Neural Tube Closure Defects Research Articles

Myocardial 15-Epi-lipoxin A 4 Generation Provides a New Mechanism for the Immunomodulatory Effects of Statins and Thiazolidinediones

“In matters of observation, chance favors only the prepared mind.” This famous maxim of Louis Pasteur, spoken in 1854 during his inaugural lecture as Professor and Dean at the University of Lille, can be applied today to the fortuitous observation that hydroxymethylglutaryl–coenzyme A (HMG-CoA) reductase inhibitors, in addition to their designed lipid-lowering effects, display a fascinating array of antiinflammatory properties. Post hoc analyses of the West of Scotland Coronary Prevention Study (WOSCOPS) population, and more recently the Cholesterol and Recurrent Events (CARE), Myocardial Ischemia Reduction With Aggressive Cholesterol Lowering (MIRACL), Long-term Intervention With Pravastatin in Ischemic Disease (LIPID), and Heart Protection Study (HPS) trials, have all found benefits conferred by statins that are independent of low-density lipoprotein cholesterol–lowering alone.1 Only through careful analyses of early clinical trials of statins administered for lowering cholesterol and cardiovascular events did scientists uncover additional benefit for these agents in cardiac protection beyond their ability to reduce cholesterol synthesis. Inflammation and immune responses are now appreciated to play pivotal roles in the pathobiology of atherosclerosis,2 and recent clinical and basic investigations have uncovered important immunomodulatory roles for statins.3 Of interest, the peroxisome proliferator-activated receptor family of transcription factors is activated by and cooperates with statins in their antiinflammatory actions. In this issue of Circulation , Birnbaum and colleagues4 present evidence for increased myocardial production of 15-epi-lipoxin (LX)A4 by atorvastatin and the peroxisome proliferator-activated receptor-γ ligand pioglitazone. The generation of 15-epi-LXA4 would provide a novel mechanism for immune regulation by statins because this arachidonic acid–derived chalone displays potent antiinflammatory and proresolving properties,5 including many that have also been observed with statins (Table). View this table: Shared Antiinflammatory Actions of Statins and 15-Epi-lipoxin A4 Article p 929 Cell activation initiates the rapid generation of eicosanoids …

Iniencefalia

Iniencephaly is a rare malformation of the base of the skull and prognosis is almost invariably lethal. This entity belongs to the group of neural tube closure defects. To date, 2000 reports have been published in the literature. Diagnosis can now be made using ultrasound morphology examination, allowing pregnancy termination to be proposed. We report 3 cases of iniencephaly diagnosed between 1990 and 2000 and review the literature on this malformation.We describe the case of a patient in whom early ultrasonographic diagnosis of iniencephaly at 13 weeks of gestation allowed induced abortion at 14 weeks.

The use of the Dhcr7 knockout mouse to accurately determine the origin of fetal sterols

Mice with a targeted mutation of 3beta-hydroxysterol Delta(7)-reductase (Dhcr7) that cannot convert 7-dehydrocholesterol to cholesterol were used to identify the origin of fetal sterols. Because their heterozygous mothers synthesize cholesterol normally, virtually all sterols found in a Dhcr7 knockout fetus having a Delta(7) or a Delta(8) double bond must have been synthesized by the fetus itself but any cholesterol had to have come from the mother. Early in gestation, most fetal sterols were of maternal origin, but at approximately E13-14, in situ synthesis became increasingly important, and by birth, 55-60% of liver and lung sterols had been made by the fetus. In contrast, at E10-11, upon formation of the blood-brain barrier, the brain rapidly became the source of almost all of its own sterols (90% at birth). New, rapid, de novo sterol synthesis in brain was confirmed by the observation that concentrations of C24,25-unsaturated sterols were low in the brains of all very young fetuses but increased rapidly beginning at approximately E11-12. Reduced activity of sterol C24,25-reductase (Dhcr24) in brain, suggested by the abundance of C24,25-unsaturated compounds, seems to be the result of suppressed Dhcr24 expression. The early fetal brain also appears to conserve cholesterol by keeping cholesterol 24-hydroxylase expression low until approximately E18.

P38 and a p38-Interacting Protein Are Critical for Downregulation of E-Cadherin during Mouse Gastrulation

During vertebrate gastrulation, an epithelial to mesenchymal transition (EMT) is necessary for migration of mesoderm from the primitive streak. We demonstrate that p38 MAP kinase and a p38-interacting protein (p38IP) are critically required for downregulation of E-cadherin during gastrulation. In an ENU-mutagenesis screen we identified the droopy eye (drey) mutation, which affects splicing of p38IP. p38IP(drey) mutant embryos display incompletely penetrant defects in neural tube closure, eye development, and gastrulation. A stronger allele (p38IP(RRK)) exhibits gastrulation defects in which mesoderm migration is defective due to deficiency in E-cadherin protein downregulation in the primitive streak. We show that p38IP binds directly to p38 and is required for p38 activation in vivo. Moreover, both p38 and p38IP are required for E-cadherin downregulation during gastrulation. Finally, p38 regulates E-cadherin protein expression downstream from NCK-interacting kinase (NIK) and independently of the regulation of transcription by Fibroblast Growth Factor (Fgf) signaling and Snail.

GCN5 Functions in Telomere Maintenance and Neural Development

We reported previously GCN5 deletion in the mouse leads to embryonic lethality due to increased apoptosis. New data show that this apoptosis is p53 dependent and may be triggered by telomere defects. Telomeres are shortened in cells from GCN5 mutant embryos, and these cells display increased numbers of chromosomal end associations and fusions. In the absence of both p53 and GCN5, an even greater incidence of telomere fusion is observed. These double mutant embryos also display defects in neural tube closure and brain development. Very similar defects in neural development are observed in mice homozygous for GCN5 HAT catalytic site mutations and in mice that carry a hypomorphic allele of GCN5. These data provide the first evidence that GCN5 may be required both for telomere maintenance and proper expression of genes required for neural development in the mouse.

Context-specific requirements for Fgfr1 signaling through Frs2 and Frs3 during mouse development

Fibroblast growth factor receptor 1 (Fgfr1) plays pleiotropic roles during embryonic development, but the mechanisms by which this receptor signals in vivo have not previously been elucidated. Biochemical studies have implicated Fgf receptor-specific substrates (Frs2, Frs3) as the principal mediators of Fgfr1 signal transduction to the MAPK and PI3K pathways. To determine the developmental requirements for Fgfr1-Frs signaling, we generated mice (Fgfr1(Delta)Frs/DeltaFrs) in which the Frs2/3-binding site on Fgfr1 is deleted. Fgfr1(Delta)Frs/DeltaFrs embryos die during late embryogenesis, and exhibit defects in neural tube closure and in the development of the tail bud and pharyngeal arches. However, the mutant receptor is able to drive Fgfr1 functions during gastrulation and somitogenesis, and drives normal MAPK responses to Fgf. These findings indicate that Fgfr1 uses distinct signal transduction mechanisms in different developmental contexts, and that some essential functions of this receptor are mediated by Frs-independent signaling.

Planar cell polarity signalling couples cell division and morphogenesis during neurulation

Environmental and genetic aberrations lead to neural tube closure defects (NTDs) in 1 out of every 1,000 births. Mouse and frog models for these birth defects have indicated that Van Gogh-like 2 (Vangl2, also known as Strabismus) and other components of planar cell polarity (PCP) signalling might control neurulation by promoting the convergence of neural progenitors to the midline. Here we show a novel role for PCP signalling during neurulation in zebrafish. We demonstrate that non-canonical Wnt/PCP signalling polarizes neural progenitors along the anteroposterior axis. This polarity is transiently lost during cell division in the neural keel but is re-established as daughter cells reintegrate into the neuroepithelium. Loss of zebrafish Vangl2 (in trilobite mutants) abolishes the polarization of neural keel cells, disrupts re-intercalation of daughter cells into the neuroepithelium, and results in ectopic neural progenitor accumulations and NTDs. Remarkably, blocking cell division leads to rescue of trilobite neural tube morphogenesis despite persistent defects in convergence and extension. These results reveal a function for PCP signalling in coupling cell division and morphogenesis at neurulation and indicate a previously unrecognized mechanism that might underlie NTDs.

Pattern of congenital brain malformations at a referral hospital in Saudi Arabia: an MRI study.

BACKGROUNDMore than 2000 different congenital cerebral malformations have been described in the literature, for which several classification systems have been proposed. With the help of these classification systems, it is now possible, with neuroimaging, to time neuroembryologic events. Magnetic resonance imaging (MRI), in particular, is useful in studying these malformations. This study evaluated the pattern of congenital brain malformations in a university referral hospital setting.PATIENTS AND METHODSThe records of all MRI brain examinations at our hospital over a period of 3 years for children younger than 15 years of age were reviewed. Cases of congenital cerebral malformations were analyzed by sex, age at presentation, type of congenital cerebral malformation, and other associated congenital cerebral malformations.RESULTSOf the 808 MR examinations of different parts of the body for children in the study period, 719 (89%), on 581 patients, were of the brain. Eighty-six children (14.8%) were found to have single or multiple congenital brain malformations. In these children, 114 congenital brain malformations were identified, the commonest being cortical migrational defects (25 patients, 22%), neural tube closure defects (22 patients, 19%), and corpus callosum dysgenesis (22 patients,19%). The least common was vascular malformation. Sixteen patients (18.6%) had more than one congenital brain malformation.CONCLUSIONNeural tube closer defects, cortical migrational abnormalities, and corpus callosum anomalies were the commonest congenital brain malformations, while vascular malformations were the least common. Most of the identified malformations demonstrated the usual pattern, but a few showed unusual patterns and associations.

Reduction in diabetes‐induced craniofacial defects by maternal immune stimulation

Maternal diabetes can induce a number of developmental abnormalities in laboratory animals and humans, including facial deformities and defects in neural tube closure. The incidence of birth defects in newborns of diabetic women is approximately 3-5 times higher than among non-diabetics. In mice, non-specific activation of the maternal immune system can reduce fetal abnormalities caused by diverse etiologies, including diabetes induced neural tube defects. This study was conducted to determine whether non-specific maternal immune stimulation could reduce diabetes-induced craniofacial defects as well. Maternal immune function was stimulated before streptozocin (STZ) treatment by maternal footpad injection with Freund's complete adjuvant (FCA), maternal intraperitoneal (i.p.) injection with granulocyte-macrophage colony-stimulating factor (GM-CSF), or maternal i.p. injection with interferon-gamma (IFNgamma). Streptozocin (200 mg/kg i.p.) was used to induce hyperglycemia (26-35 mmol blood glucose) in female ICR mice before breeding. Fetuses from 12-18 litters per treatment group, were collected at Day 17 of gestation. Craniofacial defects were observed in fetuses from all hyperglycemic groups. The incidence of defects was significantly decreased in fetuses from dams immune stimulated with IFNgamma or GM-CSF. The most common defects were reduced maxillary and mandibular lengths. Both were prevented by maternal stimulation with GM-CSF. Maternal immune stimulation reduced the incidence of diabetic craniofacial embryopathy. The mechanisms for these protective effects are unknown but may involve maternal or fetal production of cytokines or growth factors that protect the fetus from the dysregulatory effects of hyperglycemia.

Effects of dimethylsulphoxide on mice arsenite-induced dysmorphogenesis in embryo culture and cytotoxicity in embryo cells

Dimethylsulphoxide (DMSO) is a widely used vehicle for water insoluble compounds in experimental studies. Nevertheless, little is known about its potential impact on dysmorphogenesis caused by reactive oxygen species (ROS). In order to evaluate if DMSO at concentrations used as vehicle can alter in vitro sodium arsenite (Asi) teratogenicity and cytotoxicity, mouse embryos with 4–5 somites were grown for 48 h in Asi 0.4 and 4 μM, with and without 0.1% DMSO (v/v). Also embryonic mesenchymal cell were cultured, using mesenchymal mouse embryo cells obtained from gestation day 11 and treated with DMSO 0.1%, 0.2% and 0.5% (v/v) 15 min before Asi was added at final concentrations of 0.4 and 4 μM. Cytotoxicity and intracellular ROS production, were evaluated with MTT and 5-(and-6)-chloromethyl-2′,7′-dichlorodihydrofluorescein diacetate, acetyl ester (CM-H 2DCFDA), respectively. Results indicated that Asi produced growth retardation and abnormal development. Main malformations involved neural tube closure defects, abnormal rotation and optic vesicle defects among others. Co-treatment with DMSO partially reduced neural tube defects as well as facial dysmophology. Asi reduced cell viability inversely to the level of ROS production, and DMSO returned cellular viability to control values by reducing ROS intracellular production. In summary, the protective effect observed for DMSO appeared to reflect free radical scavenger properties, though other mechanisms independent to ROS production may have also been involved.

Ablation of MEKK4 Kinase Activity Causes Neurulation and Skeletal Patterning Defects in the Mouse Embryo

Skeletal disorders and neural tube closure defects represent clinically significant human malformations. The signaling networks regulating normal skeletal patterning and neurulation are largely unknown. Targeted mutation of the active site lysine of MEK kinase 4 (MEKK4) produces a kinase-inactive MEKK4 protein (MEKK4(K1361R)). Embryos homozygous for this mutation die at birth as a result of skeletal malformations and neural tube defects. Hindbrains of exencephalic MEKK4(K1361R) embryos show a striking increase in neuroepithelial cell apoptosis and a dramatic loss of phosphorylation of MKK3 and -6, mitogen-activated protein kinase kinases (MKKs) regulated by MEKK4 in the p38 pathway. Phosphorylation of MAPK-activated protein kinase 2, a p38 substrate, is also inhibited, demonstrating a loss of p38 activity in MEKK4(K1361R) embryos. In contrast, the MEK1/2-extracellular signal-regulated kinase 1 (ERK1)/ERK2 and MKK4-Jun N-terminal protein kinase pathways were unaffected. The p38 pathway has been shown to regulate the phosphorylation and expression of the small heat shock protein HSP27. Compared to the wild type, MEKK4(K1361R) fibroblasts showed significantly reduced phosphorylation of p38 and HSP27, with a corresponding heat shock-induced instability of the actin cytoskeleton. Together, these data demonstrate MEKK4 regulation of p38 and that substrates downstream of p38 control cellular homeostasis. The findings are the first demonstration that MEKK4-regulated p38 activity is critical for neurulation.

Morphogenetic movements during cranial neural tube closure in the chick embryo and the effect of homocysteine

In order to unravel morphogenetic mechanisms involved in neural tube closure, critical cell movements that are fundamental to remodelling of the cranial neural tube in the chick embryo were studied in vitro by quantitative time-lapse video microscopy. Two main directions of movements were observed. The earliest was directed medially; these cells invaginated into a median groove and were the main contributors to the initial neural tube closure. Once the median groove was completed, cells changed direction and moved anteriorly to contribute to the anterior neural plate and head fold. This plate developed into the anterior neuropore, which started to close from the 4-somite stage onwards by convergence of its neural folds. Posteriorly, from the initial closure site onwards, the posterior neuropore started to close almost instantaneously by convergence of its neural folds. Homocysteine is adversely involved in human neural tube closure defects. After application of a single dose of homocysteine to chick embryos, a closure delay at the initial closure site and at the neuropores, flattening of the head fold and neural tube, and a halt of cell movements was seen. A possible interference of Hcy with actin microfilaments is discussed.

Identification and characterization of Xenopus laevis homologs of mammalian TRAF6 and its binding protein TIFA

Tumor necrosis factor receptor (TNFR)-associated factor 6 (TRAF6) transduces signals from members of the TNFR superfamily and the Toll/IL-1R family, leading to activation of transcription factors such as NFκB and AP-1. Genetic disruption of the TRAF6 gene in mice results in various developmental abnormalities during embryogenesis, including osteopetrosis, failure of neural tube closure, defective formation of skin appendices, absence of lymph nodes, and absence of mature thymic epithelial cells. To clarify the effect of TRAF6 in development, we previously identified a TRAF-interacting protein with a forkhead-associated domain (TIFA), which binds and activates TRAF6 upon extracellular stimulation. To understand the physiological roles of TRAF6 and TIFA in early development, we studied these genes in Xenopus laevis. Here, we describe identification of X. laevis homologs of mammalian TRAF6 (XTRAF6) and TIFA (XTIFA). As was the case for the mammalian homologs, overexpression of XTRAF6 or XTIFA activated NFκB, whereas XTIFA carrying a mutation that abolishes XTRAF6 binding failed to activate NFκB, suggesting that XTIFA activates NFκB by binding to XTRAF6. XTIFA and XTRAF6 mRNAs were expressed at similar levels in zygotes from the neurula stage and then increased. Whole-mount in situ hybridization revealed that XTRAF6 mRNA was expressed in the head region and neural tube during the neurula stage, and the expression expanded to the pharyngeal apparatus during the tailbud stage. This localization is consistent with the defective neural tube closure and abnormal thymus organogenesis observed in TRAF6-deficient mice. Our results suggest possible cooperation between XTRAF6 and XTIFA during embryogenesis.

Disruption of palladin results in neural tube closure defects in mice

Palladin is a newly identified actin-associated protein which was proposed to be involved in actin cytoskeleton organization and nervous system development. Here, we show that inactivation of palladin leads to embryonic lethality due to severe defects of cranial neural tube closure and herniation of liver and intestine. It was found that palladin −/− embryos died around E15.5 and developed cranial neural tube closure defects (NTDs) with 100% penetrance. Whole mount in situ hybridization revealed that expression of palladin in early wild type embryos (E8.5) was specifically restricted in the elevating cranial neural folds where the neural tube closure is initiated. Palladin expression closely mirrors the phenotypic defects observed in palladin −/− mutants. While in E9.5 and E10.5 embryos palladin was ubiquitously expressed. In vitro study revealed that formation of stress fibers in cytoplasm, cell adherent ability to extra-cellular matrix protein fibronectin and cell migration were dramatically disturbed in palladin −/− murine embryonic fibroblast cells (MEFs). Our findings suggest that palladin plays important roles in actin stress fiber formation, cell adhesion and migration. We propose that palladin is required for the initiation of neural tube closure and provides an important new candidate that may be implicated in the etiology of human NTDs.

Neural tube closure and neural tube defects: Studies in animal models reveal known knowns and known unknowns

The vertebrate central nervous system is a hollow structure that develops first as a flat sheet of cells and subsequently rolls into a tube during embryogenesis. Failure of this rolling process, called neural tube closure, results in a class of common human birth defects called neural tube defects. The cellular and molecular mechanisms governing neural tube closure have been studied extensively in animal models, but much remains to be elucidated. In this review, I will highlight recent progress in understanding neural tube closure mechanisms and how these studies can inform our search for the genes that underlie human neural tube defects. Supplementary material for this article can be found on the American Journal of Medical Genetics (Part C) website (http://www.mrw.interscience.wiley.com/suppmat/1552-4868/suppmat/2005/135/v135.1.wallingford.html)

New semidominant mutations that affect mouse development

Dominantly acting mutations that produce visible phenotypes are frequently recovered, either during routine maintenance of colonies or from mutagenesis experiments. We have studied 12 dominant mouse mutations that cause a tail dysmorphology, a coat spotting phenotype, or a combination of these. The majority of these mutations act in a semidominant manner with the homozygous state associated with embryonic lethality and a visible phenotype at or before midgestation. The homozygous phenotypes include axis truncation and neural crest cell defects, as may be expected from the heterozygous phenotypes. The majority of mutations, however, also produced other phenotypes that include neural tube closure defects and aberrant heart looping. In one coat spotting mutant the homozygous condition is lethal before neural crest cell production commences. The mutated genes often function in processes additional to those alluded to by the heterozygous phenotype.

Consequences of elevated homocysteine during embryonic development and possible modes of action.

Elevated maternal homocysteine (Hcys) is a well-established risk factor for embryonic toxicity and the development of congenital defects, particularly neural tube closure defects and neurocristopathies. The mechanisms responsible are unclear but early work has focused on the role of folate metabolism because these defects are greatly reduced by folate supplementation. As a consequence, elevated Hcys is often looked upon as being an indirect consequence of faulty folate metabolism, although more recent studies show Hcys may act directly as a teratogen. Because Hcys is at the crossroads of protein and DNA metabolism, has a propensity to chemically modify proteins directly, can generate free radicals, and even perturb ligand binding to certain receptors, the developmental processes Hcys can potentially disturb are enumerable. But in recent years, investigators have begun identifying cellular and molecular targets for the direct action of Hcys. While elevating Hcys can alter a myriad of basic cellular activities needed for normal development, our current understanding as to the specific etiological mechanisms responsible for congenital defects is very speculative. Here we provide an overview of what is currently known regarding the toxicity and teratogenicity of elevated Hcys during embryonic development, paying particular attention to neural tube and neural crest cell morphogenesis.

Desmopressin successfully curbed nocturnal bedwetting in paediatric patients with neural tube closure defects (NTDs),

Desmopressin successfully curbed nocturnal bedwetting in paediatric patients with neural tube closure defects (NTDs),

Neural tissue continues its maturation at the site of neural tube closure defects: implications for prenatal intervention in human samples.

Our objective was to investigate the relation between the embryological development and neural tissue maturation at the site where the neural plate failed to form a neural tube. Samples from 15 aborted human fetuses with neural tube defects (NTD). All of the fetuses were between 20 and 25 gestational weeks old. Indicators of neural tissue maturation, formation of basal lamina, expression of integrins and neuron specific class III beta tubulin (tuj1) were investigated. To detect the adverse effects of the environment, if any, p53 and bcl-2 activity at both sites of the open and closed neural plate were investigated as well. No difference was found in the expression of maturation-related molecules at the site of the neural plate that remained open compared with the site where the neural tube is normally formed. While high p53 activity was noted in neural tissue at the site of the neural tube defect, no such activity was detected in the neural tissue where the neural tube is normally formed. Our results suggested that maturation and differentiation of neural tissue continued regardless of the failure of neural tube closure. Therefore, the neurological deficits that are encountered in NTD patients should be related to secondary damage such as amnion fluid toxicity, uterus contractions, labor, etc. It seems valuable to save the neural plate before the negative effects of the environment renders the neural tissue functionless.

DESMOPRESSIN FOR THE TREATMENT OF NOCTURNAL BEDWETTING IN PATIENTS WITH NEURAL TUBE CLOSURE DEFECTS

We evaluated desmopressin (DDAVP) treatment in patients with neuropathic bladder secondary to neural tube closure defects (NTDs) and nocturnal incontinence. We selected 25 patients, that is 10 males (40%) and 15 females (60%), between ages 7 and 16 years (mean 9.8) with neuropathic bladder secondary to NTDs without a ventricular-peritoneal shunt. All had a low pressure bladder and presented with daytime continence between catheterizations but had persistent nocturnal urine loss 7 nights weekly. They underwent treatment with oral DDAVP according to a certain design, namely an initial dose of 0.2 mg for 3 weeks, which was increased to 0.3 or 0.4 mg for another 3 weeks in nonresponders. The average dose was 0.2 mg. At the effective minimal dose (bedwetting decrease greater than 50%) patients continued for 6 months and then decreased by intervals of 0.05 mg every 2 weeks. In the event of recurrence treatment continued for 1 year. All patients responded to treatment during the nighttime hours except 1 who suspended treatment after 4 weeks. There were no adverse effects from DDAVP. Treating nocturnal bedwetting with DDAVP in patients with NTDs was effective and safe. Nevertheless, to our knowledge treatment duration has not yet been determined.