Deciphering the role of METTL3 in Mammalian Placenta Development and Maintenance Across Pregnancy

Abstract Placental dysfunction leads to pregnancy-associated disorders, including intrauterine growth restriction (IUGR) and preeclampsia, and also serves as a developmental cause for postnatal and adult diseases. Often, the causal alterations in the placentation process, which lead to defective pregnancies, occur early in

gestation. Defective development and differentiation of trophoblast progenitors are leading causes for pathological pregnancies. However, we have a poor understanding of molecular mechanisms that regulate trophoblast progenitor self-renewal, differentiation and function in postimplantation embryos. Studies on

mutant mouse models revealed that RNA Methyltransferase 3 (METTL3), which catalyzes N6-methyladenosine (m6A) modification on eukaryotic RNAs, is important for embryonic development. Furthermore, METTL3 expression is upregulated in pathological pregnancies, associated with Preeclampsia and IUGR. However, the

importance of METTL3 in the context of mammalian placentation is poorly understood. Our preliminary findings establish that METTL3 expression is conserved in trophoblast progenitors across mammalian species, including humans. We also found that METTL3 is essential in human trophoblast self-renewal. Thus, the overarching goal

of this proposal is to investigate importance of METTL3 in the mammalian placental development and maintenance. We will also test how altered METTL3 function in the placenta affects fetal development leading to IUGR. Two specific aims are proposed. In Aim 1 we will study Mettl3 conditional knockout and Mettl3

conditional overexpression mouse models to test the hypothesis that trophoblast cell-autonomous function of METTL3 is important placental development and maintenance. We will test role of METTL3 in trophoblast differentiation, invasion and fetal development. In Aim 2, using CTB-derived human trophoblast stem cells, we will test the hypothesis that METTL3

establishes a conserved gene expression program in mouse and human trophoblast progenitors and impairment of METTL3-dependent transcriptional program will impair self-renewal and differentiation potential of human trophoblast progenitors. In addition, we will also interrogate significance of METTL3-dependent mechanisms in the

context of pathological pregnancies associated with IUGR , especially early-onset IUGR.