Conditional deletion of WT1 in the septum transversum mesenchyme causes congenital diaphragmatic hernia in mice

Toll-like receptors ligand immunomodulators for the treatment congenital diaphragmatic hernia

BACKGROUND

Congenital diaphragmatic hernia (CDH) is a rare disease that affects the development of the diaphragm, leading to abnormal lung development. Unfortunately, there is no established therapy for CDH. Retinoic acid pathways are implicated in the ethology of CDH and macrophages are known to play a role in repairing organ damage.

METHODS

We have analyzed the effect of several Toll like receptor (TLR) ligands in the nitrofen-induced CDH model in pregnant rats widely used to study this disease and in the G2-GATA4Cre;Wt1fl/fl CDH genetic mice model. Morphometric and histological studies were carried out. Immune cell infiltration was assayed by immunochemistry and immunofluorescence and retinoic pathway gene expression analyzed in vivo and in vitro in macrophages.

RESULTS

We found that administering a single dose of atypical TLR2/4 ligands (CS1 or CS2), 3 days after nitrofen, cured diaphragmatic hernia in 73% of the fetuses and repaired the lesion with complete diaphragm closure being on the other hand nontoxic for the mothers or pups. Moreover, these immunomodulators also improved pulmonary hypoplasia and alveolar maturation and vessel hypertrophy, enhancing pulmonary maturity of fetuses. We also found that CS1 treatment rescued the CDH phenotype in the G2-GATA4Cre;Wt1fl/fl CDH genetic mice model. Only 1 out of 11 mutant embryos showed CDH after CS1 administration, whereas CDH prevalence was 70% in untreated mutant embryos. Mechanistically, CS1 stimulated the infiltration of repairing M2 macrophages (CD206+ and Arg1+) into the damaged diaphragm and reduced T cell infiltration. Additionally, those TLR ligands induced retinol pathway genes, including RBP1, RALDH2, RARα, and RARβ, in the affected lungs and the diaphragm and in macrophages in vitro.

CONCLUSIONS

Our research has shown that TLR ligand immunomodulators that influence anti-inflammatory macrophage activation can be effective in treating CDH, being nontoxic for the mothers or pups suggesting that those TLR ligands are a promising solution for CDH leading to orphan drug designation for CS1. The immune system of the fetus would be responsible for repairing the damage and closure of the hernia in the diaphragm and enhanced proper lung development after CS1 treatment.

Role of genetics and the environment in the etiology of congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) is a congenital malformation characterized by failure of diaphragm closure during embryonic development, leading to pulmonary hypoplasia and pulmonary hypertension, which contribute significantly to morbidity and mortality. The occurrence of CDH and pulmonary hypoplasia is theorized to result from both abnormalities in signaling pathways of smooth muscle cells in pleuroperitoneal folds and mechanical compression by abdominal organs within the chest cavity on the developing lungs. Although, the precise etiology of diaphragm maldevelopment in CDH is not fully understood, it is believed that interplay between genes and the environment contributes to its onset. Approximately 30% of patients with CDH possess chromosomal or single gene defects and these patients tend to have inferior outcomes compared with those without genetic associations. At present, approximately 150 gene variants have been linked to the occurrence of CDH. The variable expression of the CDH phenotype in the presence of a recognized genetic predisposition can be explained by an environmental effect on gene penetrance and expression. The retinoic acid pathway is thought to play an essential role in the interactions of genes and environment in CDH. However, apart from the gradually maturing retinol hypothesis, there is limited evidence implicating other environmental factors in CDH occurrence. This review aims to describe the pathogenesis of CDH by summarizing the genetic defects and potential environmental influences on CDH development.

Cellular origins and translational approaches to congenital diaphragmatic hernia

Congenital Diaphragmatic Hernia (CDH) is a complex developmental abnormality characterized by abnormal lung development, a diaphragmatic defect and cardiac dysfunction. Despite significant advances in management of CDH, mortality and morbidity continue to be driven by pulmonary hypoplasia, pulmonary hypertension, and cardiac dysfunction. The etiology of CDH remains unknown, but CDH is presumed to be caused by a combination of genetic susceptibility and external/environmental factors. Current research employs multi-omics technologies to investigate the molecular profile and pathways inherent to CDH. The aim is to discover the underlying pathogenesis, new biomarkers and ultimately novel therapeutic targets. Stem cells and their cargo, non-coding RNAs and agents targeting inflammation and vascular remodeling have produced promising results in preclinical studies using animal models of CDH. Shortcomings in current therapies combined with an improved understanding of the pathogenesis in CDH have given rise to novel promising experimental treatments that are currently being evaluated in clinical trials. This review provides insight into current developments in translational research, ranging from the cellular origins of abnormal cardiopulmonary development in CDH and the identification of novel treatment targets in preclinical CDH models at the bench and their translation to clinical trials at the bedside.

The etiology of congenital diaphragmatic hernia: the retinoid hypothesis 20 years later

Congenital diaphragmatic hernia (CDH) is a severe birth defect and a major cause of neonatal respiratory distress. Impacting ~2-3 in 10,000 births, CDH is associated with a high mortality rate, and long-term morbidity in survivors. Despite the significant impact of CDH, its etiology remains incompletely understood. In 2003, Greer et al. proposed the Retinoid Hypothesis, stating that the underlying cause of abnormal diaphragm development in CDH was related to altered retinoid signaling. In this review, we provide a comprehensive update to the Retinoid Hypothesis, discussing work published in support of this hypothesis from the past 20 years. This includes reviewing teratogenic and genetic models of CDH, lessons from the human genetics of CDH and epidemiological studies, as well as current gaps in the literature and important areas for future research. The Retinoid Hypothesis is one of the leading hypotheses to explain the etiology of CDH, as we continue to better understand the role of retinoid signaling in diaphragm development, we hope that this information can be used to improve CDH outcomes. IMPACT: This review provides a comprehensive update on the Retinoid Hypothesis, which links abnormal retinoic acid signaling to the etiology of congenital diaphragmatic hernia. The Retinoid Hypothesis was formulated in 2003. Twenty years later, we extensively review the literature in support of this hypothesis from both animal models and humans.

Rescuing lung development through embryonic inhibition of histone acetylation

A major barrier to the impact of genomic diagnosis in patients with congenital malformations is the lack of understanding regarding how sequence variants contribute to disease pathogenesis and whether this information could be used to generate patient-specific therapies. Congenital diaphragmatic hernia (CDH) is among the most common and severe of all structural malformations; however, its underlying mechanisms are unclear. We identified loss-of-function sequence variants in the epigenomic regulator gene SIN3A in two patients with complex CDH. Tissue-specific deletion of Sin3a in mice resulted in defects in diaphragm development, lung hypoplasia, and pulmonary hypertension, the cardinal features of CDH and major causes of CDH-associated mortality. Loss of SIN3A in the lung mesenchyme resulted in reduced cellular differentiation, impaired cell proliferation, and increased DNA damage. Treatment of embryonic Sin3a mutant mice with anacardic acid, an inhibitor of histone acetyltransferase, reduced DNA damage, increased cell proliferation and differentiation, improved lung and pulmonary vascular development, and reduced pulmonary hypertension. These findings demonstrate that restoring the balance of histone acetylation can improve lung development in the Sin3a mouse model of CDH.

Connecting clinical, environmental, and genetic factors point to an essential role for vitamin A signaling in the pathogenesis of congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) is a developmental disorder that results in incomplete diaphragm formation, pulmonary hypoplasia, and pulmonary hypertension. Although a variety of genes have been linked to its etiology, CDH is not a monogenetic disease, and the cause of the condition is still unclear in the vast majority of clinical cases. By comparing human clinical data and experimental rodent data from the literature, we present clear support demonstrating the importance of vitamin A (vitA) during the early window of pregnancy when the diaphragm and lung are forming. Alteration of vitA signaling via dietary and genetic perturbations can create diaphragmatic defects. Unfortunately, vitA deficiency is chronic among people of child-bearing age, and this early window of diaphragm development occurs before many might be aware of pregnancy. Furthermore, there is an increased demand for vitA during this critical period, which exacerbates the likelihood of deficiency. It would be beneficial for the field to further investigate the connections between maternal vitA and CDH incidence, with the goal of determining vitA status as a CDH risk factor. Regular clinical monitoring of vitA levels in child-bearing years is a tractable method by which CDH outcomes could be prevented or improved.

The role of genes and environment in the etiology of congenital diaphragmatic hernias

Structural birth defects are a common cause of abnormalities in newborns. While there are cases of structural birth defects arising due to monogenic defects or environmental exposures, many birth defects are likely caused by a complex interaction between genes and the environment. A structural birth defect with complex etiology is congenital diaphragmatic hernias (CDH), a common and often lethal disruption in diaphragm development. Mutations in more than 150 genes have been implicated in CDH pathogenesis. Although there is generally less evidence for a role for environmental factors in the etiology of CDH, deficiencies in maternal vitamin A and its derivative embryonic retinoic acid are strongly associated with CDH. However, the incomplete penetrance of CDH-implicated genes and environmental factors such as vitamin A deficiency suggest that interactions between genes and environment may be necessary to cause CDH. In this review, we examine the genetic and environmental factors implicated in diaphragm and CDH development. In addition, we evaluate the potential for gene-environment interactions in CDH etiology, focusing on the potential interactions between the CDH-implicated gene, Gata4, and maternal vitamin A deficiency.

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.

Genetically Modified Mouse Models of Congenital Diaphragmatic Hernia: Opportunities and Limitations for Studying Altered Lung Development

Congenital diaphragmatic hernia (CDH) is a relatively common and life-threatening birth defect, characterized by an abnormal opening in the primordial diaphragm that interferes with normal lung development. As a result, CDH is accompanied by immature and hypoplastic lungs, being the leading cause of morbidity and mortality in patients with this condition. In recent decades, various animal models have contributed novel insights into the pathogenic mechanisms underlying CDH and associated pulmonary hypoplasia. In particular, the generation of genetically modified mouse models, which show both diaphragm and lung abnormalities, has resulted in the discovery of multiple genes and signaling pathways involved in the pathogenesis of CDH. This article aims to offer an up-to-date overview on CDH-implicated transcription factors, molecules regulating cell migration and signal transduction as well as components contributing to the formation of extracellular matrix, whilst also discussing the significance of these genetic models for studying altered lung development with regard to the human situation.

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.

Low maternal vitamin A intake increases the incidence of teratogen induced congenital diaphragmatic hernia in mice

BACKGROUND

Congenital diaphragmatic hernia (CDH) is a severe birth defect associated with high perinatal mortality and long-term morbidity. The etiology of CDH is poorly understood although abnormal retinoid signaling has been proposed to contribute to abnormal diaphragm development. Existing epidemiological data suggest that inadequate dietary vitamin A intake is a risk factor for developing CDH.

METHODS

Using a mouse model of teratogen-induced CDH, the objective of this study was to test the hypothesis that low maternal vitamin A intake contributes to abnormal diaphragm development. To test this hypothesis, we optimized a model of altered maternal dietary vitamin A intake and a teratogenic model of CDH in mice that recapitulates the hallmark features of posterolateral diaphragmatic hernia in humans.

RESULTS

Our data uniquely show that low maternal dietary vitamin A intake and marginal vitamin A status increases the incidence of teratogen-induced CDH in mice.

CONCLUSION

Low dietary vitamin A intake and marginal vitamin A status lead to an increased incidence of teratogen-induced CDH in mice, highlighting the importance of adequate dietary vitamin A intake and CDH risk.

IMPACT

This study describes and validates a mouse model of altered maternal and fetal vitamin A status. This study links existing epidemiological data with a mouse model of teratogen-induced congenital diaphragmatic hernia, highlighting the importance of low maternal vitamin A intake as a risk factor for the development of congenital diaphragmatic hernia. This study supports the Retinoid Hypothesis, which posits that the etiology of congenital diaphragmatic hernia is linked to abnormal retinoid signaling in the developing diaphragm.

Genetic Diagnostic Strategies and Counseling for Families Affected by Congenital Diaphragmatic Hernia

Congenital diaphragmatic hernia (CDH) is a relatively common and severe birth defect with variable clinical outcome and associated malformations in up to 60% of patients. Mortality and morbidity remain high despite advances in pre-, intra-, and postnatal management. We review the current literature and give an overview about the genetics of CDH to provide guidelines for clinicians with respect to genetic diagnostics and counseling for families. Until recently, the common practice was (molecular) karyotyping or chromosome microarray if the CDH diagnosis is made prenatally with a 10% diagnostic yield. Undiagnosed patients can be reflexed to trio exome/genome sequencing with an additional diagnostic yield of 10 to 20%. Even with a genetic diagnosis, there can be a range of clinical outcomes. All families with a child with CDH with or without additional malformations should be offered genetic counseling and testing in a family-based trio approach.

Cellular Origin(s) of Congenital Diaphragmatic Hernia

Congenital diaphragmatic hernia (CDH) is a structural birth defect characterized by a diaphragmatic defect, lung hypoplasia and structural vascular defects. In spite of recent developments, the pathogenesis of CDH is still poorly understood. CDH is a complex congenital disorder with multifactorial etiology consisting of genetic, cellular and mechanical factors. This review explores the cellular origin of CDH pathogenesis in the diaphragm and lungs and describes recent developments in basic and translational CDH research.

Rare and de novo variants in 827 congenital diaphragmatic hernia probands implicate LONP1 as candidate risk gene

Congenital diaphragmatic hernia (CDH) is a severe congenital anomaly that is often accompanied by other anomalies. Although the role of genetics in the pathogenesis of CDH has been established, only a small number of disease-associated genes have been identified. To further investigate the genetics of CDH, we analyzed de novo coding variants in 827 proband-parent trios and confirmed an overall significant enrichment of damaging de novo variants, especially in constrained genes. We identified LONP1 (lon peptidase 1, mitochondrial) and ALYREF (Aly/REF export factor) as candidate CDH-associated genes on the basis of de novo variants at a false discovery rate below 0.05. We also performed ultra-rare variant association analyses in 748 affected individuals and 11,220 ancestry-matched population control individuals and identified LONP1 as a risk gene contributing to CDH through both de novo and ultra-rare inherited largely heterozygous variants clustered in the core of the domains and segregating with CDH in affected familial individuals. Approximately 3% of our CDH cohort who are heterozygous with ultra-rare predicted damaging variants in LONP1 have a range of clinical phenotypes, including other anomalies in some individuals and higher mortality and requirement for extracorporeal membrane oxygenation. Mice with lung epithelium-specific deletion of Lonp1 die immediately after birth, most likely because of the observed severe reduction of lung growth, a known contributor to the high mortality in humans. Our findings of both de novo and inherited rare variants in the same gene may have implications in the design and analysis for other genetic studies of congenital anomalies.

Exome sequencing of fetuses with congenital diaphragmatic hernia supports a causal role for NR2F2, PTPN11, and WT1 variants

BACKGROUND

To identify genes associated with congenital diaphragmatic hernia (CDH) to help understand the etiology and inform prognosis.

METHODS

We performed exome sequencing on fetuses with CDH and their parents to identify rare genetic variants likely to mediate risk. We reviewed prenatal characteristics and neonatal outcomes.

RESULTS

Data were generated for 22 parent-offspring trios. Six Likely Damaging (LD) variants were identified in five families (23 %). Three LD variants were in genes that contain variants in other CDH cohorts (NR2F2, PTPN11, WT1), while three were in genes that do not (CTR9, HDAC6, TP53). Integrating these data bolsters the evidence of association of NR2F2, PTPN11, and WT1 with CDH in humans. Of the five fetuses with a genetic diagnosis, one was terminated, two underwent perinatal demise, while two survived until repair.

CONCLUSIONS

Exome sequencing expands the diagnostic yield of genetic testing in CDH. Correlating CDH patients' exomes with clinical outcomes may enable personalized counseling and therapies.

Management of Congenital Diaphragmatic Hernia (CDH): Role of Molecular Genetics

Congenital diaphragmatic hernia (CDH) is a relatively common major life-threatening birth defect that results in significant mortality and morbidity depending primarily on lung hypoplasia, persistent pulmonary hypertension, and cardiac dysfunction. Despite its clinical relevance, CDH multifactorial etiology is still not completely understood. We reviewed current knowledge on normal diaphragm development and summarized genetic mutations and related pathways as well as cellular mechanisms involved in CDH. Our literature analysis showed that the discovery of harmful de novo variants in the fetus could constitute an important tool for the medical team during pregnancy, counselling, and childbirth. A better insight into the mechanisms regulating diaphragm development and genetic causes leading to CDH appeared essential to the development of new therapeutic strategies and evidence-based genetic counselling to parents. Integrated sequencing, development, and bioinformatics strategies could direct future functional studies on CDH; could be applied to cohorts and consortia for CDH and other birth defects; and could pave the way for potential therapies by providing molecular targets for drug discovery.

Defective mesothelium and limited physical space are drivers of dysregulated lung development in a genetic model of congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) is a developmental disorder associated with diaphragm defects and lung hypoplasia. The etiology of CDH is complex and its clinical presentation is variable. We investigated the role of the pulmonary mesothelium in dysregulated lung growth noted in the Wt1 knockout mouse model of CDH. Loss of WT1 leads to intrafetal effusions, altered lung growth, and branching defects prior to normal closure of the diaphragm. We found significant differences in key genes; however, when Wt1 null lungs were cultured ex vivo, growth and branching were indistinguishable from wild-type littermates. Micro-CT imaging of embryos in situ within the uterus revealed a near absence of space in the dorsal chest cavity, but no difference in total chest cavity volume in Wt1 null embryos, indicating a redistribution of pleural space. The altered space and normal ex vivo growth suggest that physical constraints are contributing to the CDH lung phenotype observed in this mouse model. These studies emphasize the importance of examining the mesothelium and chest cavity as a whole, rather than focusing on single organs in isolation to understand early CDH etiology.

Resolving the heterogeneity of diaphragmatic mesenchyme: a novel mouse model of congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) is a relatively common developmental defect with considerable mortality and morbidity. Formation of the diaphragm is a complex process that involves several cell types, each with different developmental origins. Owing to this complexity, the aetiology of CDH is not well understood. The pleuroperitoneal folds (PPFs) and the posthepatic mesenchymal plate (PHMP) are transient structures that are essential during diaphragm development. Using several mouse models, including lineage tracing, we demonstrate the heterogeneous nature of the cells that make up the PPFs. The conditional deletion of Wilms tumor 1 homolog (Wt1) in the non-muscle mesenchyme of the PPFs results in CDH. We show that the fusion of the PPFs and the PHMP to form a continuous band of tissue involves movements of cells from both sources. The PPFs of mutant mice fail to fuse with the PHMP and exhibit increased RALDH2 (also known as ALDH1A2) expression. However, no changes in the expression of genes (including Snai1, Snai2, Cdh1 and Vim) implicated in epithelial-to-mesenchymal transition are observed. Additionally, the mutant PPFs lack migrating myoblasts and muscle connective tissue fibroblasts (TCF4⁺/GATA4⁺), suggesting possible interactions between these cell types. Our study demonstrates the importance of the non-muscle mesenchyme in development of the diaphragm.

Unraveling the Genetics of Congenital Diaphragmatic Hernia: An Ongoing Challenge

Congenital diaphragmatic hernia (CDH) is a congenital structural anomaly in which the diaphragm has not developed properly. It may occur either as an isolated anomaly or with additional anomalies. It is thought to be a multifactorial disease in which genetic factors could either substantially contribute to or directly result in the developmental defect. Patients with aneuploidies, pathogenic variants or de novo Copy Number Variations (CNVs) impacting specific genes and loci develop CDH typically in the form of a monogenetic syndrome. These patients often have other associated anatomical malformations. In patients without a known monogenetic syndrome, an increased genetic burden of de novo coding variants contributes to disease development. In early years, genetic evaluation was based on karyotyping and SNP-array. Today, genomes are commonly analyzed with next generation sequencing (NGS) based approaches. While more potential pathogenic variants are being detected, analysis of the data presents a bottleneck-largely due to the lack of full appreciation of the functional consequence and/or relevance of the detected variant. The exact heritability of CDH is still unknown. Damaging de novo alterations are associated with the more severe and complex phenotypes and worse clinical outcome. Phenotypic, genetic-and likely mechanistic-variability hampers individual patient diagnosis, short and long-term morbidity prediction and subsequent care strategies. Detailed phenotyping, clinical follow-up at regular intervals and detailed registries are needed to find associations between long-term morbidity, genetic alterations, and clinical parameters. Since CDH is a relatively rare disorder with only a few recurrent changes large cohorts of patients are needed to identify genetic associations. Retrospective whole genome sequencing of historical patient cohorts using will yield valuable data from which today's patients and parents will profit Trio whole genome sequencing has an excellent potential for future re-analysis and data-sharing increasing the chance to provide a genetic diagnosis and predict clinical prognosis. In this review, we explore the pitfalls and challenges in the analysis and interpretation of genetic information, present what is currently known and what still needs further study, and propose strategies to reap the benefits of genetic screening.

Cell culture system to assay candidate genes and molecular pathways implicated in congenital diaphragmatic hernias

The mammalian muscularized diaphragm is essential for respiration and defects in the developing diaphragm cause a common and frequently lethal birth defect, congenital diaphragmatic hernia (CDH). Human genetic studies have implicated more than 150 genes and multiple molecular pathways in CDH, but few of these have been validated because of the expense and time to generate mouse mutants. The pleuroperitoneal folds (PPFs) are transient embryonic structures in diaphragm development and defects in PPFs lead to CDH. We have developed a system to culture PPF fibroblasts from E12.5 mouse embryos and show that these fibroblasts, in contrast to the commonly used NIH 3T3 fibroblasts, maintain expression of key genes in normal diaphragm development. Using pharmacological and genetic manipulations that result in CDH in vivo, we also demonstrate that differences in proliferation provide a rapid means of distinguishing healthy and impaired PPF fibroblasts. Thus, the PPF fibroblast cell culture system is an efficient tool for assaying the functional significance of CDH candidate genes and molecular pathways and will be an important resource for elucidating the complex etiology of CDH.

Deep whole-genome sequencing of multiple proband tissues and parental blood reveals the complex genetic etiology of congenital diaphragmatic hernias

The diaphragm is critical for respiration and separation of the thoracic and abdominal cavities, and defects in diaphragm development are the cause of congenital diaphragmatic hernias (CDH), a common and often lethal birth defect. The genetic etiology of CDH is complex. Single-nucleotide variants (SNVs), insertions/deletions (indels), and structural variants (SVs) in more than 150 genes have been associated with CDH, although few genes are recurrently mutated in multiple individuals and mutated genes are incompletely penetrant. This suggests that multiple genetic variants in combination, other not-yet-investigated classes of variants, and/or nongenetic factors contribute to CDH etiology. However, no studies have comprehensively investigated in affected individuals the contribution of all possible classes of variants throughout the genome to CDH etiology. In our study, we used a unique cohort of four individuals with isolated CDH with samples from blood, skin, and diaphragm connective tissue and parental blood and deep whole-genome sequencing to assess germline and somatic de novo and inherited SNVs, indels, and SVs. In each individual we found a different mutational landscape that included germline de novo and inherited SNVs and indels in multiple genes. We also found in two individuals a 343 bp deletion interrupting an annotated enhancer of the CDH-associated gene GATA4, and we hypothesize that this common SV (found in 1%-2% of the population) acts as a sensitizing allele for CDH. Overall, our comprehensive reconstruction of the genetic architecture of four CDH individuals demonstrates that the etiology of CDH is heterogeneous and multifactorial.

Expansion of the renal capsular stroma, ureteric bud branching defects and cryptorchidism in mice with Wilms tumor 1 gene deletion in the stromal compartment of the developing kidney

Development of the mammalian kidney is orchestrated by reciprocal interactions of stromal and nephrogenic mesenchymal cells with the ureteric bud epithelium. Previous work showed that the transcription factor Wilms tumor 1 (WT1) acts in the nephrogenic lineage to maintain precursor cells, to drive the epithelial transition of aggregating precursors into a renal vesicle and to specify and maintain the podocyte fate. However, WT1 is expressed not only in the nephrogenic lineage but also transiently in stromal progenitors in the renal cortex. Here we report that specific deletion of Wt1 in the stromal lineage using the Foxd1^cre driver line results at birth in cryptorchidism and hypoplastic kidneys that harbour fewer and enlarged ureteric bud tips and display an expansion of capsular stroma into the cortical region. In vivo and ex vivo analysis at earlier stages revealed that stromal loss of Wt1 reduces stromal proliferation, and delays and alters branching morphogenesis, resulting in a variant architecture of the collecting duct tree with an increase of single at the expense of bifurcated ureteric bud tips. Molecular analysis identified a transient reduction of Aldh1a2 expression and of retinoic acid signalling activity in stromal progenitors, and of Ret in ureteric bud tips. Administration of retinoic acid partly rescued the branching defects of mutant kidneys in culture. We propose that WT1 maintains retinoic acid signalling in the cortical stroma, which, in turn, assures proper levels and dynamics of Ret expression in the ureteric bud tips, and thus normal ramification of the ureteric tree. © 2020 The Authors. The Journal of Pathology published by John Wiley & Sons, Ltd. on behalf of The Pathological Society of Great Britain and Ireland.

Transgenic animal models of congenital diaphragmatic hernia: a comprehensive overview of candidate genes and signaling pathways

Congenital diaphragmatic hernia (CDH) is a relatively common and life-threatening birth defect, characterized by incomplete formation of the diaphragm. Because CDH herniation occurs at the same time as preacinar airway branching, normal lung development becomes severely disrupted, resulting almost invariably in pulmonary hypoplasia. Despite various research efforts over the past decades, the pathogenesis of CDH and associated lung hypoplasia remains poorly understood. With the advent of molecular techniques, transgenic animal models of CDH have generated a large number of candidate genes, thus providing a novel basis for future research and treatment. This review article offers a comprehensive overview of genes and signaling pathways implicated in CDH etiology, whilst also discussing strengths and limitations of transgenic animal models in relation to the human condition.

Spatiotemporal Analysis Reveals Overlap of Key Proepicardial Markers in the Developing Murine Heart

The embryonic epicardium, originating from the proepicardial organ (PEO), provides a source of multipotent progenitors for cardiac lineages, including pericytes, fibroblasts, and vascular smooth muscle cells. Maximizing the regenerative capacity of the adult epicardium depends on recapitulating embryonic cell fates. The potential of the epicardium to contribute coronary endothelium is unclear, due to conflicting Cre-based lineage trace data. Controversy also surrounds when epicardial cell fate becomes restricted. Here, we systematically investigate expression of five widely used epicardial markers, Wt1, Tcf21, Tbx18, Sema3d, and Scx, over the course of development. We show overlap of markers in all PEO and epicardial cells until E13.5, and find no evidence for discrete proepicardial sub-compartments that might contribute coronary endothelium via the epicardial layer. Our findings clarify a number of prevailing discrepancies and support the notion that epicardium-derived cell fate, to form fibroblasts or mural cells, is specified after epithelial-mesenchymal transition, not pre-determined within the PEO.

MYRF haploinsufficiency causes 46,XY and 46,XX disorders of sex development: bioinformatics consideration

Disorders of sex development (DSDs) are defined as congenital conditions in which chromosomal, gonadal or anatomical sex is atypical. In many DSD cases, genetic causes remain to be elucidated. Here, we performed a case-control exome sequencing study comparing gene-based burdens of rare damaging variants between 26 DSD cases and 2625 controls. We found exome-wide significant enrichment of rare heterozygous truncating variants in the MYRF gene encoding myelin regulatory factor, a transcription factor essential for oligodendrocyte development. All three variants occurred de novo. We identified an additional 46,XY DSD case of a de novo damaging missense variant in an independent cohort. The clinical symptoms included hypoplasia of Müllerian derivatives and ovaries in 46,XX DSD patients, defective development of Sertoli and Leydig cells in 46,XY DSD patients and congenital diaphragmatic hernia in one 46,XY DSD patient. As all of these cells and tissues are or partly consist of coelomic epithelium (CE)-derived cells (CEDC) and CEDC developed from CE via proliferaiton and migration, MYRF might be related to these processes. Consistent with this hypothesis, single-cell RNA sequencing of foetal gonads revealed high expression of MYRF in CE and CEDC. Reanalysis of public chromatin immunoprecipitation sequencing data for rat Myrf showed that genes regulating proliferation and migration were enriched among putative target genes of Myrf. These results suggested that MYRF is a novel causative gene of 46,XY and 46,XX DSD and MYRF is a transcription factor regulating CD and/or CEDC proliferation and migration, which is essential for development of multiple organs.

The influence of genetics in congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) is a common birth defect that is associated with significant morbidity and mortality, especially when associated with additional congenital anomalies. Both environmental and genetic factors are thought to contribute to CDH. The genetic contributions to CDH are highly heterogeneous and incompletely defined. No one genetic cause accounts for more than 1-2% of CDH cases. In this review, we summarize the known genetic causes of CDH from chromosomal anomalies to individual genes. Both de novo and inherited variants contribute to CDH. Genes causing CDH are increasingly identified from animal models and from genomic strategies including exome and genome sequencing in humans. CDH genes are often transcription factors, genes involved in cell migration or the components of extracellular matrix. We provide clinical genetic testing strategies in the clinical evaluation that can identify a genetic cause in up to ∼30% of patients with non-isolated CDH and can be useful to refine prognosis, identify associated medical and neurodevelopmental issues to address, and inform family planning options.

Mesothelium and Malignant Mesothelioma

The mesothelium is an epithelial structure derived from the embryonic mesoderm. It plays an important role in the development of a number of different organs, including the heart, lungs, and intestines. In this publication, we discuss aspects of the development of the mesothelium, where mesothelial structures can be found, and review molecular and cellular characteristics associated with the mesothelium. Furthermore, we discuss the involvement of the mesothelium in a number of disease conditions, in particular in the pathogenesis of mesotheliomas with an emphasis on malignant pleural mesothelioma (MPM)—a primary cancer developing in the pleural cavity.

Connecting muscle development, birth defects, and evolution: An essential role for muscle connective tissue

Skeletal muscle powers all movement of the vertebrate body and is distributed in multiple regions that have evolved distinct functions. Axial muscles are ancestral muscles essential for support and locomotion of the whole body. The evolution of the head was accompanied by development of cranial muscles essential for eye movement, feeding, vocalization, and facial expression. With the evolution of paired fins and limbs and their associated muscles, vertebrates gained increased locomotor agility, populated the land, and acquired fine motor skills. Finally, unique muscles with specialized functions have evolved in some groups, and the diaphragm which solely evolved in mammals to increase respiratory capacity is one such example. The function of all these muscles requires their integration with the other components of the musculoskeletal system: muscle connective tissue (MCT), tendons, bones as well as nerves and vasculature. MCT is muscle's closest anatomical and functional partner. Not only is MCT critical in the adult for muscle structure and function, but recently MCT in the embryo has been found to be crucial for muscle development. In this review, we examine the important role of the MCT in axial, head, limb, and diaphragm muscles for regulating normal muscle development, discuss how defects in MCT-muscle interactions during development underlie the etiology of a range of birth defects, and explore how changes in MCT development or communication with muscle may have led to the modification and acquisition of new muscles during vertebrate evolution.

Gene ontology enrichment analysis of congenital diaphragmatic hernia-associated genes

Congenital diaphragmatic hernia (CDH) is a commonly occurring major congenital anomaly with a profound impact on neonatal mortality. The etiology of CDH is poorly understood and is complicated by multiple clinical presentations, reflecting the location and type of diaphragm defect. With the increased power of genetic screening, more genes are being associated with CDH, creating a knowledge gap between CDH-associated genes and their contribution to diaphragm embryogenesis. Our goal was to investigate CDH-associated genes and identify common pathways that may lead to abnormal diaphragm development. A comprehensive list of CDH-associated genes was identified from the literature and categorized according to multiple factors, including type of CDH. We undertook a large-scale gene function analysis using gene ontology to identify significantly enriched biological pathways and molecular functions associated with our gene set. We identified 218 CDH-associated genes. Our gene ontology analysis showed that genes representing distinct biological pathways are significantly enriched in relation to different clinical presentations of CDH. This includes retinoic acid signaling in Bochdalek CDH, myogenesis in diaphragm eventration, and angiogenesis in central tendon defects. We have identified unique genotype-phenotype relationships highlighting the major genetic drivers of the different types of CDH.

Expression of dispatched RND transporter family member 1 is decreased in the diaphragmatic and pulmonary mesenchyme of nitrofen-induced congenital diaphragmatic hernia

PURPOSE

Congenital diaphragmatic hernia (CDH) and associated pulmonary hypoplasia (PH) are thought to be caused by a malformation of the diaphragmatic and pulmonary mesenchyme. Dispatched RND transporter family member 1 (Disp-1) encodes a transmembrane protein that regulates the release of cholesterol and palmitoyl, which is critical for normal diaphragmatic and airway development. Disp-1 is strongly expressed in mesenchymal compartments of fetal diaphragms and lungs. Recently, Disp-1 mutations have been identified in patients with CDH. We hypothesized that diaphragmatic and pulmonary Disp-1 expression is decreased in the nitrofen-induced CDH model.

METHODS

Time-mated rats received nitrofen or vehicle on gestational day 9 (D9). Fetal diaphragms and lungs were microdissected on selected endpoints D13, D15 and D18; and divided into control and nitrofen-exposed specimens (n = 12 per sample, time-point and experimental group). Diaphragmatic and pulmonary Disp-1 expression was evaluated by qRT-PCR. Immunofluorescence double staining for Disp-1 was combined with diaphragmatic and pulmonary mesenchymal markers Wt-1 and Sox-9 to localize protein expression in fetal diaphragms and lungs.

RESULTS

Relative mRNA levels of Disp-1 were significantly decreased in pleuroperitoneal folds/primordial lungs on D13 (0.18 ± 0.08 vs. 0.46 ± 0.41; p < 0.05/1.06 ± 0.27 vs. 1.34 ± 0.79; p < 0.05), developing diaphragms/lungs on D15 (0.18 ± 0.06 vs. 0.44 ± 0.23; p < 0.05/0.73 ± 0.36 vs. 1.16 ± 0.27; p < 0.05) and fully muscularized diaphragms/differentiated lungs on D18 (0.22 ± 0.18 vs. 0.32 ± 0.23; p < 0.05/0.56 ± 0.16 vs. 0.77 ± 0.14; p < 0.05) of nitrofen-exposed fetuses compared to controls. Confocal laser scanning microscopy demonstrated markedly diminished Disp-1 immunofluorescence predominately in the diaphragmatic and pulmonary mesenchyme of nitrofen-exposed fetuses on D13, D15 and D18, associated with a clear reduction of proliferating mesenchymal cells.

CONCLUSIONS

Decreased Disp-1 expression during diaphragmatic development and lung branching morphogenesis may interrupt mesenchymal cell proliferation, thus leading to diaphragmatic defects and PH in the nitrofen-induced CDH model.

Mesothelial to mesenchyme transition as a major developmental and pathological player in trunk organs and their cavities

The internal organs embedded in the cavities are lined by an epithelial monolayer termed the mesothelium. The mesothelium is increasingly implicated in driving various internal organ pathologies, as many of the normal embryonic developmental pathways acting in mesothelial cells, such as those regulating epithelial-to-mesenchymal transition, also drive disease progression in adult life. Here, we summarize observations from different animal models and organ systems that collectively point toward a central role of epithelial-to-mesenchymal transition in driving tissue fibrosis, acute scarring, and cancer metastasis. Thus, drugs targeting pathways of mesothelium’s transition may have broad therapeutic benefits in patients suffering from these diseases.

Tim Koopmans and Yuval Rinkevich review recent findings linking the mesothelium’s embryonic programs that drive epithelial-to-mesenchyme transition with adult pathologies, such as fibrosis, acute scarring, and cancer metastasis. They highlight new avenues for drug development that would target pathways of the mesothelium’s mesenchymal transition.

Mesothelial-mesenchymal transitions in embryogenesis

Most animals develop coelomic cavities lined by an epithelial cell layer called the mesothelium. Embryonic mesothelial cells have the ability to transform into mesenchymal cells which populate many developing organs contributing to their connective and vascular tissues, and also to organ-specific cell types. Furthermore, embryonic mesothelium and mesothelial-derived cells produce essential signals for visceral morphogenesis. We review the most relevant literature about the mechanisms regulating the embryonic mesothelial-mesenchymal transition, the developmental fate of the mesothelial-derived cells and other functions of the embryonic mesothelium, such as its contribution to the establishment of left-right visceral asymmetries or its role in limb morphogenesis.

Role of the Wilms' tumor suppressor gene Wt1 in pancreatic development

The Wilms tumor suppressor gene (Wt1) encodes a transcription factor involved in the development of a number of organs, but the role played by Wt1 in pancreatic development is unknown. The pancreas contains a population of pancreatic stellate cells (PSC) very important for pancreatic physiology. We described elsewhere that hepatic stellate cells originate from the WT1-expressing liver mesothelium. Thus, we checked if the origin of PSCs was similar. WT1 expression is restricted to the pancreatic mesothelium. Between embryonic day (E) 10.5 and E15.5, this mesothelium gives rise to mesenchymal cells that contribute to a major part of the PSC and other cell types including endothelial cells. Most WT1 systemic mutants show abnormal localization of the dorsal pancreas within the mesentery and intestinal malrotation by E14.0. Embryos with conditional deletion of WT1 between E9.5 and E12.5 showed normal dorsal pancreatic bud and intestine, but the number of acini in the ventral bud was reduced approximately 30% by E16.5. Proliferation of acinar cells was reduced in WT1 systemic mutants, but pancreatic differentiation was not impaired. Thus, mesothelial-derived cells constitute an important subpopulation of pancreatic mesodermal cells. WT1 expression is not essential for pancreas development, although it influences intestinal rotation and correct localization of the dorsal pancreas within the mesogastrium. Developmental Dynamics 247:924-933, 2018. © 2018 Wiley Periodicals, Inc.

Developmental origin and morphogenesis of the diaphragm, an essential mammalian muscle

The diaphragm is a mammalian skeletal muscle essential for respiration and for separating the thoracic and abdominal cavities. Development of the diaphragm requires the coordinated development of muscle, muscle connective tissue, tendon, nerves, and vasculature that derive from different embryonic sources. However, defects in diaphragm development are common and the cause of an often deadly birth defect, Congenital Diaphragmatic Hernia (CDH). Here we comprehensively describe the normal developmental origin and complex spatial-temporal relationship between the different developing tissues to form a functional diaphragm using a developmental series of mouse embryos genetically and immunofluorescently labeled and analyzed in whole mount. We find that the earliest developmental events are the emigration of muscle progenitors from cervical somites followed by the projection of phrenic nerve axons from the cervical neural tube. Muscle progenitors and phrenic nerve target the pleuroperitoneal folds (PPFs), transient pyramidal-shaped structures that form between the thoracic and abdominal cavities. Subsequently, the PPFs expand across the surface of the liver to give rise to the muscle connective tissue and central tendon, and the leading edge of their expansion precedes muscle morphogenesis, formation of the vascular network, and outgrowth and branching of the phrenic nerve. Thus development and morphogenesis of the PPFs is critical for diaphragm formation. In addition, our data indicate that the earliest events in diaphragm development are critical for the etiology of CDH and instrumental to the evolution of the diaphragm. CDH initiates prior to E12.5 in mouse and suggests that defects in the early PPF formation or their ability to recruit muscle are an important source of CDH. Also, the recruitment of muscle progenitors from cervical somites to the nascent PPFs is uniquely mammalian and a key developmental innovation essential for the evolution of the muscularized diaphragm.

Congenital diaphragmatic hernias: from genes to mechanisms to therapies

Congenital diaphragmatic hernias (CDHs) and structural anomalies of the diaphragm are a common class of congenital birth defects that are associated with significant morbidity and mortality due to associated pulmonary hypoplasia, pulmonary hypertension and heart failure. In ∼30% of CDH patients, genomic analyses have identified a range of genetic defects, including chromosomal anomalies, copy number variants and sequence variants. The affected genes identified in CDH patients include transcription factors, such as GATA4, ZFPM2, NR2F2 and WT1, and signaling pathway components, including members of the retinoic acid pathway. Mutations in these genes affect diaphragm development and can have pleiotropic effects on pulmonary and cardiac development. New therapies, including fetal endoscopic tracheal occlusion and prenatal transplacental fetal treatments, aim to normalize lung development and pulmonary vascular tone to prevent and treat lung hypoplasia and pulmonary hypertension, respectively. Studies of the association between particular genetic mutations and clinical outcomes should allow us to better understand the origin of this birth defect and to improve our ability to predict and identify patients most likely to benefit from specialized treatment strategies.

Regenerative medicine solutions in congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) remains a major challenge and associated mortality is still significant. Patients have benefited from current therapeutic options, but most severe cases are still associated to poor outcome. Regenerative medicine is emerging as a valid option in many diseases and clinical trials are currently happening for various conditions in children and adults. We report here the advancement in the field which will help both in the understanding of further CDH development and in offering new treatment options for the difficult situations such as repair of large diaphragmatic defects and lung hypoplasia. The authors believe that advancements in regenerative medicine may lead to increase of CDH patients׳ survival.