Genes regulating embryonic and fetal survival.

Embryonic mortality in both farm animals and humans occurs most frequently during the first few weeks after conception. It can be attributed to abnormalities in the earliest developmental processes during embryogenesis that include implantation, maternal recognition of pregnancy, and formation of the placenta and cardiovascular system. The molecular mechanisms that are essential for all of these early processes are being elucidated at a rapid pace using transgenic and gene knockout approaches in mice. Two important general conclusions have emerged from this work. First, placental defects can occur by a number of different molecular mechanisms and can result from defects in the development or function of its trophoblast, mesenchymal or vascular components. Second, placental and cardiovascular functions are intimately linked. Cells of the placenta, for example, produce hormones that have profound effects on maternal and fetal cardiac and vascular function. In addition, development of the two is linked mechanistically through the use of some genes that are essential for development of both. Understanding the molecular basis of these processes should help to address the major limits to the success of embryo transfer, IVF and embryo cloning practices in livestock species.