Molecular characterization and expression of Cadherin-2 and Cadherin- 4 in Nile tilapia (Oreochromis niloticus) in response to Streptococcus agalactiae stimulus

Abstract

Abstract Cadherins are a molecular family that is essential for the Ca2+ dependent process of cell-cell adhesion. Moreover, Cadherins can also act as a receptor to mediate bacteria entrying into non-phagocytic cells. In the present study, members of the Cadherins family of cytokines, Cadherin 2 (OnCdh2) and Cadherin 4 (OnCdh4), were successfully cloned and characterized from the Nile tilapia Oreochromis niloticus. Their tissue distribution and expression patterns following bacterial were also investigated. The full-length cDNA sequences of OnCdh2 and OnCdh4 contained an open reading frame of 2721 and 2802 bp, encoding 906 and 933 amino acids with a theoretical isoelectric point of 4.74 and 4.73, respectively. Prediction of protein domains showed that OnCdh2 and OnCdh4 both consisted of one Cadherin prodomain super family, one Cadherin repeat-like domain, three Cadherin tandem repeat domain, one Cadherin domain, one Cadherin cytoplasmic region and a transmembrane domain. Homology comparisons indicated that OnCdh2 and OnCdh4 showed 94.10% and 99.25% identity to the Astatotilapia calliptera and a relative low identity of 75.63–75.97% and 70.35%-74.09% with its mammalian counterparts. Moreover, the residue 16 of cadherin repeat-like domain of OnCdh2 and OnCdh4 is Proline, which indicated that it may play a role in mediating bacterial invasion into intestinal epithelial cells. Phylogenetic tree analysis showed that OnCdh2 and OnCdh4 cluster together with other fish OnCdh2 and OnCdh4 molecules. The results of tissue distribution showed that OnCdh2 and OnCdh4 were both ubiquitous in all tissues examined of healthy tilapia with the highest level of expression in heart and brain, respectively. The expression level of OnCdh2 and OnCdh4 were rapidly activated at 1 h in brain, intestine and spleen after chanllenged by S. agalactiae. Taken together, the results indicated that OnCdh2 and OnCdh4 might be involved in the process of S. agalactiae invading into Nile tilapia and the immune reponse of Nile tilapia against bacterial infection.