In some adult holometabolous insects, specific epithelial tissues form imaginal discs, small sac-like clusters of cells that form in the larval body. During metamorphosis, in response to hormones, the discs undergo dramatic changes including cell proliferation and differentiation. In Bombyx mori insects, the cuticular protein (CP) genes, which are expressed at prepupal stage in the wing discs, are divided into six groups according to their developmental expression profile and responsiveness to steroid hormones. In this article, we discuss the expression of CP genes in the wing disc, and examine the molecular mechanisms by which metamorphosis and cell transformations are regulated by hormones in insects.