Cuticular protein and transcription factor genes expressed during prepupal-pupal transition and by ecdysone pulse treatment in wing discs of Bombyx mori.

We aimed to understand the underlying mechanism that regulates successively expressed cuticular protein (CP) genes around pupation in Bombyx mori. Quantitative PCR was conducted to clarify the expression profile of CP genes and ecdysone-responsive transcription factor (ERTF) genes around pupation. Ecdysone pulse treatment was also conducted to compare the developmental profiles and the ecdysone induction of the CP and ERTF genes. Fifty-two CP genes (RR-1 13, RR-2 18, CPG 8, CPT 3, CPFL 2, CPH 8) in wing discs of B. mori were examined. Different expression profiles were found, which suggests the existence of a mechanism that regulates CP genes. We divided the genes into five groups according to their peak stages of expression. RR-2 genes were expressed until the day of pupation and RR-1 genes were expressed before and after pupation and for longer than RR-2 genes; this suggests different construction of exo- and endocuticular layers. CPG, CPT, CPFL and CPH genes were expressed before and after pupation, which implies their involvement in both cuticular layers. Expression profiles of ERTFs corresponded with previous reports. Ecdysone pulse treatment showed that the induction of CP and ERTF genes in vitro reflected developmental expression, from which we speculated that ERTFs regulate CP gene expression around pupation.