Abstract
BackgroundAlthough teleost fish developed acquired immunity firstly in evolution, innate immunity is still very important for them. Innate immunity depends on pattern recognition receptors (PRRs) to distinguish “self” and “non-self”, Peptidoglycan (PGN) recognition protein (PGRP) is one of the receptors and it can bind to multiple components of bacterial envelope.ResultsWe report the cloning and expression analysis of two PGRPs (Ccpgrp5 and Ccpgrp6) from common carp (Cyprinus carpio L). The Ccpgrp5 gene encodes a protein of 199 amino acid (aa) with PGRP domain, Ami_2 domain and four Zn2+ binding sites required for amidase activity, but without signal peptide and transmembrane domain. The Ccpgrp6 gene encodes a protein of 446 aa with PGRP domain, Ami_2 domain, signal peptide, five Zn2+ binding sites required for amidase activity and two sites for N-glycosylation. The phylogenetic analysis revealed that the CcPGRP5 and CcPGRP6 are closely related to Ctenopharyngodon idella and Danio rerio. Ccpgrp5 and Ccpgrp6 were expressed in all tissues examined including liver, spleen, muscle, oral epithelium, head kidney, gill, skin, gonad, brain, foregut and hindgut and showed different distribution characteristics. During the embryonic and early larval developmental stages of common carp, Ccpgrp6 was detected to be highly expressed at 10 days post fertilization(dpf) and 36 dpf, while Ccpgrp5 were hardly detected using Real-time quantitative PCR. After being challenged with Aeromonas hydrophila, Ccpgrp5 in adult common carp was induced and up-regulated in all the tissues, especially in gill and spleen, but not in head kidney, while Ccpgrp6 was up-regulated in all the tissues, especially in liver, head kidney and gill. The varied expression profiling of Ccpgrp5 and Ccpgrp6 indicated they had different roles in the host immune response.ConclusionsThese results indicated the two PGRPs, especially Ccpgrp6, played an important role in the immune defense of common carp during larva development and against Aeromonas hydrophila, providing insight to further exploration of protecting fish against bacteria infectious disease.
Highlights
Teleost fish developed acquired immunity firstly in evolution, innate immunity is still very important for them
The cDNA of Ccpgrp5 (GenBank Accession number MF818332) is 757 bp in length including a 20 bp 5′-untranslated region (UTR), an 597 bp open reading frame (ORF) and a 140 bp 3’-UTR, which encodes a protein of 199 amino acids with a predicted isoelectric point (PI) of 7.095 (Fig. 1)
The ORF of Ccpgrp6 encoded a putative protein of 461 amino acids with a predicted isoelectric point (PI) of 6.467 (Fig. 2).The sequence of CcPGRP6 shared 98% sequence identities and 99% query cover with previous PGRP6 sequence of Cyprinus carpio (KU642466)
Summary
Teleost fish developed acquired immunity firstly in evolution, innate immunity is still very important for them. Innate immunity depends on pattern recognition receptors (PRRs) to distinguish “self” and “non-self”, Peptidoglycan (PGN) recognition protein (PGRP) is one of the receptors and it can bind to multiple components of bacterial envelope. The first peptidoglycan recognition protein was found in the blood of Bombyx mori, which can bind to PGN without Ca2+, activate prophenoloxidase cascade and induce humoral melanization [7, 8]. On one hand PGRPs have amidase activity to hydrolyze the lactyl-amide bond between MurNAc and 1-Ala in the PGN and on the other hand trigger the Toll or Immune deficiency (Imd) signal transduction pathway to generate antimicrobial peptides [5]. As to vertebrate PGRPs, there are four paralogs in mammals They usually presented disulphide-linked homo and heterodimers with both recognition and effector functions [13]. Recent studies indicated that PGRP could induce oxidative, thiol, and metal stress responses simultaneously in bacteria through three independent pathways [15]
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