Cellular mechanisms underlying Pax3-related neural tube defects and their prevention by folic acid

Neural tube defects (NTDs), including spina bifida and anencephaly, are among the most common birth defects worldwide, but their underlying genetic and cellular causes are not well understood. Some NTDs are preventable by supplemental folic acid. However, despite widespread use of folic acid supplements and implementation of food fortification in many countries, the protective mechanism is unclear. Pax3 mutant (splotch; Sp2H) mice provide a model in which NTDs are preventable by folic acid and exacerbated by maternal folate deficiency. Here, we found that cell proliferation was diminished in the dorsal neuroepithelium of mutant embryos, corresponding to the region of abolished Pax3 function. This was accompanied by premature neuronal differentiation in the prospective midbrain. Contrary to previous reports, we did not find evidence that increased apoptosis could underlie failed neural tube closure in Pax3 mutant embryos, nor that inhibition of apoptosis could prevent NTDs. These findings suggest that Pax3 functions to maintain the neuroepithelium in a proliferative, undifferentiated state, allowing neurulation to proceed. NTDs in Pax3 mutants were not associated with abnormal abundance of specific folates and were not prevented by formate, a one-carbon donor to folate metabolism. Supplemental folic acid restored proliferation in the cranial neuroepithelium. This effect was mediated by enhanced progression of the cell cycle from S to G2 phase, specifically in the Pax3 mutant dorsal neuroepithelium. We propose that the cell-cycle-promoting effect of folic acid compensates for the loss of Pax3 and thereby prevents cranial NTDs

Dynamic acetylation profile during mammalian neurulation

Neural tube defects (NTDs) result from failure of neural tube closure during embryogenesis. These severe birth defects of the central nervous system include anencephaly and spina bifida, and affect 0.5-2 per 1,000 pregnancies worldwide in humans. It has been demonstrated that acetylation plays a pivotal role during neural tube closure, as animal models for defective histone acetyltransferase proteins display NTDs. Acetylation represents an important component of the complex network of posttranslational regulatory interactions, suggesting a possible fundamental role during primary neurulation events. This study aimed to assess protein acetylation contribution to early patterning of the central nervous system both in human and murine specimens

Use of high-frequency ultrasound to study the prenatal development of cranial neural tube defects and hydrocephalus in Gldc-deficient mice

Objective: We used non-invasive high-frequency ultrasound (HFUS) imaging to investigate embryonic brain development in a mouse model for neural tube defects (NTDs) and non-ketotic hyperglycinemia (NKH). Method: Using HFUS, we imaged embryos carrying loss of function alleles of Gldc encoding glycine decarboxylase, a component of the glycine cleavage system in mitochondrial folate metabolism, which is known to be associated with cranial NTDs and NKH in humans. We serially examined the same litter during the second half of embryonic development and quantified cerebral structures. Genotype was confirmed using PCR. Histology was used to confirm ultrasound findings. Results: High-frequency ultrasound allowed in utero detection of two major brain abnormalities in Gldc-deficient mouse embryos, cranial NTDs (exencephaly) and ventriculomegaly (corresponding with the previous finding of post-natal hydrocephalus). Serial ultrasound allowed individual embryos to be analysed at successive gestational time points. From embryonic day 16.5 to 18.5, the lateral ventricle volume reduced in wild-type and heterozygous embryos but increased in homozygous Gldc-deficient embryos. Conclusion: Exencephaly and ventriculomegaly were detectable by HFUS in homozygous Gldc-deficient mouse embryos indicating this to be an effective tool to study CNS development. Longitudinal analysis of the same embryo allowed the prenatal onset and progression of ventricle enlargement in Gldc-deficient mice to be determined

Post-translational regulation of CRMP in developing and regenerating chick spinal cord

It is becoming apparent that regulation at the protein level plays crucial roles in developmental and pathological processes. Therefore, we performed a proteomics screen to identify proteins that are differently expressed or modified at stages of development permissive (E11) and nonpermissive for regeneration (E15) of the chick spinal cord. Proteins regulated either developmentally or in response to spinal-cord injury included collapsin-response-mediator proteins (Crmps), known to modulate microtubule dynamic and axonal growth. No significant changes in Crow transcripts following injury were observed, indicating regulation mainly at the protein level. Analysis of Crmp-2 protein and its phosphorylated forms, pS522 and pT514, showed that Crmp-2 is developmentally regulated and also expressed in neural progenitors in vivo and in neurospheres. Its cellular localization changed both with development and following spinal-cord injury. In addition, although overall levels of Crmp-2 expression were not affected by injury, abundance of certain phosphorylated forms was altered. pT514 Crmp-2 appeared to be associated with dividing neural progenitors and was greatly reduced at nonpermissive stages for regeneration, whereas it did not seem affected by injury. In contrast, phosphorylation of Crmp-2 at S522 was upregulated early after injury in regenerating spinal cords and the ratio between phosphorylated to total Crmp-2 increased, as indicated by 2D Western blots. Altogether, this study shows highly dynamic regulation of Crimp-2 forms during development and identifies post-translational changes in Crmp-2 as putative contributors to the maintenance of spinal-cord regenerative ability, possibly via a transient stabilization of the neuronal cytoskeleton