ERK/MAPK regulates ecdysteroid and sorbitol metabolism for embryonic diapause termination in the silkworm, Bombyx mori

The eggs of the silkworm Bombyx mori undergo a state of suspended overt development and diminished metabolism called ‘diapause’ to escape adverse environmental conditions. Termination of Bombyx embryonic diapause requires 2–3 months of low temperature (5 °C), but the molecular mechanisms underlying diapause termination are unknown. Diapause termination requires a decrease in the sorbitol concentration, which arrests embryonic development, and the secretion factors from yolk cells that promote embryonic development. In the present study, we report that 20-hydroxyecdysone promoted the development of denuded embryos and that ecdysteroid-phosphate phosphatase (EPPase), which is a key enzyme for active ecdysteroid production, was induced by incubation of diapausing eggs at 5 °C. In dechorionated egg cultures, extracellular signal-regulated kinase (ERK), which is activated by incubating diapausing eggs at 5 °C, regulated sorbitol–glycogen conversion, ecdysteroid secretion via gene transcription of key enzymes, sorbitol dehydrogenase-2, and EPPase, suggesting that ERK has a key role in diapause termination.