Abstract
Antimicrobial peptides serve as an important component of the innate immune system of all species by functioning to provide a rapid first line defense against infection. Arthropod antimicrobial peptides have been well described in insects, whereas only a few molecules have been identified in crustaceans. Five variants (types 1-5) of Marsupenaeus japonicus crustin-like peptide cDNA that were obtained from a hemocyte cDNA library and polymerase chain reaction (PCR) amplification are reported here. Marsupenaeus japonicus crustin-like peptide type 1, the predominant type, has a cDNA consisting of 679 nucleotides and an open reading frame consisting of 573 base pairs coding for 191 amino acid residues. Other types contain varying glycine-rich repeats at the N-terminal amino acid sequences. The deduced amino acid sequences of these variants are highly similar to those of Litopenaeus setiferus (80% identity), Litopenaeus vannamei (80% identity) and Carcinus maenas crustins (44% identity). Expression of Marsupenaeus japonicus crustin-like peptide mRNA was detected in hemocytes, but not in the heart, hepatopancreas, gill, fore-gut, mid-gut, muscle, subcuticular epithelium or ovary. The expression level of crustin-like peptide mRNA increased significantly 1, 3 and 7 days post-peptidoglycan feeding as determined by quantitative real-time PCR. These results suggest that crustin-like peptide could have an important role in shrimp defense mechanisms.
