TTF-1 and HNF-3 beta 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 tracheoe sophageal fistula (EA-TEF), the authors have studied the organogenesis of t his congenital anomaly. The authors previously have proposed that the "dist al esophagus" actually is of respiratory lineage. In this report this hypot hesis is tested by examining the expression of two foregut patterning trans cription factors, thyroid transcription factor-1 (TTF-1) and hepatocyte nuc lear factor-3 beta (HNF-3 beta), within the developing TEF. Methods: Pregnant Sprague-Dawley rats were injected with 2.2 mg/kg of Adria mycin intraperitoneally on days 6 to 9 of gestation. Using microdissection, the trachea, blind-ending esophagus, TEF, and stomach were isolated from e mbryos of various gestional ages. Immunohistochemistry was performed using polyclonal antibodies to TTF-1 and HNF-3 beta. Results: TTF-1 is a homeodomain protein that previously has been shown to b e 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 pe ripheral lung parenchyma. TTF-1 was expressed strongly in the lung, fistula , and distal esophagus, but not in the proximal esophagus. HNF-3 beta is a forkhead transcription factor important in foregut patterning that binds an d activates the TTF-1 promotor sequence. HNF-3 beta 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 respirato ry-derived structure and thus supports our theory of TEF organogenesis. The conservation of HNF-3 beta expression both in the TEF as well as the norma l developing trachea and esophagus suggests that global foregut patterning is intact in the formation of this anomaly, and the defect lies at the leve r of the respiratory Versus gastrointestinal commitment. J Pediatr Surg 34: 1322-1326. Copyright (C) 1999 by W.B. Saunders Company.