Expression of heat shock protein70 in pig oocytes: Heat shock response during oocyte growth

The heat shock response of growing and fully-grown pig oocytes was analyzed in vitro by determining heat shock protein70 (HSP70) synthesis under both normal conditions (39 °C; 0 and 6 h) and after heat shock (43 °C; 1, 4 and 6 h). The expression of HSP70 in oocytes was detected by immunoblotting analysis. Growing oocytes measuring 80–99 μm synthesized a high number of HSP70 without heat shock effect, and these were capable of increasing the synthesis of HSP70 after heat shock to a maximum after 1 h. Growing oocytes measuring 100–115 μm also synthesized HSP70 without heat shock and after it, but the HSP70 synthesis was not statistically changed by increasing duration of heat shock. In fully-grown oocytes, great amounts of HSP70 were found without heat shock treatment, and the contents of HSP70 significantly decreased after heat shock. These results indicate that growing oocytes are able to synthesize HSP70 after heat shock. This ability declines at the end of the growth period, and fully-grown oocytes are unable to induce HSP70 synthesis after heat shock. HSP70 is synthesized and stored during oocyte growth. The high HSP70 synthesis in non-heat-treated growing oocytes and a great amount of HSP70 in fully-grown oocytes support the hypothesis that HSP70 is important for oocyte growth and maturation.