Avian blastoderm dormancy arrests cells in G₂ and suppresses apoptosis

In most avian species, the early embryo suspends development when the ambient temperature is too low; the resultant dormant state is called cold torpor. However, very little is known about dormant avian embryos at the cellular level. To investigate the molecular processes that occur in the chicken blastoderm during cold torpor, we performed transcriptome analysis and investigated cellular responses in dormant embryos. In embryos stored at low temperature, we observed up-regulation of genes and proteins related to endoplasmic reticulum stress and stress-activated protein kinase signaling. In addition, the proportion of early apoptotic cells rose dramatically during torpor, whereas the proportion of late apoptotic cells was unchanged. Cell cycle analysis revealed that mitotic arrest occurred at the G₂ phase in a DNA damage-independent manner and that the arrest was alleviated after incubation at 37°C. Our data suggest that the dormant avian embryo tolerates cold stress by inducing stress-tolerance pathways, inhibiting late apoptosis, and triggering cell cycle arrest at the G₂ phase.-Ko, M. H., Hwang, Y. S., Rim, J. S., Han, H. J., Han, J. Y. Avian blastoderm dormancy arrests cells in G₂ and suppresses apoptosis.