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Bain_ Madan_ Betts


									Reactive oxygen species and the early bovine embryo: arrest, apoptosis and the role of
Nathan T. Bain1, Pavneesh Madan1, Dean H. Betts,2
  Department of Biomedical Sciences, Ontario Veterinary College, University of Guelph,
Guelph, ON Canada N1G 2W1
  Department of Physiology and Pharmacology, University of Western Ontario,
London, ON, Canada N6A 5C1
        The in vitro production (IVP) of embryos suffers from a high degree of early
developmental failure. This inefficiency has been linked to the effects of reactive oxygen species
(ROS) brought on by the unavoidable exposure of embryos to atmospheric levels of O2 during
the IVP process. P66Shc, a stress-response protein involved in oxidative stress signalling, was
examined as a potential mediator between oxidative stress and developmental failure.
        The expression of p66Shc was quantified through real-time PCR and semi-quantitative
immunofluorescence. Significant differences (p <0.05) in p66Shc expression were found between
groups of embryos with respect to time of first cleavage, in vitro O2 concentration, catalase
supplementation and H2O2 treatment. Furthermore, all instances of increased p66Shc expression
correlated with increased H2A-X staining (ROS-associated DNA damage) and DCF staining
(H2O2 quantification).
        siRNA molecules designed to selectively knockdown p66Shc were microinjected into
zygote-stage embryos. P66Shc knockdown was confirmed by mRNA and protein quantification.
Two, non-overlapping anti-p66Shc siRNA molecules produced a significant decrease in
developmental failure at both the 2-4 cell and 9-16 cell stage of development. P66Shc knockdown
was also found to correlate with significantly decreased levels of H2A-X and DCF staining.
Lastly, p66Shc knockdown also induced a resistance to H2O2-induced developmental failure.
         The strong correlative relationship between ROS, developmental failure and p66Shc
expression, as well as the protective effects of p66Shc knockdown support the view of p66Shc as a
mediator of oxidative stress-induced developmental failure.

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