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.