Several million babies worldwide have been born via Assisted Reproductive Technologies (ART). Although the majority of ART pregnancies result in healthy babies, ART is associated with a number of adverse effects, including increased risk for low birth weight, abnormal placental development, and rare imprinting disorders. Evidence from animal studies support that ART procedures can induce these effects independent from underlying infertility. Important for proper development and growth, imprinted genes are a unique subset of genes that are monoallelically expressed specific to the parent-of-origin. Notably, imprinted gene expression is regulated by DNA methylation at a discrete element known as the imprinting control region (ICR). Term placentae from mice generated by in vitro fertilization (IVF) display abnormal biallelic expression correlated with ICR hypomethylation for several imprinted genes. Additionally, IVF induces abnormal placental overgrowth. The main objective of this proposal is to test how individual IVF procedures affect placental function and to elucidate the underlying genetic and epigenetic mechanisms of this abnormal placentation. Because the placenta has been shown to be capable of compensating for environmental perturbations, the epigenetic and morphological changes observed may not result in physiological consequences. To address this, formation, cell composition, pathology, and nutrient transport function of the placenta will be assessed in natural, embryo transfer with and without superovulation, embryo culture, and IVF concepti in Aim 1. Because different cell types have distinct epigenetic and expression profiles, several limitations currently exist making molecular analyses of complex tissues, like the placenta, difficult. To remedy this, laser capture microdissection (LCM) and single-molecule quantitative fluorescence in situ hybridization (FISH) will be utilized. To determine gene expression changes that may be responsible for the abnormal placental phenotype, transcriptome analyses will be performed in Aim 2 on ectoplacental cone and chorion (E7.5) and junctional zone and labyrinth (E14.5) isolated by LCM from natural and IVF concepti.
In Aim 3, gene expression and single-molecule FISH methods will be employed to test the hypothesis that particular imprinted genes play a role in the underlying mechanism resulting in IVF-induced placental overgrowth. Determining how epigenetic changes influence placentation is important not only in the context of IVF, because the placenta is critical for overall offspring and maternal health. Furthermore, the pipeline developed during this fellowship may prove indispensible for future epigenetic investigations of other complex tissues.
Many healthy children have been conceived through Assisted Reproduction Technologies (ART), but ART pregnancies are still associated with complications, including abnormal placentation. Using a mouse model, this project will determine the physiological and genetic placental effects induced by ART and elucidate the underlying epigenetic mechanisms. Understanding how abnormal placentation occurs, not only in the context of ART, is important because proper formation and function of the placenta is critical to the survival and long- term health of babies, as well as the health of the mother during her pregnancy.