Genomic and transcriptomic analyses of variable fetal-placental responses to a restricted uterine environment.
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(1) Lamb production, the main source of income for sheep flocks worldwide, is dependent on the birth of viable lambs with appropriate birthweight - a key determinate of neonatal survival (Dwyer, 2008; Fogarty et al., 2000; Smith, 1977). Unfavorable conditions during pregnancy, such as under-nutrition (Belkacemi et al., 2010; Igwebuike, 2010) and a multi-fetal pregnancy (Gootwine et al., 2007) generally lead to fetal mortality or birth of small lambs, with low survival rates and poor post-natal growth (Wu et al., 2006; Rhind et al., 2001; Greenwood and Bell, 2003; Louey et al., 2005). Pregnancy depends upon cross-talk between the maternal and the fetal compartments via the placenta (Bazer et al., 2012). When there is an insufficient supply of nutrients from the mother, compensatory adaptations to enhance size, architecture and function of the placenta allow demands for fetal-placental growth to be met. Under nutritional constraints affecting maternal metabolic status, endocrine signals may alter placental gene expression to decrease growth and nutrient transport by the placenta (Lan et al., 2013). On the other hand, fetal endocrine signaling under metabolic stress may induce/enhance placental functions to meet fetal metabolic demands (Gaccioli et al., 2013). The relative roles of the maternal and fetal compartments to induce modifications in placental development and function are not clear. As the mother and her fetus(es) share genetic background, it is difficult to separate their respective roles in regulating fetal-placental growth and functionality.