Temperature-dependent activation of ERK/MAPK in yolk cells and its role in embryonic diapause termination in the silkworm Bombyx mori

The silkworm Bombyx mori requires 2–3 months of low temperature (5 °C) to terminate embryonic diapause. The molecular mechanisms, however, are unknown. Extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinase (MAPK) is temperature-dependently activated in the yolk cells of diapausing eggs after 45 days at 5 °C, coincident with the acquisition of developmental competence of the embryos at 25 °C. Yolk cell granulation and dissociation also begin in diapause eggs incubated at 5 °C for 45 days. We used dechorionated egg culture as a model system of diapause termination and observed that both yolk cell dissociation and embryonic development are inhibited by MAPK–ERK kinase (MEK) inhibitor U0126. Therefore, we suggest that ERK in yolk cells has a role in regulating changes in yolk morphology and termination of embryonic diapause in B. mori.