ABSTRACT
The placenta is the rst organ formed during pregnancy. It connects the developing fetus to the mother’s uterine wall and inuences almost every aspect of fetal development and growth such as gas exchange, nutrient uptake, waste elimination, and hormone production. The placenta produces miRNAs. Evolving evidence has shown that placental miRNA expression/ production not only plays critical roles in placental development but also mediates maternal immune tolerance during pregnancy. First, the nding of differential miRNA expression pro-les between rst-trimester and term placentas demonstrates spatial and temporal miRNA synthesis and regulation during placental development (Gu et al. 2013; Farrokhnia et al. 2014). Second, identication of placental-specic miRNAs, chromosome 14 miRNA cluster (C14MC) miRNAs imprinted from maternal chromosome (Seitz et al. 2004), and chromosome 19 miRNA cluster (C19MC) miRNAs imprinted from paternal chromosome (Noguer-Dance et al. 2010) emphasizes inherited genetic regulation during placenta development and their potential role in immunomodulation during pregnancy. Third, demonstration of altered miRNA expression in placentas in miscarriage, preeclampsia, intrauterine growth restriction, etc., provides evidence that deregulation of placental miRNAs is associated with placental disorders (Pineles et al. 2007; Mayor-Lynn et al. 2011; Ventura et al. 2013). Moreover, detection of trophoblast-derived miRNAs in the maternal circulation and ndings of different patterns of circulating miRNAs at different gestational age and pregnancy disorders (Gilad et al. 2008; Luo et al. 2009) further indicate that placental miRNAs could serve as valuable biomarkers of placental function and the likelihood of molecular regulators acting on the maternal systemic vasculature and immune systems during pregnancy.
