Apoptosis is a process involved in organogenesis and embryo body formation where the selective elimination of cells is required. High temperature-induced programmed cell death is a cause of failures of in vitro fertilization and summer embryo mortality in cows. The molecular mechanisms of these phenomena as of yet remain unclear, but involvement of heat shock proteins (HSPs) in both events is obvious. HSPs are called chaperone proteins because they protect other proteins from denaturation under high temperature conditions. Expression of HSPs is stimulated by DNA damage, cytostatics, as well as UV radiation. Programmed cell death may undergo one of two distinct molecular pathways: receptor path or mitochondrial path. Nevertheless, concerning the mechanism of high temperature-caused death of oocytes and embryos it is worth mentioning about the sfingomyelin-ceramide pathway of apoptosis. It is known that two cattle breeds, Brahman and Senegal, are resistant to heat shock. Moreover, embryos after preincubation in 40°C presented better adaptation for heat shock. This finding was evoked by the expression of HSP 70. Germs cultured under in vivo or in vitro conditions present divergences in morphological (nuclear chromatine condensation, cell membrane blebbing, apoptotic bodies formation) and biochemical features of apoptosis. Results of previous original studies have shown the higher survival ratio of cattle embryos developing in the maternal reproductive tract, than germs cultured in vitro. These findings may suggest the significance of secretions of chemical substances by uterine tissues during normal pregnancy.
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