A clip-domain serine proteinase homolog (SPH) in oriental river prawn, Macrobrachium nipponense provides insights into its role in innate immune response.

In this study, a clip-domain serine proteinase homolog designated as MnSPH was cloned and characterized from a freshwater prawn Macrobrachium nipponense. The full-length cDNA of MnSPH was 1897 bp and contained a 1701 bp open reading frame (ORF) encoding a protein of 566 amino acids, a 103 bp 5'-untranslated region, and a 93 bp 3'-untranslated region. Sequence comparison showed that the deduced amino acids of MnSPH shared 30-59% identity with sequences reported in other animals. Tissue distribution analysis indicated that the MnSPH transcripts were present in all detected tissues with highest in the hepatopancreas and ovary. The MnSPH mRNA levels in the developing ovary were stable at the initial three developmental stages, then increased gradually from stage IV (later vitellogenesis), and reached a maximum at stage VI (paracmasis). Furthermore, the expression of MnSPH mRNA in hemocytes was significantly up-regulated at 1.5 h, 6 h, 12 h and 48 h post Aeromonas hydrophila injection. The increased phenoloxidase activity also demonstrated a clear time-dependent pattern after A. hydrophila challenge. These results suggest that MnSPH participates in resisting to pathogenic microorganisms and plays a pivotal role in host defense against microbe invasion in M. nipponense.