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The cDNA encoding the kuruma shrimp, Marsupenaeus japonicus α2-macroglobulin (α2M) was obtained by screening a haemocyte cDNA library and 5′ RACE PCR amplification. The full length cDNA of 4748 bp contains an open reading frame of 4518 nucleotides that translates into a 1505-amino acid putative peptide, with a 5′untranslated region (UTR) of 59 bp and a 3′UTR of 171 bp. The open reading frame encodes an N-terminal signal sequence of 17 residues and a mature protein of 1488 residues. The entire amino acid sequence is similar to the α2M sequences of arthropods (30–31% identity), mammals (26–27% identity) and fish (25–28% identity). The M. japonicus α2M sequence contains putative functional domains including a bait region, an internal thiol ester site, and a receptor-binding domain, which are present in mammalian α2Ms. In a healthy shrimp, the mRNA of α2M was mainly expressed in haemocytes. In addition, the expression level of α2M mRNA was dramatically increased by through time upon oral administration of peptidoglycan (PG), which is an immune stimulant. The highest expression of α2M mRNA was observed 7 days after feeding with PG. These results suggest that the shrimp α2M is an important molecule in immune system. [Copyright &y& Elsevier]

Gene expression in haemocytes of the kuruma prawn (Penaeus japonicus) was investigated using an expressed sequence tag (EST) approach. Partial nucleotide sequences of cDNA library clones constructed from normal and white spot syndrome virus (WSSV)—infected P. japonicus haemocytes were determined. Of 635 clones obtained from the normal library, 284 (44·7%) significantly matched sequences in GenBank, and of 370 clones obtained from WSSV-infected library, 174 (47·0%) significantly matched sequences in the database. One hundred fifty-two deduced proteins were newly identified. Of these, 28 types were involved in biodefence. For the prophenoloxidase system, there are prophenoloxidase, coagulation factor G-β chain precursor, factor D, Masquarade-like protease, transglutaminase (TGase), clottable protein and eight types of protease inhibitors (two types of antileukoproteinase, alpha-2-macroglobulin, chelonianin, elastase inhibitor, two types of Kazal inhibitor and Kunitz-type inhibitor). For antibacterial peptides, there are bactinecin 11, penaeidin-2 precursor and lysozyme c type. The others defence-related proteins are basophil leukocyte interleukin-3-regulated protein, natural killer enhancing factor (NK-EF), integral membrane protein (CD34+), ESM-1, Notch homologue and Drac homologue. For the adhesion proteins, there are β-integrin, cell adhesion molecule (CAM) and three types of collagens. All ESTs representing protease inhibitors and tumour-related proteins were found only in the WSSV-infected library. Those encoding for apoptotic peptides were expressed at high levels in infected library. The putative defence proteins accounted for 2·7% of total ESTs in a normal shrimp library and 15·7% of the total ESTs in an infected library. [Copyright &y& Elsevier]