Molecular isolation and characterization of a spatzle gene from Macrobrachium rosenbergii

Spatzle protein is an extracellular ligand of Toll receptor in Toll signaling pathway involved in the embryonic dorsoventral patterning and in the innate immunity. In this study, a spatzle gene of freshwater prawn, Macro brachium rosenbergii (MrSpz) was isolated and characterized. The open reading frame of MrSpz consisted of 747 nucleotides encoding 248 amino acid residues containing a signal peptide and C-terminal spatzle activated domain. MrSpz shared high similarity to spatzle of Fenneropenaeus chinensis (FcSpz) at 92% identity and Marsupenaeus japonicus (MjSpz) at 83% identity. Phylogenetic analysis was performed and the results revealed that MrSpz was a member of the Glade containing LvSpz3 of Litopenaeus vannamei, FcSpz and Penaeus monodon spatzle protein. The expression distribution at transcriptional level in various tissues of normal prawn revealed that the MrSpz was detected in gills, heart and hepatopancreas while no expression was observed in hemocyte, muscle and stomach. In the Aeromonas caviae challenged prawn, the expression level of MrSpz in hemocyte was increased gradually at 6, 12 and 24 h post-injection. Furthermore, in MrSpz knocked down prawn injected with Aeromonas caviae, the mortality rate were higher than that of non-related dsRNA group and control group. These results suggest that MrSpz protein may play a key role in the innate immunity of M. rosenbergii, especially in response to Gram-negative bacteria A. caviae invasion.