title: Β-defensin in Nile tilapia (Oreochromis niloticus): Sequence, tissue expression, and anti-bacterial activity of synthetic peptides.
abstract: Beta-defensins (β-defensins) are small cationic amphiphilic peptides that are widely distributed in plants, insects, and vertebrates, and are important for their antimicrobial properties. In this study, the β-defensin (Onβ-defensin) gene of the Nile tilapia (Oreochromis niloticus) was cloned from spleen tissue. Onβ-defensin has a genomic DNA sequence of 674 bp and produces a cDNA of 454 bp. Sequence alignments showed that Onβ-defensin contains three exons and two introns. Sequence analysis of the cDNA identified an open reading frame of 201 bp, encoding 66 amino acids. Bioinformatic analysis showed that Onβ-defensin encodes a cytoplasmic protein molecule containing a signal peptide. The deduced amino acid sequence of this peptide contains six conserved cysteine residues and two conserved glycine residues, and shows 81.82% and 78.33% sequence similarities with β-defensin-1 of fugu (Takifugu rubripes) and rainbow trout (Oncorhynchus mykiss), respectively. Real-time quantitative PCR showed that the level of Onβ-defensin expression was highest in the skin (307.1-fold), followed by the spleen (77.3-fold), kidney (17.8-fold), and muscle (16.5-fold) compared to controls. By contrast, low levels of expression were found in the liver, heart, intestine, stomach, and gill (<3.0-fold). Artificial infection of tilapia with Streptococcus agalactiae (group B streptococcus [GBS] strain) resulted in a significantly upregulated expression of Onβ-defensin in the skin, muscle, kidney, and gill. In vitro antimicrobial experiments showed that a synthetic Onβ-defensin polypeptide had a certain degree of inhibitory effect on the growth of Escherichia coli DH5α and S. agalactiae. The results indicate that Onβ-defensin plays a role in immune responses that suppress or kill pathogens.
authors: Key Laboratory of Tropical & Subtropical Fisheries Resource Application & Cultivation, Ministry of Agriculture, Pearl River Fisheries Institute, Chinese Academy of Fishery Sciences, Guangzhou 510380, China.
authors: Jun-Jian
authors: JJ
authors: Dong
authors: Key Laboratory of Tropical & Subtropical Fisheries Resource Application & Cultivation, Ministry of Agriculture, Pearl River Fisheries Institute, Chinese Academy of Fishery Sciences, Guangzhou 510380, China; College of Fisheries and Life Science, Shanghai Ocean University, Shanghai 201306, China.
authors: Fang
authors: F
authors: Wu
authors: Key Laboratory of Tropical & Subtropical Fisheries Resource Application & Cultivation, Ministry of Agriculture, Pearl River Fisheries Institute, Chinese Academy of Fishery Sciences, Guangzhou 510380, China; College of Fisheries and Life Science, Shanghai Ocean University, Shanghai 201306, China. Electronic address: gzyexing@163.com.
authors: Xing
authors: X
authors: Ye
authors: Key Laboratory of Tropical & Subtropical Fisheries Resource Application & Cultivation, Ministry of Agriculture, Pearl River Fisheries Institute, Chinese Academy of Fishery Sciences, Guangzhou 510380, China.
authors: Cheng-Fei
authors: CF
authors: Sun
authors: Key Laboratory of Tropical & Subtropical Fisheries Resource Application & Cultivation, Ministry of Agriculture, Pearl River Fisheries Institute, Chinese Academy of Fishery Sciences, Guangzhou 510380, China; College of Fisheries and Life Science, Shanghai Ocean University, Shanghai 201306, China.
authors: Yuan-Yuan
authors: YY
authors: Tian
authors: Key Laboratory of Tropical & Subtropical Fisheries Resource Application & Cultivation, Ministry of Agriculture, Pearl River Fisheries Institute, Chinese Academy of Fishery Sciences, Guangzhou 510380, China.
authors: Mai-Xin
authors: MX
authors: Lu
authors: Key Laboratory of Tropical & Subtropical Fisheries Resource Application & Cultivation, Ministry of Agriculture, Pearl River Fisheries Institute, Chinese Academy of Fishery Sciences, Guangzhou 510380, China; College of Fisheries and Life Science, Shanghai Ocean University, Shanghai 201306, China.
authors: Rui
authors: R
authors: Zhang
authors: Key Laboratory of Tropical & Subtropical Fisheries Resource Application & Cultivation, Ministry of Agriculture, Pearl River Fisheries Institute, Chinese Academy of Fishery Sciences, Guangzhou 510380, China; College of Fisheries and Life Science, Shanghai Ocean University, Shanghai 201306, China.
authors: Zhi-Hang
authors: ZH
authors: Chen
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D023681:Cichlids / Q000235:genetics / Q000276:immunology*; D005393:Fish Diseases / Q000276:immunology; D029941:Fish Proteins / Q000737:chemistry / Q000235:genetics* / Q000276:immunology*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016415:Sequence Alignment; D013290:Streptococcal Infections / Q000276:immunology / Q000662:veterinary; D023083:beta-Defensins / Q000737:chemistry / Q000235:genetics / Q000276:immunology*
chemical_list: D029941:Fish Proteins; D023083:beta-Defensins
keywords: Bacteriostatic activity; Gene expression; Oreochromis niloticus; Synthetic polypeptide; β-Defensin