For the sea cucumber Apostichopus japonicus, a C-type lectin (AJCTL) was identified using rapid amplification of cDNA ends (RACE) PCR techniques. The full-length cDNA of AJCTL is composed of 710bp with a 618bp open reading frame (ORF) that encodes a polypeptide of 205 amino acids with a N-terminal signal peptide and a C-terminal C-type lectin domain (CTLD). The calculated molecular mass of the whole protein is 22.5kDa and its predicted isoelectric point is 5.59. AJCTL belongs to the group VII of regulatory proteins and it might function as a Ca(2+)-dependent monosaccharide binding lectin specifically and recognizing mannose-type ligands. In situ hybridization demonstrated that the expression of AJCTL was located in the body wall, longitudinal muscles, intestinum and respiratory tree. This became apparent especially in the cytoplasm of epidermal cells and granular haemocytes. Real-time PCR data suggested that AJCTL was mostly synthesized in the longitudinal muscles and intestinum and less pronounced in the respiratory tree and body wall of adults. After 12h stimulation by Vibrio harveyi, at increasing bacterial concentration gradient, the expression of AJCTL in sea cucumber increased as well. This indicated that CTL is related to an innate immune response.
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