Molecular cloning of mannose receptor in Carassius auratus var. Qihe and effects of Aeromonas hydrophila infection on its gene expression

Mannose receptor (MR), a member of the C type lectin receptor superfamily, is thought to be involved in the non-specific immune responses in animals. To illustrate the MR molecular structure of Carassius auratus var. Qihe (CaMR) and the role it played in anti-infection immunity, homology cloning and RACE techniques were used in the present study to obtain the complete cDNA sequence, and the real-time fluorescent quantitative PCR (qPCR) technique was used to measure the effect of Aeromonas hydrophila (A. hydrophila) infection on its gene expression. The full-length cDNA of CaMR contains 4473 bp, including 81bp at 5′UTR and 90 bp at 3′UTR. The open reading frame encodes a putative protein of 1433 aa with a signal peptide of 20 aa. The predicted amino acid sequences showed that CaMR contained a cysteine-rich domain (CRD), a single fibronectin typeⅡ domain (FNⅡD), eight C-type lectin-like domains (CTLDs), a transmembrane domain and a short C-terminal cytoplasmic domain, sharing highly conserved structures with MRs from the other species. Amino acid sequence homology and phylogenic tree showed the close relationship between CaMR and other cyprinid fishes. The MR mRNA could be detected in all the examined tissues with highest level in headkidney. The temporal expression patterns of MR in the headkidney, spleen, and heart post of infection with A. hydrophila first rose and then fell, while in the intestine decreased continually. The current research provides a basis for further revealing the function of CaMR in immune reaction and for its application in disease prevention and treatment of Carassius auratus var. Qihe.