Cloning and expression analysis of StAR gene in Esox lucius

【Objective】 The aim of this study was to clone the steroidal hormone synthesis acute regulatory protein (StAR) gene(ElStAR) and analyze its expression in tissues, so as to provide basic data for studying the biological function of StAR gene and revealing gonadogenesis mechanism of Esox lucius.【Method】 Specific primers were designed based on the genomic sequence of E. lucius in GenBank(NC_047581.1), and the cDNA sequence of ElStAR gene was cloned by RT-PCR. Bioinformatics analysis was carried out by online softwares such as ClustalX, ExPASy, TargetP 1.1, TMHMM 2.0 and SignalP 5.0, and the tissue expression of ElStAR gene was analyzed by real-time fluorescence quantitative PCR.【Result】 The cDNA sequence of ElStAR gene was 1485 bp in length and its open reading frame(ORF) was 864 bp, and encoded 287 amino acids. Amino acid sequence of StAR had the highest similarity with Salvelinus alpinus(93.33%), higher than 75.00% with Salmo trutta, Morone saxatilis, Sparus aurata, Scophthalmus maximus, Danio rerio and Cynoglossus semilaevis, and the lowest similarity with Mus musculus(59.15%). The phylogenetic tree based on StAR amino acid sequence similarity also showed that pike was in the same branch as Salmonidae fish such as Salvelinus alpinus and Salmo trutta. ElStAR protein had a relative molecular weight of 32.23 kD and a theoretical isoelectric point(PI) of 8.98. It was an unstable hydrophilic protein. It had START domain, no signal peptide and transmembrane structure, which was consistent with the basic characteristics of mitochondrial targeting peptide. The secondary structure of ElStAR protein was composed of α- helix(40.77%), random coil(35.89%), extended chain(18.12%) and β- fold(5.23%), and its tertiary structure was composed of α- helix fit multiple β- fold with curling and circling. ElStAR gene was expressed in testis, ovary, head kidney, liver, muscle and brain of E. lucius. The relative expression in testis was extremely significantly higher than that in ovary(P<0.01), and showed the expression pattern of gender dimorphism.【Conclusion】 ElStAR gene encodes a protein with very conservative structure and function, with a typical START domain, and plays an important role in the transportation and regulation of cholesterol. There are extremely significant differences in the expression of ElStAR gene in testis and ovary of E. lucius, the gene may play an important supporting role in maintaining the development and formation of testis of pike.