BmCalpains are involved in autophagy and apoptosis during metamorphosis and after starvation in Bombyx mori

Apoptosis and autophagy play crucial roles during Bombyx mori metamorphosis and in response to various adverse conditions, including starvation. Recently, calpain, one of the major intracellular proteases, has been reported to be involved in apoptosis and autophagy in mammals. BmATG5 and BmATG6 have been identified to mediate apoptosis following autophagy induced by 20-hydroxyecdysone and starvation in B. mori. However, B. mori calpains and their functions remain unclear. In this study, phylogenetic analysis of calpains from B. mori, Drosophila melanogaster and Homo sapiens were performed and the results showed distinct close relationships of BmCalpain-A/B with DmCalpain- A/B, BmCalpain-C with DmCalpain-C, and BmCalpain-7 with HsCalpain-7. Then, the expression profiles of BmCalpains were analyzed by quantitative real-time polymerase chain reaction, and results showed that expression ofBmCalpain-A/B, BmCalpain-C and BmCalpain-7 was significantly increased during B. mori metamorphosis and induced in the fat body and midgut of starved larvae, which is consistent with the expression profiles ofBmAtgS, BmAtg6 and BmCaspase-1. Moreover, the apoptosis-associated cleavage of BmATG6 in Bm-12 cells was significantly enhanced when BmCalpain-A/B and BmCalpain-7 were induced by starvation, and was partially inhibited by the inhibitor of either calpain or caspase, but completely inhibited when both types of inhibitors were applied together. Our results indicated that BmCalpains, including BmCalpain-A/B, -C and -7, may be involved in autophagy and apoptosis during B. mori metamorphosis and after starvation, and may also contribute to the apoptosis-associated cleavage of BmATG6.

Inducing and isolation of antibacterial peptides from oriental fruit fly, Bactrocera dorsalis Hendel

One antibacterial activity fraction from an immunized dipteran insect, Bactrocera dorsalis, was isolated and purified by prepurification, ion-exchange chromatography, gel filtration chromatography and reverse-phase high performance liquid chromatography （HPLC）. The final purified fraction was checked on the Smart system HPLC and was judged as a pure fraction. The results of physical and biological analysis revealed that this fraction is heat stable and showed strong activities against Gram-positive bacterial growth. It possesses antibicrobial peptide properties and is worth further investigation.

Clathrin-dependent endocytosis predominantly mediates protein absorption by fat body from the hemolymph in Bombyx mori

During insect larval-pupal metamorphosis,proteins in the hemolymph are absorbed by the fat body for the maintenance of intracellular homeostasis;however,the type of proteins and how these proteins are internalized into the fat body are unclear.In Bombyx mori,the developmental profiles o f total proteins in the hemolymph and fat body showed that hemolymph-decreased protein bands(55-100 kDa)were in accordance with those protein bands that increased in the fat body.Inhibition o f clathrin-dependent endocytosis predominantly blocked the transportation o f 55-100 kDa proteins from the hemolymph into the fat body,which was further verified by RNA interference treatment o f Bmclathrin.Six hexamerins were shown to comprise〜90%of the total identified proteins in both the hemolymph and fat body by mass spectrum(MS)analysis.In addition,hemolymphspecific proteins were mainly involved in material transportation,while fat body-specific proteins particularly participated in metabolism.In this paper,four hexamerins were found for the first time,and potential proteins absorbed by the fat body from the hemolymph through clathrin-dependent endocytosis were identified.This study sheds light on the protein absorption mechanism during insect metamorphosis.