Proteomic analysis of the silkworm midgut during larval-pupal transition

Metamorphosis is a key process in holometabolous insects since specific larval tissues, such as the midgut, the silk gland and the fat body, are remodeled into adult organs, or even disintegrate. However, the role of proteins and factors involved in the remodeling of these organs is still unclear. For this reason we undertook a proteomic study on the larval midgut of Bombyx mori to identify proteins whose expression significantly changes during larval-pupal metamorphosis and thus can have a role in this process. 2D-PAGE analysis showed upregulation or new expression of midgut proteins at 45 (pI 5.2), 29.8 (pI 6.11) and 20-kDa (pI 6-7) during the pupal stage. In addition zymogram analysis demonstrated the occurrence of protease activity at 37-kDa at the same developmental stage. By using MALDI-TOF-MS analysis the protein spots from 2D gel were identified as Hemolin, low molecular weight 30-kDa lipoproteins, HSP 20.8 and HSP 20.4, while the proteolytic band was identified as 37-kDa serine protease. The evidence herein presented suggests that the identified proteins could be involved in the immune protection during the remodeling of silkworm midgut that occurs at larval-pupal transition and represents a platform of knowledge necessary for future functional studies.