Fig. 7.

Pharmacological inhibition of folate uptake systems affects Xenopus laevis neural tube formation. Embryos at stage 13 (14.75 hpf) were incubated with 100 nM-1.5 mM methotrexate (MTX), 1 nM-300 μM methotrexate ester, 1 nM-100 μM pyrimethamine, 100-500 μM trimetrexate or vehicle (control, 0.3% DMSO or saline). Embryos were fixed and photographed under a macroscope when controls reached neural tube closure, at stage 20 (22 hpf). Shown are representative examples. Arrowheads indicate defective neural tube closure. Rescue of 1.5 mM MTX-induced NTD phenotype was performed by preincubating two- to four-cell-stage embryos with 10 mM folinic acid (FA). Graph shows mean±s.e.m. percentage defective embryos; n≥6 independent experiments with n≥10 embryos per group, per experiment; *P<0.01; two-way ANOVA.