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.