Expression and localisation of heat shock protein 70 in cultured bovine oocytes and embryos

Effects of elevated in vitro temperature on in vitro produced early bovine embryos were analysed in order to determine its impact on the expression of heat shock protein 70 (hsp70). In vitro matured bovine oocytes, 2-cell and 8-cell embryos, and day 9 hatched blastocysts subjected to control and elevated temperature conditions were analysed by semiquantitative reverse transcription polymerase chain reaction methods for hsp70 mRNA expression. Results revealed the expression of hsp70 mRNA under control conditions and that early embryos can respond to heat stress by transcribing hsp70 mRNA. Confocal laser scanning microscopy used to localise the hsp70 protein in oocytes and embryos revealed that the distribution of hsp70 in the ooplasm of immature and mature oocytes is unaffected by exposure to elevated temperatures and that this protein was closely associated with the meiotic spindle, indicating its possible role in stabilising this structure. In 8-cell embryos derived under control conditions, hsp70 was evenly distributed in the cytoplasm but appeared as aggregates in some embryos exposed to elevated temperature. In heat-stressed hatched blastocysts, a more even distribution was noted following heat stress relative to corresponding controls, indicating their competence to respond to elevated temperature.