The effects of antibodies to heat shock protein 70 in fertilization and embryo development

The role of heat shock proteins in shielding organisms from environmental s tress is illustrated by the large-scale synthesis of these proteins by the organisms studied to date. However, recent evidence also suggests an import ant role for heat shock proteins in fertilization and early development of mammalian embryos. We found that the presence of anti-HSP70 antibody signif icantly reduced tight binding of spermatozoa to the zona pellucida of bovin e oocytes and interrupted completion of meiosis II and pronuclear formation . Furthermore, the presence of antiUSP70 in culture medium from day 3 to da y 9 of development increased apoptosis and significantly reduced the number of embryos reaching the blastocyst stage. We further observed that the pro portion of apoptotic cells in bovine blastocysts was significantly lower af ter in-vitro culture with a prior exposure to increased temperature. Howeve r, nuclear localization of the p53 protein, which is thought to be essentia l for the up-regulation of genes involved in apoptosis and cell cycle arres t, was detected in the majority of nuclei in blastocysts exposed to increas ed temperature, whereas in their untreated (control) counterparts, p53 prot ein was only detected in the cytoplasm. The decrease in apoptosis after exp osure of blastocysts to increased temperature may be attributed to cell cyc le arrest resulting from nuclear localization of the p53 protein and/or to an increase in heat shock protein synthesis. We propose that HSP70 plays a critical role in fertilization and early embryonic development.