Inositol- and folate-resistant neural tube defects in mice lacking the epithelial-specific factor Grhl-3

The neural tube defects (NTDs) spina bifida and anencephaly are widely prevalent severe birth defects. The mouse mutant curly tail (ct/ ct) has served as a model of NTDs for 50 years, even though the responsible genetic defect remained unrecognized. Here we show by gene targeting, mapping and genetic complementation studies that a mouse homolog of the Drosophila grainyhead (grh) gene, grainyhead- like- 3 (Grhl3), is a compelling candidate for the gene underlying the curly tail phenotype. The NTDs in Grhl3- null mice are more severe than those in the curly tail strain, as the Grhl3 alleles in ct/ ct mice are hypomorphic. Spina bifida in ct/ ct mice is folate resistant, but its incidence can be markedly reduced by maternal inositol supplementation periconceptually. The NTDs in Grhl3 (-/-) embryos are also folate resistant, but unlike those in ct/ ct mice, they are resistant to inositol. These findings suggest that residual Grhl3 expression in ct/ ct mice may be required for inositol rescue of folate- resistant NTDs.