Cathepsin B protease is required for metamorphism in silkworm, Bombyx mori

Cathepsin B belongs to lysosomal cysteine protease of the papain family. Temporal and spatial expression analysis of cathepsin B of Bombyx mori (BmCtB) was carried out based on Expression Sequence Tags (ESTs) data, oligonucleotide microarray, reverse transcription polymerase chain reaction (RT-PCR) and quantitative real-time PCR. Expression of BmCtB was observed in all of the tissues and stages. Among the 10 tested tissues, the fat body and posterior silk gland are the two most enriched tissues with BmCtB. During Bombyx development, there was an expression fastigium of BmCtB during metamorphosis. RNA interference was used to suppress the expression of cathepsin B during metamorphosis. Significant developmental defective phenotypes were obtained in the RNAi treated group. The dramatically reduced expression of BmCtB was confirmed by Northern blot and quantitative real-time PCR. These evidences strongly suggest cathepsin B proteinase was predominantly involved in the metabolism process of fat body and the posterior silk gland and was critical for metamorphism and development of silkworm, Bombyx mori.