Wnt to build a tube: contributions of Wnt signaling to epithelial tubulogenesis.

Epithelial tubes are crucial to the function of organ systems including the cardiovascular system, pulmonary system, gastrointestinal tract, reproductive organ systems, excretory system, and auditory system. Using a variety of animal model systems, recent studies have substantiated the role of Wnt signaling via the canonical/beta-catenin-mediated trajectory, the non-canonical Wnt trajectories, or both, in forming epithelial tubular tissues. This review focuses on the involvement of the Wnt pathways in the induction, specification, proliferation, and morphogenesis involved in tubulogenesis within tissues including the lungs, kidneys, ears, mammary glands, gut, and heart. The ultimate goal is to describe the developmental processes forming the various tubulogenic organ systems to determine the relationships between these processes. (c) 2009 Wiley-Liss, Inc.