Embryo

Alterations in Ultrastructural Morphology of Two-Cell Bovine Embryos Produced In Vitro and In Vivo Following a Physiologically-Relevant Heat Shock

Abstract
Exposure of cultured preimplantation embryos to temperatures similar to those experienced by heat-stressed cows inhibits subsequent development. In this study, the effects of heat shock on the ultrastructure of two-cell bovine embryos were examined to determine mechanisms for inhibition of development. Two-cell embryos produced in vitro were harvested at ~28 h post-insemination and cultured for 6 h in one of three temperatures: 38.5°C (cow body temperature), 41.0°C (characteristic temperature for heat-stressed cows), or 43.0°C (severe heat shock). Ultrastructural examinations revealed that both heat shocks resulted in the movement of organelles towards the center of the blastomere. In addition, heat shock increased the percent of mitochondria exhibiting a swollen morphology. Furthermore, the distance between the membranes comprising the nuclear envelope was increased, but only when embryos were treated at 43.0°C. To determine if ultrastructural responses to heat shock were similar between embryos produced in vitro and in vivo, two-cell embryos were collected from superovulated Angus cows 48 h post-insemination and treated ex-vivo for six h at 38.5° or 41.0°C. Again, heat shock caused an increase in number of swollen mitochondria and movement of organelles away from the periphery of the blastomere. In conclusion, exposure of two-cell bovine embryos to physiologically-relevant elevated temperatures causes disruption in ultrastructural morphology that is inimical to development. The observation that overall morphology and response to heat was similar between embryos produced in vitro and in vivo implies that the latter can be a good model for understanding embryonic responses to heat shock.

Key words: Embryo • Environment

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