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.

The avian-specific small heat shock protein HSP25 is a constitutive protector against environmental stresses during blastoderm dormancy.

Small heat shock proteins (sHSPs) range in size from 12 to 42 kDa and contain an α-crystalline domain. They have been proposed to play roles in the first line of defence against various stresses in an ATP-independent manner. In birds, a newly oviposited blastoderm can survive several weeks in a dormant state in low-temperature storage suggesting that blastoderm cells are basically tolerant of environmental stress. However, sHSPs in the stress-tolerant blastoderm have yet to be investigated. Thus, we characterised the expression and function of sHSPs in the chicken blastoderm. We found that chicken HSP25 was expressed especially in the blastoderm and was highly upregulated during low-temperature storage. Multiple alignments, phylogenetic trees, and expression in the blastoderms of Japanese quail and zebra finch showed homologues of HSP25 were conserved in other avian species. After knockdown of chicken HSP25, the expression of pluripotency marker genes decreased significantly. Furthermore, loss of function studies demonstrated that chicken HSP25 is associated with anti-apoptotic, anti-oxidant, and pro-autophagic effects in chicken blastoderm cells. Collectively, these results suggest avian HSP25 could play an important role in association with the first line of cellular defences against environmental stress and the protection of future embryonic cells in the avian blastoderm.