Development of the human gastrointestinal tract: Twenty years of progress  Robert K. Montgomery, Andrew E. Mulberg, Richard J. Grand  Gastroenterology  Volume 116, Issue 3, Pages 702-731 (March 1999) DOI: 10.1016/S0016-5085(99)70193-9 Copyright © 1999 American Gastroenterological Association Terms and Conditions

Fig. 1 Genomic organization of Drosophila homeotic genes and mammalian hox genes. Schematic representation of the Drosophila complex and the related homology groups in mouse. Numbers and corresponding colors in mouse fetus represent the locations of organ defects that have been identified in mouse gastrointestinal development by gene-targeting experiments with the indicated hox genes. (Modified and reprinted with permission.17) Gastroenterology 1999 116, 702-731DOI: (10.1016/S0016-5085(99)70193-9) Copyright © 1999 American Gastroenterological Association Terms and Conditions

Fig. 2 Effects of environment on development of isolated pancreatic epithelium. In isolation, the epithelium does not undergo morphogenesis or differentiation. Recombination with the separated mesenchyme, supplying soluble mesenchymal factors, resulted in the development of exocrine structures. Culture with an ECM gel (Matrigel) resulted in the formation of ductal structures. When the isolated epithelium was grown under the renal capsule in association with a nonspecific mesenchyme, mature islet cells developed with no ductal or exocrine differentiation. Thus pancreatic differentiation results from the interplay of intrinsic gene expression, soluble mesenchymal factors, and ECM components. (Modified and reprinted with permission.112) Gastroenterology 1999 116, 702-731DOI: (10.1016/S0016-5085(99)70193-9) Copyright © 1999 American Gastroenterological Association Terms and Conditions

Fig. 3 Types of epithelial-mesenchymal interaction in the gastrointestinal tract. As described in detail in the text, patterns of expression of ECM components have been correlated with development in the human small intestine. ECM components are produced by both mesenchymal and epithelial cells. Binding sites on these components and receptors on the epithelial cells have been identified. Intracellular signaling pathways activated by ECM binding are beginning to be elucidated. Direct cell-to-cell contacts have been observed, but the role of these interactions is not well understood. Mesenchymal cells produce soluble factors that bind to receptors on the epithelial cells. Many potential mediators have been identified in developing human intestine, and details of signaling pathways are being clarified in model organisms. Gastroenterology 1999 116, 702-731DOI: (10.1016/S0016-5085(99)70193-9) Copyright © 1999 American Gastroenterological Association Terms and Conditions