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

Extraembryonic gut endoderm cells undergo programmed cell death during development

Despite a distinct developmental origin, extraembryonic cells in mice contribute to gut endoderm and converge to transcriptionally resemble their embryonic counterparts. Notably, all extraembryonic progenitors share a non-canonical epigenome, raising several pertinent questions, including whether this landscape is reset to match the embryonic regulation and if extraembryonic cells persist into later development. Here we developed a two-colour lineage-tracing strategy to track and isolate extraembryonic cells over time. We find that extraembryonic gut cells display substantial memory of their developmental origin including retention of the original DNA methylation landscape and resulting transcriptional signatures. Furthermore, we show that extraembryonic gut cells undergo programmed cell death and neighbouring embryonic cells clear their remnants via non-professional phagocytosis. By midgestation, we no longer detect extraembryonic cells in the wild-type gut, whereas they persist and differentiate further in p53-mutant embryos. Our study provides key insights into the molecular and developmental fate of extraembryonic cells inside the embryo.

Y-27632 Impairs Angiogenesis on Extra-Embryonic Vasculature in Post-Gastrulation Chick Embryos

Y-27632 inhibits Rho-associated coiled-coil-containing protein kinase (ROCK) signaling, which is involved in various embryonic developmental processes, including angiogenesis, by controlling actin cytoskeleton assembly and cell contractility. Administration of Y-27632 impairs cytoskeletal arrangements in post-gastrulation chick embryos, leading to ventral body wall defects (VBWDs). Impaired angiogenesis has been hypothesized to contribute to VBWDs. ROCK is essential in transmitting signals downstream of vascular endothelial growth factor (VEGF). VEGF-mediated angiogenesis induces gene expressions and alterations of the actin cytoskeleton upon binding to VEGF receptors (VEGFRs). The aim of this study was to investigate effects of Y-27632 on angiogenesis in post-gastrulation chick embryos during early embryogenesis. After 60 h incubation, embryos in shell-less culture were treated with Y-27632 or vehicle for controls. Y-27632-treated embryos showed reduced extra-embryonic blood vessel formation with impaired circulation of the yolk sac, confirmed by fractal analysis. Western blot confirmed impaired ROCK downstream signaling by decreased expression of phosphorylated myosin light chain. Interestingly, RT-PCR demonstrated increased gene expression of VEGF and VEGFR-2 1 h post-treatment. Protein levels of VEGF were higher in Y-27632-treated embryos at 8 h following treatment, whereas no difference was seen in membranes. We hypothesize that administration of Y-27632 impairs vessel formation during angiogenesis, which may contribute to failure of VWB closure, causing VBWDs.

Anatomy and embryology of abdominal wall defects

Abdominal wall defects are one of the most frequently encountered human congenital anomalies. They are seen in as many as 1 in 2,000 live births with evidence to suggest that their incidence is increasing. While often discussed together abdominal wall defects consist mainly of two entities namely gastroschisis and omphalocele. There are marked differences in their theories of embryo-pathogenesis, clinical presentation/anatomy and overall outcomes. There is no clear consensus explaining the precise embryological mechanisms leading to the development of abdominal wall defects. Many clinicians and embryologists have attempted to explain the genesis of congenital abdominal wall defects because of failure of progression of various phases of normal embryonic development. This review summarizes the mechanisms involved in normal and abnormal development of the ventral abdominal wall leading to the development of gastroschisis and omphalocele.

Embryology of the Abdominal Wall and Associated Malformations—A Review

In humans, the incidence of congenital defects of the intraembryonic celom and its associated structures has increased over recent decades. Surgical treatment of abdominal and diaphragmatic malformations resulting in congenital hernia requires deep knowledge of ventral body closure and the separation of the primary body cavities during embryogenesis. The correct development of both structures requires the coordinated and fine-tuned synergy of different anlagen, including a set of molecules governing those processes. They have mainly been investigated in a range of vertebrate species (e.g., mouse, birds, and fish), but studies of embryogenesis in humans are rather rare because samples are seldom available. Therefore, we have to deal with a large body of conflicting data concerning the formation of the abdominal wall and the etiology of diaphragmatic defects. This review summarizes the current state of knowledge and focuses on the histological and molecular events leading to the establishment of the abdominal and thoracic cavities in several vertebrate species. In chronological order, we start with the onset of gastrulation, continue with the establishment of the three-dimensional body shape, and end with the partition of body cavities. We also discuss well-known human etiologies.

Hand2 delineates mesothelium progenitors and is reactivated in mesothelioma

The mesothelium lines body cavities and surrounds internal organs, widely contributing to homeostasis and regeneration. Mesothelium disruptions cause visceral anomalies and mesothelioma tumors. Nonetheless, the embryonic emergence of mesothelia remains incompletely understood. Here, we track mesothelial origins in the lateral plate mesoderm (LPM) using zebrafish. Single-cell transcriptomics uncovers a post-gastrulation gene expression signature centered on hand2 in distinct LPM progenitor cells. We map mesothelial progenitors to lateral-most, hand2-expressing LPM and confirm conservation in mouse. Time-lapse imaging of zebrafish hand2 reporter embryos captures mesothelium formation including pericardium, visceral, and parietal peritoneum. We find primordial germ cells migrate with the forming mesothelium as ventral migration boundary. Functionally, hand2 loss disrupts mesothelium formation with reduced progenitor cells and perturbed migration. In mouse and human mesothelioma, we document expression of LPM-associated transcription factors including Hand2, suggesting re-initiation of a developmental program. Our data connects mesothelium development to Hand2, expanding our understanding of mesothelial pathologies.

Caldesmon ablation in mice causes umbilical herniation and alters contractility of fetal urinary bladder smooth muscle

The actin-, myosin-, and calmodulin-binding protein caldesmon (CaD) is expressed in two splice isoforms: h-CaD, which is an integral part of the actomyosin domain of smooth muscle cells, and l-CaD, which is widely expressed and is involved in many cellular functions. Despite extensive research for many years, CaD's in vivo function has remained elusive. To explore the role of CaD in smooth muscle contraction in vivo, we generated a mutant allele that ablates both isoforms. Heterozygous animals were viable and had a normal life span, but homozygous mutants died perinatally, likely because of a persistent umbilical hernia. The herniation was associated with hypoplastic and dysmorphic abdominal wall muscles. We assessed mechanical parameters in isometrically mounted longitudinal strips of E18.5 urinary bladders and in ring preparations from abdominal aorta using wire myography. Ca²⁺ sensitivity was higher and relaxation rate was slower in Cald1^−/− compared with Cald1^+/+ skinned bladder strips. However, we observed no change in the content and phosphorylation of regulatory proteins of the contractile apparatus and myosin isoforms known to affect these contractile parameters. Intact fibers showed no difference in actin and myosin content, regardless of genotype, although KCl-induced force tended to be lower in homozygous and higher in heterozygous mutants than in WTs. Conversely, in skinned fibers, myosin content and maximal force were significantly lower in Cald1^−/− than in WTs. In KO abdominal aortas, resting and U46619 elicited force were lower than in WTs. Our results are consistent with the notion that CaD impacts smooth muscle function dually by (1) acting as a molecular brake on contraction and (2) maintaining the structural integrity of the contractile machinery. Most importantly, CaD is essential for resolution of the physiological umbilical hernia and ventral body wall closure.

Midgut development in rat embryos using microcomputed tomography

The development of the mammalian gut was first described more than a century ago. Since then, it has been believed that a series of highly orchestrated developmental processes occur before the intestine achieves its final formation. The key steps include the formation of the umbilicus, the so-called "physiological herniation" of the midgut into the umbilical cord, an intestinal "rotation", and the "return of the gut" into the abdominal cavity. However, this sequence of events is predominantly based on histological sections of dissected embryos, a 2D technique with methodological limitations. For a better understanding of spatial relationships in the embryo, we utilized microcomputed tomography (µCT), a nondestructive 3D imaging method. Here, we show the detailed processes and mechanisms of intestinal development in rat embryos, including the development of the umbilicus, the formation of loops inside the umbilical coelom, and the subsequent shift of these loops into the abdominal cavity. Our 3D datasets of developing intestines will substantially advance the understanding of normal mammalian midgut embryology and offer new possibilities to reveal unknown mechanisms in the pathogenesis of congenital disorders.

Development and Therapeutic Potential of NUAKs Inhibitors

NUAK isoforms, NUAK1 (ARK5) and NUAK2 (SNARK), are important members of the AMPK family of protein kinases. They are involved in a broad spectrum of physiological and cellular events, and sometimes their biological roles overlap. NUAK isoform dysregulation is associated with numerous pathological disorders, including neurodegeneration, metastatic cancer, and diabetes. Therefore, they are promising therapeutic targets in metabolic diseases and cancers; consequently, various NUAK-targeted inhibitors have been disclosed. The first part of this review comprises a brief discussion of the homology, expression, structure, and characteristics of NUAK isoforms. The second part focuses on NUAK isoforms' involvement in crucial biological operations, including mechanistic findings, highlighting how their abnormal functioning contributes to disease progression and quality of life. The third part summarizes the key findings and applications of targeting NUAK isoforms for treating multiple cancers and neurodegenerative disorders. The final part systematically presents a critical review and analysis of the literature on NUAK isoform inhibitions through small molecules.

The Fgf8 subfamily (Fgf8, Fgf17 and Fgf18) is required for closure of the embryonic ventral body wall

The closure of the embryonic ventral body wall in amniotes is an important morphogenetic event and is essential for life. Defects in human ventral wall closure are a major class of birth defect and a significant health burden. Despite this, very little is understood about how the ventral body wall is formed. Here, we show that fibroblast growth factor (FGF) ligands FGF8, FGF17 and FGF18 are essential for this process. Conditional mouse mutants for these genes display subtle migratory defects in the abdominal muscles of the ventral body wall and an enlarged umbilical ring, through which the internal organs are extruded. By refining where and when these genes are required using different Cre lines, we show that Fgf8 and Fgf17 are required in the presomitic mesoderm, whereas Fgf18 is required in the somites. This study identifies complex and multifactorial origins of ventral wall defects and has important implications for understanding their origins during embryonic development.

Teratogenesis in the chick embryo following post-gastrulation exposure to Y-27632 -effect of Y-27632 on embryonic development

The pyridine derivative Y-27632 inhibits Rho-associated coiled-coil-containing protein kinase (ROCK) signaling, which is involved in numerous developmental processes during embryogenesis, primarily by controlling actin-cytoskeleton assembly and cell contractility. Somite formation requires rearrangement of the cytoskeleton and assists in major morphological mechanisms, including ventral body wall formation. Administration of Y-27632 impairs cytoskeletal arrangements in post-gastrulation chick embryos leading to ventral body wall defects (VBWD) at later stages of development. The aim of this study was to investigate the effect of Y-27632 on somite development in post-gastrulation chick embryos during early embryogenesis. After 60 h incubation, embryos in shell-less culture were treated with Y-27632 or vehicle for controls. Following administration, abnormality rates were assessed. In treatment groups, embryos showed a kinked longitudinal body axis. Western blot confirmed impaired ROCK downstream signaling by decreased expression of phosphorylated cofilin-2. Histology, Lysotracker studies and RT-PCR demonstrated increased cell death in somites, the neural tube and the ectoderm. RT-PCR and Western blot of factors known to be involved during somitogenesis revealed reduced expression in the treatment group compared to controls. We hypothesize that administration of Y-27632 disrupts somite development causing axial kinking and embryo malformation, which may lead to VBWD.

Development of the amniote ventrolateral body wall

In vertebrates, the trunk consists of the musculoskeletal structures of the back and the ventrolateral body wall, which together enclose the internal organs of the circulatory, digestive, respiratory and urogenital systems. This review gives an overview on the development of the thoracic and abdominal wall during amniote embryogenesis. Specifically, I briefly summarize relevant historical concepts and the present knowledge on the early embryonic development of ribs, sternum, intercostal muscles and abdominal muscles with respect to anatomical bauplan, origin and specification of precursor cells, initial steps of pattern formation, and cellular and molecular regulation of morphogenesis.

Body Wall Defects: Gastroschisis and Omphalocoele in Pigs (Sus scrofa domesticus)

Body wall defects (BWDs) are not well studied and categorized in veterinary medicine. BWDs can be an isolated occurrence, but often occur with other major developmental abnormalities. Thirty-two body wall malformations of domestic pigs (Sus scrofa domesticus) are presented and classified, distinguishing between body wall dysplasia (umbilical hernia, abdominal wall distension and gastroschisis), omphalocoele and thoracoabdominoschisis (Cantrell syndrome, shistosomus reflexus, body stalk anomalies).

Bioinformatic Analysis of Gene Variants from Gastroschisis Recurrence Identifies Multiple Novel Pathogenetic Pathways: Implication for the Closure of the Ventral Body Wall

We investigated whether likely pathogenic variants co-segregating with gastroschisis through a family-based approach using bioinformatic analyses were implicated in body wall closure. Gene Ontology (GO)/Panther functional enrichment and protein-protein interaction analysis by String identified several biological networks of highly connected genes in UGT1A3, UGT1A4, UGT1A5, UGT1A6, UGT1A7, UGT1A8, UGT1A9, UGT1A10, AOX1, NOTCH1, HIST1H2BB, RPS3, THBS1, ADCY9, and FGFR4. SVS–PhoRank identified a dominant model in OR10G4 (also as heterozygous de novo), ITIH3, PLEKHG4B, SLC9A3, ITGA2, AOX1, and ALPP, including a recessive model in UGT1A7, UGT1A6, PER2, PTPRD, and UGT1A3. A heterozygous compound model was observed in CDYL, KDM5A, RASGRP1, MYBPC2, PDE4DIP, F5, OBSCN, and UGT1A. These genes were implicated in pathogenetic pathways involving the following GO related categories: xenobiotic, regulation of metabolic process, regulation of cell adhesion, regulation of gene expression, inflammatory response, regulation of vascular development, keratinization, left-right symmetry, epigenetic, ubiquitination, and regulation of protein synthesis. Multiple background modifiers interacting with disease-relevant pathways may regulate gastroschisis susceptibility. Based in our findings and considering the plausibility of the biological pattern of mechanisms and gene network modeling, we suggest that the gastroschisis developmental process may be the consequence of several well-orchestrated biological and molecular mechanisms which could be interacting with gastroschisis predispositions within the first ten weeks of development.

Insights into embryology and development of omphalocele

Congenital abdominal wall defects are one of the most common human birth defects with an incidence of about 1 in 2000 live births. While often discussed together abdominal wall defects consist mainly of two distinct entities namely gastroschisis and omphalocele. There is no clear consensus explaining the precise embryological mechanisms leading to the development of an omphalocele. Many clinicians and embryologists have attempted to explain congenital malformation as a result of failure of progression of normal embryonic development. This review summarizes the mechanisms involved in normal and abnormal development of the ventral abdominal wall.

Mice doubly deficient in Six4 and Six5 show ventral body wall defects reproducing human omphalocele

Omphalocele is a human congenital anomaly in ventral body wall closure and may be caused by impaired formation of the primary abdominal wall (PAW) and/or defects in abdominal muscle development. Here, we report that mice doubly deficient in homeobox genes Six4 and Six5 showed the same ventral body wall closure defects as those seen in human omphalocele. SIX4 and SIX5 were localized in surface ectodermal cells and somatic mesoderm-derived mesenchymal and coelomic epithelial cells (CECs) in the PAW. Six4^-/-;Six5^-/- fetuses exhibited a large omphalocele with protrusion of both the liver and intestine, or a small omphalocele with protrusion of the intestine, with complete penetrance. The umbilical ring of Six4^-/-;Six5^-/- embryos was shifted anteriorly and its lateral size was larger than that of normal embryos at the E11.5 stage, before the onset of myoblast migration into the PAW. The proliferation rates of surface ectodermal cells in the left and right PAW and somatic mesoderm-derived cells in the right PAW were lower in Six4^-/-;Six5^-/- embryos than those of wild-type embryos at E10.5. The transition from CECs of the PAW to rounded mesothelial progenitor cells was impaired and the inner coelomic surface of the PAW was relatively smooth in Six4^-/-;Six5^-/- embryos at E11.25. Furthermore, Six4 overexpression in CECs of the PAW promoted ingression of CECs. Taken together, our results suggest that Six4 and Six5 are required for growth and morphological change of the PAW, and the impairment of these processes is linked to the abnormal positioning and expansion of the umbilical ring, which results in omphalocele.

Location, Location, Location: Signals in Muscle Specification

Muscles control body movement and locomotion, posture and body position and soft tissue support. Mesoderm derived cells gives rise to 700 unique muscles in humans as a result of well-orchestrated signaling and transcriptional networks in specific time and space. Although the anatomical structure of skeletal muscles is similar, their functions and locations are specialized. This is the result of specific signaling as the embryo grows and cells migrate to form different structures and organs. As cells progress to their next state, they suppress current sequence specific transcription factors (SSTF) and construct new networks to establish new myogenic features. In this review, we provide an overview of signaling pathways and gene regulatory networks during formation of the craniofacial, cardiac, vascular, trunk, and limb skeletal muscles.

Exposure to sub-lethal dose of a combination insecticide during early embryogenesis influences the normal patterning of mesoderm resulting in incomplete closure of ventral body wall of chicks of domestic hen

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Chlorpyrifos and cypermethrin treatment induced developmental anomalies in chicks.

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Protrusion of visceral organs and microphthalmia were the major anomalies observed.

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Treated embryos were conspicuous with incomplete ventral body wall and sternum.

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Altered expression pattern of E-cadherin, Shh, bmp4, Wnt11 and Pitx2 were recorded.

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Impairment of major regulators of development is suspected to induce VBWD.

Pesticide exposure to the non target groups especially during embryonic development has quite often resulted in congenital malformations. A commercially available combination insecticide (Ci, 50% chlorpyrifos and 5% cypermethrin) is known to induce ventral body wall defects (VBWDs) wherein abdominal viscera protrude out of the ventral body wall. Herein, an attempt was made to understand the mechanistic insight into Ci induced VBWDs. For this, before incubation, the chick embryos were dosed with the test chemical and then at different developmental stages of incubation, they were monitored for the changes in the expression of certain genes, which are indispensable for the ventral body wall closure since they regulate the cell fate, proliferation and survival. Concurrently, histopathological changes during the embryonic development were examined to corroborate the above observations. The results of mRNA profiling revealed a significant downregulation of Shh on day 4 and upregulation on day 10, while bmp4, Pitx2, E-cadherin, Wnt11, Wnt6, Pxn, MyoD1, Caspase-3, AHR, Cyp3A4, showed a significant upregulation on day 4 and/or on day 10. N-cadherin, fgf8, bmp1 showed no significant changes. The possible means by which these skewed expression patterns of regulatory molecules culminated into the VBWD are discussed.

Visceral endoderm and the primitive streak interact to build the fetal-placental interface of the mouse gastrula

Hypoblast/visceral endoderm assists in amniote nutrition, axial positioning and formation of the gut. Here, we provide evidence, currently limited to humans and non-human primates, that hypoblast is a purveyor of extraembryonic mesoderm in the mouse gastrula. Fate mapping a unique segment of axial extraembryonic visceral endoderm associated with the allantoic component of the primitive streak, and referred to as the "AX", revealed that visceral endoderm supplies the placentae with extraembryonic mesoderm. Exfoliation of the AX was dependent upon contact with the primitive streak, which modulated Hedgehog signaling. Resolution of the AX's epithelial-to-mesenchymal transition (EMT) by Hedgehog shaped the allantois into its characteristic projectile and individualized placental arterial vessels. A unique border cell separated the delaminating AX from the yolk sac blood islands which, situated beyond the limit of the streak, were not formed by an EMT. Over time, the AX became the hindgut lip, which contributed extensively to the posterior interface, including both embryonic and extraembryonic tissues. The AX, in turn, imparted antero-posterior (A-P) polarity on the primitive streak and promoted its elongation and differentiation into definitive endoderm. Results of heterotopic grafting supported mutually interactive functions of the AX and primitive streak, showing that together, they self-organized into a complete version of the fetal-placental interface, forming an elongated structure that exhibited A-P polarity and was composed of the allantois, an AX-derived rod-like axial extension reminiscent of the embryonic notochord, the placental arterial vasculature and visceral endoderm/hindgut.

Sequence variants identification at the KCNQ1OT1:TSS differentially Methylated region in isolated omphalocele cases

Background

Omphalocele is a congenital midline ventral body wall defect that can exist as isolated malformation or as part of a syndrome. It can be considered one of the major and most frequent clinical manifestation of Beckwith-Wiedemann Syndrome (BWS) in case of loss of methylation at KCNQ1OT1: Transcription Star Site-Differentially Methylated Region (TSS-DMR) or in presence of CDKN1C mutations. The isolated form of the omphalocele accounts approximately for about the 14% of the total cases and its molecular etiology has never been fully elucidated.

Methods

Given the tight relationship with BWS, we hypothesized that the isolated form of the omphalocele could belong to the heterogeneous spectrum of the BWS associated features, representing an endophenotype with a clear genetic connection. We therefore investigated genetic and epigenetic changes affecting BWS imprinted locus at 11p15.5 imprinted region, focusing in particular on the KCNQ1OT1:TSS DMR.

Results

We studied 21 cases of isolated omphalocele detected during pregnancy or at birth and identified the following rare maternally inherited variants: i) the non-coding variant G > A at nucleotide 687 (NR_002728.3) at KCNQ1OT1:TSS-DMR, which alters the methylation pattern of the imprinted allele, in one patient; ii) the deletion c.624-629delGGCCCC at exon 1 of CDKN1C, with unknown clinical significance, in two unrelated cases.

Conclusions

Taken together, these findings suggest that KCNQ1OT1:TSS-DMR could be a susceptibility locus for the isolated omphalocele.

Electronic supplementary material

The online version of this article (10.1186/s12881-017-0470-z) contains supplementary material, which is available to authorized users.

PRDM1/BLIMP1 is widely distributed to the nascent fetal-placental interface in the mouse gastrula

BACKGROUND

PRDM1 is a transcriptional repressor that contributes to primordial germ cell (PGC) development. During early gastrulation, epiblast-derived PRDM1 is thought to be restricted to a lineage-segregated germ line in the allantois. However, given recent findings that PGCs overlap an allantoic progenitor pool that contributes widely to the fetal-umbilical interface, posterior PRDM1 may also contribute to soma.

RESULTS

Within the posterior mouse gastrula (early streak, 12-s stages, embryonic days ∼6.75-9.0), PRDM1 localized to all tissues containing putative PGCs; however, PRDM1 was also found in all three primary germ layers, their derivatives, and two presumptive growth centers, the allantoic core domain and ventral ectodermal ridge. While PRDM1 and STELLA colocalized predominantly within the hindgut, where putative PGCs reside, other colocalizing cells were found in non-PGC sites. Additional PRDM1 and STELLA cells were found independent of each other throughout the posterior region, including the hindgut. The Prdm1-Cre-driven reporter supported PRDM1 localization in the majority of sites; however, some Prdm1 descendants were found in sites independent of PRDM1 protein, including allantoic mesothelium and hindgut endoderm.

CONCLUSIONS

Posterior PRDM1 contributes more broadly to the developing fetal-maternal connection than previously recognized, and PRDM1 and STELLA, while overlapping in putative PGCs, also co-localize in several other tissues. Developmental Dynamics 246:50-71, 2017. © 2016 Wiley Periodicals, Inc.

Development of the ventral body wall in the human embryo

Migratory failure of somitic cells is the commonest explanation for ventral body wall defects. However, the embryo increases ~ 25-fold in volume in the period that the ventral body wall forms, so that differential growth may, instead, account for the observed changes in topography. Human embryos between 4 and 10 weeks of development were studied, using amira reconstruction and cinema 4D remodeling software for visualization. Initially, vertebrae and ribs had formed medially, and primordia of sternum and hypaxial flank muscle primordium laterally in the body wall at Carnegie Stage (CS)15 (5.5 weeks). The next week, ribs and muscle primordium expanded in ventrolateral direction only. At CS18 (6.5 weeks), separate intercostal and abdominal wall muscles differentiated, and ribs, sterna, and muscles began to expand ventromedially and caudally, with the bilateral sternal bars fusing in the midline after CS20 (7 weeks) and the rectus muscles reaching the umbilicus at CS23 (8 weeks). The near-constant absolute distance between both rectus muscles and approximately fivefold decline of this distance relative to body circumference between 6 and 10 weeks identified dorsoventral growth in the dorsal body wall as determinant of the 'closure' of the ventral body wall. Concomitant with the straightening of the embryonic body axis after the 6th week, the abdominal muscles expanded ventrally and caudally to form the infraumbilical body wall. Our data, therefore, show that the ventral body wall is formed by differential dorsoventral growth in the dorsal part of the body.

Epiboly generates the epidermal basal monolayer and spreads the nascent mammalian skin to enclose the embryonic body

Epiboly is a morphogenetic process that is employed in the surface ectoderm of anamniotes during gastrulation to cover the entire embryo. We propose here that mammals also utilise this process to expand the epidermis and enclose the body cavity and spinal cord with a protective surface covering. Our data supports a model whereby epidermal spreading is driven by the primary establishment of the epidermal basal progenitor monolayer through radial cell intercalation of a multi-layered epithelium towards the basal lamina. By using a suspension organotypic culture strategy, we find that this process is fibronectin-dependent and autonomous to the skin. The radial cell rearrangements that drive epidermal spreading also require ROCK activity but are driven by cell protrusions and not myosin II contractility. Epidermal progenitor monolayer formation and epidermal spreading are delayed in Crash mice, which possess a dominant mutation in Celsr1, an orthologue of the core planar cell polarity (PCP) Drosophila protein Flamingo (also known as Stan). We observe a failure of ventral enclosure in Crash mutants suggesting that defective epidermal spreading might underlie some ventral wall birth defects.

Summary: The nascent mammalian epidermis spreads to enclose the embryo trunk through a process akin to epiboly, which has important implications for human birth defects of the abdominal wall.

Impaired cytoskeletal arrangements and failure of ventral body wall closure in chick embryos treated with rock inhibitor (Y-27632)

AIM

Rho-associated kinase (ROCK) signaling regulates numerous fundamental developmental processes during embryogenesis, primarily by controlling actin-cytoskeleton assembly and cell contractility. ROCK knockout mice exhibit a ventral body wall defect (VBWD) phenotype due to disorganization of actin filaments at the umbilical ring. However, the exact molecular mechanisms leading to VBWD still remain unclear. Improper somitogenesis has been hypothesized to contribute to failure of VBW closure. We designed this study to investigate the hypothesis that administration of ROCK inhibitor (Y-27632) disrupts cytoskeletal arrangements in morphology during early chick embryogenesis, which may contribute to the development of VBWD.

METHODS

At 60 h incubation, chick embryos were explanted into shell-less culture and treated with 50 µL of vehicle for controls (n = 33) or 50 µL of 500 µM of Y-27632 for the experimental group (Y-27, n = 56). At 8 h post-treatment, RT-PCR was performed to evaluate mRNA levels of N-cadherin, E-cadherin and connexin43. Immunofluorescence confocal microscopy was performed to analyze the expression and distribution of actin, vinculin and microtubules in the neural tube and somites. A further cohort of embryos was treated in ovo by dropping 50 µL of vehicle or 50 µL of different concentrations of Y-27632 onto the embryo and allowing development to 12 and 14 days for further assessment.

RESULTS

Gene expression levels of N-cadherin, E-cadherin and connexin43 were significantly decreased in treated embryos compared with controls (p < 0.05). Thickened actin filament bundles were recorded in the neural tube of Y-27 embryos. In somites, cells were dissociated with reduced actin distribution in affected embryos. Clumping of vinculin expression was found in the neural tube and somites, whereas reduced expression of microtubules was observed in Y-27 embryos compared with controls. At 12 and 14 days of development, affected embryos presented with an enlarged umbilical ring and herniation of abdominal contents through the defect.

CONCLUSION

ROCK inhibition alters cytoskeletal arrangement during early chick embryogenesis, which may contribute to failure of anterior body wall closure causing VBWD at later stages of development.

The receptor tyrosine kinase Pvr promotes tissue closure by coordinating corpse removal and epidermal zippering

A leading cause of human birth defects is the incomplete fusion of tissues, often manifested in the palate, heart or neural tube. To investigate the molecular control of tissue fusion, embryonic dorsal closure and pupal thorax closure in Drosophila are useful experimental models. We find that Pvr mutants have defects in dorsal midline closure with incomplete amnioserosa internalization and epidermal zippering, as well as cardia bifida. These defects are relatively mild in comparison to those seen with other signaling mutants, such as in the JNK pathway, and we demonstrate that JNK signaling is not perturbed by altering Pvr receptor tyrosine kinase activity. Rather, modulation of Pvr levels in the ectoderm has an impact on PIP3 membrane accumulation, consistent with a link to PI3K signal transduction. Polarized PI3K activity influences protrusive activity from the epidermal leading edge and the protrusion area changes in accord with Pvr signaling intensity, providing a possible mechanism to explain Pvr mutant phenotypes. Tissue-specific rescue experiments indicate a partial requirement in epithelial tissue, but confirm the essential role of Pvr in hemocytes for embryonic survival. Taken together, we argue that inefficient removal of the internalizing amnioserosa tissue by mutant hemocytes coupled with impaired midline zippering of mutant epithelium creates a situation in some embryos whereby dorsal midline closure is incomplete. Based on these observations, we suggest that efferocytosis (corpse clearance) could contribute to proper tissue closure and thus might underlie some congenital birth defects.

Dermatan sulfate epimerase 1 deficient mice as a model for human abdominal wall defects

BACKGROUND

Dermatan sulfate (DS) is a highly sulfated polysaccharide with a variety of biological functions in extracellular matrix organization and processes such as tumorigenesis and wound healing. A distinct feature of DS is the presence of iduronic acid, produced by the two enzymes, DS-epimerase 1 and 2, which are encoded by Dse and Dsel, respectively.

METHODS

We have previously shown that Dse knockout (KO) mice in a mixed C57BL/6-129/SvJ background have an altered collagen matrix structure in skin. In the current work we studied Dse KO mice in a pure NFR genetic background.

RESULTS

Dse KO embryos and newborns had kinked tails and histological staining revealed significantly thicker epidermal layers in Dse KO mice when compared with heterozygote (Het) or wild-type (WT) littermates. Immunochemical analysis of the epidermal layers in newborn pups showed increased expression of keratin 5 in the basal layer and keratin 1 in the spinous layer. In addition, we observed an abdominal wall defect with herniated intestines in 16% of the Dse KO embryos. Other, less frequent, developmental defects were exencephaly and spina bifida.

CONCLUSION

We conclude that the combination of defective collagen structure in the dermis and imbalanced keratinocyte maturation could be responsible for the observed developmental defects in Dse KO mice. In addition, we propose that Dse KO mice could be used as a model in pathogenetic studies of human fetal abdominal wall defects.

Constitutive activation of ectodermal β-catenin induces ectopic outgrowths at various positions in mouse embryo and affects abdominal ventral body wall closure

Vertebrate limbs originate from the lateral plate mesoderm (LPM) and the overlying ectoderm. While normal limb formation in defined regions has been well studied, the question of whether other positions retain limb-forming potential has not been fully investigated in mice. By ectopically activating β-catenin in the ectoderm with Msx2-cre, we observed that local tissue outgrowths were induced, which either progressed into limb-like structure within the inter-limb flank or formed extra tissues in other parts of the mouse embryo. In the presumptive abdominal region of severely affected embryos, ectopic limb formation was coupled with impaired abdominal ventral body wall (AVBW) closure, which indicates the existence of a potential counterbalance of limb formation and AVBW closure. At the molecular level, constitutive β-catenin activation was sufficient to trigger, but insufficient to maintain the ectopic expression of a putative limb-inducing factor, Fgf8, in the ectoderm. These findings provide new insight into the mechanism of limb formation and AVBW closure, and the crosstalk between the Wnt/β-catenin pathway and Fgf signal.

Ectodermal Wnt signaling regulates abdominal myogenesis during ventral body wall development

Defects of the ventral body wall are prevalent birth anomalies marked by deficiencies in body wall closure, hypoplasia of the abdominal musculature and multiple malformations across a gamut of organs. However, the mechanisms underlying ventral body wall defects remain elusive. Here, we investigated the role of Wnt signaling in ventral body wall development by inactivating Wls or β-catenin in murine abdominal ectoderm. The loss of Wls in the ventral epithelium, which blocks the secretion of Wnt proteins, resulted in dysgenesis of ventral musculature and genito-urinary tract during embryonic development. Molecular analyses revealed that the dermis and myogenic differentiation in the underlying mesenchymal progenitor cells was perturbed by the loss of ectodermal Wls. The activity of the Wnt-Pitx2 axis was impaired in the ventral mesenchyme of the mutant body wall, which partially accounted for the defects in ventral musculature formation. In contrast, epithelial depletion of β-catenin or Wnt5a did not resemble the body wall defects in the ectodermal Wls mutant. These findings indicate that ectodermal Wnt signaling instructs the underlying mesodermal specification and abdominal musculature formation during ventral body wall development, adding evidence to the theory that ectoderm-mesenchyme signaling is a potential unifying mechanism for the origin of ventral body wall defects.

Repair of umbilical and epigastric hernias

Umbilical and epigastric hernias are primary midline defects that are present in up to 50% of the population. In the United States, only about 1% of the population carries this specific diagnosis, and only about 11% of these are repaired. Repair is aimed at symptoms relief or prevention, and the patient's goals and expectations should be explicitly identified and aligned with the health care team. This article details some relevant and interesting anatomic issues, reviews existing data, and highlights some common and important surgical techniques. Emphasis is placed on a patient-centered approach to the repair of umbilical and epigastric hernias.

Novel exomphalos genetic mouse model: the importance of accurate phenotypic classification

BACKGROUND

Rodent models of abdominal wall defects (AWD) may provide insight into the pathophysiology of these conditions including gut dysfunction in gastroschisis, or pulmonary hypoplasia in exomphalos. Previously, a Scribble mutant mouse model (circletail) was reported to exhibit gastroschisis. We further characterise this AWD in Scribble knockout mice.

METHOD

Homozygous Scrib knockout mice were obtained from heterozygote matings. Fetuses were collected at E17.5-18.5 with intact amniotic membranes. Three mutants and two control fetuses were imaged by in amnio micro-MRI. Remaining fetuses were dissected, photographed and gut length/weight measured. Ileal specimens were stained for interstitial cells of Cajal (ICC), imaged using confocal microscopy and ICC quantified.

RESULTS

127 fetuses were collected, 15 (12%) exhibited AWD. Microdissection revealed 3 mutants had characteristic exomphalos phenotype with membrane-covered gut/liver herniation into the umbilical cord. A further 12 exhibited extensive AWD, with eviscerated abdominal organs and thin covering membrane (intact or ruptured). Micro-MRI confirmed these phenotypes. Gut was shorter and heavier in AWD group compared to controls but morphology/number of ICC was not different.

DISCUSSION

The Scribble knockout fetus exhibits exomphalos (intact and ruptured), in contrast to the original published phenotype of gastroschisis. Detailed dissection of fetuses is essential ensuring accurate phenotyping and result reporting.

Thoracoabdominal wall defect with complete ectopia cordis and gastroschisis: a case report and review of the literature

Ventral wall defects are extremely rare anomalies that are likely caused by the failure of the ventral wall to close during week 4 of development. We report a case of severe thoracoabdominal wall defect including complete thoracic ectopia cordis and gastroschisis. This combination represents a novel constellation of findings in a single patient. This unique case further demonstrates an anatomically normal heart with age-appropriate development and an intact diaphragm. We review the literature of other reports and discussions of entities that share overlapping features with this case.

Genetic dissection of ventral folding morphogenesis in mouse: embryonic visceral endoderm-supplied BMP2 positions head and heart

Ventral folding morphogenesis (VFM), a vital morphogenetic process in amniotes, mediates gut endoderm internalization, linear heart tube formation, ventral body wall closure and encasement of the fetus in extraembryonic membranes. Aberrant VFM underlies a number of birth defects such as gastroschisis and ectopia cordis in human and misplacement of head and heart in mouse. Recent cell lineage-specific mouse mutant analyses identified the Bone Morphogenetic Protein (BMP) pathway and Anterior Visceral Endoderm (AVE) as key regulators of anterior VFM. Loss of BMP2 expression solely from embryonic visceral endoderm (EmVE) and the AVE blocks formation of foregut invagination, and simultaneously, aberrantly positions the heart anterior/dorsal to the head, suggesting a mechanistic link between foregut and head/heart morphogenesis.

Disturbance of SHH signalling pathway during early embryogenesis in the cadmium-induced omphalocele chick model

INTRODUCTION

Administration of cadmium (Cd) after 60 h (H) incubation induces ventral body wall defect (VBWD) similar to the omphalocele phenotype in the chick embryo. In this model, the earliest histological changes have been observed in somites commencing at 4-h post-treatment (4H). The molecular mechanism by which Cd acts in this critical period of embryogenesis still remains unclear. Sonic hedgehog (SHH) signalling plays an important role in vertebrate development, including somitogenesis and thus ventral body wall formation. Patched (PTCH), a cell membrane receptor for SHH, is expressed in somites and Patched knockout mice display somite dysfunction. Another transmembrane receptor, Smoothened (SMO), is also expressed in somites and transduces the SHH signal regulated by PTCH. We designed this study to test the hypothesis that SHH signalling is downregulated during the critical period of early embryogenesis in the Cd-induced omphalocele chick model.

METHODS

After 60 h of incubation, chicks were exposed to either chick saline or 50 μL of 50 μM cadmium acetate and divided into two groups: control and Cd (n = 24 for each group). Chicks were harvested 1, 4, and 8 h post-treatment. Real-time RT-PCR was performed to evaluate the relative mRNA expression level of SHH, PTCH and SMO. Immunofluorescence confocal microscopy was then performed to evaluate protein expression/distribution of SHH, PTCH and SMO.

RESULTS

The relative mRNA expression levels of SHH, PTCH and SMO were significantly downregulated in the Cd group compared to controls at 4H post treatment, whereas, there were no significant differences at the other time points. Immunohistochemistry revealed that the intensity of SHH, PTCH and SMO was markedly diminished at 4 h in Cd-treated embryos compared to controls.

CONCLUSION

Disturbance of the SHH signalling pathway as evidenced by SHH, PTCH and SMO downregulation during the narrow window of early embryogenesis may result in somite maldevelopment, contributing to the omphalocele phenotype in the Cd chick model.

Eya1 and Eya2 gene expression is down-regulated during somitic myogenesis in the cadmium-induced omphalocele chick model

PURPOSE

The molecular mechanisms underlying omphalocele are still largely unknown. Recently, established cadmium (Cd)-induced omphalocele chick model has been used to investigate the pathogenesis of omphalocele. The earliest histologic changes in this model has been observed in somites 4 hours posttreatment, leading us to hypothesize that disruption of migration of somite-derived cells ventrally may cause omphalocele phenotype. Eyes absent (Eya) genes are expressed in the somite (dermomyotome) and play a key role in somitic myogenesis. We designed this study to investigate the hypothesis that Eya1 and Eya2 gene expression is down-regulated during the critical period of early embryogenesis in the Cd-induced omphalocele chick model.

METHODS

After 60 hours of incubation, chicks were exposed to either chick saline or Cd and divided into control and Cd (n = 24 for each group). Chicks were then harvested 1 hour, 4 hours, and 8 hours posttreatment. Real-time quantitative polymerase chain reaction was performed to evaluate gene expression levels of Eya1 and Eya2 in the chick embryo, and they were statistically analyzed. Immunofluorescence confocal microscopy was also performed to evaluate protein expression and distribution pattern of Eya1 and Eya2.

RESULTS

At 4 hours posttreatment, the relative messenger RNA expression levels of Eya1 and Eya2 were significantly down-regulated in the Cd group compared with controls (P < .05). The intensity of Eya1 and Eya2 immunofluorescence was also markedly diminished at 4 hours in the Cd-treated embryos, whereas in control embryos, strong intensity of immunofluorescence of them was expressed in the dermomyotomal cells.

CONCLUSION

Down-regulation of Eya genes during the critical period of early embryogenesis may contribute to omphalocele phenotype in the Cd chick model, interfering with migration of embryonic body wall ventrally.

EphB2/B3 gene expression is down-regulated during early embryogenesis in the cadmium-induced omphalocele chick model

PURPOSE

In the chick embryo, the administration of cadmium (Cd) induces omphalocele phenotype. The earliest histologic change in this model is observed in the somite 4 hours (H) post treatment, postulating that disruption of somite development in embryogenesis may cause omphalocele phenotype. EphB2 and EphB3 are involved in many embryonic developmental processes, including somitogenesis. EphB2(-/-)EphB3(-/-) double knockouts display omphalocele phenotype. We hypothesized that EphB2/B3 genes are down-regulated in the Cd chick model during the critical period of embryogenesis.

METHODS

After 60H incubation, chicks were harvested 1H, 4H, and 8H post treatment with saline or Cd and divided into control and Cd groups. Reverse transcriptase-polymerase chain reaction was performed to evaluate gene expression levels of EphB2/B3. Immunofluorescence confocal microscopy was performed to evaluate protein expression/distribution of EphB2/B3.

RESULTS

At 4H post treatment, the messenger RNA expression levels of EphB2/B3 were significantly down-regulated in the Cd group compared with controls (P < .05). The intensity of EphB2/B3 immunofluorescence was markedly diminished at 4H in the Cd-treated embryos, whereas strong immunoreactivity was observed in the somite in controls.

CONCLUSION

Downregulation of EphB2/B3 during the narrow window of early embryogenesis may interfere with normal somitogenesis, preventing migration of embryonic body wall ventrally and thus causing omphalocele.

STELLA-positive subregions of the primitive streak contribute to posterior tissues of the mouse gastrula

The developmental relationship between the posterior embryonic and extraembryonic regions of the mammalian gastrula is poorly understood. Although many different cell types are deployed within this region, only the primordial germ cells (PGCs) have been closely studied. Recent evidence has suggested that the allantois, within which the PGCs temporarily take up residence, contains a pool of cells, called the Allantoic Core Domain (ACD), critical for allantoic elongation to the chorion. Here, we have asked whether the STELLA-positive cells found within this region, thought to be specified PGCs, are actually part of the ACD and to what extent they, and other ACD cells, contribute to the allantois and fetal tissues. To address these hypotheses, STELLA was immunolocalized to the mouse gastrula between Early Streak (ES) and 12-somite pair (-s) stages (~6.75-9.0 days post coitum, dpc) in histological sections. STELLA was found in both the nucleus and cytoplasm in a variety of cell types, both within and outside of the putative PGC trajectory. Fate-mapping the headfold-stage (~7.75-8.0 dpc) posterior region, by which time PGCs are thought to be segregated into a distinct lineage, revealed that the STELLA-positive proximal ACD and intraembryonic posterior primitive streak (IPS) contributed to a wide range of somatic tissues that encompassed derivatives of the three primary germ layers. This contribution included STELLA-positive cells localizing to tissues both within and outside of the putative PGC trajectory. Thus, while STELLA may identify a subpopulation of cells destined for the PGC lineage, our findings reveal that it may be part of a broader niche that encompasses the ACD and through which the STELLA population may contribute cells to a wide variety of posterior tissues of the mouse gastrula.

Presenilin genes are downregulated during somitogenesis in the cadmium-induced omphalocele chick model

PURPOSE

Although the precise pathogenesis of ventral body wall (VBW) defects is not clearly understood, it has recently postulated that disruption of somite development during early embryogenesis may cause failure of proper VBW formation. The administration of cadmium (Cd) after 60 h of incubation induces omphalocele spectrum in the chick embryo. Previous studies have shown that one of the earliest histological changes seen in this model is abnormal cell death in the somite, occurring at 4 h post treatment (4H). However, the molecular mechanism by which Cd acts in this critical period of embryogenesis still remains unclear. Presenilins are expressed in somites and play an important role in vertebrate development, including somitogenesis and thus VBW formation. We designed this study to test the hypothesis that gene expression levels of presenilin 1 (PSEN1) and presenilin 2 (PSEN2) are downregulated during the critical period of early embryogenesis in the Cd-induced omphalocele in the chick model.

METHODS

After 60 h of incubation, chick embryos were exposed to either saline or 50 μM cadmium and divided into two groups: control and Cd (n = 8 at each time point for each group). Real-time RT-PCR was performed to evaluate the relative mRNA expression levels of PSEN1 and PSEN2 in the Cd-induced omphalocele chick model. Differences between two groups at each time point were analysed statistically and the significance was accepted at p < 0.05. Immunofluorescence confocal microscopy was performed to evaluate the protein expression/distribution of presenilins in the somite of chick embryo.

RESULTS

The relative mRNA expression levels of PSEN1 and PSEN2 were significantly downregulated in the Cd group at 4H compared with controls (p < 0.005) (Table). However, there were no significant differences at the other time points. At 4H, immunofluorescence of presenilins (green) was markedly diminished in the Cd-treated embryos, whereas strong immunofluorescence of them was seen in the somite (dermomyotome) in controls (Fig. 1). 1 Immunofluorescence Confocal Microscopy for PSEN1 and PSEN2 in the dermomyotome of the somite in the trunk level of chick embryo 4H post treatment. Intensity of PSEN1 immunofluorescence (green) was markedly diminished in Cd-treated embryos, whereas strong PSEN1 expression was seen in the dermomyotome in controls. PSEN2 immunofluorescence was also decreased in the Cd-treated embryos, whereas strong PSEN2 immunofluorescence (green) was observed predominantly in the dermomyotome in controls. Immunofluorescence in orange is DNA counter staining by DAPI CONCLUSION: We provide evidence, for the first time, that gene expression of presenilins is downregulated during the narrow window of very early embryogenesis in the Cd chick model. Decreased expression of presenilins may contribute to omphalocele phenotype in Cd chick model, by disrupting somite development.

Semaphorin and Eph receptor signaling guide a series of cell movements for ventral enclosure in C. elegans

BACKGROUND

In the last stage of the Caenorhabditis elegans body wall closure, an open pocket in the epidermis is closed by the migration of marginal epidermal P/pocket cells to the ventral midline. The cellular and molecular mechanisms of this closure remain unknown.

RESULTS

Cells within the pocket align to form a bridge for migration of contralateral P cell pair P9/10 L,R (and neighboring P cells) to the midline. Bridge formation involves rearrangement of five sister pairs of PLX-2/plexin and VAB-1/Eph receptor expressing "plexin band" cells, of which three pairs form a scaffold for bridge assembly and two pairs form the bridge. Bridge formation requires VAB-1 kinase-dependent extension of presumptive bridge cells over scaffold cells toward the ventral midline. An unassembled vab-1 null mutant bridge obstructs P cell migration, which is largely overcome by plexin band expression of VAB-1 or VAB-1(delC) (a kinase deletion of VAB-1). VAB-1 also functions redundantly with MAB-20/semaphorin to prevent perdurant gaps between sister plexin band cells that block P cell migration.

CONCLUSIONS

The Eph receptor mediates cellular extensions required for bridge formation, independently facilitates P cell migration to the midline, and functions redundantly with PLX-2/plexin to prevent gaps in the bridge used for P9/10 cell migration in body wall closure.

Anterior visceral endoderm directs ventral morphogenesis and placement of head and heart via BMP2 expression

In amniotes, ventral folding morphogenesis achieves gut internalization, linear heart tube formation, ventral body wall closure, and encasement of the fetus in extraembryonic membranes. Impairment of ventral morphogenesis results in human birth defects involving body wall, gut, and heart malformations and in mouse misplacement of head and heart. Absence of knowledge about genetic pathways and cell populations directing ventral folding in mammals has precluded systematic study of cellular mechanisms driving this vital morphogenetic process. We report tissue-specific mouse mutant analyses identifying the bone morphogenetic protein (BMP) pathway as a key regulator of ventral morphogenesis. BMP2 expressed in anterior visceral endoderm (AVE) signals to epiblast derivatives during gastrulation to orchestrate initial stages of ventral morphogenesis, including foregut development and positioning of head and heart. These findings identify unanticipated functions for the AVE in organizing the gastrulating embryo and indicate that visceral endoderm-expressed BMP2 coordinates morphogenetic cell behaviors in multiple epiblast lineages.

Hedgehog signaling in the posterior region of the mouse gastrula suggests manifold roles in the fetal-umbilical connection and posterior morphogenesis

Although many fetal birth defects, particularly those of the body wall and gut, are associated with abnormalities of the umbilical cord, the developmental relationship between these structures is largely obscure. Recently, genetic analysis of mid-gestation mouse embryos revealed that defects in Hedgehog signaling led to omphalocoele, or failure of the body wall to close at the umbilical ring (Matsumaru et al. [ 2011] PLos One 6:e16260). However, systematic spatiotemporal localization of Hedgehog signaling in the allantois, or umbilical precursor tissue, and the surrounding regions has not been documented. Here, a combination of reagents, including the Ptc1:lacZ and Runx1:lacZ reporter mice, immunohistochemistry for Smoothened (Smo), Sonic Hedgehog (Shh), and Indian hedgehog (Ihh), and detailed PECAM-1/Flk-1/Runx-1 analysis, revealed robust Hedgehog signaling in previously undocumented posterior sites over an extended period of time (∼7.0-9.75 dpc). These included the recently described proximal walls of the allantois (Ventral and Dorsal Cuboidal Mesothelia; VCM and DCM, respectively); the ventral embryonic surface continuous with them; hemogenic arterial endothelia; hematopoietic cells; the hindgut; ventral ectodermal ridge (VER); chorionic ectoderm; and the intraplacental yolk sac (IPY), which appeared to be a site of placental hematopoiesis. This map of Hedgehog signaling in the posterior region of the mouse conceptus will provide a valuable foundation upon which to elucidate the origin of many posterior midline abnormalities, especially those of the umbilical cord and associated fetal defects. Developmental Dynamics 240:2175-2193, 2011. © 2011 Wiley-Liss, Inc.

Are abdominal wall defects and external genitalia anomalies randomly expressed in some families?

Familial cases of isolated abdominal wall defects with variable expressivity in more than one generation have rarely been observed. We report four affected individuals within a small three-generation family with either variable non-syndromic abdominal wall defects or external genital anomalies. We discuss the possible transmission of non-syndromic abdominal wall defects. It could be hypothesized that similar developmental defects may result in anomalies like hypospadias in males or developmental anomalies of the labia minora or labia majora in females.

BMPR1A-mediated BMP1 signalling is disrupted in the cadmium-induced omphalocele in the chick model

PURPOSE

In the chick embryo, administration of cadmium (Cd) induces omphalocele phenotype. The earliest histological changes in this model are observed commencing at 4-h post treatment (4H). The molecular mechanisms by which Cd acts during the critical period of embryogenesis remain unclear. Bone morphogenetic proteins (BMPs) and their receptors (BMPRs) regulate many fundamental biological processes and are involved in various embryonic morphogenesis, including ventral body wall (VBW) formation. Homozygous BMP1 mutant mice cause VBW defects. It has been reported that BMPR1A conditional knockouts also exhibit omphalocele phenotype. We designed this study to test the hypothesis that gene expression levels of BMP1 and BMPR1A are downregulated during the critical period of embryogenesis in the Cd chick model.

METHODS

After 60-h incubation, chick embryos were exposed to either Cd or saline and then harvested 1H, 4H and 8H. Chicks were divided into control (n = 24) and Cd (n = 24). RT-PCR was performed and differences between the two groups were tested statistically (significance was accepted at p < 0.05). Immunohistochemical study was also performed to evaluate those proteins expression/distribution.

RESULTS

The gene expression levels of BMP1 and BMPR1A at 4H were significantly downregulated in Cd group compared to controls. Immunoreactivity of BMP1 and BMPR1A was also markedly decreased in Cd-treated embryos compared to controls.

CONCLUSION

Disruption of BMPR1A-mediated BMP1 signalling during the narrow window of early embryogenesis may interfere with normal VBW formation, causing omphalocele phenotype in the Cd chick model.