Isolation and expression of cathepsin B cDNA in hemocytes during metamorphosis of Bombyx mori.

By using RT-PCR and 5'- and 3'-RACE methods, we isolated cathepsin B cDNA from hemocytes of Bombyx mori. The predicted open reading frame encoded 337 amino acids with 54% identity with the human cathepsin B, and 55% identity with the 29-kDa proteinase of the blowfly. Three active sites characteristic for cathepsin B were conserved in the deduced amino acid sequences of BmCtB cDNA at positions Cys-111, His-280 and Asn-300. Northern analysis identified a 1.3-kb mRNA. Expression of BmCtB was observed in the hemocytes from the day of wandering and was strongest at day 1 pupa. With in situ hybridization, strong signals were observed in the granular cells and plasmatocytes of day 0 pupa, but not in those of day 5 of the fifth larval instar. The results indicate another function of cathepsin B and insect hemocyte during metamorphosis.

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