Fig. 7

Regulation of cuticle protein expression in the molting midguts by 20E. (a) Detection of cuticle protein in the molting midguts. (a) Molting midguts dissected from three larvae (IV-M: 6 h) were lysed and 15 μg total proteins were loaded per lane for Coomassie staining. Two bands that likely contained different cuticle proteins according to their molecular weight sizes were excised for a LC-MS/MS assay. (b) Detection of CPG21 in the molting midguts by Western blot. CPG21 appeared during the feeding and molting stage. Unfortunately, there was no corresponding probe for CPG21 in the microarray. Thus, we could not assay for its transcription change. b–d Expression of selected cuticle genes at the indicated developmental stages according to qRT-PCR assay. These genes were selected according to the microarray assay (Fig. 2, Additional file 2: Table S2). The expression levels of these genes were upregulated at different times during the molting stage. e–n 20E injection induced the expression of selected cuticle genes in the midgut according to qRT-PCR assay. Among 10 selected genes, only one gene (BGIBMGA000249-TA; m) did not exhibit a clear response to 20E injection. Each column represents the mean of three independent measurements  ±  S.E.M. o Production of new peritrophic membrane during the molting stage. A new peritrophic membrane was produced and covered the old one. The arrowhead indicates the newly produced peritrophic membrane, and the arrow indicates the old peritrophic membrane and enclosed food contents. Food debris was small and visible in the gut. The peritrophic membrane is composed of many cuticle proteins [47, 48] that are likely produced by midgut cells during the molting stage