A new rodent experimental model of esophageal atresia and tracheoesophageal fistula: preliminary report

Optimization of tracheoesophageal fistula model established with T-shaped magnet system based on magnetic compression technique

BACKGROUND

The magnetic compression technique has been used to establish an animal model of tracheoesophageal fistula (TEF), but the commonly shaped magnets present limitations of poor homogeneity of TEF and poor model control. We designed a T-shaped magnet system to overcome these problems and verified its effectiveness via animal experiments.

AIM

To investigate the effectiveness of a T-shaped magnet system for establishing a TEF model in beagle dogs.

METHODS

Twelve beagles were randomly assigned to groups in which magnets of the T-shaped scheme (study group, n = 6) or normal magnets (control group, n = 6) were implanted into the trachea and esophagus separately under gastroscopy. Operation time, operation success rate, and accidental injury were recorded. After operation, the presence and timing of cough and the time of magnet shedding were observed. Dogs in the control group were euthanized after X-ray and gastroscopy to confirm establishment of TEFs after coughing, and gross specimens of TEFs were obtained. Dogs in the study group were euthanized after X-ray and gastroscopy 2 wk after surgery, and gross specimens were obtained. Fistula size was measured in all animals, and then harvested fistula specimens were examined by hematoxylin and eosin (HE) and Masson trichrome staining.

RESULTS

The operation success rate was 100% for both groups. Operation time did not differ between the study group (5.25 min ± 1.29 min) and the control group (4.75 min ± 1.70 min; P = 0.331). No bleeding, perforation, or unplanned magnet attraction occurred in any animal during the operation. In the early postoperative period, all dogs ate freely and were generally in good condition. Dogs in the control group had severe cough after drinking water at 6-9 d after surgery. X-ray indicated that the magnets had entered the stomach, and gastroscopy showed TEF formation. Gross specimens of TEFs from the control group showed the formation of fistulas with a diameter of 4.94 mm ± 1.29 mm (range, 3.52-6.56 mm). HE and Masson trichrome staining showed scar tissue formation and hierarchical structural disorder at the fistulas. Dogs in the study group did not exhibit obvious coughing after surgery. X-ray examination 2 wk after surgery indicated fixed magnet positioning, and gastroscopy showed no change in magnet positioning. The magnets were removed using a snare under endoscopy, and TEF was observed. Gross specimens showed well-formed fistulas with a diameter of 6.11 mm ± 0.16 mm (range, 5.92-6.36 mm), which exceeded that in the control group (P < 0.001). Scar formation was observed on the internal surface of fistulas by HE and Masson trichrome staining, and the structure was more regular than that in the control group.

CONCLUSION

Use of the modified T-shaped magnet scheme is safe and feasible for establishing TEF and can achieve a more stable and uniform fistula size compared with ordinary magnets. Most importantly, this model offers better controllability, which improves the flexibility of follow-up studies.

Novel magnetic compression technique for establishment of a canine model of tracheoesophageal fistula

BACKGROUND

Clinically, tracheoesophageal fistula (TEF) is lack of effective surgical strategies. One reason is due to the lack of appropriate animal models of acquired TEF, which is usually complex and difficult. Recently, the magnetic compression technique has been applied for digestive tract anastomosis or vascular anastomosis in animals. In this study, an animal model of TEF in dogs was developed by using the magnetic compression technique, hoping to provide a new method for mimicking TEF.

AIM

To establish a TEF model in dogs by using the magnetic compression technique.

METHODS

Six male beagles were used as models with two Nd-Fe-B permanent magnets for TEF. The parent magnet and the daughter magnet were placed in the cervical esophagus and trachea, respectively. The anterior wall of the esophagus and the posterior wall of the trachea were compressed when the two magnets coupled. After 4-6 d, the necrotic tissue between the two magnets fell off and the parent and daughter magnets disengaged from the target location, leaving a fistula. Gastroscopy/bronchoscopy, upper gastrointestinal contrast study, and histological analysis were performed.

RESULTS

The establishment of the TEF model in all six beagles was successful. The average time of magnet placement was 4.33 ± 1.11 min (range, 3-7 min). Mean time for the magnets to disengage from the target location was 4.67 ± 0.75 d (range, 4-6 d). TEFs were observed by gastroscopy/bronchoscopy and esophageal angiography. The gross anatomical structure of the esophagus and the trachea was in good condition. There was no esophageal mucosa or pseudostratified ciliated columnar epithelium at the site of the fistula according to histological analysis.

CONCLUSION

It is simple, feasible, and minimally invasive to use the magnetic compression technique for the establishment of the TEF model in dogs.

Bodyweight, not age, determines oesophageal length and breaking strength in rats

BACKGROUND/PURPOSE

Delayed primary repair is still the method of choice in the management of long-gap oesophageal atresia in many centres, but the timing of anastomoses varies. Some assume the infant's bodyweight to be an important factor, whereas others prefer age. We therefore aimed to clarify whether age or bodyweight determined oesophageal length in a rodent model.

METHODS

We explanted the oesophagi of 20 Sprague-Dawley rats, aged 15 to 444 days (n = two per time point), measured bodyweight, oesophageal length, weight, and linear breaking strength to measure tissue resilience. Univariate and multivariate regression analyses were conducted to determine the influence of age and bodyweight on oesophageal length and linear breaking strength.

RESULTS

All parameters were highly correlated (R > 0.8), except for age and linear breaking strength (R = 0.65). Both age and bodyweight were univariate significant predictors of oesophageal length, weight, and linear breaking strength (p < 0.0001). Multivariate analyses showed bodyweight to be a significant predictor of oesophageal length (p < 0.0001), whereas age was not (p = 0.18) [adjusted R² = 0.9031]. This was also true for linear breaking strength (p = 0.0007 and p = 0.97, respectively) [adjusted R² = 0.71]. Moreover, the influence of age was negligible, as the adjusted R² and the regression coefficient of bodyweight and its 95% confidence interval were almost identical between univariate und multinomial regressions.

CONCLUSIONS

Only weight determines oesophageal length and tissue resilience in rodents, whereas age is irrelevant. If a similar relationship exists in humans, it may facilitate choosing the optimum time point for delayed primary anastomosis.

LEVEL OF EVIDENCE

IV - Experimental Paper.

Esophageal duplication and congenital esophageal stenosis

Esophageal duplication and congenital esophageal stenosis (CES) may represent diseases with common embryologic etiologies, namely, faulty tracheoesophageal separation and differentiation. Here, we will re-enforce definitions for these diseases as well as review their embryology, diagnosis, and treatment.

Effect of folic acid in a modified experimental model of anorectal malformations adriamycin-induced in rats

PURPOSE

To determine the effect of a single dose of adriamycin (ADR) to induce anorectal malformations (ARMs) and determine the effect of folic acid (FA) in this model.

METHODS

Ten female Wistar rats were divided randomly in two groups. Group A - ADR; Group B - FA+ADR. Dams from group B received daily, since two weeks before the pregnancy to the end of pregnancy, FA (50mg/kg) by gavage. Dams from both groups received ADR (6mk/kg) by intraperitoneal injection on gestational day (GD) 8. Their fetuses were harvested by cesarean section on GD21 and were examined looking for ARMs. The thickness of anal stratified squamous epithelium (ASSE) and intestinal epithelium (IE) were analyzed. p≤0.05*.

RESULTS

81 fetuses were harvested. The number of fetuses; number of ARMs; mean (∆%) (± SD) were determined to be, respectively: ADR - 41[29;65%(±37%)] versus FA+ADR - 40[04;16%(±36%)] (p=0.05). AMRs were significantly lower in FA+ADR group than in ADR group (p=0.05). The thickness (µm) of ASSE (± SD) and IE (± SD) were measured, respectively: ADR - [25.98(±0.74) and 19.48(±1.68)] versus FA+ADR - [24.74(±0.91) and 24.80(±0.81)] (p<0.005). The thickness of IE was significantly enlarged when FA was given (p<0.005).

CONCLUSIONS

Single dose of adriamycin on D8 was able to induce anorectal malformations. Folic acid reduces the number and enlarged the IE of ARMs ADR-induced.

Lung maturity in esophageal atresia: Experimental and clinical study

INTRODUCTION

Esophageal atresia and tracheoesophageal fistula (EA-TEF) survivors suffer respiratory morbidity of unclear pathogenesis. Defective lung morphogenesis has been described in the rat model. This study examined fetal lung growth and maturity in rats and patients with EA-TEF.

METHODS

Pregnant rats received either adriamycin or vehicle. Control and adriamycin-exposed lungs, with and without EA-TEF, were weighed and processed for RT-PCR, DNA quantification, immunofluorescence and immunoblot analysis of TTF1, VEGF, Sp-B, and α-sma. Twenty human lungs were also processed for immunofluorescence and Alcian-blue staining.

RESULTS

Lungs from fetuses with EA-TEF (E21) showed decreased total DNA; FGF7 and TTF1 mRNA expressions were upregulated at E15 and E18, respectively. Protein expression and immunofluorescent distribution of maturity markers were similar. Lungs from stillborns with EA-TEF showed decreased epithelial expression of Sp-B and VEGF whereas those from newborns tended to have less Sp-B and more VEGF and mucous glands.

DISCUSSION

The lungs of rats with EA-TEF were hypoplastic but achieved near-normal maturity. Stillborns with EA-TEF exhibited an apparently disturbed differentiation of the airway epithelium. Newborns with EA-TEF demonstrated subtle differences in the expression of differentiation markers, and increased number of mucous glands that could influence postnatal respiratory adaptation and explain some respiratory symptoms of EA-TEF survivors.

The effects of adriamycin on E-cadherin mediated cell-cell adhesion and apoptosis during early kidney development

Adriamycin (ADR) is strongly teratogenic. We investigated the effects of ADR on apoptosis and the intensity of E-cadherin expression in developing kidneys. An experimental group of rats was given 2 mg/kg/day ADR on days 6-9 of gestation and a control group was given saline on the same schedule. Embryos were decapitated on days 13, 15, 17 and 19 of gestation, and processed and embedded in paraffin for routine light microscopy. Kidney specimens were stained with hematoxylin and eosin or periodic acid-Schiff, or immunostained for E-cadherin. Apoptosis was assessed using the TUNEL method. Weight loss and developmental deficiency were determined in embryos of the experimental group. ADR damaged or destroyed tubule epithelial cells, which caused apparent dilatation of the tubule lumen. Also, the brush borders of proximal tubules were damaged and glomerular spaces were dilated. ADR caused apoptosis of kidney tissue by days 15, 17 and 19 of development and E-cadherin expression was up-regulated during kidney development compared to controls. We found that ADR can cause apoptosis and increased E-cadherin expression in the developing rat kidney. E-cadherin expression and apoptosis may contribute to the development of ADR nephrotoxicity.

The multifactorial origin of respiratory morbidity in patients surviving neonatal repair of esophageal atresia

Esophageal atresia with or without tracheoesophageal fistula (EA ± TEF) occurs in 1 out of every 3000 births. Current survival approaches 95%, and research is therefore focused on morbidity and health-related quality of life issues. Up to 50% of neonates with EA ± TEF have one or more additional malformations including those of the respiratory tract that occur in a relatively high proportion of them and particularly of those with vertebral, anal, cardiac, tracheoesophageal, renal, and limb association. Additionally, a significant proportion of survivors suffer abnormal pulmonary function and chronic respiratory tract disease. The present review summarizes the current knowledge about the nature of these symptoms in patients treated for EA ± TEF, and explores the hypothesis that disturbed development and maturation of the respiratory tract could contribute to their pathogenesis.

Adriamycin-Induced Models of VACTERL Association

Animal models are of great importance for medical research. They have enabled analysis of the aetiology and pathogenesis of complex congenital malformations and have also led to major advances in the surgical and therapeutic management of these conditions. Animal models allow us to comprehend the morphological and molecular basis of disease and consequently to discover novel approaches for both surgical and medical therapy. The anthracycline antibiotic adriamycin was incidentally found to have teratogenic effects on rats, producing a range of defects remarkably similar to the VACTERL association of congenital anomalies in humans, providing a reproducible animal model of this condition. VACTERL association is a spectrum of birth defects which includes vertebral, anal, cardiovascular, tracheo-oesophageal, renal and limb anomalies. In recent years, adriamycin rodent models of VACTERL have provided valuable insights into the pathogenesis of this complex association, particularly in relation to tracheo-oesophageal malformations. The adriamycin rat model and adriamycin mouse model are now well established in the investigation of the morphology of faulty organogenesis and the regulation of gene expression in tracheo-oesophageal anomalies.

Considering the Embryopathogenesis of VACTERL Association

The nonrandom co-occurrence of vertebral, anorectal, cardiac, tracheoesophageal, genitourinary, and limb malformations, recognized as the VACTERL association, has not been satisfactorily explained from either a causation or embryopathogenesis standpoint. Few familial cases have been identified and maternal diabetes is the only environmental influence implicated to date. Mutations in single genes have been found in a number of syndromes with one or more of the VACTERL malformations, but these syndromes usually have other features which distinguish them from the VACTERL association. Animal models have provided clues to molecular pathways that may be involved in the embryogenesis of the VACTERL structures. What is lacking is the systematic study of individual genes and pathways in well-composed cohorts of patients, which is now possible with high throughput molecular technologies.

Foregut duplication cyst associated with esophageal atresia and tracheoesophageal fistula: a case report and literature review

A case of esophageal atresia associated with a foregut duplication cyst is reported and the literature reviewed. This is the first documented occurrence in conjunction with Down syndrome and the second case where both anomalies were treated at the initial surgery.

Abnormal control of lung branching in experimental esophageal atresia

PURPOSE

Esophageal atresia and tracheo-esophageal fistula (EA-TEF) result from abnormal division of the foregut into esophagus and trachea thus, it may influence airway branching and lung development. The present study examined lung morphogenesis in fetuses with EA-TEF focusing in the expression of FGF10 and its receptor FGFR2 IIIb.

METHODS

Pregnant rats received either 1.75 mg/kg i.p. adriamycin or vehicle on E7, E8 and E9. Embryos were recovered at E15, E18 and E21 and lungs processed for immunohistochemistry and RT-PCR. Three groups were studied: control, adriamycin-exposed with EA-TEF, and adriamycin-exposed without EA-TEF. Comparisons were performed with Mann-Whitney or t tests (significance level, 5 %).

RESULTS

Lung weight at E15 and E18 were significantly lower in adriaEA fetuses in which the relative mRNA levels of FGF10 were significantly higher. These differences disappeared near term. The receptor FGFR2 IIIb messenger was only significantly increased in adria noEA fetuses at E15. Immunohistochemical study was consistent with these findings.

CONCLUSIONS

Abnormal expression of FGF10 during earlier stages of development, when the lungs are smaller than controls, suggests a compensatory response aimed at "catching up" delayed tracheobronchial branching. Whether similar changes take place in the human condition and influence respiratory physiology remain to be determined.

Lung hypoplasia in rats with esophageal atresia and tracheo-esophageal fistula

INTRODUCTION

Survivors of esophageal atresia and tracheo-esophageal fistula (EA-TEF) often suffer chronic respiratory tract disease. EA-TEF results from abnormal emergence of the trachea from the foregut. This study in a rat model tests the hypothesis that primary lung maldevelopment might be a downstream consequence of this defect.

RESULTS

The lung was hypoplastic in rats with EA-TEF although the histological pattern was normal. Maturation and arteriolar wall thickness were unchanged, but mesenchymal control of airway branching was weakened. This branching was deficient from embryonal day (E13) on in adriamycin-treated explants.

DISCUSSION

In conclusion, the lungs were hypoplastic in rats with experimental EA-TEF due to defective embryonal airway branching. However, arteriolar wall and respiratory epithelial patterns remained normal. These findings suggest that similarly defective lung development might contribute to chronic respiratory disease in EA-TEF patients.

METHODS

Pregnant rats received either 1.75 mg/kg i.p. adriamycin or vehicle on E7, E8, and E9. Lungs were recovered at E15, E18, and E2. Lung weight/body weight ratio, total DNA and protein, radial alveolar count, arteriolar wall thickness, lung maturity, and mesenchymal control of airway branching were assessed. E13 lungs were cultured for 72 h and explant airway branching was measured daily. For comparisons, nonparametric tests (*P < 0.05) were used.

Abnormal notochord branching is associated with foregut malformations in the adriamycin treated mouse model

Oesophageal atresia (OA) and tracheooesophageal fistula (TOF) are relatively common human congenital malformations of the foregut where the oesophagus does not connect with the stomach and there is an abnormal connection between the stomach and the respiratory tract. They require immediate corrective surgery and have an impact on the future health of the individual. These abnormalities are mimicked by exposure of rat and mouse embryos in utero to the drug adriamycin. The causes of OA/TOF during human development are not known, however a number of mouse mutants where different signalling pathways are directly affected, show similar abnormalities, implicating multiple and complex signalling mechanisms. The similarities in developmental outcome seen in human infants and in the adriamycin treated mouse model underline the potential of this model to unravel the early embryological events and further our understanding of the processes disturbed, leading to such abnormalities. Here we report a systematic study of the foregut and adjacent tissues in embryos treated with adriamycin at E7 and E8 and analysed between E9 and E12, comparing morphology in 3D in 149 specimens. We describe a spectrum of 8 defects, the most common of which is ventral displacement and branching of the notochord (in 94% of embryos at E10) and a close spatial correspondence between the site of notochord branching and defects of the foregut. In addition gene expression analysis shows altered dorso-ventral foregut patterning in the vicinity of notochord branches. This study shows a number of features of the adriamycin mouse model not previously reported, implicates the notochord as a primary site of disturbance in such abnormalities and underlines the importance of the model to further address the mechanistic basis of foregut congenital abnormalities.

Etiology of esophageal atresia and tracheoesophageal fistula: "mind the gap"

Esophageal atresia and tracheoesophageal fistula (EA/TEF) are major congenital malformations affecting 1:3500 live births. Current research efforts are focused on understanding the etiology of these defects. We describe well-known animal models, human syndromes, and associations involving EA/TEF, indicating its etiologically heterogeneous nature. Recent advances in genotyping technology and in knowledge of human genetic variation will improve clinical counseling on etiologic factors. This review provides a clinical summary of environmental and genetic factors involved in EA/TEF.

Embryology of anorectal malformations

Today, the normal and abnormal development of the hindgut is still a matter of speculation. However, as the result of recent studies in appropriate animal models, most embryologic events that finally lead to abnormal hindgut development are better known than in the past: (1) the process of maldevelopment starts in early embryonic stages; (2) the cloacal membrane is always too short in its dorsal part, thus, the dorsal cloaca is missing; and (3) as a result, the hindgut remains attached to the sinus urogenitalis, forming the recto-urethral fistula. In the past, an impaired process of septation was believed to be the main cause of abnormal hindgut development. In contrast to this, our results indicate that the development of the septum is more passive than active. Furthermore, the results of our studies in normal and abnormal development indicate that (1) the embryonic cloaca never passes through a stage that is similar to any form of anorectal malformation in neonates, including the so-called "cloacas" in female embryos, and (2) to explain abnormal development, studies in abnormal embryos are mandatory.

Congenital anomalies of the esophagus

Congenital malformations of the esophagus are frequently encountered by pediatric surgeons, especially esophageal atresia with or without tracheo-esophageal fistula. However, the molecular mechanisms underlying the development of these various anomalies are not clear. Here we present a brief overview of the embryologic development of the tracheoesophageal tube, along with some of the genetic controls which, when defective can lead to abnormal separation of this tube.

Mesenchymal expression of Tbx4 gene is not altered in Adriamycin mouse model

PURPOSE

The Adriamycin mouse model (AMM) is a reproducible teratogenic model of esophageal atresia/tracheo-esophageal fistula (EA/TEF). Tbx4 is a member of the T-box family of transcription factor genes, which is reported to play a key role in separation of the respiratory tract and the esophagus. Up-regulation of Tbx4 is reported to cause TEF in the chick. Optical projection tomography (OPT) is a technique that allows three-dimensional (3D) imaging of gene expression in small tissue specimens in an anatomical context. The aim of this study was to investigate the temporo-spatial expression of Tbx4 during the critical period of separation of the trachea and esophagus in normal and Adriamycin treated embryos using OPT.

MATERIALS AND METHODS

Time-mated CBA/Ca mice received intraperitoneal injections of Adriamycin (6 mg/kg) or saline on days 7 and 8 of gestation. Embryos were harvested on days 9-12, stained following whole mount in situ hybridization with labeled RNA probes to detect Tbx4 transcripts (n = 5 for each treatment/day of gestation). Immunolocalization with the endoderm marker Hnf3beta was used to visualize morphology. Embryos were scanned by OPT to obtain 3D representations of gene expression domains. Animal licence no. B100/4106.

RESULTS

OPT elegantly revealed Tbx4 gene expression in both controls and in the disorganized pulmonary mesenchyme in the treated embryos. Although characteristic morphological abnormalities were observed in Adriamycin treated embryos, there was no significant difference in Tbx4 transcript distribution around lung primordia in comparison with control embryos.

CONCLUSION

Although previously reported morphological abnormalities of notochord and esophagus were observed in AMM, Tbx4 gene expression was unaltered, suggesting that esophageal anomalies can occur in the presence of normal Tbx4 gene expression in this model.

Lung organogenesis

Developmental lung biology is a field that has the potential for significant human impact: lung disease at the extremes of age continues to cause major morbidity and mortality worldwide. Understanding how the lung develops holds the promise that investigators can use this knowledge to aid lung repair and regeneration. In the decade since the "molecular embryology" of the lung was first comprehensively reviewed, new challenges have emerged-and it is on these that we focus the current review. Firstly, there is a critical need to understand the progenitor cell biology of the lung in order to exploit the potential of stem cells for the treatment of lung disease. Secondly, the current familiar descriptions of lung morphogenesis governed by growth and transcription factors need to be elaborated upon with the reinclusion and reconsideration of other factors, such as mechanics, in lung growth. Thirdly, efforts to parse the finer detail of lung bud signaling may need to be combined with broader consideration of overarching mechanisms that may be therapeutically easier to target: in this arena, we advance the proposal that looking at the lung in general (and branching in particular) in terms of clocks may yield unexpected benefits.

Fgf10 gene expression is delayed in the embryonic lung mesenchyme in the adriamycin mouse model

BACKGROUND

The adriamycin mouse model is a well-established teratogenic model of esophageal atresia/tracheoesophageal fistula. Fibroblast growth factor 10 (Fgf10) plays a key role in branching of the lung buds during lung morphogenesis. Fgf10 knockout mice exhibit the absence of the lungs. Optical projection tomography (OPT) is a technique that allows three-dimensional (3D) imaging of gene expression in small tissue specimens in an anatomical context. The aim of this study was to investigate the temporo-spatial expression of Fgf10 during the critical period of separation of the trachea and esophagus in normal and adriamycin-treated embryos using OPT.

METHODS

Time-mated CBA/Ca mice received intraperitoneal injections of adriamycin (6 mg/kg) or saline on days 7 and 8 of gestation. Embryos were harvested on days 10-13, stained after whole mount in situ hybridization with labeled RNA probes to detect Fgf10 transcripts (n = 5 for each treatment/day of gestation). Immunolocalization with endoderm marker Hnf3 beta was used to visualize morphology. Embryos were scanned by OPT to obtain 3D representations of gene expression domains.

RESULTS

Computer reconstructed specimens allowed precise staging of developing embryos according to Theiler Staging (TS) criteria. OPT elegantly displayed Fgf10 gene expression in the pulmonary mesenchyme around the tip of the lung buds in both controls and treated embryos in the same spatial territory. Fgf10 gene expression was first detected in the control embryos at TS17. However, Fgf10 gene expression in adriamycin-treated embryos was first only observed at TS18 in 67% of the specimens.

CONCLUSION

Delayed Fgf10 gene expression during the critical period of separation of the trachea and esophagus may affect lung bud formation in the adriamycin model leading to tracheoesophageal malformations.

Genetic and environmental factors in the etiology of esophageal atresia and/or tracheoesophageal fistula: an overview of the current concepts

Esophageal atresia and/or tracheoesophageal fistula (EA/TEF) are severe congenital anomalies. Although recent years have brought significant improvement in clinical treatment, our understanding of the etiology of these defects is lagging. Many genes and genetic pathways have been implicated in the development of EA/TEF, but only a few genes have been shown to be involved in humans, in animals, or in both. Extrapolating data from animal models to humans is not always straightforward. Environmental factors may also carry a risk, but the mechanisms are yet to be elucidated. This review gives an overview of the current state of knowledge about both genetic and environmental risk factors in the etiology of EA/TEF.

Foregut separation and tracheo-oesophageal malformations: the role of tracheal outgrowth, dorso-ventral patterning and programmed cell death

Foregut division—the separation of dorsal (oesophageal) from ventral (tracheal) foregut components—is a crucial event in gastro-respiratory development, and frequently disturbed in clinical birth defects. Here, we examined three outstanding questions of foregut morphogenesis. The origin of the trachea is suggested to result either from respiratory outgrowth or progressive septation of the foregut tube. We found normal foregut lengthening despite failure of tracheo-oesophageal separation in Adriamycin-treated embryos, whereas active septation was observed only in normal foregut morphogenesis, indicating a primary role for septation. Dorso-ventral patterning of Nkx2.1 (ventral) and Sox2 (dorsal) expression is proposed to be critical for tracheo-oesophageal separation. However, normal dorso-ventral patterning of Nkx2.1 and Sox2 expression occurred in Adriamycin-treated embryos with defective foregut separation. In contrast, Shh expression shifts dynamically, ventral-to-dorsal, solely during normal morphogenesis, particularly implicating Shh in foregut morphogenesis. Dying cells localise to the fusing foregut epithelial ridges, with disturbance of this apoptotic pattern in Adriamycin, Shh and Nkx2.1 models. Strikingly, however, genetic suppression of apoptosis in the Apaf1 mutant did not prevent foregut separation, indicating that apoptosis is not required for tracheo-oesophageal morphogenesis. Epithelial remodelling during septation may cause loss of cell-cell or cell-matrix interactions, resulting in apoptosis (anoikis) as a secondary consequence.

Caudal regression and tracheoesophageal malformation induced by adriamycin: a novel chick model of VATER association

VATER association represents a cluster of Vertebral, Anal, Tracheo-Esophageal, Radial and Renal malformations, and caudal regression syndrome is an entity consisting of a spectrum of congenital anomalies of lower spine and hips associated with genitourinary and lower limb defects. The concurrence of various malformations may be explained by a common defect in blastogenesis, but direct evidence is yet to be accumulated. Here, by the use of autofluorescence and the teratogenic effect of adriamycin, we demonstrated that adriamycin administered to eggs of White Leghorns distributes to the caudal portion of the embryo and foregut epithelium and induces caudal regression and tracheal and pulmonary agenesis. The induction of caudal regression syndrome-like anomaly was developmental stage and dose dependent. Embryos with caudal regression demonstrated tracheoesophageal anomalies, one of the defects included in VATER association. The stages at which anomalies were produced corresponded to that of human embryos between days 22 and 26 (Carnegie stages 10-11). In view of the antitumor activity of adriamycin by intercalating to double-stranded DNA of undifferentiated cells undergoing rapid cell division, it is possible that adriamycin had preferentially attacked cells in the caudal end where pronounced proliferation takes place during this narrow period of greatest susceptibility.

The lung primordium an outpouching from the foregut! Evidence-based dogma or myth?

BACKGROUND/PURPOSE

This study examines and challenges the "evidence-based legitimacy" of the theory, "the lung primordium is an outpouching from the foregut."

METHOD

A literature review was undertaken using computer database, journals, and relevant anatomical and embryological texts.

RESULTS

The independent path of development taken by the tracheobronchial system and the oesophagus once identified as separate entities; the lack of morphologic, molecular, biological, and genetic supportive evidence for the "common-origin" theory; the distinct longitudinal line of demarcation between the nonsegmented muscles of the esophagus and the highly segmented cartilaginous structure of the tracheobronchial tree; the absence of a tracheoesophageal septum in the process of separation; the differences in epithelial lining; and the diametrically opposed mucociliary cascade of the upper airway vs the mucociliary escalator of the tracheobronchial tree all seriously challenge the authenticity of a common origin to these 2 entities.

CONCLUSION

To the extent that the foregut is seen as consisting of 2 separate semitubular splanchnopleuric entities ventrodorsally juxtaposed, it is true that the lung primordium as an outpouching of, and not from, the foregut. This must never be confused with the notion that the esophagus and tracheobronchial tree have a common origin. In fact, they develop from 2 completely separate segments of the trilaminar germ disk, but because of head fold development are brought together to create a common tracheoesophageal chamber that is later separated, facilitated by the prochordal membrane diverticulum.

Investigation of histopathologic changes in the ureter walls in experimental congenital obstructive uropathy

BACKGROUND/PURPOSE

The aim of this study is to determine the histopathologic changes in the ureter wall in experimental urinary bladder hypoplasia and agenesis.

METHODS

Timed pregnant rats were randomly divided and received intraperitoneal Adriamycin (ADR) at 2 mg/kg on gestational days (GD) 6 to 9 (ADR group) and saline at 2 mL/kg on GD 6 to 9 (SF group). The control (C) group did not receive any medication in their pregnancy. Fetuses were harvested near term on GD 21 and dissected under a dissecting microscope and examined for urinary system abnormalities.

RESULTS

Diameter of ureter lumen was significantly increased, but wall thickness, tunica muscularis, and epithelial thickness of the ureter were decreased in the ADR group as compared with the C and SF groups.

CONCLUSIONS

Diameter of the ureter lumen was increased, but wall thickness, tunica muscularis, and uroepithelium of the ureter were decreased in the ADR group in the intrauterine period. The diameter of the ureter lumen and wall thickness of ureter (tunica muscularis of ureter and uroepithelium) were increased following obstructive uropathy after the birth.

Adriamycin produces a reproducible teratogenic model of gastrointestinal atresia in the mouse

Gastrointestinal atresia is a major cause of bowel obstruction in the newborn. Experimental models and clinical observations have demonstrated the heterogeneous nature of its pathogenesis. A proportion is due to late intra-uterine vascular insults and some are genetic in nature. Epidemiological studies have found gastrointestinal atresia to occur with other birth defects, in particular VACTERL anomalies, suggesting that a subset of cases may result from an early disturbance to intestinal morphogenesis. Adriamycin is teratogenic in rats, producing gastrointestinal atresia and VACTERL anomalies. The mouse is the foremost mammal studied by developmental biologists, offering an expanding wealth of knowledge and scientific research techniques. The aim of this study was to create an Adriamycin mouse model for investigating the development of gastrointestinal atresia. CBA/Ca mice were accurately time-mated (n = 30). Four different doses of Adriamycin (0-saline control, 4, 5 and 6 mg/kg) at three different timings of injections were compared (12 groups). Dams received two intraperitoneal injections, 24 h apart, commencing on day 7, 7.5 or 8. Foetuses were harvested on day 18. Gastrointestinal atresia and VACTERL anomalies were examined using a dissecting microscope. Adriamycin produced type IIIa gastrointestinal atresia in six treatment groups. The effect of Adriamycin depended on the timing and dose of the injections. VACTERL anomalies were only found in four treatment groups, proposing overlapping critical embryological windows for these malformations. Gastrointestinal atresia can be induced by the teratogen Adriamycin, occurring with and without VACTERL anomalies. This produces a reproducible mouse model in which the molecular pathogenesis of gastrointestinal atresia may be studied.

Non-VACTERL-type anomalies are frequent in patients with esophageal atresia/tracheo-esophageal fistula and full or partial VACTERL association

BACKGROUND

The VACTERL association is the nonrandom co-occurrence of Vertebral anomalies, Anal atresia, Cardiovascular malformations, Tracheo-esophageal fistula (TEF) and/or Esophageal atresia (EA), Renal anomalies, and/or Limb-anomalies. The full phenotype of patients with EA/TEF and other anomalies of the VACTERL spectrum of defects association is not well described in the literature.

METHODS

Data on patients with EA/TEF seen in two pediatric surgical centers in the Netherlands between January 1988 and August 2006 were evaluated for defects of the VACTERL spectrum as well as non-VACTERL-type defects. The presence of two or more defects of the VACTERL spectrum in addition to EA/TEF was the criterion for inclusion in this study. A detailed description was made of all defects.

RESULTS

Of 463 patients with EA and/or TEF, 107 (23.1%) fulfilled the inclusion criterion, of which seventeen cases had a recognized etiology and were excluded, leaving 90 cases (19.4%) for analysis. Other than the esophagus and the trachea, the vertebrae/ribs and the cardiovascular system were most commonly affected (68.9 and 65.6%, respectively). Interestingly, 70% of cases had additional non-VACTERL-type defects, with high occurrences for single umbilical artery (20%), genital defects (23.3%), and respiratory tract anomalies (13.3%).

CONCLUSIONS

Many patients with EA/TEF and at least two other defects of the VACTERL spectrum also display non-VACTERL-type congenital anomalies.

The Adriamycin rat/mouse model and its importance to the paediatric surgeon

The teratogenic effect of Adriamycin (doxorubicin) in the rat model, and more recently in the mouse, has provided paediatric surgeons with a reliable, easily reproducible method of studying the embryology and molecular biology for a range of complex congenital anomalies. Concomitantly these animal models have stimulated interest among embryologists for the effect on the notochord, shedding more light on the important organizational role of this structure in the developing embryo. Finally, as more is learnt of the pathogenesis of the various malformations induced by Adriamycin, future therapeutic interventions involving gene therapy, drugs or surgery may arise. This article reviews the establishment of the Adriamycin rat and mouse models, examines their impact on various congenital malformations, and suggests targets for further research.

Intrinsic esophageal innervation in esophageal atresia without fistula

Esophageal atresia and tracheo-esophageal fistula (EA + TEF) are often associated with malformations of neural crest origin. Esophageal innervation is also derived from the neural crest and it is abnormal in EA + TEF in which there is motor dysfunction. Our aim was to examine the intrinsic esophageal innervation in children with isolated EA in which different embryogenic mechanisms might be involved. Specimens from the proximal and distal esophageal segments of 6/35 patients who had esophageal replacement for isolated EA between 1965 and 2006 were suitable for the study. They were sectioned and immunostained with anti-neurofilament (NF) and anti-S-100 antibodies. The muscle and neural surfaces on each section were measured with the assistance of image processing software. The surface of the ganglia and the number of neurons per ganglion were determined at high power microscopy. The findings were compared with those of six autopsy specimens from newborns dead of other diseases by means of standard statistical tests and a significance threshold of P < 0.05. Unmatched age/size of babies in isolated EA and control groups precluded comparison of the relative surfaces occupied by neural elements. Patients with pure EA had denser fibrilar network and larger ganglia than controls. The number of neurons/ganglion were similar in both groups although the cells from EA patients were larger. The findings were similar at both esophageal levels studied. In spite of methodologic biases, it seems that intrinsic esophageal fibrilar network is denser and the intramural ganglia larger with larger cells in patients with pure EA than in controls on both esophageal ends of the organ. These neural anomalies are only in part reminiscent of those described in regular EA/TEF but may as well explain esophageal dysfunction in patients with repaired isolated EA.

Visualizing expression patterns of Shh and Foxf1 genes in the foregut and lung buds by optical projection tomography

Congenital malformations of the foregut are common in humans. The respiratory and digestive tubes are both derived by division of the foregut primordium. Sonic hedgehog (Shh) and Fork head box F1 (Foxf1) genes encode regulatory molecules that play a pivotal role in gut and lung morphogenesis and are therefore important candidate genes to be examined in models of foregut developmental disruption. Optical projection tomography (OPT) is a new, rapid and non-invasive technique for three-dimensional (3D) imaging of small biological tissue specimens that allows visualization of the tissue distribution of RNA in developing organs while also recording morphology. To explore the application of OPT in this context, we visualized Shh and Foxf1 gene expression patterns in the mouse foregut and lung buds at several stages of development. Time-mated CBA/Ca mice were harvested on embryonic days 9-12. The embryos were stained following whole mount in situ hybridization with labelled RNA probes to detect Shh and Foxf1 transcripts at each stage. The embryos were scanned by OPT to obtain 3D representations of gene expression domains in the context of the changing morphology of the embryo. OPT analysis of Shh and Foxf1 expression in the foregut and lung buds revealed extra details of the patterns not previously reported, particularly in the case of Foxf1 where gene expression was revealed in a changing pattern in the mesenchyme around the developing lung. Shh expression was also revealed in the epithelium of the lung bud itself. Both genes were detected in complementary patterns in the developing bronchi as late as E12, showing successful penetration of molecular probes and imaging at later stages. OPT is a valuable tool for revealing gene expression in an anatomical context even in internal tissues like the foregut and lung buds across stages of development, at least until E12. This provides the possibility of visualizing altered gene expression in an in vivo context in genetic or teratogenic models of congenital malformations.

The current state of congenital tracheal stenosis

Congenital tracheal stenosis (CTS) is an uncommon condition that has challenged pediatric surgeons for decades. Patients with CTS can present with a wide spectrum of symptoms and varying degrees of severity. In addition, a variety of techniques have been devised to repair this malformation. A review of these procedures and our suggestions for clinical standards and practice guidelines will be presented in this paper. A retrospective review of the literature on CTS from 1964 to 31 March, 2006. There is not one standard technique for the repair of CTS, as individualized approach to each patient and airway lesion is necessary to optimize patient management; nevertheless there is a consensus about segmental resection and anastomosis being best for short segment stenosis while slide tracheoplasty is most effective for the long-segment ones. Conservative management is also an option for select group of patients with careful and close follow up. Survival following surgery over the years has improved, but mortality remained high, particularly in a specific subset of patients presenting at the age less than 1 month with associated cardiac malformations. In conclusion, CTS remains a significant challenge for pediatric surgeons. Additional research is required to improve our understanding of the pathogenesis of CTS, and to develop evidence-based treatment protocols for the entire spectrum of presentation including conservative management.

Adriamycin produces a reproducible teratogenic model of vertebral, anal, cardiovascular, tracheal, esophageal, renal, and limb anomalies in the mouse

BACKGROUND/PURPOSE

The Adriamycin rat model is an established model for vertebral, anal, cardiac, tracheal, esophageal, renal, and limb (VACTERL) anomalies and gastrointestinal atresias. Mice are the foremost mammal studied by developmental biologists, providing greater availability of molecular probes, antibodies, and transferable knowledge with transgenic studies. Only tracheoesophageal malformations have been previously described in the Adriamycin mouse model. The aim of this study was to carry out a dose-response analysis of the teratogenicity of Adriamycin in the mouse to determine the effect of the dose and timing of exposure in producing tracheoesophageal malformations and show if it causes other VACTERL anomalies.

METHODS

CBA/Ca mice were accurately time mated (n = 30). Four different doses (0 [saline], 4, 5, and 6 mg/kg) of Adriamycin (EBEWE Pharma Ges.m.b.H. Nfg.KG, A-4866 Unterach, Austria) at 3 different timings of injections were compared. Dams received 2 intraperitoneal injections, 24 hours apart, commencing on day 7, 7.5, or 8. Fetuses were harvested on day 18. Anomalies were examined using a dissecting microscope and serial transverse sections.

RESULTS

Administering Adriamycin at 6 mg/kg on days 7 and 8 had the most teratogenic effect, with 80% of fetuses having 3 or more VACTERL anomalies: anorectal malformation, 100%; tracheoesophageal malformation, 50%; right-sided aortic arch, 58.3%; bladder agenesis/bilateral hydronephrosis, 100%.

CONCLUSION

This study establishes a mouse model that should provide insights into the cellular and molecular mechanisms underlying VACTERL anomalies.

Exploiting mechanical stimuli to rescue growth of the hypoplastic lung

Impaired lung development afflicts a range of newborns cared for by paediatric surgeons. As a result the speciality has led in the development of surgical models that illustrate the biomechanical regulation of lung growth. Using transgenic mutants, biologists have similarly discovered much about the biochemical regulation of prenatal lung growth. Airway smooth muscle (ASM) and its prenatal contractility airway peristalsis (AP) represent a novel link between these areas: ASM progenitors produce an essential biochemical factor for lung morphogenesis, whilst calcium-driven biomechanical ASM activity appears to regulate the same. In this invited paper, I take the opportunity both to review our recent findings on lung growth and prenatal ASM, and also to discuss mechanisms by which ASM contractility can regulate growth. Finally, I will introduce some novel ideas for exploration: ASM contractility could help to schedule parturition (pulmonary parturition clock) and could even be a generic model for smooth muscle regulation of morphogenesis in similar organs.

Aberrant Bmp signaling and notochord delamination in the pathogenesis of esophageal atresia

Human foregut malformation known as esophageal atresia with tracheoesophageal fistula (EA/TEF) occurs in 1 in 4,000 live births with unknown etiology. We found that mice lacking Noggin (Nog(-/-)) displayed Type C EA/TEF, the most common form in humans, and notochordal defects strikingly similar to the adriamycin-induced rat EA/TEF model. In accord with esophageal atresia, Nog(-/-) embryos displayed reduction in the dorsal foregut endoderm, which was associated with reduced adhesion and disrupted basement membrane. However, significant apoptosis in the Nog(-/-) dorsal foregut was not observed. Instead, non-notochordal, likely endodermal, cells were found in Nog(-/-) notochord, suggesting that Noggin function is required in the notochordal plate for its proper delamination from the dorsal foregut. Notably, ablating Bmp7 function in Nog(-/-) embryos rescued EA/TEF and notochord branching defects, establishing a critical role of Noggin-mediated Bmp7 antagonism in EA/TEF pathogenesis.

Stephen L. Gans Distinguished Overseas Lecture. The neural crest in pediatric surgery

AIM

This review highlights the relevance of the neural crest (NC) as a developmental control mechanism involved in several pediatric surgical conditions and the investigative interest of following some of its known signaling pathways.

METHODS

The participation of the NC in facial clefts, ear defects, branchial fistulae and cysts, heart outflow tract and aortic arch anomalies, pigmentary disorders, abnormal enteric innervation, neural tumors, hemangiomas, and vascular anomalies is briefly reviewed. Then, the literature on clinical and experimental esophageal atresia-tracheoesophageal fistula (EA-TEF) and congenital diaphragmatic hernia (CDH) is reviewed for the presence of associated NC defects. Finally, some of the molecular signaling pathways involved in both conditions (sonic hedgehog, Hox genes, and retinoids) are summarized.

RESULTS

The association of facial, cardiovascular, thymic, parathyroid, and C-cell defects together with anomalies of extrinsic and intrinsic esophageal innervation in babies and/or animals with both EA-TEF and CDH strongly supports the hypothesis that NC is involved in the pathogenesis of these malformative clusters. On the other hand, both EA-TEF and CDH are observed in mice mutant for genes involved in the previously mentioned signaling pathways.

CONCLUSIONS

The investigation of NC-related molecular pathogenic pathways involved in malformative associations like EA-TEF and CDH that are induced by chromosomal anomalies, chemical teratogens, and engineered mutations is a promising way of clarifying why and how some pediatric surgical conditions occur. Pediatric surgeons should be actively involved in these investigations.

Adriamycin mouse model: a variable but reproducible model of tracheo-oesophageal malformations

A spectrum of tracheo-oesophageal malformations is seen in humans: oesophageal atresia, tracheal agenesis and laryngotracheo-oesophageal clefts. They are thought to share a common but unknown aetiology. These birth defects are frequently associated with other VACTERL anomalies. The adriamycin rat model (ARM) has proved to be a valuable model of the VACTERL anomalies, illustrating the dysmorphogenesis of oesophageal atresia and tracheal agenesis. As organogenesis relies on temporaspatially co-ordinated signalling systems, the next step would be to study the molecular pathogenesis of tracheo-oesophageal malformations. However, the mouse is the foremost mammal studied by developmental biologists, offering an expanding wealth of knowledge and scientific research techniques with which to investigate these anomalies. A limited dose response analysis of the teratogenicity of adriamycin in the mouse has identified a dose and timing of injections that produced tracheo-oesophageal malformations and other VACTERL anomalies. A clear account of the types and variability of the tracheo-oesophageal malformations produced by this dose is essential in order to be able to plan and interpret any future investigations of early gestation fetuses. CBA/Ca mice were accurately time-mated (n = 10). Nine dams received intraperitoneal injections of adriamycin (6 mg/kg) and one control dam received saline injections, on days 7 and 8. Fetuses were harvested on day 18, near term. Tracheo-oesophageal malformations were examined by dissecting microscope and serial transverse sections. Results are reported in the standard teratological manner as mean percentage per litter (+/-SEM). The resorption rate of the adriamycin treated fetuses was 50.4%. There were 29 adriamycin treated fetuses for inspection. Tracheo-oesophageal malformations were found in 29.2% (+/-10.3), affecting five out of nine litters. Oesophageal atresia occurred in 15.6% (+/-8.1), laryngotracheo-oesophageal cleft in 10.4% (+/-7) and tracheal agenesis in 3.1% (+/-3.1). All of these malformations occurred with a tracheo-oesophageal fistula. Unlike the ARM, the AMM can produce fetuses with complete laryngotracheo-oesophageal cleft as well as oesophageal atresia or tracheal agenesis. Their occurrence was found to be reproducible but variable. These are important considerations when planning and interpreting experiments using this model.

In vitro effects of adriamycin: a dose-response study

The in vivo effects of adriamycin (ADR) on the mouse and rat embryos are well described in the literature. However, there is a lack of knowledge about the in vitro effects of ADR. The aim of this study was to investigate the effects of ADR on the developing mouse embryo and to identify a dose of ADR, which could be used for further studies of ADR effects in vitro. CD1 mouse embryos were collected at day 8.5 post conception. They were cultured in the presence of different doses of ADR (0, 125, 250, 375 and 500 microM). After 24 h, the culture was stopped and the embryos (n = 77) were scored morphologically using the Brown-Fabro scoring system and the mean score for each organ was calculated. Dose-response plots were generated and the effective dose 50 (ED50) for each organ was identified from the plots. The effects of ADR on the developing embryo were found to be dose related and there is a dose-response relationship in most of the plots. The dose-response plots were found to be parallel for some organs. A dose of 250 microM ADR was identified as the appropriate dose for further in vitro studies. The effects of ADR on the embryos were dose related and there is a dose-response relationship in most of the developing systems. The presence of parallel dose-response plots for some regions is suggestive of similar mechanism of action of ADR on these regions. A dose of 250 microM of ADR was identified for the first time in the literature and could be used for further studies of the effects of ADR on the mouse foregut in vitro.

Expression of homeotic genes Hoxa3, Hoxb3, Hoxd3 and Hoxc4 is decreased in the lungs but not in the hearts of adriamycin-exposed mice

Exposure of rat and mouse embryos to adriamycin (doxorubicin chlorhydrate) induces esophageal atresia (EA) and VACTERL association. Sonic hedgehog (Shh) and Gli2/Gli3 pathways are involved in these conditions and knockout mice for homeotic Hox genes Hoxa3, Hoxb3, Hoxc3, Hoxc4 and Hoxa5 show phenotypes with some of the associated VACTERL features. This study aims at evaluating the possible influence of Hoxa3, Hoxb3, Hoxd3 and Hoxc4 as upstream regulators of this complex signalling. Pregnant mice were exposed either to 4 mg/kg of adriamycin (EA group) or vehicle (controls) on embryonic days 7.5 and 8.5. Embryos were recovered at four endpoints (E12.5-E15.5) and randomly assigned for immunohistochemical or molecular biology studies. Lungs and hearts were separately harvested and processed for Hoxa3, Hoxb3, Hoxd3 and Hoxc4 quantitative RT-PCR measurements. Antibodies for Hoxa3, Hoxb3 and Hoxd3 proteins were used for immunohistochemical studies. RT-PCR studies showed a drastic and statistically significant decrease of the four genes in the lungs of EA mice when compared to controls, with a slight recovery from E15.5. Hearts of both groups showed a similar expression of all the genes throughout gestation. Control embryos expressed the hox3 paralogous genes in heart, skin, foregut derivatives and their surrounding mesoderm through E12.5-E15.5 whereas adriamycin-exposed embryos showed a severe decrease in expression of these three proteins in the same tissues but not in the heart. Adriamycin drastically reduced the expression of Hoxa3, Hoxb3, Hoxd3 and Hoxc4 in mice embryonic lungs. Their expression in the heart did not seem to be influenced by adriamycin in this experimental setting.

Abnormal separation of the respiratory primordium in the adriamycin mouse model of tracheoesophageal malformations

BACKGROUND/PURPOSE

Organogenesis relies on temperospatially coordinated signaling systems. The adriamycin rat model provided insights into the dysmorphogenesis of tracheoesophageal malformations. An adriamycin mouse model (AMM) would facilitate the investigation of their molecular pathogenesis. To transfer the knowledge gained from the rat, we describe a histological account of the critical period of organogenesis of these malformations in the AMM.

METHOD

CBA/Ca mice were accurately time-mated (n = 18). Dams received intraperitoneal injections of adriamycin (6 mg/kg) (n = 12) or saline control (n = 6) on days 7 and 8. Fetuses were harvested on days 9, 9.5, 10, 11, 12, and 13, resin embedded, and 1-mum sections of the developing foregut were examined.

RESULTS

Day 11 control fetuses showed normal separation of the respiratory primordium, with apoptotic bodies at the point of separation. A more caudal point of separation of the distal foregut without apoptotic bodies was found in 4 of 10 AMM fetuses. Day 13 AMM fetuses had dorsal or ventral outpouchings of the foregut, indicating which malformation they would develop. Abnormal branching of the notochord was seen from day 9.5 in AMM fetuses. This was not always associated with abnormal tracheoesophageal development.

CONCLUSION

This study confirms that the abnormal observations made in the rat model apply to the mouse.

The etiology of tracheal mucosal injury in proximal esophageal atresia plus distal tracheoesophageal fistula: an animal study

Tracheal mucosal damage has been reported in autopsy specimens of cases with proximal esophageal atresia and distal tracheoesophageal fistula (EA-TEF) (Gross classification type C). Such changes have not been reported for isolated EA (Gross classification type A). Our hypothesis is that passage of amniotic fluid (AF) through fistula via larynx and trachea may damage tracheal mucosa. An experimental study was conducted to investigate this hypothesis in the Adriamycin-induced EA-TEF model. In the first stage of the study, we tested whether the fetuses with EA-TEF associated with pyloric atresia cannot swallow AF whereas the fetuses EA-TEF without intestinal atresia can swallow AF. Carbon solution was injected into the AF for this purpose. In the second stage of study, at the 21st day of their gestation, fetuses were extirpated and dissected under microscope. In both stages, fetuses were divided into four groups as control, fetuses without tracheoesophageal abnormalities, fetuses with EA-TEF only, fetuses with pyloric atresia associated with EA-TEF. Lungs and tracheas of the all fetuses were removed for histopathological examination. While carbon particles were present in the trachea, stomachs of the fetuses without tracheoesophageal anomalies, with EA-TEF only and control fetuses, carbon particles were absent in both trachea and stomachs of the fetuses with pyloric atresia associated with EA-TEF. Histopatological examination of the tracheal mucosa showed damage throughout the trachea in the fetuses with EA-TEF only group. Tracheal mucosa was found to be normal in other groups. Bronchial mucosa and lung tissues were found to be normal in all groups. Amniotic fluid swallowed through the TEF causes histopathological changes in the tracheal mucosa of the fetuses with EA-TEF only group. These findings may also contribute to the development of new fetal treatment modalities.

Morphogenesis of the trachea and esophagus: current players and new roles for noggin and Bmps

The development of the anterior foregut of the mammalian embryo involves changes in the behavior of both the epithelial endoderm and the adjacent mesoderm. Morphogenetic processes that occur include the extrusion of midline notochord cells from the epithelial definitive endoderm, the folding of the endoderm into a foregut tube, and the subsequent separation of the foregut tube into trachea and esophagus. Defects in foregut morphogenesis underlie the constellation of human birth defects known as esophageal atresia (EA) and tracheoesophageal fistula (TEF). Here, we review what is known about the cellular events in foregut morphogenesis and the gene mutations associated with EA and TEF in mice and humans. We present new evidence that about 70% of mouse embryos homozygous null for Nog, the gene encoding noggin, a bone morphogenetic protein (Bmp) antagonist, have EA/TEF as well as defects in lung branching. This phenotype appears to correlate with abnormal morphogenesis of the notochord and defects in its separation from the definitive endoderm. The abnormalities in foregut and lung morphogenesis of Nog null mutant can be rescued by reducing the gene dose of Bmp4 by 50%. This suggests that normal foregut morphogenesis requires that the level of Bmp4 activity is carefully controlled by means of antagonists such as noggin. Several mechanisms are suggested for how Bmps normally function, including by regulating the intercellular adhesion and behavior of notochord and foregut endoderm cells. Future research must determine how Noggin/Bmp antagonism fits into the network of other factors known to regulate tracheal and esophagus development, both in mouse or humans.

Oesophageal atresia and tracheo-oesophageal fistula

Oesophageal atresia-tracheo-oesophageal fistula has featured in paediatric surgery since its beginnings. The first successful primary repair was in 1941. With overall survival now exceeding 90% in dedicated centres, the emphasis has changed to reducing morbidity and achieving improvements in the quality of life. An overview of current and emerging strategies in managing patients with this condition is presented. Advances in developmental biology and molecular genetics reflecting improved understanding of the pathogenesis are highlighted.

Faulty bone morphogenetic protein signaling in esophageal atresia with tracheoesophageal fistula

BACKGROUND

The organogenesis of esophageal atresia with tracheoesophageal fistula remains unclear. We have previously demonstrated that the fistula tract develops from a trifurcation of the embryonic lung bud and displays pulmonary lineage traits. Unlike the lung, the fistula grows without branching. Bone morphogenetic proteins (BMPs) are known to be important in lung branching. We studied possible BMP signaling defects as a potential cause for the absence of branching in the fistula tract.

METHODS

Adriamycin was administered to pregnant rats on days 6-9 of gestation to induce tracheoesophageal fistula. Microdissection was performed at E13 and E17 isolating the foregut. Tissues were analyzed using immunohistochemistry for BMP ligand (BMP2, BMP4, BMP7) and receptor (BMPRIA, BMPRIB, BMPRII) expression.

RESULTS

Immunohistochemistry revealed the presence of all 3 BMP ligands at E13, localized specifically to the esophageal mucosa but absent in the fistula and lung. At E17, the ligands were again present in the esophageal mucosa, and additionally in the fistula tract mucosa, but remained absent in the lung. At E17, all of the BMP receptors were also localized to the luminal surface of esophagus and fistula. However, in the lung epithelium, only BMPRII was found, whereas BMPRIA and BMPRIB remained absent.

CONCLUSIONS

The normal expression pattern of BMP4 was increased at the branch tips and low between branches. Among other results, we show here a constant expression level of BMP ligands throughout the entire epithelium of the fistula tract. This diffuse expression suggests defective BMP signaling in the fistula tract and explains its nonbranching phenotype.