Altered signal transduction in Folr1-/- mouse embryo fibroblasts

Mice lacking the gene for Folr1 (folic acid receptor 1) have an NTD (neural tube defect) that is rescued by maternal folate supplementation. Primary cultures of MEFs (mouse embryonic fibroblasts) were established from these embryos and the effect on various signalling pathways examined. TGF beta 1 (transforming growth factor beta 1) inhibited the proliferation of wildtype and Folr1(-/-) MEFs, and folate restriction, either in growth medium or through folate uptake, led to further inhibition of growth. This effect may be Smad-independent because reporter assays using the Smad-dependent reporter, p3TP-lux, revealed attenuation of TGF beta 1/Smad signalling in Folr1(-/-) MEFs. Signalling through the canonical Wnt pathway, measured by Wnt-3a stimulated expression of the target gene, Axin2, demonstrated increased activity in Folr1(-/-) MEFs. Only minor changes in the expression of a panel of TGF beta (transforming growth factor beta) and Wnt pathway-associated genes were revealed when Folr1(-/-) MEFs were compared with wild-type cells. These results demonstrate that under conditions of reduced folate (Folr(-/-)) signalling, pathways crucial for proper development of the neural tube are significantly altered.