No abstract

Risk of neural tube defects (NTDs) is determined by genetic and environmental factors, among which folate status appears to play a key role. However, the precise nature of the link between low folate status and NTDs is poorly understood, and it remains unclear how folic acid prevents NTDs. We investigated the effect of folate level on risk of NTDs in splotch (Sp(2)(H)) mice, which carry a mutation in Pax3. Dietary folate restriction results in reduced maternal blood folate, elevated plasma homocysteine and reduced embryonic folate content. Folate deficiency does not cause NTDs in wild-type mice, but causes a significant increase in cranial NTDs among Sp(2)(H) embryos, demonstrating a gene-environment interaction. Control treatments, in which intermediate levels of folate are supplied, suggest that NTD risk is related to embryonic folate concentration, not maternal blood folate concentration. Notably, the effect of folate deficiency appears more deleterious in female embryos than males, since defects are not prevented by exogenous folic acid. Folate-deficient embryos exhibit developmental delay and growth retardation. However, folate content normalized to protein content is appropriate for developmental stage, suggesting that folate availability places a tight limit on growth and development. Folate-deficient embryos also exhibit a reduced ratio of s-adenosylmethionine (SAM) to s-adenosylhomocysteine (SAH). This could indicate inhibition of the methylation cycle, but we did not detect any diminution in global DNA methylation, in contrast to embryos in which the methylation cycle was specifically inhibited. Hence, folate deficiency increases the risk of NTDs in genetically predisposed splotch embryos, probably via embryonic growth retardation.

Neural tube defects (NTDs) are the second most common congenital malformations in humans affecting the development of the central nervous system. Although NTD pathogenesis has not yet been fully elucidated, many risk factors, both genetic and environmental, have been extensively reported. Classically divided in two main sub‐groups (open and closed defects) NTDs present extremely variable prognosis mainly depending on the site of the lesion. Herein, we review the literature on the histological and pathological features, epidemiology, prenatal diagnosis, and prognosis, based on the type of defect, with the aim of providing important information based on NTDs classification for clinicians and scientists.

BACKGROUND: the inhibition of histone deacetylase (HDAC) has been reported as an effective mechanism on therapy in neoplastic diseases. Among HDAC inhibitors, Trichostatin A (TSA) and Valproic Acid (VPA) prevent the tumorigenesis in rodent and human models. Malformations as neural tube and axial skeletal defects are well-known VPA side effects. Recent hypotheses suggest the HDAC inhibitor activity as the teratogenic mechanism of VPA. The teratogenic potency of TSA is, at the moment, unknown. The aim of the present work is to investigate the HDAC inhibition on embryos exposed in utero to TSA or VPA and to compare the teratogenic potential of these two molecules on the axial skeleton morphogenesis. METHODS: Pregnant CD mice were i.p. treated on day 8 post coitum (9.00 a.m.) with 400 mg/kg VPA or with 0, 2, 4, 8, 16 mg/kg TSA. Embryos explanted 1 hr after the treatment from some females exposed to 400 mg/kg VPA or to 16 mg/kg TSA were processed for Western blotting and immunohistochemical analysis, in order to evaluate the histone hyperacetylation in the total embryo homogenates and to visualize the hyperacetylated tissues. Foetuses at term were processed for skeletal examination. RESULTS: Both VPA and TSA were able to induce hyperacetylation on embryos, specifically at the level of the caudal neural tube and of somites. At term, TSA showed teratogenic effects at the axial skeleton, quite similar to those observed after VPA exposure. CONCLUSIONS: In conclusion, both VPA and TSA are teratogenic in mice. A direct correlation between somite hyperacetylation and axial abnormalities could suggest the HDAC inhibition as the mechanism of the teratogenic effects. Birth Defects Res B 74:392-398, 2005. r 2005 Wiley-Liss Inc.

Foregut division—the separation of dorsal (oesophageal) from ventral (tracheal) foregut components—is a crucial event in gastro-respiratory development, and frequently disturbed in clinical birth defects. Here, we examined three outstanding questions of foregut morphogenesis. The origin of the trachea is suggested to result either from respiratory outgrowth or progressive septation of the foregut tube. We found normal foregut lengthening despite failure of tracheo-oesophageal separation in Adriamycin-treated embryos, whereas active septation was observed only in normal foregut morphogenesis, indicating a primary role for septation. Dorso-ventral patterning of Nkx2.1 (ventral) and Sox2 (dorsal) expression is proposed to be critical for tracheo-oesophageal separation. However, normal dorso-ventral patterning of Nkx2.1 and Sox2 expression occurred in Adriamycin-treated embryos with defective foregut separation. In contrast, Shh expression shifts dynamically, ventral-to-dorsal, solely during normal morphogenesis, particularly implicating Shh in foregut morphogenesis. Dying cells localise to the fusing foregut epithelial ridges, with disturbance of this apoptotic pattern in Adriamycin, Shh and Nkx2.1 models. Strikingly, however, genetic suppression of apoptosis in the Apaf1 mutant did not prevent foregut separation, indicating that apoptosis is not required for tracheo-oesophageal morphogenesis. Epithelial remodelling during septation may cause loss of cell-cell or cell-matrix interactions, resulting in apoptosis (anoikis) as a secondary consequence.