Prevention of spinal neural tube defects in the curly tail mouse mutant by a specific effect of retinoic acid.

Curly tail mouse mutant embryos (ct/ct) develop spinal neural tube defects (NTD) in 54% of cases, comprising isolated tail flexion defects and spinal bifida with tail flexion defects. Both types of spinal NTD result from delayed closure of the posterior neuropore (PNP). Previous studies (Seller et al. [1979] Proc. R. Soc. Lond. Biol. 206:95-107; Seller and Perkins [1982] Prenat. Diagn. 2:297-300) described a paradoxical effect of retinoic acid (RA) on the phenotypic expression of the ct mutation: Treatment with low doses of RA on day 8 of gestation increased the incidence of total NTD, whereas low doses of RA administered on day 9 resulted in reduced incidence of total NTD. In order to investigate further the reported preventive effect of RA, we have carried out detailed analyses of the effects of maternal treatment with 5 mg/kg RA on the incidence of NTD at different developmental stages, and on the development and growth of ct/ct embryos. We found that 5 mg/kg RA reduces the incidence of spinal NTD in a stage-specific manner, without increasing the incidence of cranial NTD. The effect of RA is specific: There were no other alterations in morphogenesis, growth, development, resorption rate, or litter size. RA was more effective in the prevention of isolated tail flexion defects than of spina bifida. Prevention of isolated tail flexion defects was maximal (50% reduction) when RA was administered between 10 days 4 hours and 10 days 8 hours post coitum (p.c.) inclusive (24 to 34 somite stage).(ABSTRACT TRUNCATED AT 250 WORDS)

Chen WH ，Morriss-Kay GM ，Copp AJ 《DEVELOPMENTAL DYNAMICS》

Relationship between timing of posterior neuropore closure and development of spinal neural tube defects in mutant (curly tail) and normal mouse embryos in culture.

The relationship between timing of closure of the posterior neuropore (PNP) and development of spinal neural tube defects (NTD) has been studied in individual mutant curly tail mouse embryos maintained in culture. Moderate delay in PNP closure results in development of tail flexion defects whereas extreme delay of PNP closure is associated with development of open NTD. Experimental enlargement of the PNP at the stage of 25 to 29 somites leads to delayed PNP closure and development of tail flexion defects in 36% and 38% respectively of non-mutant A/Strong embryos. In curly tail embryos, the effect of experimental enlargement of the PNP summates with the genetic predisposition to produce an increased incidence of spinal NTD among which open defects are proportionately more common. These results indicate that a causal relationship exists between delay in PNP closure and development of spinal NTD in mouse embryos. The method described for distinguishing between prospective normal and abnormal curly tail embryos at a stage prior to the appearance of malformations provides an opportunity to study the morphogenetic processes that precede the development of genetically determined spinal NTD.

Copp AJ 《-》

Effect of mitomycin C on the neural tube defects of the curly-tail mouse.

Around 60% of the mouse mutants called curly-tail, have tail aberrations in the form of a coil or a kink, with or without lumbosacral spina bifida, and rarely, exencephaly. These neural tube defects (NTD) are the result of an incompletely penetrant recessive gene. A single injection of various doses (1-6 mg/kg) of the DNA inhibitor mitomycin C was given to pregnant curly-tail mice on day 7, 8, or 9 of gestation, and its effect on the NTD of the embryos was noted. No dose used was lethal to the embryo. When given on day 7 or day 8, mitomycin C markedly increased the number of exencephalics, and additionally, on day 8, it reduced the number of posterior abnormalities. However, on day 9, no exencephaly was produced, and there was a drastic reduction in the number of tail and spinal defects, the overall incidence of NTD being as low as 15% with 2 mg/kg. A twofold effect of mitomycin C on the curly-tail embryos was thus observed--according to the time in development it was administered, firstly, a teratogenic effect, and later, a "remedial" or preventive effect.

Seller MJ ，Perkins KJ 《-》

Neural tube development in mutant (curly tail) and normal mouse embryos: the timing of posterior neuropore closure in vivo and in vitro.

A dye-injection technique has been used to determine the developmental stage at which posterior neuropore (PNP) closure occurs in normal and mutant curly tail mouse embryos. In vivo, the majority of non-mutant embryos undergo PNP closure between 30 and 34 somites whereas approximately 50% of all mutant embryos show delayed closure, and around 20% maintain an open PNP even at advanced stages of development. A similar result has been found for embryos developing in vitro from the headfold stage. Later in development, 50--60% of mutant embryos in vivo develop tail flexion defects, and 15--20% lumbosacral myeloschisis. This supports the view that delayed PNP closure is the main developmental lesion leading to the appearance of caudal neural tube defects in curly tail mice. The neural tube is closed in the region of tail flexion defects, but it is locally over-expanded and abnormal in position. The significance of these observations is discussed in relation to possible mechanisms of development of lumbosacral and caudal neural tube defects. This paper constitutes the first demonstration of the development of a genetically induced malformation in vitro.

Copp AJ ，Seller MJ ，Polani PE 《-》

Etiology, pathogenesis and prevention of neural tube defects.

Spina bifida, anencephaly, and encephalocele are commonly grouped together and termed neural tube defects (NTD). Failure of closure of the neural tube during development results in anencephaly or spina bifida aperta but encephaloceles are possibly post-closure defects. NTD are associated with a number of other central nervous system (CNS) and non-neural malformations. Racial, geographic and seasonal variations seem to affect their incidence. Etiology of NTD is unknown. Most of the non-syndromic NTD are of multifactorial origin. Recent in vitro and in vivo studies have highlighted the molecular mechanisms of neurulation in vertebrates but the morphologic development of human neural tube is poorly understood. A multisite closure theory, extrapolated directly from mouse experiments highlighted the clinical relevance of closure mechanisms to human NTD. Animal models, such as circle tail, curly tail, loop tail, shrm and numerous knockouts provide some insight into the mechanisms of NTD. Also available in the literature are a plethora of chemically induced preclosure and a few post-closure models of NTD, which highlight the fact that CNS malformations are of hetergeneitic nature. No Mendelian pattern of inheritance has been reported. Association with single gene defects, enhanced recurrence risk among siblings, and a higher frequency in twins than in singletons indicate the presence of a strong genetic contribution to the etiology of NTD. Non-availability of families with a significant number of NTD cases makes research into genetic causation of NTD difficult. Case reports and epidemiologic studies have implicated a number of chemicals, widely differing therapeutic drugs, environmental contaminants, pollutants, infectious agents, and solvents. Maternal hyperthermia, use of valproate by epileptic women during pregnancy, deficiency and excess of certain nutrients and chronic maternal diseases (e.g. diabetes mellitus) are reported to cause a manifold increase in the incidence of NTD. A host of suspected teratogens are also available in the literature. The UK and Hungarian studies showed that periconceptional supplementation of women with folate (FA) reduces significantly both the first occurrence and recurrence of NTD in the offspring. This led to mandatory periconceptional FA supplementation in a number of countries. Encouraged by the results of clinical studies, numerous laboratory investigations focused on the genes involved in the FA, vitamin B12 and homocysteine metabolism during neural tube development. As of today no clinical or experimental study has provided unequivocal evidence for a definitive role for any of these genes in the causation of NTD suggesting that a multitude of genes, growth factors and receptors interact in controlling neural tube development by yet unknown mechanisms. Future studies must address issues of gene-gene, gene-nutrient and gene-environment interactions in the pathogenesis of NTD.

Padmanabhan R 《CONGENITAL ANOMALIES》