The developmental mechanics of divergent buckling patterns in the chick gut

Tissue buckling is an increasingly appreciated mode of morphogenesis in the embryo, but it is often unclear how geometric and material parameters are molecularly determined in native developmental contexts to generate diverse functional patterns. Here, we study the link between differential mechanical properties and the morphogenesis of distinct anteroposterior compartments in the intestinal tract-the esophagus, small intestine, and large intestine. These regions originate from a simple, common tube but adopt unique forms. Using measured data from the developing chick gut coupled with a minimal theory and simulations of differential growth, we investigate divergent lumen morphologies along the entire early gut and demonstrate that spatiotemporal geometries, moduli, and growth rates control the segment-specific patterns of mucosal buckling. Primary buckling into wrinkles, folds, and creases along the gut, as well as secondary buckling phenomena, including period-doubling in the foregut and multiscale creasing-wrinkling in the hindgut, are captured and well explained by mechanical models. This study advances our existing knowledge of how identity leads to form in these regions, laying the foundation for future work uncovering the relationship between molecules and mechanics in gut morphological regionalization.

The molecular and cellular choreography of early mammalian lung development

Mammalian lung development starts from a specific cluster of endodermal cells situated within the ventral foregut region. With the orchestrating of delicate choreography of transcription factors, signaling pathways, and cell-cell communications, the endodermal diverticulum extends into the surrounding mesenchyme, and builds the cellular and structural basis of the complex respiratory system. This review provides a comprehensive overview of the current molecular insights of mammalian lung development, with a particular focus on the early stage of lung cell fate differentiation and spatial patterning. Furthermore, we explore the implications of several congenital respiratory diseases and the relevance to early organogenesis. Finally, we summarize the unprecedented knowledge concerning lung cell compositions, regulatory networks as well as the promising prospect for gaining an unbiased understanding of lung development and lung malformations through state-of-the-art single-cell omics.

Development of the foregut and the formation of the trachea and esophagus in rat embryos. A symphony of confusion

Introduction: During embryonic development, the trachea emerges from an area of the foregut, which is often referred to as "anterior" or "common" foregut tube or simply foregut. To explain this process of differentiation, four competing models exist to date. The outgrowth and watershed models propose a foregut that remains constant in length. In the outgrowth model, the trachea buds off and elongates from the foregut, while in the watershed model, a mesenchymal wedge splits the growing foregut into the trachea and esophagus. In contrast, the septation model proposes a cranial splitting and thus a shortening of the "common" foregut tube into the trachea and esophagus by an emerging septum. Finally, the splitting and extension model describes an interaction of cranial splitting of the foregut and simultaneous caudal tracheal and esophageal growth. Methods: Here we examine the development of the undifferentiated foregut by micro computed tomography, which allows precise measurements. Results: Our results show that this area of the foregut transforms into the larynx, a process, which is independent from tracheal and esophageal development. Discussion: These observations are only consistent with the outgrowth model.

Outcome of Newborns with Tracheoesophageal Fistula: An Experience from a Rapidly Developing Country: Room for Improvement

Methods

This is a retrospective review of the medical electronic charts of patients with TEF that were followed at Sidra Medicine in the state of Qatar. The review included the patients who were operated upon in the period of 2011-2021 but continued to follow at our institution in the period of 2018-2021. Demographic data, associated anomalies, preoperative, operative, and postoperative courses, and growth parameters were collected.

Results

A total of 35 patients with TEF (24 males and 11 females) were collected. 49% were full term. We identified seven patients (20%) with isolated TEF, TEF with VACTERL association in 29% of our patients, other chromosomal anomalies in 17%, or associated with other anomalies (not related to VACTERL) in 34% of the patients. The majority of the patients (94%) were of type C-TEF (TEF with esophageal atresia-EA/TEF). All patients were operated except for one patient who died at 2 days of life due to cardiac complications. Median age at which surgery was performed was 2 days (range 1-270 days). Median follow-up was 32 months (range 7-115 months). Immediate postoperative complications were encountered in eleven patients (33%) and included anastomosis leak in 12%, air leak in 6%, sepsis in 6%, chylothorax in 3%, vocal cord palsy and fistula recurrence (combined) in 3%, and failure of TEF closure in 3% of the patients. Long-term respiratory complications were encountered in 43% of our patients. Long-term gastrointestinal complications included gastroesophageal reflux (GERD) in 63%, dysphagia in 31%, and anastomotic stricture in 34% of the patients. Growth was affected in around a quarter of the patients at 6 months after surgery and 22% at 12-month assessment postoperatively. While only five patients died at our institution, only one was directly related to failure of TEF closure and postoperative complications.

Conclusion

This descriptive study reports the clinical outcome of TEF from a rapidly developing country. The distribution of the patients' characteristics and postoperative complications was almost comparable to those from developed countries. This study would aid in addressing the prognostic factors and establishment of evidence-based management pathways of newborns with TEF to improve the clinical outcome in our center and other pediatric tertiary centers in developing countries.

iPSCs derived from esophageal atresia patients reveal SOX2 dysregulation at the anterior foregut stage

A series of well-regulated cellular and molecular events result in the compartmentalization of the anterior foregut into the esophagus and trachea. Disruption of the compartmentalization process leads to esophageal atresia/tracheoesophageal fistula (EA/TEF). The cause of EA/TEF remains largely unknown. Therefore, to mimic the early development of the esophagus and trachea, we differentiated induced pluripotent stem cells (iPSCs) from EA/TEF patients, and iPSCs and embryonic stem cells from healthy individuals into mature three-dimensional esophageal organoids. CXCR4, SOX17 and GATA4 expression was similar in both patient-derived and healthy endodermal cells. The expression of the key transcription factor SOX2 was significantly lower in the patient-derived anterior foregut. We also observed an abnormal expression of NKX2.1 (or NKX2-1) in the patient-derived mature esophageal organoids. At the anterior foregut stage, RNA sequencing revealed the critical genes GSTM1 and RAB37 to be significantly lower in the patient-derived anterior foregut. We therefore hypothesize that a transient dysregulation of SOX2 and the abnormal expression of NKX2.1 in patient-derived cells could be responsible for the abnormal foregut compartmentalization.

Neonatal Respiratory Distress and Airway Emergency: Report of Two Cases

We discuss two cases of congenital airway malformations seen in our neonatal intensive care unit (NICU). The aim is to report extremely rare events characterized by immediate respiratory distress after delivery and the impossibility to ventilate and intubate the airway. The first case is a male twin born at 34 weeks by emergency caesarean section. Immediately after delivery, the newborn was cyanotic and showed severe respiratory distress. Bag-valve-mask ventilation did not relieve the respiratory distress but allowed for temporary oxygenation during subsequent unsuccessful oral-tracheal intubation (OTI) attempts. Flexible laryngoscopy revealed complete subglottic obstruction. Postmortem analysis revealed a poly-malformative syndrome, unilateral multicystic renal dysplasia with a complete subglottic diaphragm, and a tracheo-esophageal fistula (TEF). The second case is a male patient that was vaginally born at 35 weeks. Antenatally, an ultrasound (US) arose suspicion for a VACTERL association (vertebral defects, anal atresia, TEF with esophageal atresia and radial or renal dysplasia, plus cardiovascular and limb defects) and a TEF, and thus, fetal magnetic resonance (MRI) was scheduled. Spontaneous labor started shortly thereafter, before imaging could be performed. Respiratory distress, cyanosis, and absence of an audible cry was observed immediately at delivery. Attempts at OTI were unsuccessful, whereas bag-valve-mask ventilation and esophageal intubation allowed for sufficient oxygenation. An emergency tracheostomy was attempted, although no trachea could be found on cervical exploration. Postmortem analysis revealed tracheal agenesis (TA), renal dysplasia, anal atresia, and a single umbilical artery. Clinicians need to be aware of congenital airway malformations and subsequent difficulties upon endotracheal intubation and must plan for multidisciplinary management of the airway at delivery, including emergency esophageal intubation and tracheostomy.

Esophagus-Like Bronchus: A Noncommunicating Bronchopulmonary Foregut Malformation

We describe a previously unreported bronchopulmonary foregut malformation wherein a segment of a bronchus of the lower lobe of the left lung in a 4-year-old girl was entirely esophageal in structure. No communication was identified between the tracheobronchial tree and the esophagus by radiologic examination or at surgery. The esophagus-like bronchus was associated with an adjacent atretic bronchus and a downstream cavity in the lower lobe of the left lung. The child sought clinical attention because of recurrent pulmonary infections localized to the lower lobe of the lung. We posit that this esophagus-like bronchus is a novel noncommunicating bronchopulmonary foregut malformation.

Care recommendations for the respiratory complications of esophageal atresia-tracheoesophageal fistula

Tracheoesophageal fistula (TEF) with esophageal atresia (EA) is a common congenital anomaly that is associated with significant respiratory morbidity throughout life. The objective of this document is to provide a framework for the diagnosis and management of the respiratory complications that are associated with the condition. As there are no randomized controlled studies on the subject, a group of experts used a modification of the Rand Appropriateness Method to describe the various aspects of the condition in terms of their relative importance, and to rate the available diagnostic methods and therapeutic interventions on the basis of their appropriateness and necessity. Specific recommendations were formulated and reported as Level A, B, and C based on whether they were based on "strong", "moderate" or "weak" agreement. The tracheomalacia that exists in the site of the fistula was considered the main abnormality that predisposes to all other respiratory complications due to airway collapse and impaired clearance of secretions. Aspiration due to impaired airway protection reflexes is the main underlying contributing mechanism. Flexible bronchoscopy is the main diagnostic modality, aided by imaging modalities, especially CT scans of the chest. Noninvasive positive airway pressure support, surgical techniques such as tracheopexy and rarely tracheostomy are required for the management of severe tracheomalacia. Regular long-term follow-up by a multidisciplinary team was considered imperative. Specific templates outlining the elements of the clinical respiratory evaluation according to the patients' age were also developed.

Infantile hypertrophic pyloric stenosis in patients with esophageal atresia

BACKGROUND

Patients born with esophageal atresia (EA) have a higher incidence of infantile hypertrophic pyloric stenosis (IHPS), suggestive of a relationship. A shared etiology makes sense from a developmental perspective as both affected structures are foregut derived. A genetic component has been described for both conditions as single entities and EA and IHPS are variable components in several monogenetic syndromes. We hypothesized that defects disturbing foregut morphogenesis are responsible for this combination of malformations.

METHODS

We investigated the genetic variation of 15 patients with both EA and IHPS with unaffected parents using exome sequencing and SNP array-based genotyping, and compared the results to mouse transcriptome data of the developing foregut.

RESULTS

We did not identify putatively deleterious de novo mutations or recessive variants. However, we detected rare inherited variants in EA or IHPS disease genes or in genes important in foregut morphogenesis, expressed at the proper developmental time-points. Two pathways were significantly enriched (p < 1 × 10^-5 ): proliferation and differentiation of smooth muscle cells and self-renewal of satellite cells.

CONCLUSIONS

None of our findings could fully explain the combination of abnormalities on its own, which makes complex inheritance the most plausible genetic explanation, most likely in combination with mechanical and/or environmental factors. As we did not find one defining monogenetic cause for the EA/IHPS phenotype, the impact of the corrective surgery could should be further investigated.

Generation of esophageal organoids and organotypic raft cultures from human pluripotent stem cells

The human and murine esophagus have some substantial differences that limit the utility of mouse as a model to study human esophagus development and disease. Due to these limitations several recent reports describe the development of methods to generate human esophageal tissues via the directed differentiation of pluripotent stem cells. Methods for differentiation are based on knowledge of years of studying embryonic development of the esophagus in vertebrate animal models. Esophageal tissues derived from human pluripotent stem cells have been used to study both development and diseases affecting the esophagus. Here, we provide a detailed protocol for the directed differentiation of human pluripotent stem cells into human esophageal organoids and organotypic raft cultures, that are highly similar, morphologically and transcriptionally, to the human esophagus epithelium. We discuss limitations of the current esophageal models and the importance of engineering more complex tissue models with muscle and enteric nerves. Moving forward, these models might be utilized for the development of personalized treatments, as well as other therapeutic solutions.

Oesophageal atresia

Oesophageal atresia (EA) is a congenital abnormality of the oesophagus that is caused by incomplete embryonic compartmentalization of the foregut. EA commonly occurs with a tracheo-oesophageal fistula (TEF). Associated birth defects or anomalies, such as VACTERL association, trisomy 18 or 21 and CHARGE syndrome, occur in the majority of patients born with EA. Although several studies have revealed signalling pathways and genes potentially involved in the development of EA, our understanding of the pathophysiology of EA lags behind the improvements in surgical and clinical care of patients born with this anomaly. EA is treated surgically to restore the oesophageal interruption and, if present, ligate and divide the TEF. Survival is now ~90% in those born with EA with severe associated anomalies and even higher in those born with EA alone. Despite these achievements, long-term gastrointestinal and respiratory complications and comorbidities in patients born with EA are common and lead to decreased quality of life. Oesophageal motility disorders are probably ubiquitous in patients after undergoing EA repair and often underlie these complications and comorbidities. The implementation of several new diagnostic and screening tools in clinical care, including high-resolution impedance manometry, pH-multichannel intraluminal impedance testing and disease-specific quality of life questionnaires now provide better insight into these problems and may contribute to better long-term outcomes in the future.

TULP3: A potential biomarker in colorectal cancer?

Colorectal cancer (CRC) is the second most common cancer in women and the third most common cancer in men globally. The identification of differentially expressed genes associated to patient's clinical data may represent a useful approach to find important genes in CRC carcinogenesis. Previously, the TULP3 transcription factor was identified as a possible prognostic biomarker in pancreatic ductal adenocarcinoma. Considering that pancreatic and colorectal tissues have the same embryonic origin, we investigated the profile of TULP3 expression in CRC hypothesizing that it may have a role in its development. We comparatively analysed TULP3 gene expression in CRC and normal adjacent colonic tissue and assessed association of expression profiles with survival and clinicopathological information, using publicly available datasets. TULP3 expression levels were increased in CRC when compared to the adjacent non-tumoral tissue. In addition, higher TULP3 gene expression was associated to lymphatic and vascular invasion in colon adenocarcinoma (COAD) and rectum adenocarcinoma (READ), respectively. In summary, our results point to a possible role of TULP3 as a diagnostic and prognostic biomarker in CRC. Additional studies are necessary to confirm these preliminary findings.

Congenital complete absence of tracheal rings with trifurcate carina: Case report of a rare clinical and endoscopic presentation

We describe the case of a child with isolated absence of cartilaginous tracheal rings and a trifurcate carina. At 6 months of age, the patient presented to our multidisciplinary airway clinic with stridor and recurrent severe respiratory infections requiring hospitalization. Radiographs showed airway narrowing. Exam demonstrated biphasic stridor. Flexible fiberoptic laryngoscopy demonstrated only mild laryngomalacia. Operative bronchoscopy demonstrated severe tracheomalacia with absence of any visible tracheal rings and a trifurcate carina. Subsequent CT imaging corroborated these findings and did not demonstrate any other major abnormality. The patient did not require operative intervention and his subsequent course was uncomplicated.

Repair of congenital esophageal atresia with tracheoesophageal fistula repair in Ontario over the last 20years: Volume and outcomes

BACKGROUND/PURPOSE

This study was designed to determine the volume, postoperative surgical outcomes and, if possible, the relationship between outcome and institutional / surgeon volume in neonates undergoing repair of esophageal atresia with tracheoesophageal fistula (EA-TEF) over the last 20years in Ontario.

METHODS

Using administrative databases, a population based cohort study of patients undergoing EA-TEF repair in Ontario between 1993 and 2012 was conducted.

RESULTS

465 patients with the diagnosis of EA-TEF met inclusion criteria. The mean number of EA-TEF repairs per year per was 5.8. There was a significant difference in hospital annual volume between institutions (range 12.3-3.35: p<0.05). The average number of cases/surgeon for the last 10 study years ranged between 0.5 and 2 cases/year. Primary outcome revealed that repair of recurrent fistula or intestinal interposition was 5.3%, with no reportable difference between institutions. Secondary outcomes revealed that 45.6% underwent dilatation for esophageal strictures, and 19.8% underwent some type of drainage procedure of the chest. These rates were not significantly different between institutions.

CONCLUSION

This study provides insight into the outcomes following EA-TEF repair in Ontario and the difficulty in determining surgeon or institution volume outcome relationships, as both primary and secondary outcome event rates are very low.

LEVEL OF EVIDENCE

2.

Notum attenuates Wnt/β-catenin signaling to promote tracheal cartilage patterning

Tracheobronchomalacia (TBM) is a common congenital disorder in which the cartilaginous rings of the trachea are weakened or missing. Despite the high prevalence and clinical issues associated with TBM, the etiology is largely unknown. Our previous studies demonstrated that Wntless (Wls) and its associated Wnt pathways are critical for patterning of the upper airways. Deletion of Wls in respiratory endoderm caused TBM and ectopic trachealis muscle. To understand mechanisms by which Wls mediates tracheal patterning, we performed RNA sequencing in prechondrogenic tracheal tissue of Wls^f/f;Shh^Cre/wt embryos. Chondrogenic Bmp4, and Sox9 were decreased, while expression of myogenic genes was increased. We identified Notum, a deacylase that inactivates Wnt ligands, as a target of Wls induced Wnt signaling. Notum's mesenchymal ventral expression in prechondrogenic trachea overlaps with expression of Axin2, a Wnt/β-catenin target and inhibitor. Notum is induced by Wnt/β-catenin in developing trachea. Deletion of Notum activated mesenchymal Wnt/β-catenin and caused tracheal mispatterning of trachealis muscle and cartilage as well as tracheal stenosis. Notum is required for tracheal morphogenesis, influencing mesenchymal condensations critical for patterning of tracheal cartilage and muscle. We propose that Notum influences mesenchymal cell differentiation by generating a barrier for Wnt ligands produced and secreted by airway epithelial cells to attenuate Wnt signaling.

Update on Foregut Molecular Embryology and Role of Regenerative Medicine Therapies

Esophageal atresia (OA) represents one of the commonest and most severe developmental disorders of the foregut, the most proximal segment of the gastrointestinal (GI) tract (esophagus and stomach) in embryological terms. Of intrigue is the common origin from this foregut of two very diverse functional entities, the digestive and respiratory systems. OA appears to result from incomplete separation of the ventral and dorsal parts of the foregut during development, resulting in disruption of esophageal anatomy and frequent association with tracheo-oesophageal fistula. Not surprisingly, and likely inherent to OA, are associated abnormalities in components of the enteric neuromusculature and ultimately loss of esophageal functional integrity. An appreciation of such developmental processes and associated defects has not only enhanced our understanding of the etiopathogenesis underlying such devastating defects but also highlighted the potential of novel corrective therapies. There has been considerable progress in the identification and propagation of neural crest stem cells from the GI tract itself or derived from pluripotent cells. Such cells have been successfully transplanted into models of enteric neuropathy confirming their ability to functionally integrate and replenish missing or defective enteric nerves. Combinatorial approaches in tissue engineering hold significant promise for the generation of organ-specific scaffolds such as the esophagus with current initiatives directed toward their cellularization to facilitate optimal function. This chapter outlines the most current understanding of the molecular embryology underlying foregut development and OA, and also explores the promise of regenerative medicine.

Studying Wnt Signaling During Patterning of Conducting Airways

Wnt signaling pathways play critical roles during development of the respiratory tract. Defining precise mechanisms of differentiation and morphogenesis controlled by Wnt signaling is required to understand how tissues are patterned during normal development. This knowledge is also critical to determine the etiology of birth defects such as lung hypoplasia and tracheobronchomalacia. Analysis of earliest stages of development of respiratory tract imposes challenges, as the limited amount of tissue prevents the performance of standard protocols better suited for postnatal studies. In this paper, we discuss methodologies to study cell differentiation and proliferation in the respiratory tract. We describe techniques such as whole mount staining, processing of the tissue for confocal microscopy and immunofluorescence in paraffin sections applied to developing tracheal lung. We also discuss methodologies for the study of tracheal mesenchyme differentiation, in particular cartilage formation. Approaches and techniques discussed in the current paper circumvent the limitation of material while working with embryonic tissue, allowing for a better understanding of the patterning process of developing conducting airways.

Esophageal development and epithelial homeostasis

The esophagus is a relatively simple organ that evolved to transport food and liquids through the thoracic cavity. It is the only part of the gastrointestinal tract that lacks any metabolic, digestive, or absorptive function. The mucosa of the adult esophagus is covered by a multilayered squamous epithelium with a remarkable similarity to the epithelium of the skin despite the fact that these tissues originate from two different germ layers. Here we review the developmental pathways involved in the establishment of the esophagus and the way these pathways regulate gut-airway separation. We summarize current knowledge of the mechanisms that maintain homeostasis in esophageal epithelial renewal in the adult and the molecular mechanism of the development of Barrett's metaplasia, the precursor lesion to esophageal adenocarcinoma. Finally, we examine the ongoing debate on the hierarchy of esophageal epithelial precursor cells and on the presence or absence of a specific esophageal stem cell population. Together the recent insights into esophageal development and homeostasis suggest that the pathways that establish the esophagus during development also play a role in the maintenance of the adult epithelium. We are beginning to understand how reflux of gastric content and the resulting chronic inflammation can transform the squamous esophageal epithelium to columnar intestinal type metaplasia in Barrett's esophagus.

Endodermal Wnt signaling is required for tracheal cartilage formation

Tracheobronchomalacia is a common congenital defect in which the walls of the trachea and bronchi lack of adequate cartilage required for support of the airways. Deletion of Wls, a cargo receptor mediating Wnt ligand secretion, in the embryonic endoderm using ShhCre mice inhibited formation of tracheal-bronchial cartilaginous rings. The normal dorsal-ventral patterning of tracheal mesenchyme was lost. Smooth muscle cells, identified by Acta2 staining, were aberrantly located in ventral mesenchyme of the trachea, normally the region of Sox9 expression in cartilage progenitors. Wnt/β-catenin activity, indicated by Axin2 LacZ reporter, was decreased in tracheal mesenchyme of Wls(f/f);Shh(Cre/+) embryos. Proliferation of chondroblasts was decreased and reciprocally, proliferation of smooth muscle cells was increased in Wls(f/f);Shh(Cre/+) tracheal tissue. Expression of Tbx4, Tbx5, Msx1 and Msx2, known to mediate cartilage and muscle patterning, were decreased in tracheal mesenchyme of Wls(f/f);Shh(Cre/+) embryos. Ex vivo studies demonstrated that Wnt7b and Wnt5a, expressed by the epithelium of developing trachea, and active Wnt/β-catenin signaling are required for tracheal chondrogenesis before formation of mesenchymal condensations. In conclusion, Wnt ligands produced by the tracheal epithelium pattern the tracheal mesenchyme via modulation of gene expression and cell proliferation required for proper tracheal cartilage and smooth muscle differentiation.

Upper Airway Anomalies in Congenital Tracheoesophageal Fistula and Esophageal Atresia Patients

Objective:

To examine the prevalence of upper airway anomalies in patients diagnosed with congenital tracheoesophageal fistula and esophageal atresia (TEF/EA).

Methods:

A retrospective review was conducted of all TEF/EA patients seen at a tertiary pediatric hospital between January 2008 and December 2013. Inclusion criteria included evaluation by the otolaryngology service. Exclusion criteria included age >18 years, acquired TEF/EA, subsequent rule out of TEF/EA, and otolaryngology evaluation for reasons not pertaining to the airway. Data collected and analyzed included demographics, comorbidities, presenting symptoms, surgical interventions, laryngoscopic and bronchoscopic examinations, and subsequent medical and surgical management.

Results:

Four hundred and thirty patients were diagnosed with TEF/EA at our institution. In all, 32.3%, or 139 children, were included in the analysis; 56.1% (n = 78) male, 43.9% (n = 61) female. Of the analyzed patients, 4.3% (n = 6) were diagnosed with laryngomalacia. Eighteen patients (12.9%) were diagnosed with subglottic stenosis. Thirty (21.6%) had vocal fold paresis or immobility. Laryngeal cleft was diagnosed in 25.9% (n = 36). Tracheomalacia was the most common airway finding, diagnosed in 37.4% (n = 52) patients.

Conclusion:

Patients diagnosed with congenital TEF/EA have a high rate of secondary upper airway anomalies. Consideration should be given to perform a complete airway evaluation in all of these patients.

A Molecular atlas of Xenopus respiratory system development

BACKGROUND

Respiratory system development is regulated by a complex series of endoderm-mesoderm interactions that are not fully understood. Recently Xenopus has emerged as an alternative model to investigate early respiratory system development, but the extent to which the morphogenesis and molecular pathways involved are conserved between Xenopus and mammals has not been systematically documented.

RESULTS

In this study, we provide a histological and molecular atlas of Xenopus respiratory system development, focusing on Nkx2.1+ respiratory cell fate specification in the developing foregut. We document the expression patterns of Wnt/β-catenin, fibroblast growth factor (FGF), and bone morphogenetic protein (BMP) signaling components in the foregut and show that the molecular mechanisms of respiratory lineage induction are remarkably conserved between Xenopus and mice. Finally, using several functional experiments we refine the epistatic relationships among FGF, Wnt, and BMP signaling in early Xenopus respiratory system development.

CONCLUSIONS

We demonstrate that Xenopus trachea and lung development, before metamorphosis, is comparable at the cellular and molecular levels to embryonic stages of mouse respiratory system development between embryonic days 8.5 and 10.5. This molecular atlas provides a fundamental starting point for further studies using Xenopus as a model to define the conserved genetic programs controlling early respiratory system development.

BMP antagonism by Noggin is required in presumptive notochord cells for mammalian foregut morphogenesis

Esophageal atresia with tracheoesophageal fistula (EA/TEF) is a serious human birth defect, in which the esophagus ends before reaching the stomach, and is aberrantly connected with the trachea. Several mouse models of EA/TEF have recently demonstrated that proper dorsal/ventral (D/V) patterning of the primitive anterior foregut endoderm is essential for correct compartmentalization of the trachea and esophagus. Here we elucidate the pathogenic mechanisms underlying the EA/TEF that occurs in mice lacking the BMP antagonist Noggin, which display correct dorsal/ventral patterning. To clarify the mechanism of this malformation, we use spatiotemporal manipulation of Noggin and BMP receptor 1A conditional alleles during foregut development. Surprisingly, we find that the expression of Noggin in the compartmentalizing endoderm is not required to generate distinct tracheal and esophageal tubes. Instead, we show that Noggin and BMP signaling attenuation are required in the early notochord to correctly resolve notochord cells from the dorsal foregut endoderm, which in turn, appears to be a prerequisite for foregut compartmentalization. Collectively, our findings support an emerging model for a mechanism underlying EA/TEF in which impaired notochord resolution from the early endoderm causes the foregut to be hypo-cellular just prior to the critical period of compartmentalization. Our further characterizations suggest that Noggin may regulate a cell rearrangement process that involves reciprocal E-cadherin and Zeb1 expression in the resolving notochord cells.

[Malformations of the esophagus: diagnosis and therapy]

Esophageal malformations are rare and can occur sporadically or as a component of various syndromes. The variations and classifications are manifold. With the available modern operation techniques most malformations can be resolved with good results. However, esophageal malformations are often combined with further malformations which limit the prognosis. The separation of the trachea and esophagus after gastrulation is not yet completely researched. The results so far indicate that the localized expression of various homeodomain transcription factors is essential for normal development of the trachea and esophagus.