Molecular characterization and expression analysis of a chicken-type lysozyme gene from housefly (Musca domestica)

Lysozymes can hydrolyze bacteria and play an important role in animal digestion and innate immunity. The cDNA of a chicken-type lysozyme gene (Mdlys) was cloned from housefly (Musca domestica). The 484 bp full-length cDNA contains a 426 bp open reading frame (ORF) that encodes MdLys of 141 amino acids. Phylogenetic analysis indicated that the MdLys was similar to chicken-type lysozymes. Spatio-temporal expression of Malys was analyzed by RT-PCR. The Mdlys transcript can be detected in both midgut and fat body and was expressed at a relatively lower level at the embryo stage. Mdlys mRNA was upregulated 2 h post bacterial challenge, maintained for 2 to 6 h, and slightly declined from 12 to 24 h post-injection. Western blot analysis showed that MdLys was highly expressed in midgut and was also detected in the hemolymph and fat body. MdLys expression was slightly increased in midgut after challenging with Escherichia coli or Staphylococcus aureus. Its expression was also slightly increased in the fat body after challenging with S. aureus, but no obvious change occurred after E. coli challenge. MdLys expression in the hemolymph was not affected by bacterial challenge. In the developmental stages, MdLys expression levels had no obvious change from the first instar to the pupae stage. There was also no variation under 24 h starvation stress. Recombinant MdLys displayed inhibitory activity against Gram-negative and Gram-positive bacteria. Together, these results suggest that MdLys may play an important role in the innate immunity of houseflies.