Brigid Hogan and Tadashi Okubo, from Duke University Medical Center, studied the lungs of transgenic mice that had developed under the influence of artificially high levels of activity in the Wnt signaling pathway, caused by the presence of an activated b catenin gene. They found that although externally the lungs looked normal, the interior of the lungs had lost the normal branching tree-like structure lined with rounded alveolar cells. Instead, a few wide bronchial tubes opened directly into large sacs that were lined with a rapidly proliferating cuboidal epithelium.
Looking more closely at these epithelial cells, the researchers found that many of them were not expressing genes typical of lung cells, such as the genes encoding secretoglobin and surfactants. In addition, microarrays comparing the transgenic cells with normal lung epithelial cells showed a general reduction in the expression of lung-specific genes and a strong expression, instead, of genes characteristic of intestinal cells.
"A striking feature of the microarray data was the high expression in transgenic lungs of genes normally associated with the specification and differentiation of gut secretory cell lineages," say Hogan and Okubo. These included the gene encoding the Atoh1 transcription factor, which is normally turned off in lung cells.
"In particular there was a very high level of expression of genes characteristic of Paneth cells, which are normally found in the base of crypts in the small intestine," they continue.