Neural tube defects induced by folate deficiency in mutant curly tail (Grhl3) embryos are associated with alteration in folate one-carbon metabolism but are unlikely to result from diminished methylation.
BACKGROUND
Folate one-carbon metabolism has been implicated as a determinant of susceptibility to neural tube defects (NTDs), owing to the preventive effect of maternal folic acid supplementation and the higher risk associated with markers of diminished folate status.


METHODS
Folate one-carbon metabolism was compared in curly tail (ct/ct) and genetically matched congenic (+(ct)/+(ct)) mouse strains using the deoxyuridine suppression test in embryonic fibroblast cells and by quantifying s-adenosylmethionine (SAM) and s-adenosylhomocysteine (SAH) in embryos using liquid chromatography tandem mass spectrometry. A possible genetic interaction between curly tail and a null allele of 5,10-methylenetetrahydrofolate reductase (MTHFR) was investigated by generation of compound mutant embryos.


RESULTS
There was no deficit in thymidylate biosynthesis in ct/ct cells, but incorporation of exogenous thymidine was lower than in +(ct)/+(ct) cells. In +(ct)/+(ct) embryos the SAM/SAH ratio was diminished by dietary folate deficiency and normalized by folic acid or myo-inositol treatment, in association with prevention of NTDs. In contrast, folate deficiency caused a significant increase in the SAM/SAH ratio in ct/ct embryos. Loss of MTHFR function in curly tail embryos significantly reduced the SAM/SAH ratio but did not cause cranial NTDs or alter the frequency of caudal NTDs.


CONCLUSIONS
Curly tail fibroblasts and embryos, in which Grhl3 expression is reduced, display alterations in one-carbon metabolism, particularly in the response to folate deficiency, compared to genetically matched congenic controls in which Grhl3 is unaffected. However, unlike folate deficiency, diminished methylation potential appears to be insufficient to cause cranial NTDs in the curly tail strain, nor does it increase the frequency of caudal NTDs.
De Castro
Sandra C P
SC
Neural Development Unit, UCL Institute of Child Health, London, UK.
Leung
Kit-Yi
KY
Savery
Dawn
D
Burren
Katie
K
Rozen
Rima
R
Copp
Andrew J
AJ
Greene
Nicholas D E
ND
D000818:Animals; D002244:Carbon / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics; D005260:Female; D005347:Fibroblasts / Q000378:metabolism; D005492:Folic Acid / Q000378:metabolism*; D005494:Folic Acid Deficiency / Q000150:complications* / Q000235:genetics; D008745:Methylation; D042965:Methylenetetrahydrofolate Reductase (NADPH2) / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008817:Mice, Mutant Strains; D009436:Neural Tube Defects / Q000209:etiology* / Q000378:metabolism; D011247:Pregnancy; D012435:S-Adenosylhomocysteine / Q000032:analysis / Q000378:metabolism; D012436:S-Adenosylmethionine / Q000032:analysis / Q000378:metabolism; D013938:Thymidine Monophosphate / Q000096:biosynthesis; D014157:Transcription Factors / Q000235:genetics
D004268:DNA-Binding Proteins; C499942:Grhl3 protein, mouse; D014157:Transcription Factors; D013938:Thymidine Monophosphate; D002244:Carbon; D012436:S-Adenosylmethionine; D005492:Folic Acid; D012435:S-Adenosylhomocysteine; D042965:Methylenetetrahydrofolate Reductase (NADPH2)