Computer simulation analysis of normal and abnormal development of the mammalian diaphragm

Morphofunctional Characterization of Different Tissue Factors in Congenital Diaphragmatic Hernia Affected Tissue

Congenital diaphragm hernia (CDH) is a congenital disease that occurs during prenatal development. Although the morbidity and mortality rate is rather significant, the pathogenesis of CDH has been studied insignificantly due to the decreased accessibility of human pathological material. Therefore the aim of our work was to evaluate growth factors (transforming growth factor-beta (TGF-β), basic fibroblast growth factor (bFGF), insulin-like growth factor 1 (IGF-1), hepatocyte growth factor (HGF)) and their receptors (fibroblast growth factor receptor 1 (FGFR1), insulin-like growth factor 1 (IGF-1R)), muscle (dystrophin, myosin, alpha actin) and nerve quality (nerve growth factor (NGF), nerve growth factor receptor (NGFR), neurofilaments (NF)) factors, local defense factors (ß-defensin 2, ß-defensin 4), programmed cell death (TUNEL), and separate gene (Wnt-1) expression in human pathological material to find immunohistochemical marker differences between the control and the CDH patient groups. A semi-quantitative counting method was used for the evaluation of the tissues and structures in the Biotin-Streptavidin-stained slides. Various statistically significant differences were found in immunoreactive expression between the patient and the control group tissue and the morphological structures as well as very strong, strong, and moderate correlations between immunoreactives in different diaphragm cells and structures. These significant changes and various correlations indicate that multiple morphopathogenetic pathways are affected in CDH pathogenesis. This work contains the evaluation of the causes for these changes and their potential involvement in CDH pathogenesis.

Local cell interactions and self-amplifying individual cell ingression drive amniote gastrulation

Gastrulation generates three layers of cells (ectoderm, mesoderm, endoderm) from a single sheet, while large scale cell movements occur across the entire embryo. In amniote (reptiles, birds, mammals) embryos, the deep layers arise by epithelial-to-mesenchymal transition (EMT) at a morphologically stable midline structure, the primitive streak (PS). We know very little about how these events are controlled or how the PS is maintained despite its continuously changing cellular composition. Using the chick, we show that isolated EMT events and ingression of individual cells start well before gastrulation. A Nodal-dependent ‘community effect’ then concentrates and amplifies EMT by positive feedback to form the PS as a zone of massive cell ingression. Computer simulations show that a combination of local cell interactions (EMT and cell intercalation) is sufficient to explain PS formation and the associated complex movements globally across a large epithelial sheet, without the need to invoke long-range signalling.

DOI:http://dx.doi.org/10.7554/eLife.01817.001

A key process during the development of an embryo involves a single layer of cells reorganizing into three ‘germ layers’: the ectoderm, which becomes the skin and nervous system; the mesoderm, which gives rise to the skeleton, muscles and the circulatory and urinogenital systems, and the endoderm, which gives rise to the lining of the gut and associated organs. The process of forming these three layers is known as gastrulation.

To date most experiments on gastrulation in vertebrates have been performed on frog embryos. However, the embryos of amniotes, the group of ‘higher’ vertebrates that comprises reptiles, birds and mammals, differ from those of frogs in a number of ways. Now Voiculescu et al. have used a combination of experimental and computational techniques to shed new light on gastrulation in chick embryos.

Just prior to gastrulation, the cells of the amniote embryo are arranged in a flat disk, one cell thick, called the epiblast. The cells of the epiblast then move to form the mesoderm and endoderm (in a process called epithelial-to-mesenchymal transition). These cell movements also lead to the formation of a structure called the primitive streak that establishes the left-right symmetry of the organism, and also defines the midline of the body.

Now Voiculescu et al. have shown that the epithelial-to-mesenchymal transition starts before the primitive streak appears, and that two main processes drive gastrulation. One involves cells inserting themselves between other cells at the midline of the epiblast, which causes a double whorl-like movement within the plane of the epiblast. At the same time small numbers of cells leave the epiblast, and as these cells accumulate under the epiblast, they initiate a positive feedback effect by which they encourage more cells to leave the epiblast. Voiculescu et al. found that this ‘community effect’ involves signalling by a protein called Nodal. This protein effectively amplifies the epithelial-to-mesenchymal transition and leads to the appearance of the primitive streak at the midline.

Using computational modelling, Voiculescu et al. argue that the movements of gastrulation can be explained entirely based on local interactions between cells, without the need for cells to send signals over long distances to guide cell movements, as had been generally believed.

DOI:http://dx.doi.org/10.7554/eLife.01817.002

Congenital diaphragmatic hernia candidate genes derived from embryonic transcriptomes

Congenital diaphragmatic hernia (CDH) is a common (1 in 3,000 live births) major congenital malformation that results in significant morbidity and mortality. The discovery of CDH loci using standard genetic approaches has been hindered by its genetic heterogeneity. We hypothesized that gene expression profiling of developing embryonic diaphragms would help identify genes likely to be associated with diaphragm defects. We generated a time series of whole-transcriptome expression profiles from laser captured embryonic mouse diaphragms at embryonic day (E)11.5 and E12.5 when experimental perturbations lead to CDH phenotypes, and E16.5 when the diaphragm is fully formed. Gene sets defining biologically relevant pathways and temporal expression trends were identified by using a series of bioinformatic algorithms. These developmental sets were then compared with a manually curated list of genes previously shown to cause diaphragm defects in humans and in mouse models. Our integrative filtering strategy identified 27 candidates for CDH. We examined the diaphragms of knockout mice for one of the candidate genes, pre-B-cell leukemia transcription factor 1 (Pbx1), and identified a range of previously undetected diaphragmatic defects. Our study demonstrates the utility of genetic characterization of normal development as an integral part of a disease gene identification and prioritization strategy for CDH, an approach that can be extended to other diseases and developmental anomalies.

Teratogen screening: state of the art

Due to the number of new substances coming into use every year and the increasing amounts of chemicals, which are introduced into the environment, there is a high demand for a rapid, reliable and cost-effective method for detection of developmental toxicity. To meet this challenge various in vitro techniques have been established additional to in vivo animal testing. This review introduces the techniques in existence at the moment. Requirements on an ideal in vitro teratogenicity test system are stated, and the advantages and disadvantages of the present methods are discussed.

Pulmonary disease is a component of distal arthrogryposis type 5

We report on a three-generation family with distal arthrogryposis type 5 (DA5). The family has four affected members in three generations with an apparent autosomal dominant pattern of inheritance. Three affected individuals were examined. All have distal joint contractures with absent flexion creases, limited mobility of all small and large joints, unusual stance with shortened heel cords and pes cavus, firm muscles, short stature, decreased extraocular movements, and pectus excavatum. The propositus has pulmonary hypertension secondary to chronic hypoxia from restrictive chest disease, alveolar hypoventilation, and residence at 7,000 feet above sea level. Cardiac catheterization documented pulmonary artery pressure of 54 mmHg and a pulmonary capillary wedge pressure of 10 mmHg. Pulmonary function tests showed severe chest restriction (forced vital capacity 30% of predicted; total lung capacity 51% predicted); and reduction of maximal inspiratory and expiratory pressures. Arterial blood gases documented alveolar hypoventilation. Restrictive chest disease is a component of DA5. This implies involvement of the skeletal, and/or respiratory muscles. All individuals diagnosed with DA5 should be evaluated for chest disease, alveolar hypoventilation, as treatment of chronic hypoxia may delay or reverse pulmonary hypertension.

Development of the diaphragm and genetic mouse models of diaphragmatic defects

Improving our understanding of diaphragmatic development is essential to making progress in defining the pathogenesis and genetic etiologies of congenital diaphragmatic defects in humans. As mouse genetic technology has given us new tools to manipulate and observe development, a number of mouse models have recently emerged that provide valuable insight to this field. In this article, we review our current understanding of diaphragmatic embryogenesis including the origin of diaphragmatic tissue. We use rodent models to review the muscularization of the diaphragm and review selected genetic models of abnormal muscularization. We also review models of posterior diaphragmatic defects and discuss evidence for the pleuroperitoneal fold (PPF) tissue contributing to the diaphragm. Finally, we discuss models of anterior and central hernias. It may be simplistic to subdivide this review based on anatomic regions of the diaphragm, as evidence is emerging that defects in different regions of the diaphragm in humans and in mice may be etiologically related. However, at this time we do not have enough knowledge to make more mechanistic or genetic classifications though with time, genetic progress in the field of diaphragm development will allow us to do this.

Impaired mesenchymal cell function in Gata4 mutant mice leads to diaphragmatic hernias and primary lung defects

Congenital diaphragmatic hernia (CDH) is an often fatal birth defect that is commonly associated with pulmonary hypoplasia and cardiac malformations. Some investigators hypothesize that this constellation of defects results from genetic or environmental triggers that disrupt mesenchymal cell function in not only the primordial diaphragm but also the thoracic organs. The alternative hypothesis is that the displacement of the abdominal viscera in the chest secondarily perturbs the development of the heart and lungs. Recently, loss-of-function mutations in the gene encoding FOG-2, a transcriptional co-regulator, have been linked to CDH and pulmonary hypoplasia in humans and mice. Here we show that mutagenesis of the gene for GATA-4, a transcription factor known to functionally interact with FOG-2, predisposes inbred mice to a similar set of birth defects. Analysis of wild-type mouse embryos demonstrated co-expression of Gata4 and Fog2 in mesenchymal cells of the developing diaphragm, lungs, and heart. A significant fraction of C57Bl/6 mice heterozygous for a Gata4 deletion mutation died within 1 day of birth. Developmental defects in the heterozygotes included midline diaphragmatic hernias, dilated distal airways, and cardiac malformations. Heterozygotes had any combination of these defects or none. In chimeric mice, Gata4(-/-) cells retained the capacity to contribute to cells in the diaphragmatic central tendon and lung mesenchyme, indicating that GATA-4 is not required for differentiation of these lineages. We conclude that GATA-4, like its co-regulator FOG-2, is required for proper mesenchymal cell function in the developing diaphragm, lungs, and heart.