Abstract: 【Aim】 Identify a new defensin gene from the housefly, Musca domestica, and analyze its function. 【Methods】 We identified the cDNA sequence of a new defensin gene from M. domestica transcriptome database and named Md-defensin-1 gene (Mdde-1). Bioinformatics web site and software were used to predict the structure information and real-time fluorescent quantitative PCR technique to study the gene expression profiles. Meanwhile, Mdde-1 promoter sequence was obtained using genome walking method and its activity was validated using cell transfection technology. 【Results】 The Mdde-1 sequence contains a 276 bp open reading frame, encoding 91 amino acid residues. A putative signal peptide of 23 amino acid residues and a potential propeptide of 28 amino acid residues are present at the N-terminus followed by a mature peptide of 40 amino acid residues, which contains a typical CSαβ motif. The results of real-time quantitative PCR indicated that the expression level of Mdde-1 was up-regulated significantly after the 2nd instar larvae of M. domestica were challenged by the gram positive bacterium Staphylococcus aureus while down-regulated after they were challenged by the gram negative bacterium Escherichia coli. The expression of Mdde-1 was up-regulated after the housefly larvae suffered heat shock. In order to further study its regulatory mechanism, we cloned Mdde-1 prompter and verified its activity. 【Conclusion】 The results suggest that Mdde-1 is a new defensin from housefly, and it plays an important role in immune challenge by gram-positive bacteria. Mdde-1 promoter activity has been first proved. This study lays the foundation for further research on antibacterial mechanism of housefly defensin.

Key words: Musca domestica, innate immunity, antimicrobial peptide, defensin, gene cloning, promoter