Neural tube, formation

Takeuchi, T, Yamazaki, Y., Katoh-Fukui, Y, Tsuchiya, R., Rondo, S Motoyama, J. and Higashinakagawa, T. (1995) Gene trap capture of a novel mouse gene, jumonji, required for neural tube formation. Genes and Development,... 

Supplements of folic acid (0.4 mg/day), or possibly less, can reduce the rate of NTDs. To achieve an extra 0.4 mg folic acid per day, using food, one would have to drink eight glasses of orange juice or eat three servings of Brussels sprouts per day (Wald and Bower, 1995). Since it is not likely that any population, as a whole, would be expected to consume folic acid supplements on a consistent, daily basis, food fortification has become an attractive option. Because neural tube formation occurs early in pregnancy, it is probably necessary for folic acid supplements (when taken) to be consumed for 2-3 weeks (every day) prior to the day of conception, and for 2-3 weeks (every day) after conception, in order for the vitamin to produce its apparent effect. 

Smith, J. L. and Schoenwolf, G. C. (1989) Notochordal induction of cell wedging in the chick neural plate and its role in neural tube formation. J. Exp. Tool. 250, 49-62. 

Figure 1 Diagram of neural tube formation in an amphibian embryo, seen as transverse sections of embryos of different stages.

Figure 2 Computer simulation of neural tube formation (after Odell et al. [16]). T is the elapsed time.

Following manual stimulation of active contraction in the apices of the top two cells to initiate the simulation, the apices of the neighbouring active cells are stretched and so triggered, automatically, to contract. This leads to a wave of contraction propagated, domino-like, from cell to cell. These coordinated changes in cell shape lead to an overall change in tissue form similar to that seen in neural tube formation (Fig. 2). 

In view of the apparent complexity of the events of early embryonic development it is perhaps surprising that embryos also have powers of regeneration or repair. For example, if a linear wound is made in the tissue of an amphibian early embryo, much at the same time as the embryo is undergoing neural tube formation, the wound will heal rapidly [19](Fig, 4). 

The best examples of pleiotropy have been provided by developmental biologists. Two examples illustrate the pleiotropic action of developmental genes. Sonic hedgehog participates in the formation of the different cell types that form the neural tube, in limb development and in somitogenesis, a process by which mesodermic cells aggregate to form bones and muscles. 

Cell adhesion molecules (CAMs) play critical roles in all facets of nervous system development and maintenance. Important phenomena in which CAMs are involved include initial formation of the neural tube and the neural crest, migration of all neurons and glial cells, axonal outgrowth and guidance, target selection, synaptic stabilization and plasticity, myelination and nerve regeneration after injury (see Chs 4,24,28-30 and 53). Adhesion molecules interact with each other and with nonadhesive cell-surface and/or cytoplasmic molecules, and, in the two... 

Carbamazepine Neural tube defects affecting brain formation... 

High doses of folic acid can mask signs of B12 deficiency, which is a risk in elderly people. Patients taking phenytoin (Dilantin) for seizures should be cautious about taking folic acid because it can increase the risk of seizures. During the first trimester of pregnancy, folic acid deficiency can affect the development of the central nervous system (CNS) of the fetus this can lead to neural tube defects (NTDs) such as spina bifida, a defective closure of the bony structure of the spinal cord, or anencephaly, lack of brain mass formation... 

Tung EW, Winn LM (2011) Valproic acid increases formation of reactive oxygen species and induces apoptosis in postimplantation embryos a role for oxidative stress in valproic acid-induced neural tube defects. Mol Pharmacol 80(6) 979-987... 

Spina bifida is one of a class of birth defects characterized by the incomplete or incorrect formation of the neural tube early in development. In the United States, the prevalence of neural-tube defects is approximately 1 case per 1000 births. A variety of studies have demonstrated that prevalence of neural-tube defects is reduced by as much as 70% when women take folic acid as a dietary supplement before and during the first trimester of pregnancy. One hypothesis is that more folate derivatives are needed for the synthesis of DNA precursors when cell division is frequent and substantial amounts of DNA must be synthesized. 

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