Expression profile of several genes on ecdysteroidogenic pathway related to diapause in pupal stage of Bombyx mori bivoltine strain

Ecdysone is involved in regulation of embryonic diapause in the silkworm, Bombyx mori. However, its mechanism still remains unclear. To explore the role of ecdysteroidogenic pathway (EP) genes in diapause process of bivoltine B. mori, the eggs of Qiufeng, a bivoltine strain, were used as the study materials and arranged into diapause eggs producers (DEPs) and non-diapause eggs producers (NDEPs), respectively. The differential expression of EP genes between two groups was analysed during the early pupal stage. The expression of Shadow was significantly increased in the NDEPs in day-3 pupae and reached the peak simultaneously, indicating that Shadow was in coincidence with diapause process. To validate this hypothesis, a repression of Shadow by RNA interference was performed in day-2 pupae of NDEPs. The expression of Shadow was downregulated by RNAi, and beta Ftz-F1, a downstream gene of EP, was also decreased. Furthermore, the genes encoding the kynurenine-synthetase were upregulated in the ovary, and Brown, AdenoK which link Shadow to the kynurenine-synthase gene were also upregulated in the fat body. The progeny eggs appeared a light purple colour at 48 h after oviposition, revealing a certain tendency to diapause. We speculate that inhibition of Shadow upregulates 3-hydroxy-kynurenine synthesis by increasing the expression of Brown and AdenoK. In addition, Shadow was cloned, and expressed in E. toll for further functional study of Shadow protein. Our study provided insight into the role of EP genes in the process of diapause of B. mori.