Mesenchymal–epithelial interactions during digestive tract development and epithelial stem cell regeneration

The gastrointestinal tract develops from a simple and uniform tube into a complex organ with specific differentiation patterns along the anterior–posterior and dorso-ventral axes of asymmetry. It is derived from all three germ layers and their cross-talk is important for the regulated development of fetal and adult gastrointestinal structures and organs. Signals from the adjacent mesoderm are essential for the morphogenesis of the overlying epithelium. These mesenchymal–epithelial interactions govern the development and regionalization of the different gastrointestinal epithelia and involve most of the key morphogens and signaling pathways, such as the Hedgehog, BMPs, Notch, WNT, HOX, SOX and FOXF cascades. Moreover, the mechanisms underlying mesenchyme differentiation into smooth muscle cells influence the regionalization of the gastrointestinal epithelium through interactions with the enteric nervous system. In the neonatal and adult gastrointestinal tract, mesenchymal–epithelial interactions are essential for the maintenance of the epithelial regionalization and digestive epithelial homeostasis. Disruption of these interactions is also associated with bowel dysfunction potentially leading to epithelial tumor development. In this review, we will discuss various aspects of the mesenchymal–epithelial interactions observed during digestive epithelium development and differentiation and also during epithelial stem cell regeneration.     

Guest Editorial: From Cartagena to Ballarat: A Report on the Joint Fifth World Congress on Action Learning,Action Research,and Process Management and Ninth World Congress on Participatory Action Research

Systemic Practice and Action Research -     

Water balance and fluid consumption in the southern grasshopper mouse, Onychomys torridus

Weight loss was rapid and fluid consumption decreased sharply when Onychomys torridus were exposed to salinities greater than 0.3 Molar. The southern grasshopper mouse is physiologically unspecialized for maintaining water balance in its xeric habitat. The southern grasshopper mouse is capable of weight maintenance on smaller daily water rations than is the northern grasshopper mouse ( Onychomys leucogaster ) . Differences in the water balance of O. torridus and O. leucogaster may influence their local distributions in areas of sympatry.