[Frontiers in Bioscience 16, 2352-2366, June 1, 2011] 2352 The role of Wnt in cell signaling and cell adhesion during early vertebrate development Janssens Sylvie 1,2 , Crabbe Ellen 1,2 , Vleminckx Kris 1,2 1 Department for Molecular Biomedical Research, VIB, B-9052 Ghent, 2 Department of Biomedical Molecular Biology, Ghent University, B-9052 Ghent, Belgium TABLE OF CONTENTS 1. Abstract 2. Introduction 3. Overview of the Wnt pathway 4. Interaction between Wnt and cell adhesion molecules 5. Interplay between Wnt and cell adhesion during early development 5.1. Gastrulation 5.1.1. Epithelial bending 5.1.2. EMT and delamination of cells 5.1.3. Cell rearrangements – Convergent extension 5.1.4. Cell migration 5.2. Somitogenesis 5.2.1. Separation of somites 5.2.2. Somite epithelialization 5.2.3. Compartmentalization 5.3. Neurulation 5.3.1. Neural tube formation: shaping, bending and fusion 5.3.2. Neural crest induction and migration 6. Summary and perspective 7. Acknowledgement 8. References 1. ABSTRACT During embryonic development, a group of dividing blastomeres is ultimately shaped into a structured, functional organism. To achieve this goal, individual cells and groups of cells need to move to new positions, organize themselves, and differentiate into specialized cell types. In these processes, intercellular contacts and contacts between cells and their environment play critical roles. The cells interact physically via cell adhesion molecule and communicate through signaling pathways. One of the pathways active during embryonic development is the Wnt pathway. Interestingly, Wnt and cell adhesion are often active in the same processes and crosstalk between them exists by reciprocal regulation and sharing of components. In this review, we will focus on how Wnt signaling cooperates with cell adhesion to ensure smooth processing of gastrulation, somitogenesis and neurulation. 2. INTRODUCTION Attachment of cells is mediated by cell adhesion molecules on the cell surface. To achieve strong attachment, cell adhesion molecules can be complexed in focal adhesions, adherens junctions and desmosomes, where they cluster and form links with the cytoskeleton. The disruption and reestablishment of cell contacts are indispensable for processes that guide vertebrate morphogenesis, including cell sorting, cell movements, cell migration and separation or fusion of tissues. Several of these morphogenetic events are controlled by developmental signaling pathways. The importance of Wnt signaling in vertebrate development was discovered almost 20 years ago, when it was shown that injection of Wnt RNA in Xenopus embryos can induce formation of a complete secondary body axis (1). Since then, Wnt signaling has been implicated in a variety of cellular