Molecular mechanisms of development of the gastrointestinal tract

The gut offers a complex but rich organ system to study visceral pattern formation. The gut is an early evolutionary advance. Data supports that the molecular controls of gut pattern formation are be conserved across species. The gut develops in a stereotyped manner in many different species, by using a basic mechanism of development, the epithelial-mesenchymal interaction. Signaling between the endoderm and mesoderm is essential for normal gut development. The signaling molecules involved are just being described and include factors known to be critical in embryonic development of other systems. The gut has four major patterned axes: anterior-posterior (AP), dorsal-ventral (DV), left-right (LR), and radial (RAD). The molecular pathways used to control pattern in each of these axes are the subject of this review. Major advances in the understanding of AP and LR axis formation in the gut have been described within the past few years. RAD and DV axes are now hot topics for investigation. Despite advances in these areas of gut development, basic events remain poorly understood. Discovery of specific factors that control gut pattern formation may provide a template for the study of pattern formation in other visceral/organ systems.