Gene expression patterns in bovine in vitro-produced and nuclear transfer-derived embryos and their implications for...

Bovine in vitro-produced (IVP) and nuclear transfer (NT)-derived embryos differ from their in vivo-developed counterparts in a number of characteristics. A preeminent observation is the occurrence of the large offspring syndrome, which is correlated with considerable embryonic fetal and postnatal losses. We summarize here results from our studies in which we compared gene expression patterns from IVP and NT-derived embryos with those from their IVP counterparts. Numerous aberrations were found in IVP and NT-derived embryos, including a complete lack of expression, an induced expression, or a significant up- or downregulation of a specific gene. These alterations may affect a number of physiological functions and are considered as a kind of stress response of the embryos to deficient environmental conditions. We hypothesize that the alterations are caused by epigenetic modifications, primarily by changes in the methylation patterns. Unravelling these epigenetic modifications is promising to reveal the underlying mechanisms of the large offspring syndrome.