Heat shock-induced apoptosis in preimplantation bovine embryos is a developmentally regulated phenomenon

Apoptosis is a form of cell death that can function to elimi-nate cells damaged by environmental stress. One stress that can compromise embryonic development is elevated temperature (i.e., heat shock). For the current studies, we hypothesized that heat shock induces apoptosis in bovine embryos in a develop-mentally regulated manner. Studies were performed to 1) deter-mine whether heat shock can induce apoptosis in preimplanta-tion embryos, 2) test whether heat-induced apoptosis is devel-opmentally regulated, 3) evaluate whether heat shock-induced changes in caspase activity parallel patterns of apoptosis, and 4) ascertain whether exposure to a mild heat shock can protect embryos from heat-induced apoptosis. As determined by TUNEL reaction, exposure of bovine embryos $16 cells on Day 5 after insemination to 41 or 428C for 9 h increased the percentage o