Analysis of the Development of Normal Foregut and Tracheoesophageal Fistula in an Adriamycin Rat Model Using Three-Dimensional Image Reconstruction

Abstract

To examine the developmental process of the normal trachea and esophagus and their maldevelopment leading to tracheoesophageal fistula (TEF), we performed three-dimensional (3-D) image reconstruction of the developing foregut in normal and adriamycin (ADM)-induced TEF rats. Microscopic images of serial sections of embryos from seven normal and 14 ADM-treated rats killed every half a day after 11-14 days' gestation were traced and reconstructed using a 3-D construction imaging system (TRI, RATOC System Engineering, Tokyo, Japan). In the normal embryos, the lung bud appeared just below the pharyngeal foregut on day 11 and it elongated caudally to shape into the trachea as they grew. A 'tracheoesophageal septum" did not emerge. In the TEF embryos, although the lung bud appeared in a similar position on day 11, the trachea and esophagus did not separate and only a common foregut tube elongated caudally, then bilateral bronchial primordia emerged directly from it. Furthermore, abnormal development of the notochord was evident, being retarded in separation from the foregut, finally descending along a more ventral course and bending sharply around the level of the bifurcation. Microscopically, less mesenchymal cellularity around the foregut was noted in the TEF embryos. The trachea seemed to be formed only by caudal elongation of the lung bud in the normal embryos. In the ADM-induced TEF embryos, the upper foregut appeared to develop only into the trachea, and this maldevelopment may be implicated in the abnormal interaction between the foregut and the surrounding mesenchyme.

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

“…The need for 3D visualization of events in the developing embryo has previously been recognized and addressed in a number of recent studies [17][18][19][20][21][22]. Williams et.al.…”

“…and Sasaki et.al. [21,22] described tracheo-oesophageal separation during embryogenesis by compiling sequential 2D images from H & E stained sections at several stages of foregut development. They clearly demonstrated the developmental events in great detail, but reconstruction from images of serial sections presents a number of technical problems.…”

Adriamycin-Induced Models of VACTERL Association

“…Crisera et al [1999a] have reported that the fistula arises as the posterior branch of a tracheal trifurcation with the main bronchi, elongates caudally and fistulalises into the stomach. Splide et al [2002a] also reported a discontinuity between the fistula and the stomach, while other authors reported that the fistula developed from caudal foregut maintaining a connection with the stomach throughout Sasaki et al, 2001]. The fistula is lined with ciliated columnar respiratory epithelium from its proximal origin, transitioning into stratified squamous oesophageal epithelial lining at a variable distance caudally [Merei et al, 1997a].…”

“…In the ventral foregut mesoderm, condensed cellular patterns are associated with the outgrowth of the lung buds [Morrisey and Hogan, 2010]. Possoegel et al [1998] and others have reported disturbances in mesodermal cell pattern, describing the cellular architecture as disorganised and loosely arranged around the foregut in the ARM with loss of the circular pattern detected in control embryos at both E12 and E13 [Sasaki et al, 2001]. As well as signalling derangements discussed anon, failure of these fields to form could physically deter organogenesis; however, the detail of this mechanism is unexplained.…”

Congenital Diseases of Esophagus

“…In irst theory, the respiratory system develops as a result of rapid outgrowth from the original foregut tube [2], but in an alternative theory, there is active growth of a mesenchymal septum which develops in the coronal plane and, as a result, separates the foregut lumen into ventral (respiratory) and dorsal (gastrointestinal) structures [3]; however, direct evidence of septum formation has been lacking, casting doubt on this theory.…”