Alteration of constitutive heat shock protein 70 (HSC70) production by in vitro culture of porcine preimplanted embryos

摘要

All organisms are effective in producing a series of proteins named heat shock proteins (HSP) in response to a variety of environmental stressors including changes in temperature, oxidative stress, free oxygen radicals, viral and bacterial infections, heavy metals, ethanol and ischaemia (Lindquist, 1986). However, pre-treatment of cells with a mild stress just sufficient to induce HSP expression results in protection to subsequent shock (Craig and Jacobsen, 1984). Members of this class are classified on the basis of their molecular weight (HSP110, HSP90, HSP70, etc). HSP70 proteins are chaperones involved in important cellular processes and have been classified into constitutive and inducible forms. Recent evidence suggests an important role for HSP70 in fertilization and early embryonic development: HSP70 constitutive synthesis occurs in early murine (Wittig et al., 1983) and bovine embryos (Edwards and Hansen, 1996), while HSP70 induction by high temperature has been shown to occur only at the morula/blastocyst stage. Kojima and colleagues (1996) did not observe a HSP70 increase after heat shock exposure in pre-implantation pig embryos, despite use of an antibody ineffective in discriminating between the HSP/HSC isoforms. In the pig, embryonic development to the blastocyst stage is difficult under in-vitro conditions. Protocols (Dobrinsky et al., 1996) have been developed to overcome the blockage at the four cell stage, although in-vitro culture of pig embryos results in altered and delayed development. The present study aimed at examining the effects of culture conditions on HSP70 production in pre-implantation pig embryos.