Metamorphosis is a development process involving the programmed cell death of obsolete larval organs. Aspartic proteinase cathepsin D (BmCatD) is involved in the silkworm Bombyx mori metamorphosis. Here we show a novel functional role of cysteine proteinase cathepsin B during B. mori metamorphosis. The B. mori cathepsin B (BmCatB) was expressed in the fat body, epidermis, ovary, testis, and hemocyte of the larval and pupal stages. The BmCatB was ecdysoneinduced, expressed in the fat body of the molting, the final larval instar and pupal stages, and its expression led to programmed cell death. RNA interference (RNAi)-mediated BmCatB knock-down inhibited the programmed cell death of larval and pupal fat body, resulting in the arrest of larval-pupal transformation. BmCatB RNAi is up-regulated the expression of BmCatD. Based on these results we concluded that BmCatB is critically involved in the histolysis of the larval and pupal fat body, indicating that BmCatB and BmCatD are mutally regulated during silkworm metamorphosis.

The effects of pollens of Bt Chinese cabbage (Brassica campestris), expressing the insecticidal protein Cry1Ac toxin (Bt Chinese cabbage) on Bombix mori larvae, were determined in laboratory studies. When reared on an artificial diet containing pollens of Bt Chinese cabbage, decreased survival rate and body weight of B. mori larvae were observed. ELISA test using Cry1Ac-antibody implied that the Cry toxin was detected not only in the whole body and alimentary canal but also in the hemolymph and remaining body parts, suggesting that the ingested Cry1Ac protein is distributed inside the body through epithelial membrane of the midgut of B. mori. Taken together, it was suggested that the pollens of Bt Chinese cabbage adversely affect non-target insect B. mori larvae.

SAGE technique is a sequenced-based approach that identifies which genes are expressed and quantifies their level of expression. The SAGE catalog of gene expression for a given cell or tissue is defined as the 'transcriptome'. With a goal of obtaining a set of quantitative information of expressed genes of posterior silk gland (PSG) of silkworm, we have generated a SAGE tag library from the PSGat day 4 of 5th instars of Bombyx mori. In this study, atotal of 2,406 tags were identified, representing 682 unique transcripts. Of these SAGE tags, 1,982 tags were detected twice or more accounted for 82% of the total tag population, whereas 445 tags were detected only once accounted for 18% of the total tag population. Four percent (27 tags) of the unique tags were detected at least ten times each, which corresponds to a representation of more than 53% of the total tag population. In addition, we have discussed a comparative aspect of the transcript abundance between expressed sequenced tags (ESTs) and the SAGE tags.

The insect baculovirus expression vector system (BEVS) is useful for the production of biologically active recombinant proteins. However, the overexpression of foreign proteins in this system often results in misfolded proteins and the formation of protein aggregates. To overcome this limitation, we have developed a versatile baculovirus expression and secretion system using the Bombyx mori protein disulfide isomerase (bPDI) as a fusion partner. bPDI gene fusion improved the secretion and antibacterial activity of recombinant nuecin proteins. Thus, bPDI gene fusion is a useful addition to the BEVS for the large-scale production of bioactive recombinant proteins.

The efficiency to detect mutagenicity of the system using a specific locus mutation of Bombyx mori was examined and improved. In the system, mutagenicity could be detected by the egg colour manifested by the pe and/or re genes, which is a kind of recessive visible mutation of the insect. Among tested four mutagens, MMC had specially high sensitivity in the oocytes of silkworm and EMS had in the spermatozoa. PCB and dioxin showed a positive effect in both the oocytes and spermatozoa. In a consequence of sensitivity of mutagen by mating number of male moth of B. mori, treated mutagen, there was no difference between one mating - and three mating - male moth in sensitivity of mutagen. Sun3ho, B. mori variety, which showed high sensitivity to mutagens was improved in the major characteristics by crossing of C5 and N12.