Cloning, molecular characterization, and expression analysis of the signal transducer and activator of transcription 3 (STAT3) gene from grass carp (Ctenopharyngodon idellus)

Abstract Signal transducer and activator of transcription 3 (STAT 3 ) binds to Janus kinase 2 (JAK 2 ) to initiate the JAK 2 /STAT 3 signal transduction pathway, which plays an important role in cancer cell proliferation, immune regulation, reproduction, lipid metabolism, and other physiological processes of the organism. In this study, the cDNA sequence of the STAT 3 gene from grass carp was cloned using RACE (rapid-amplification of cDNA ends). Twelve characteristics of the STAT 3 gene and its encoded protein sequence were predicted and analyzed using bioinformatics methods; these features included the general physical and chemical properties, the hydrophobicity, the secondary structure and the three-dimensional structure of the protein. Quantitative real-time PCR was employed to detect grass carp STAT 3 expression pattern in different tissues. The results showed that the full-length STAT 3 gene from grass carp is 2739-bp long and contains a 216-bp 5′UTR, a 300-bp 3′UTR, and a 2223-bp open reading frame (ORF) that encodes a 740-amino acid peptide. The deduced protein exhibited 99%∼94% homology to the STAT 3 protein of zebrafish ( Danio rerio ), medaka ( Oryzias latipes ), turbot ( Scophthalmus maximus ), white-spotted char ( Salvelinus leucomaenis ), mandarin fish ( Siniperca chuatsi ), rainbow trout ( Oncorhynchus mykiss ), and green pufferfish ( Tetraodon fluviatilis ). The deduced grass carp STAT 3 protein contains a protein interaction domain, an alpha domain, a DNA binding domain, and an SH2 domain. The STAT 3 protein of grass carp is a hydrophilic and non-secretory protein, and its molecular mass and isoeletronic point were found to be 98,5412.1 Da and 6.39, respectively. The structural elements of STAT 3 included α-helixes, β-sheets, and loops. The grass carp STAT 3 is expressed in all of the six tissues tested, which were the liver, spleen, gill, muscle, heart, and brain. The highest expression level was found in the liver ( P P P 3 from grass carp, including its deduced protein and its signal transduction function.