Mechanisms of folate action during nervous system development

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Project summary Neural tube defects (NTDs) are among the most common serious birth defects diagnosed in human fetuses and newborns with a combined incidence of ~1/1,000 in the United States and an estimated of 300,000 or more newborns worldwide each year. NTDs result from the failure of neural tube closure during the early fetal development. A combination of genetic and environmental factors appears to regulate the formation of the neural tube. Notably, folate supplementation during pregnancy prevents NTDs by unclear mechanisms. Our recently published study demonstrates that folate receptor 1 (Folr1), one of folate uptake systems, localizes to the apical surface of Xenopus laevis neural plate and is necessary for neural plate cell apical constriction during neural plate folding. Moreover, we find that Folr1 interacts with adherens junction components, C-cadherin and β- catenin suggesting that folate signaling might regulate neural plate cell-cell adhesion during neural tube formation. Our overall research goal is to elucidate the cellular and molecular mechanisms underlying neural tube formation. We will test the hypothesis that folate participates in the changes in cell shape that neural cells undergo during neurulation by recruiting its receptor and triggering a novel and dynamic signaling pathway. The first specific aim will consist in determining the molecular mechanisms underlying folate/Folr1 promotion of neural plate cell apical constriction during neural tube formation. We will identify the molecular mechanisms of Folr1 regulation of cell adhesion remodeling necessary for neural tube formation. In the second specific aim we will discover the signaling pathways recruited by folate/Folr1 that are necessary for neural plate cell apical constriction and neural tube formation. We will interrogate the ubiquitination pathway through gain and loss of function approaches and epistasis experiments. We will assess the role of folate in cell adhesion molecule and cytoskeletal dynamics by live imaging embryos expressing fluorescently tagged proteins or reporters of cell adhesion and cytoskeletal components during neural tube formation. We will use state-of-the-art methodologies including proteomics of immunoprecipitates, super resolution microscopy, reporters of cytoskeletal and cell adhesion dynamics and optogenetic approaches to manipulate signaling pathways. Although folate fortification has been a highly effective public health measure in reducing NTDs, the lack of mechanism-based understanding of NTD prevention leads to general concerns regarding unintended consequences resulting from supplementation. Optimal folate supplementation, risk groups and treatment of folate-insensitive NTDs are some of the unsolved clinical aspects awaiting for the full elucidation of the molecular and cellular mechanisms underlying folate action in neural tube formation.