Knocking down 10-formyltetrahydrofolate dehydrogenase increased oxidative stress and impeded zebrafish embryogenesis by obstructing morphogenetic movement

BACKGROUND: Folate is an essential nutrient for cell survival and embryogenesis. 10-Formyltetrahydrofolate dehydrogenase (FDH) is the most abundant folate enzyme in folate-mediated one-carbon metabolism. FDH converts 10-formyltetrahydrofolate to tetrahydrofolate and CO2, the only pathway responsible for formate oxidation in methanol intoxication. FDH has been considered a potential chemotherapeutic target because it was down-regulated in cancer cells. However, the normal physiological significance of FDH is not completely understood, hampering the development of therapeutic drug/regimen targeting FDH. METHODS: Fdh expression in zebrafish embryos was knocked-down using morpholino oligonucleotides. The morphological and biochemical characteristics of fdh morphants were examined using specific dye staining and whole-mount in-situ hybridization. Embryonic folate contents were determined by HPLC. RESULTS: The expression of fdh was consistent in whole embryos during early embryogenesis and became tissue-specific in later stages. Knocking-down fdh impeded morphogenetic movement and caused incorrect cardiac positioning, defective hematopoiesis, notochord malformation and ultimate death of morphants. Obstructed F-actin polymerization and delayed epiboly were observed in fdh morphants. These abnormalities were reversed either by adding tetrahydrofolate or antioxidant or by co-injecting the mRNA encoding FDH N-terminal domain, supporting the anti-oxidative activity of FDH and the in vivo function of tetrahydrofolate conservation for FDH N-terminal domain. CONCLUSIONS: FDH functioned in conserving the unstable tetrahydrofolate and contributing to the intracellular anti-oxidative capacity of embryos, which was crucial in promoting proper cell migration during embryogenesis. GENERAL SIGNIFICANCE: These newly reported tetrahydrofolate conserving and anti-oxidative activities of FDH shall be important for unraveling FDH biological significance and the drug development targeting FDH.