Timeless is a critical gene in the diapause of silkworm, Bombyx mori

The diapause is a specific physiological phenomenon induced by circadian zeitgebers of temperature and photoperiod at the stage of maternal embryonic development. In this research, the authors investigated the linkage of diapause and the regulation of circadian rhythm by inspecting the expression profiles of a circadian clock gene timeless (tim) under diapause-inducing temperature and photoperiod in Bombyx mori. The results show that the level of tim mRNA was higher in 25LL than in 20LD or in 15DD during the late embryonic stages (EAT 2520-3240°C·h), which is the most effective inducing period of temperature and photoperiod on diapause in the progeny. The tim transcription level was significantly higher in darkness than in light during postembryonic development, which contradicted the results found in the pupa and adult stages at 25°C. Exposure of maternal embryos to a high temperature (25°C) resulted in up-regulated levels of tim mRNA in egg stage of progeny. However, this up-regulation only occurred before egg-age at 72 h, which was a pivot for diapause and diapause termination. In conclusion, diapause-inducing temperature and photoperiod of incubation directly affect tim gene expression throughout the life cycle of B. mori.Key words: Circadian clock gene, timless gene, diapause, temperature, photoperiod, Bombyx mori.