Finally, a sense of closure? Animal models of human ventral body wall defects

Altered PITX2 and LEF1 gene expression in the cadmium-induced omphalocele in the chick model

PURPOSE

Although, recent studies have suggested that disruption of somitogenesis may be involved in ventral body wall (VBW) defects; the molecular mechanisms of VBW defects remain unclear. In the chick embryo, the administration of cadmium (Cd) induces VBW defects similar to the human omphalocele. In this model, the earliest histological change in the somite occurs commencing at 4 h post-Cd treatment (4 h). PITX2 is expressed in somites, and PITX2 mutants have been shown to display VBW defects. PITX2 interacts with lymphoid enhancer factor-1 (LEF1) to regulate somite myogenesis. We designed this study to investigate the hypothesis that PITX2 and LEF1 genes are downregulated during the critical period of early embryogenesis in the Cd-induced omphalocele chick model.

MATERIALS AND METHODS

Chick embryos were exposed to Cd or saline after 60 h incubation and harvested at 1, 4, and 8 h posttreatment. Chicks were then divided into two groups: control (n = 24), and Cd (n = 24). RT-PCR was performed and analyzed statistically (significant difference was accepted at p < 0.05). Immunohistochemistry was also performed to evaluate expression/distribution of those proteins.

RESULTS

The mRNA expression levels of PITX2 and LEF1 at 4 h were significantly decreased in the Cd group compared with controls, whereas there were no differences at the other time points. Immunoreactivity of those proteins at 4 h was also markedly decreased in somites in the Cd-treated embryos compared with controls.

CONCLUSIONS

Downregulation of PITX2 and LEF1 genes may interfere with ventral body wall formation in Cd chick model causing omphalocele by disrupting somite myogenesis.

Epigenetic effect of cadmium on global de novo DNA hypomethylation in the cadmium-induced ventral body wall defect (VBWD) in the chick model

Administration of the heavy metal cadmium (Cd) induces ventral body wall defects (VBWD) in the chick embryo. In this model, the expression of most genes involved in body wall formation is altered 4h-posttreatment. However, the mechanism by which Cd results in the initiation of altered gene expression remains unclear. Epigenetic mechanisms can change genome function under exogenous influences. Moreover, Cd is one of the environmental factors that can affect epigenomic programming. De novo DNA methylation is essential for normal embryogenesis and is regulated by the DNA methyltransferases (DNMT)3A and DNMT3B. The objective of this study was to investigate the hypothesis that gene expression levels of DNMT3A/3B were altered, resulting in global DNA methylation changes during the critical period of embryogenesis in the Cd chick model. After 60-h incubation, chick embryos (n = 48) were harvested at 1, 4, and 8 h after treatment with saline or Cd, and divided into controls and Cd groups. Quantitative reverse transcription PCR was performed to evaluate the gene expression levels of DNMT3A/3B in the chick embryos and was statistically analyzed using Student's t-test. Immunohistochemistry was performed using a monoclonal antibody against 5-methylcytidine (5'MeC), which labels methyl-rich regions within the nucleus. DNMT3A/3B gene expression levels at 4 h were significantly downregulated in the Cd group compared with controls (p < 0.005/p < 0.00001, respectively). Immunoreactivity of 5'MeC was markedly diminished in the Cd group at 4 h. Our findings demonstrates for the first time that Cd impacts on the expression levels of DNMT3A/3B, which may underlie the pathogenesis of VBWD in the Cd chick model.

Disruption of GLI3-ZIC3 interaction in the cadmium-induced omphalocele chick model

PURPOSE

Administration of heavy metal cadmium (Cd) after 60-h incubation induces omphalocele spectrum in the chick embryo. Although previous studies have shown that the earliest detectable histological changes in the chick Cd model occurs commencing at 4-h post-treatment (4H). However, the molecular mechanism by which Cd acts in the critical period of early embryogenesis still remains unclear. Zic3, a Gli superfamily transcription factor, is expressed in somites and plays an important role in vertebrate development, including somitogenesis and thus ventral body wall formation. Gli3 is also expressed in somites and interacts with Zic3 physically and functionally. It has been reported that Gli3 homozygous double mutants display omphalocele. Zic3 mutant mice have also been known to result in omphalocele phenotype. We designed this study to test the hypothesis that Gli3 and Zic3 gene expression is downregulated during the critical period of very early embryogenesis in the Cd-induced omphalocele in the chick model.

METHODS

After 60-h incubation, chick embryos were exposed to either saline or 50 μM cadmium and divided into two groups: control and Cd (n = 24 for each group). Real-time reverse transcription polymerase chain reaction was performed to evaluate the relative mRNA expression levels of Gli3 and Zic3 in the Cd-induced omphalocele chick model. Differences between the two groups at each time point were analyzed statistically and the significance was accepted at p < 0.05. Immunohistochemistry was also performed to evaluate the expression/distribution of those proteins in chick embryo.

RESULTS

The relative mRNA expression level of Gli3 and Zic3 was significantly decreased in the Cd group at 4H when compared with controls (p < 0.05). However, there were no significant differences at the other time points. At 4H, immunoreactivity of GLI3 and ZIC3 was also markedly decreased in Cd-treated embryos, whereas strong expression of them was seen in the somite in controls.

CONCLUSION

We provide evidence, for the first time, that Gli3 and Zic3 gene expression is downregulated during the narrow window of very early embryogenesis in Cd chick model. Disruption of Gli3-Zic3 interaction in the critical period for ventral body wall formation may contribute to omphalocele phenotype in Cd chick model.

Genetic analysis of Hedgehog signaling in ventral body wall development and the onset of omphalocele formation

Background

An omphalocele is one of the major ventral body wall malformations and is characterized by abnormally herniated viscera from the body trunk. It has been frequently found to be associated with other structural malformations, such as genitourinary malformations and digit abnormalities. In spite of its clinical importance, the etiology of omphalocele formation is still controversial. Hedgehog (Hh) signaling is one of the essential growth factor signaling pathways involved in the formation of the limbs and urogenital system. However, the relationship between Hh signaling and ventral body wall formation remains unclear.

Methodology/Principal Findings

To gain insight into the roles of Hh signaling in ventral body wall formation and its malformation, we analyzed phenotypes of mouse mutants of Sonic hedgehog (Shh), GLI-Kruppel family member 3 (Gli3) and Aristaless-like homeobox 4 (Alx4). Introduction of additional Alx4^Lst mutations into the Gli3^Xt/Xt background resulted in various degrees of severe omphalocele and pubic diastasis. In addition, loss of a single Shh allele restored the omphalocele and pubic symphysis of Gli3^Xt/+; Alx4^Lst/Lst embryos. We also observed ectopic Hh activity in the ventral body wall region of Gli3^Xt/Xt embryos. Moreover, tamoxifen-inducible gain-of-function experiments to induce ectopic Hh signaling revealed Hh signal dose-dependent formation of omphaloceles.

Conclusions/Significance

We suggest that one of the possible causes of omphalocele and pubic diastasis is ectopically-induced Hh signaling. To our knowledge, this would be the first demonstration of the involvement of Hh signaling in ventral body wall malformation and the genetic rescue of omphalocele phenotypes.

The physiological roles of vesicular GABA transporter during embryonic development: a study using knockout mice

Background

The vesicular GABA transporter (VGAT) loads GABA and glycine from the neuronal cytoplasm into synaptic vesicles. To address functional importance of VGAT during embryonic development, we generated global VGAT knockout mice and analyzed them.

Results

VGAT knockouts at embryonic day (E) 18.5 exhibited substantial increases in overall GABA and glycine, but not glutamate, contents in the forebrain. Electrophysiological recordings from E17.5-18.5 spinal cord motoneurons demonstrated that VGAT knockouts presented no spontaneous inhibitory postsynaptic currents mediated by GABA and glycine. Histological examination of E18.5 knockout fetuses revealed reductions in the trapezius muscle, hepatic congestion and little alveolar spaces in the lung, indicating that the development of skeletal muscle, liver and lung in these mice was severely affected.

Conclusion

VGAT is fundamental for the GABA- and/or glycine-mediated transmission that supports embryonic development. VGAT knockout mice will be useful for further investigating the roles of VGAT in normal physiology and pathophysiologic processes.

Prediction of regulatory networks in mouse abdominal wall

Sequence specific transcription factors are essential for pattern formation and cell differentiation processes in mammals. The formation of the abdominal wall depends on a flawless merge of several developmental fields in time and space. The absence of Pitx2 leads to an open abdominal wall in mice, while mutations in humans result in umbilical defects, suggesting that a single homeobox transcription factor coordinates the formation and patterning of this anatomical structure. Gene expression analysis from abdominal tissue including the abdominal wall after removal of the major organs, of wild type, Pitx2 heterozygote and mutant mice, at embryonic day 10.5, identified 275 genes with altered expression levels. Pitx2 target genes were clustered using the "David Bioinformatics Functional Annotation Tool" web application, which bins genes according to gene ontology (GO) key word enrichment. This provided a way to both narrow the target gene list and to start identifying potential gene families regulated by Pitx2. Target genes in the most enriched bins were further analyzed for the presence and the evolutionary conservation of Pitx2 consensus binding sequence, TAATCY, on the -20 kb, intronic and coding gene sequences. Twenty Pitx2 target genes that passed all the above criteria were classified as genes involved in cell transport and growth. Data from these studies suggest that Pitx2 acts as an inhibitor of protein transport and cell apoptosis contributing to the open body wall phenotype. This work provides the framework to which the developmental network leading to abdominal wall syndromes can be built.

HoxB2, HoxB4 and Alx4 genes are downregulated in the cadmium-induced omphalocele in the chick model

PURPOSE

In the chick embryo, administration of cadmium (Cd) induces omphalocele phenotype. HoxB2 and HoxB4, expressed in cell types that contribute to ventral body wall (VBW) formation, act together to mediate proper closure of the VBW, involving a key downstream transcription factor, Alx4. HoxB2 and HoxB4 knockout mice display VBW defects with specific downregulation of Alx4 gene expression, while homozygous Alx4 knockouts show omphalocele phenotype. Although the earliest histological changes in the Cd chick model occur commencing at 4H post treatment, the exact timing and molecular mechanism by which Cd acts is still unclear. We hypothesized that HoxB2, HoxB4 and Alx4 genes are downregulated during the critical timing of very early embryogenesis in the Cd-induced omphalocele chick model.

METHODS

After 60H incubation, chick embryos were harvested at 1H, 4H and 8H after treatment with saline or Cd and divided into controls and Cd group (n = 24 for each group). RT-PCR was performed to investigate the gene expression of HoxB2, HoxB4 and Alx4 and statistically analyzed (significance was accepted at p < 0.05). Immunohistochemical staining was also performed to evaluate the protein expression/distribution of HoxB2, HoxB4 and Alx4 in the chick embryo.

RESULTS

The expression levels of HoxB2, HoxB4 and Alx4 gene at 4H were significantly downregulated in the Cd group as compared to controls, whereas there were no significant differences at the other time points. Immunoreactivity of HoxB2, HoxB4 and Alx4 at 4H is also markedly decreased in the ectoderm and the dermomyotome in the Cd chick model as compared to controls.

CONCLUSION

Downregulation of HoxB2, HoxB4 and Alx4 expression during the narrow window of early embryogenesis may cause omphalocele in the Cd chick model by interfering with molecular signaling required for proper VBW formation. Furthermore, these results support the concept that HoxB2, HoxB4 and Alx4 genes work together to mediate proper VBW formation.

Msx1 and Msx2 gene expression is downregulated in the cadmium-induced omphalocele in the chick model

PURPOSE

The administration of cadmium (Cd) induces an omphalocele phenotype in the chick embryo. The molecular mechanism by which Cd acts still remains unclear. Msx1 and Msx2 are expressed in the developing body wall and regulate cellular proliferation and differentiation. It has been reported that Msx1/Msx2 double-mutant mice display an omphalocele phenotype. We hypothesized that gene expression levels of Msx1 and Msx2 are downregulated in the Cd chick model during the critical period of embryogenesis.

METHODS

After 60 hours of incubation, chick embryos were exposed to either Cd or saline and harvested at 1 hour (1H), 4H, and 8H after treatment. Chicks were divided into 2 groups: control and Cd (n = 8 for each group at each time-point). Real-time polymerase chain reaction was performed to evaluate the messenger RNA levels of Msx1 and Msx2 in the Cd-induced omphalocele chick model and analyzed statistically. Immunohistochemistry was also performed to examine protein expression of Msx1 and Msx2 at each time-point.

RESULTS

Messenger RNA expression levels of Msx1 and Msx2 at 1H were significantly decreased in the Cd group compared with controls (P < .01), whereas there were no significant differences at the other time-points. Immunoreactivity of Msx1 and Msx2 at 1H was remarkably decreased in Cd group compared with controls.

CONCLUSION

Downregulation of Msx1 and Msx2 gene expression during the narrow window of early embryogenesis may cause an omphalocele by disrupting cellular proliferation and differentiation in the developing body wall.

The role of transforming growth factor-beta 2 and 3 in formation of ventral body wall in the cadmium-induced omphalocele chick model

PURPOSE

In the chick embryo, the administration of cadmium (Cd) induces ventral body wall defects (VBWDs) similar to the human omphalocele. Transforming growth factors beta (TGFs-beta) are involved in many developmental processes, including ventral body wall formation. The Tgfbeta2(-/-) Tgfbeta3(-/-) double knockout mice and Tgfbeta2(-/-) Tgfbeta3(+/-) mutants show VBWD, whereas Tgfbeta2(+/-) Tgfbeta3(-/-) mutants display normal ventral body wall fusion. We designed this study to investigate the messenger RNA (mRNA) levels of TGF-beta2 and TGF-beta3 in the Cd-induced omphalocele chick model during early embryogenesis.

METHODS

Chick embryos were exposed to either Cd or saline, harvested 1 hour (1H), 4H, and 8H after treatment and then divided into 2 groups: control and Cd (n = 8 at each time-point, respectively). Reverse transcription polymerase chain reaction was performed to evaluate the mRNA levels of TGF-beta2 and TGF-beta3 and statistically analyzed.

RESULTS

The mRNA expression levels of TGF-beta2 at 1H were significantly decreased in the Cd group compared to controls (P < .05). However, the levels of TGF-beta3 were not altered at all the time-points studied.

CONCLUSION

We provide evidence, for the first time, that TGF-beta2 gene expression is downregulated during a narrow window of early embryogenesis in the Cd chick model. Our data show that TGF-beta2 is the key gene involved in the formation of ventral body wall.

Pitx2-dependent occupancy by histone deacetylases is associated with T-box gene regulation in mammalian abdominal tissue

The homeodomain transcription factor Pitx2 and the T-box transcription factors are essential for organogenesis. Pitx2 and T-box genes are induced by growth factors and function as transcriptional activators or repressors. Gene expression analyses on abdominal tissue were used to identify seven of the T-box genes of the genome as Pitx2 target genes in the abdomen at embryonic day.10.5. Pitx2 activated Tbx4, Tbx15, and Mga and repressed Tbx1, Tbx2, Tbx5, and Tbx6 expression. As expected, activated genes showed reduced expression patterns, and repressed T-box genes showed increased expression patterns in the abdomen of Pitx2 mutants. Pitx2 occupied chromatin sites near all of these T-box genes. Co-occupancy by coactivators, corepressors, and histone acetylation at these sites was frequently Pitx2-dependent. Genes repressed by Pitx2 generally showed increased histone acetylation and decreased histone deacetylase (HDAC)/corepressor occupancy in Pitx2 mutants. The lower N-CoR, HDAC1, and HDAC3 occupancy observed at multiple sites along Tbx1 chromatin in mutants is consistent with the model that increased histone acetylation and gene expression of Tbx1 may result from a loss of recruitment of corepressors by Pitx2. Genes activated by Pitx2 showed less consistent patterns in chromatin analyses. Reduced H4 acetylation and increased HDAC1/nuclear receptor corepressor (N-CoR) occupancy at some Tbx4 sites were accompanied by increased H3 acetylation and reduced HDAC3 occupancy at the same or other more distal chromatin sites in mutants. Pitx2-dependent occupancy by corepressors resulted in alteration of the acetylation levels of several T-box genes, whereas Pitx2-dependent occupancy by coactivators was more site-localized. These studies will provide the basic scientific underpinning to understand abdominal wall syndromes.

Cleft palate is caused by CNS dysfunction in Gad1 and Viaat knockout mice

Background

Previous studies have shown that disruption of GABA signaling in mice via mutations in the Gad1, Gabrb3 or Viaat genes leads to the development of non-neural developmental defects such as cleft palate. Studies of the Gabrb3 and Gad1 mutant mice have suggested that GABA function could be required either in the central nervous system or in the palate itself for normal palatogenesis.

Methodology/Principal Findings

To further examine the role of GABA signaling in palatogenesis we used three independent experimental approaches to test whether Gad1 or Viaat function is required in the fetal CNS for normal palate development. We used oral explant cultures to demonstrate that the Gad1 and Viaat mutant palates were able to undergo palatogenesis in culture, suggesting that there is no defect in the palate tissue itself in these mice. In a second series of experiments we found that the GABA_A receptor agonist muscimol could rescue the cleft palate phenotype in Gad1 and Viaat mutant embryos. This suggested that normal multimeric GABA_A receptors in the CNS were necessary for normal palatogenesis. In addition, we showed that CNS-specific inactivation of Gad1 was sufficient to disrupt palate development.

Conclusions/Significance

Our results are consistent with a role for Gad1 and Viaat in the central nervous system for normal development of the palate. We suggest that the alterations in GABA signaling lead to non-neural defects such as cleft palate as a secondary effect due to alterations in or elimination of fetal movements.

Teratogens inducing congenital abdominal wall defects in animal models

Congenital abdominal wall defects are common anomalies which include gastroschisis, omphalocele and umbilical cord hernia. Recent reports indicate that gastroschisis is increasing in prevalence, whereas omphalocele has remained steady, suggesting that environmental factors may play a part in their pathogenesis. The aim of this study is to review animal teratogen studies resulting in abdominal wall defects to investigate their possible causes. Each report was examined not only for the teratogens causing the defects, but also to carefully identify the defect occurring and its correlation with the known clinical anomalies. We found many discrepancies between the nomenclature used by animal teratology investigators and that used by clinicians. We were able to confirm the induction of gastroschisis by 22 teratogens, omphalocele by 9 teratogens and umbilical cord hernia by 8. There is no doubt that environmental factors may be responsible, at least in part, for all three of the clinical abdominal wall defects. Future studies should take care to appreciate the differences between these anomalies and describe them in detail, so that accurate and meaningful conclusions can be obtained.

Disruption of calreticulin-mediated cellular adhesion signaling in the cadmium-induced omphalocele in the chick model

PURPOSE

Administration of cadmium (Cd) causes omphalocele in the chick embryo. The earliest histological changes in the chick Cd model are the breakdown of adherens junctions (AJs). Calreticulin (CRT) plays a key role in Ca(2+) signaling and cell adhesion. Ca(2+) signaling in the Cd chick model is known to be altered. The calcium-dependent adhesion molecule, E-cadherin, and its associate, beta-catenin, are key components of AJs regulated by CRT. CRT knockouts display omphalocele. We hypothesized that CRT, E-cadherin and beta-catenin are downregulated during early embryogenesis in the Cd chick model.

METHODS

After 60 h (H) incubation, chicks were harvested 1H, 4H, and 8H post treatment with saline or Cd and divided into controls and Cd. RT-PCR was performed to evaluate mRNA levels of CRT, E-cadherin and beta-catenin in the Cd chick model.

RESULTS

The mRNA levels of CRT were significantly decreased in the Cd group at 1H compared to controls (p < 0.05). The mRNA levels of E-cadherin and beta-catenin were significantly decreased at 4H in the Cd group compared to controls (p < 0.05). There were no significant differences at 8H.

CONCLUSION

Downregulation of CRT, E-cadherin and beta-catenin genes may cause omphalocele in the Cd chick model by disrupting CRT-mediated Ca(2+) signaling and AJs.

Descriptive epidemiology of nonsyndromic omphalocele in Texas, 1999-2004

Omphalocele is a congenital malformation that involves protrusion of abdominal contents into the umbilicus. Though omphalocele may present as a manifestation of several chromosomal and Mendelian syndromes, the etiology for nonsyndromic omphalocele is unknown. The present study sought to estimate the birth prevalence of nonsyndromic omphalocele in offspring of women residing in Texas from 1999 to 2004, and to describe prevalence as a function of parental and infant demographic characteristics. Data on 325 cases with nonsyndromic omphalocele and 2,208,758 live births delivered during 1999-2004 were obtained from the Texas Birth Defects Registry. These data were used to estimate omphalocele birth prevalence and obtain both crude and adjusted prevalence ratios for the association of nonsyndromic omphalocele with parental and infant demographic characteristics. Nonsyndromic omphaloceles were significantly more common among the offspring of women without previous live births (adjusted prevalence ratio: 1.80, 95% CI: 1.41-2.30), compared to the offspring of women with previous live births. The prevalence of nonsyndromic omphalocele was also increased among women aged 25-29 (adjusted prevalence ratio: 1.68, 95% CI: 1.12-2.50) and women aged 40 and older (adjusted prevalence ratio: 4.83, 95% CI: 2.63-8.86) compared to the offspring of women age <20, and in infants of multiple gestation pregnancies compared to singleton infants (adjusted prevalence ratio: 2.03, 95% CI: 1.22-3.37). In addition, among Hispanic women, the prevalence of nonsyndromic omphalocele was higher in the offspring of those born in the U.S. as compared to those born elsewhere (adjusted prevalence ratio: 1.50, 95% CI: 1.12-2.00). These findings augment the existing omphalocele literature.

Teratogenic effect of retinoic acid in swiss mice

PURPOSE

To identify the types of malformations resulting from the administration of retinoic acid (RA) to Swiss mice on different days of pregnancy.

METHODS

Twenty-four pregnant Swiss mice were divided into 4 groups of 6 animals each. The experimental groups received a single intraperitoneal injection of RA (70 mg/kg) on gestational days 7, 8 and 9 (D7, D8 and D9), while control animals (C) received only saline solution.

RESULTS

Were obtained: exencephaly (C:0; D7:16.1%; D8:25.4%; D9:0), myelomeningocele (C:0; D7:25.8%, D8:30.9%, D9:0), spina bifida occulta (C:0, D7:29%, D8:41.8%, D90), gastroschisis (C:0, D7:6.4% D8:5.4%, D9:0), omphalocele (C:0, D7:6.4%, D8:14.5%, D9:0), lower limb alterations (C:0, D7:74.1%, D8:80%, D9:0), imperforated anus (C:0, D7:100%, D8:100%, D9:100%), and tail agenesis/alteration (C: D7:100%, D8:100%, D9:100%).

CONCLUSION

The experimental model using Swiss mice proved to be efficient in the induction of the different types of defects, with the eighth gestational day being the one that most favored the induction of neural tube defect, omphalocele, gastroschisis, lower limb defects, imperforated anus and tail agenesis/alteration. On this basis, this is a useful model for future investigation of neural development and of the formation of the appendicular skeleton.

Interpreting neonatal lethal phenotypes in mouse mutants: insights into gene function and human diseases

The mouse represents the model of choice to study the biological function of mammalian genes through mutation of its genome. However, the biggest challenge of mouse geneticists remains the phenotypic analysis of mouse mutants. A survey of mouse mutant databases reveals a surprisingly high number of gene mutations leading to neonatal death. These genetically modified mouse mutants have been instrumental in elucidating gene function and have become important models of congenital human diseases. The main complication when phenotyping mutant mice dying during the neonatal period is the large spectrum of physiological systems whose defects can challenge neonatal survival. Here, we present a comprehensive review of gene mutations leading to neonatal lethality and discuss the impact of these mutations on the major physiological processes critical to mouse newborn survival: parturition, breathing, suckling, and homeostasis. Selected examples of mouse mutants are highlighted to illustrate how the precise identification of the timing and cause of death associated with these physiological processes allows for a more profound understanding of the underlying cellular and molecular defects. This review provides a guide for the analysis of neonatal lethal phenotypes in mutant mice that will be helpful for dissecting out the function of specific genes during mouse development.

Mice with disrupted TGFbeta signaling have normal cerebella development, but exhibit facial dysmorphogenesis and strain-dependent deficits in their body wall

The transforming growth factor betas (TGFbetas) are context-dependent regulators of neurons in vitro, but their physiological functions in the brain are unclear. Haploinsufficiency of either Tgfbeta1 or Tgfbeta2 leads to age-related deterioration of neurons, but the development of the brain is normal in the full absence of either of these genes. However, some individuals with mis-sense mutations of TGFbeta receptors are mentally retarded, suggesting that the TGFbeta isoforms can compensate for each other during brain development. This possibility was tested by generating mice (NSE x PTR) with neuron-specific expression of a dominant-negative inhibitor of TGFbeta signaling. The NSE x PTR mice with a FVBxC57Bl/6 genetic background were viable and developed normally despite strong neuronal expression of the inhibitor of TGFbeta signaling. Their cerebella were of normal size and contained normal numbers of neurons. When the genetic background of the mice was changed to C57BL/6, the phenotype of the mice became neonatal lethal, with the neonates exhibiting various malformations. The malformations correlated with sites of non-neuronal expression of the transgenes and included facial dysmorphogenesis, incomplete closure of the ventral body wall and absence of intestinal motility. The C57BL/6 Tgfbm1-3 alleles, which modulate the phenotype of Tgfbeta1(-/-) mice, were not major determinants of the NSE x PTR phenotype. The data suggest that the development of the cerebellum is insensitive to the level of TGFbeta signaling, although this may be dependent on the genetic background.

Genetic interaction between Bmp2 and Bmp4 reveals shared functions during multiple aspects of mouse organogenesis

Vertebrate Bmp2 and Bmp4 diverged from a common ancestral gene and encode closely related proteins. Mice homozygous for null mutations in either gene show early embryonic lethality, thereby precluding analysis of shared functions. In the current studies, we present phenotypic analysis of compound mutant mice heterozygous for a null allele of Bmp2 in combination with null or hypomorphic alleles of Bmp4. Whereas mice lacking a single copy of Bmp2 or Bmp4 are viable and have subtle developmental defects, compound mutants show embryonic and postnatal lethality due to defects in multiple organ systems including the allantois, placental vasculature, ventral body wall, skeleton, eye and heart. Within the heart, BMP2 and BMP4 function coordinately to direct normal lengthening of the outflow tract, proper positioning of the outflow vessels, and septation of the atria, ventricle and atrioventricular canal. Our results identify numerous BMP4-dependent developmental processes that are also very sensitive to BMP2 dosage, thus revealing novel functions of Bmp2.

Influences of reduced expression of maternal bone morphogenetic protein 2 on mouse embryonic development

Bone morphogenetic protein 2 (BMP2) was originally found by its osteoinductive ability, and recent genetic analyses have revealed that it plays critical roles during early embryogenesis, cardiogenesis, decidualization as well as skeletogenesis. In the course of evaluation of the conditional allele for Bmp2, we found that the presence of a neo cassette, a selection marker needed for gene targeting events in embryonic stem cells, in the 3' untranslated region of exon 3 of Bmp2, reduced the expression levels of Bmp2 both in embryonic and maternal mouse tissues. Some of the embryos that were genotyped as transheterozygous for the floxed allele with the neo cassette over the conventional null allele (fn/-) showed a lethal phenotype including defects in cephalic neural tube closure and ventral abdominal wall closure. The number of embryos exhibiting these abnormalities was increased when, due to different genotypes, expression levels of Bmp2 in maternal tissues were lower. These results suggest that the expression levels of Bmp2 in both embryonic and maternal tissues influence the normal neural tube closure and body wall closure with different thresholds.

Schistosoma reflexum in a cat: insights into aetiopathogenesis

A foetal cat exhibiting multiple congenital malformations and meeting the criteria for being considered as a case of true schistosoma reflexum (SR) is described. SR in animals is briefly compared with relatively similar malformation entities in humans. Murine gene mutations producing severe ventral body wall defects associated with anomalies of internal organs and other structures are briefly reviewed. New insights into aetiopathogenic mechanisms possibly implicated in the development of SR are suggested. This is probably the first case of true SR reported in the cat.

Bovine meroanencephaly and gastroschisis: a macro and microscopic study

Congenital malformations correspond to one of the main causes of embryonic loss during the gestational process. They result from interaction of several factors such as multifactor heredity, chromosomal and genetic alterations and environmental agents; however, unknown aetiology also can be present. In this article, we have used 10 embryos, from a frigorific area of Dracena, SP, Brazil, which were fixed in Bouin solution for a macro- and micro-scopic description. We could verify the presence of an encephalic tissue mass on the embryo's dorsal cranial area, resulting from the non-formation of part of the cranial cap and from the non-closing of cephalic neuropore and consequent neuroepithelial cells disorganization. In the abdominal area, the embryos did not show the complete fusion of the body lateral pleats during the abdominal wall formation, and the liver extruded into the amniotic cavity without involvement of the intestine.

Development of gastroschisis: review of hypotheses, a novel hypothesis, and implications for research

Gastroschisis, a ventral body wall defect, is a continuing challenge and concern to researchers, clinicians, and epidemiologists seeking to identify its cause(s) and pathogenesis. Concern has been renewed in recent years because, unlike most other birth defects, rates of gastroschisis are reportedly increasing in many developed and developing countries. No tenable explanation or specific causes have been identified for this trend. Rates of gastroschisis are particularly high among pregnancies of very young women. Such an intriguing association, not observed to this degree with other birth defects, may afford clues to the defect's cause. Understanding the causes of gastroschisis may provide insight to the defect's origin. In pursuing such causal studies, it would be helpful to understand the embryogenesis of gastroschisis. To date, four main embryologic hypotheses have been proposed: (1) Failure of mesoderm to form in the body wall; (2) Rupture of the amnion around the umbilical ring with subsequent herniation of bowel; (3) Abnormal involution of the right umbilical vein leading to weakening of the body wall and gut herniation; and (4) Disruption of the right vitelline (yolk sac) artery with subsequent body wall damage and gut herniation. Although based on embryological phenomena, these hypotheses do not provide an adequate explanation for how gastroschisis would occur. Therefore, we propose an alternative hypothesis, based on well described embryonic events. Specifically, we propose that abnormal folding of the body wall results in a ventral body wall defect through which the gut herniates, leading to the clinical presentation of gastroschisis. This hypothesis potentially explains the origin of gastroschisis as well as that of other developmental defects of the ventral wall.

Omphalocele induction in the chick embryo by administration of cadmium

BACKGROUND

Ventral body wall (VBW) defects occur in 1:2000 live births. We examined the association of VBW defect with somite abnormality and lordosis in the chick using in vitro and in ovo methods.

METHODS

Explanted chick embryos were treated at 60 hours with 50 microL sodium acetate or 0.001% cadmium acetate solution to produce VBW defects. Mortality and abnormality rates were assessed. A further cohort of chicks was treated in ovo by dropping 50 microL 0.001% to 0.01% cadmium acetate onto the embryo and allowing development to 16.5 days for further assessment of the defect and skeletal staining with alcian blue and alizarin red.

RESULTS

Cadmium treatment at 24 hours induced VBW defects in chicks treated in both shell-less culture and in ovo. Material herniating through the VBW defects was covered by a membrane in all fresh specimens. Membrane removal revealed large defects containing liver and bowel. These criteria clearly indicate that the defect observed is an omphalocele. Affected embryos had reduced somite numbers within 24 hours. Chicks exhibiting exomphalos at 16.5 days invariably had lumbosacral lordosis.

CONCLUSIONS

The cadmium-treated chick embryo is a reliable model for exomphalos. A positive association was found between exomphalos and lumbar lordosis in the chick.

Deficient Alk3-mediated BMP signaling causes prenatal omphalocele-like defect

BMP signaling plays important roles in many embryonic developmental processes. Alk3 is one of two BMP type I receptors that transduces BMP signal from the cell surface into cell. Conventional knockout of Alk3 resulted in early embryonic lethality around E7.5-E9.5. In this study, we have generated embryonic mesoderm-specific Alk3 conditional knockout by crossing Dermo1-Cre and floxed Alk3 mice. Abrogation of Alk3-mediated BMP signaling in this mouse resulted in severe defect of secondary ventral body wall formation, replicating the omphalocele phenotype in human. Our finding suggests that Alk3 plays an essential role in the formation of embryonic ventral abdominal wall, and abrogation of BMP signaling activity due to gene mutations in its signaling components could be one of the underlying causes of omphalocele at birth.

Patterns of severe abdominal wall defects: Insights into pathogenesis, delineation, and nomenclature

BACKGROUND

During the last decade, descriptions of malformation complexes involving an abdominal wall defect (AWD) have repeatedly appeared in the literature, and there has been frequent confusion regarding nomenclature, definitions, and delineations. The aims of this work were to evaluate possible embryological relationships among AWD cases, review the related nomenclature, identify patterns involving AWDs, and stress the importance of complete clinical descriptions. METHODS Cases diagnosed as AWD complexes were selected from live--and stillborn infants of the Hospital Materno Infantil Ramón Sardá, Buenos Aires, and from the Laboratory of Perinatal Pathology, Buenos Aires, Argentina. They were sorted by the location of the AWD, the umbilical cord length, and the presence or absence of a persistent cloaca. The findings in 26 cases were described, according to proposed definitions.

RESULTS

Three patterns could be identified: 1) the AWD involving the umbilical ring, a persistent or exstrophic cloaca, and a spinal cord anomaly; 2) the AWD extending laterally to the umbilical ring, severe unilateral limb defects, and same-sided agenesis of abdominal organs; and 3) the AWD not involving the umbilical ring, clefts, exencephaly, and amputations. Furthermore, overlapping among these patterns was observed, and possible involved mechanisms are discussed.

CONCLUSIONS

The observed overlapping among patterns suggested that malformation complexes involving AWDs might not be independent conditions but rather belong to a common and broader spectrum of anomalies. Complete clinical descriptions, the avoidance of synonyms and generalizations, and strictly defined inclusion criteria are proposed for a better understanding of pathogenetic pathways in, and relationships among, AWD complexes.

A new serine/threonine protein kinase, Omphk1, essential to ventral body wall formation

Here, we report a new serine/threonine protein kinase of the SNF1 subfamily Omphk1. Two Omphk homologues exist in each vertebrate species, and one homologue exists in Drosophila and Caenorhabditis elegans; the kinase domain is highly conserved among these homologues, and several domains are conserved among vertebrate Omphk. Omphk1 expression dynamically changes in the developing central nervous system, is found ubiquitously in epidermis, and is present uniquely in several other tissues. Its expression is also found in each tissue associated with the ventral body wall closure: the primary body wall composed of primitive ectoderm and each component of the secondary body wall. Concomitantly, its null mutant exhibits omphalocele with a failure in closure of the secondary body wall. There are no apparent gross morphological defects in brain, however, despite the unique Omphk1 expression in this tissue.

Left-Sided Gastroschisis

Gastroschisis is a periumbilical, abdominal wall defect arising to the right of the umbilicus. We describe the clinical course of a left-sided gastroschisis in a term female born at 39 weeks’ gestation. To our knowledge, there have been only 14 left-sided abdominal wall defects reported in the literature. We discuss our case and review the literature to try to determine if there is any clinic difference between right- versus left-sided lesions to make recommendations as to management.

Mutation of an upstream cleavage site in the BMP4 prodomain leads to tissue-specific loss of activity

ProBMP4 is initially cleaved at a site adjacent to the mature ligand (the S1 site) allowing for subsequent cleavage at an upstream (S2) site. Mature BMP4 synthesized from a precursor in which the S2 site cannot be cleaved remains in a complex with the prodomain that is targeted for lysosomal degradation, and is thus less active when overexpressed in Xenopus. Here we report that mice carrying a point mutation that prevents S2 processing show severe loss of BMP4 activity in some tissues, such as testes and germ cells, whereas other tissues that are sensitive to Bmp4 dosage, such as the limb, dorsal vertebrae and kidney, develop normally. In a haploinsufficient background, inability to cleave the S2 site leads to embryonic and postnatal lethality due to defects in multiple organ systems including the allantois, placental vasculature, ventral body wall, eye and heart. These data demonstrate that cleavage of the S2 site is essential for normal development and, more importantly, suggest that this site might be selectively cleaved in a tissue-specific fashion. In addition, these studies provide the first genetic evidence that BMP4 is required for dorsal vertebral fusion and closure of the ventral body wall.

Ventral abdominal wall dysmorphogenesis of Msx1/Msx2 double-mutant mice

Msx1 and Msx2 genes encode the homeodomain transcription factors. Several gene knockout mice and expression studies suggest that they possess functionally redundant roles in embryogenesis. In this study, we revealed that Msx1 and Msx2 were expressed during ventral body wall formation in an overlapping manner. Msx1/Msx2 double-mutant mice displayed embryonic abdominal wall defects with disorganized muscle layers and connective tissues. These findings indicate that Msx1 and Msx2 play roles in concert during embryonic ventral abdominal wall formation.

The morphogenesis of the exstrophy-epispadias complex: a new concept based on observations made in early embryonic cases of cloacal exstrophy

BACKGROUND

The term exstrophy-epispadias complex (EEC) has been coined for a group of congenital malformations that includes epispadias, bladder exstrophy and cloacal exstrophy. It is usually thought that these malformations develop against a similar embryological background. This background, however, is still obscure. This is mainly due to the lack of availability of abnormal human or non-human embryos showing the crucial developmental steps in the morphogenesis of EEC malformations. In this paper, we present chick embryos that show cloacal exstrophy at early developmental stages. To the best of our knowledge, this is the first documentation of this rare malformation in young embryos.

MATERIALS AND METHODS

Embryos with cloacal exstrophy (n=4) were found among embryos from two experimental series (n=50) that were primarily performed to document the early morphogenesis of facial and cardiovascular malformations. The malformations were induced by the administration of suramin according to established protocols. Suramin can induce a spectrum of malformations including facial clefts, heart defects, and cloacal exstrophy.

RESULTS AND CONCLUSIONS

Besides the presence of an abnormal opening into the cloaca, all embryos were characterised by an abnormal broadening of the caudal trunk at the level of the leg buds, which, in the youngest embryos, was associated with the abnormal presence of large aneurysmatic swellings of the dorsal aortae at this side. We postulate that these aneurysmatic swellings might be the primary defects leading to the development of EEC malformations. These space-occupying anomalies seem to cause abnormal distensions of the developing pelvis and of the infra-umbilical portion of the developing body wall. In consequence, the mid-portion of the developing ventral body wall between the origin of the umbilical cord and the cloacal plate becomes stretched and thinned out. Tension and thinning of the ventral body wall might ultimately lead to its rupture with exposure of the lumen of the embryonic cloaca and allantois. This new concept on the morphogenesis of the EEC is the first not to be inferred from the conditions seen in fetal or postnatal human cases but is based entirely on data from malformed embryos.