Purification and cDNA cloning of evolutionally conserved larval cuticle proteins of the silkworm, Bombyx mori

A specific set of structural proteins termed larval cuticle proteins (LCPs) accumulates in integuments during larval development of the silkworm, Bombyx mori. Two major larval cuticle proteins, LCP17 and LCP22, were purified from the guanidine hydrochloride extract of the larval cuticle, and specific antibodies were raised against these proteins. Immunoblot analysis revealed that both LCPs are actively synthesized during larval intermolt stages, whereas the LCP17 epitope is also slightly but significantly detectable in pupal integuments. cDNA clones for LCPs were isolated by immunoscreening of the cDNA expression library constructed from larval epidermal mRNA. Predicted amino acid sequences of LCP17 and LCP22 are homologous to cuticle proteins from other insect species, including Manduca sexta, Drosophila melanogaster and Locusta migratoria. This fact suggests that these cuticle protein genes originated from a common ancestral gene and have been conserved during evolution. Northern blot hybridization demonstrated that the expression of LCP17 as welt as LCP22 mRNA is controlled in a stage-specific manner in the epidermis of the final instar larvae, suggesting a common regulatory mechanism for transcription of these two intermolt genes.