-glucan of fungal cell walls, double-stranded RNA of viruses and endogenous molecules released from damaged cells [5,6,7,8]
toll-like receptors (TLRs) are characterised by the N-terminal leucine-rich repeats and a transmembrane region followed by a cytoplasmic Toll/IL-1R homology (TIR) domain [8]
Summary
The immune system protects an organism against diseases by identifying and eliminating the pathogen [1]. TRAF6, the most evolutionarily ancient TRAF family member, is the only TRAF participating in signal transduction of both the TNF receptor superfamily and the IL-1R/TLR superfamily, which play essential roles in innate immunity, adaptive immunity and bone homeostasis [17] Both genes have been identified and their functions studied in a broad range of aquatic animals: such as Zhikong scallop (Chlamys farreri) [18], common carp (Cyprinus carpio) [19], miiuy croaker (Miichthys miiuy) [20], whiteleg shrimp (Litopenaeus vannamei) (MyD88) [21], penaeid shrimp (Fenneropenaeus chinensis) [22], zebrafish (Danio rerio) [23], orange-spotted grouper. This study provides an insight into the role of MaMyD88 and MaTRAF6 in antibacterial response mechanisms of the blunt snout bream immune system, which can facilitate the utilisation of molecular tools for selective breeding of disease-resistant blunt snout bream broodstock in order to reduce mortality and increase productivity during the cultivation
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