TTF-1 and HNF-3beta in the developing tracheoesophageal fistula: further evidence for the respiratory origin of the distal esophagus'.

PURPOSE: Using an established rat model of esophageal atresia with tracheoesophageal fistula (EA-TEF), the authors have studied the organogenesis of this congenital anomaly. The authors previously have proposed that the "distal esophagus" actually is of respiratory lineage. In this report this hypothesis is tested by examining the expression of two foregut patterning transcription factors, thyroid transcription factor-1 (TTF-1) and hepatocyte nuclear factor-3beta (HNF-3beta), within the developing TEF. METHODS: Pregnant Sprague-Dawley rats were injected with 2.2 mg/kg of Adriamycin intraperitoneally on days 6 to 9 of gestation. Using microdissection, the trachea, blind-ending esophagus, TEF, and stomach were isolated from embryos of various gestional ages. Immunohistochemistry was performed using polyclonal antibodies to TTF-1 and HNF-3beta. RESULTS: TTF-1 is a homeodomain protein that previously has been shown to be expressed in the lung and trachea but not in the gastrointestinal tract, and which, when deleted in a developing lung, results in a mouse with no peripheral lung parenchyma. TTF-1 was expressed strongly in the lung, fistula, and distal esophagus, but not in the proximal esophagus. HNF-3beta is a forkhead transcription factor important in foregut patterning that binds and activates the TTF-1 promotor sequence. HNF-3beta was expressed globally in the fistula and lung as well as the esophagus. CONCLUSIONS: The expression of the lung-specific transcription factor TTF-1 within the TEF strongly implies that the "distal esophagus" is a respiratory-derived structure and thus supports our theory of TEF organogenesis. The conservation of HNF-3beta expression both in the TEF as well as the normal developing trachea and esophagus suggests that global foregut patterning is intact in the formation of this anomaly, and the defect lies at the level of the respiratory versus gastrointestinal commitment.

Esophageal atresia with tracheoesophageal fistula: suggested mechanism in faulty organogenesis.

BACKGROUND/PURPOSE: The organogenesis of esophageal atresia with tracheoesophageal fistula (EA-TEF) is unknown. Using an established model for EA-TEF in rats, the authors proposed to study this aberrancy of development in the hope of gaining insight into its mechanism of formation. METHODS: Pregnant Sprague-Dawley rats were injected with 2.2 mg/kg of Adriamycin intraperitoneally on days 6 through 9 of gestation. Using microdissection, the trachea, blind-ending esophagus, TEF, and stomach were isolated from embryos of various gestional ages. The specimens were analyzed histologically with routine H&E staining. RESULTS: The classic EA-TEF developed in the embryos, with proximal EA and distal TEF. As expected, the atresia formed as a blind-ending pouch, but the distal fistula began as an apparent equal trifurcation of the tracheal anlage into two mainstem bronchi and the fistula tract leading to the stomach. Histological analysis of the fistula tract showed respiratorylike pseudostratified columnar epithelium. CONCLUSIONS: TEF develops as the middle branch of a tracheal trifurcation. EA-TEF occurs by a primary atresia of the esophagus. As a secondary phenomenon, the distal foregut anlage is switched toward the pulmonary phenotype. It trifurcates, and its middle branch grows caudally to fistulize into the stomach.