Expression of 20-hydroxyecdysone-induced genes in the silkworm brain and their functional analysis in post-embryonic development

The insect brain is the center of developmental control, from which ecdysone governs brain morphogenesis and regulates gene expression cascades associated with molting and metamorphosis. In order to identify the 20-hydroxyecdysone (20E)-inducible genes responsible for molting and metamorphosis, we constructed a 20E-induced subtraction complementary DNA library from the fifth instar larval brain of the silkworm Bombyx mori. We isolated 10 genes, designated as bombeil-1 to bombeil-10, three of which did not show any sequence similarity to previously identified Bombyx genes. Whole-mount in situ hybridization revealed that all of these bombeil messenger RNAs were exclusively located in two pairs of lateral neurosecretory cells in the larval brain, known as prothoracicotropic hormone (PTTH)-producing cells. RNA-interference knockdown targeting bombeil-2 resulted in larval–pupal molt defects, and adult wing and leg malformations. These results, together with the cell-specific co-localization of bombeil transcripts with PTTH, suggest that bombeil genes play important roles during larval–pupal–adult development.