Responsiveness of early embryos to environmental insults: Potential protective roles of HSP70 and glutathione

Early embryos are not as passive as previously thought. In the bovine, embr yos as early as the 2-cell stage can respond to environmental insults at bo th the cellular and molecular level by altering expression of specific gene s and synthesis of proteins. Moreover, sex related differences exist in how early embryos respond to otherwise hostile environments. As aggressive as early embryos may be to tolerate environment insults, the majority will fai l to continue in development. Reduced developmental potential of embryos ex posed to elevated temperatures is likely due to direct effects on the early embryo. However, as embryos proceed in development they acquire the abilit y to better withstand environmental insults. Developmental acquisition of t olerance to environmental stress may be contingent upon acquisition of prot ective biochemical mechanisms or simply due to increased cell numbers. Corr elative evidence has suggested a potential role of heat shock protein 70 an d glutathione for protection of embryos in face of elevated temperature. Of these two possibilities, HSP70 appears least likely to play a significant role in developmental acquisition of thermotolerance. Bovine embryos as ear ly as the 2-cell stage, are able to mount a heat shock response; a developm ental stage that is most sensitive to elevated temperatures. A more likely candidate for conferring increased resistance of early embryos to elevated temperature is glutathione. (C) 2000 by Elsevier Science Inc.