on kinetic specificity rather than thermodynamic specificity, as different types of cadherin homotypic bonds have different lifetimes. Structure Cadherins are synthesized as polypeptides and undergo many post-translational modifications to become the proteins which mediate cell-cell adhesion and recognition. These polypeptides are approximately 720–750 amino acids long. Each cadherin has a small C-terminal cytoplasmic component, a transmembrane component, and the remaining bulk of the protein is extra-cellular (outside the cell). The transmembrane component consists of single chain glycoprotein repeats. Because cadherins are Ca2+ dependent, they have five tandem extracellular domain repeats that act as the binding site for Ca2+ ions. Their extracellular domain interacts with two separate trans dimer conformations: strand-swap dimers (S-dimers) and X-dimers. To date, over 100 types of cadherins in humans have been identified and sequenced. The functionality of cadherins relies upon the formation of two identical subunits, known as homodimers. The homodimeric cadherins create cell-cell adhesion with cadherins present in the membranes of other cells through changing conformation from cis-dimers to trans-dimers. Once the cell-cell adhesion between cadherins present in the cell membranes of two different cells has formed, adherens junctions can then be made when protein complexes, usually composed of α-, β-, and γ-catenins, bind to the cytoplasmic portion of the cadherin. Regulatory proteins include p-120 catenin, -catenin, -catenin, and vinculin. Binding of p-120 catenin and -catenin to the homodimer increases the stability of the classical cadherin. -catenin is engaged by p120-catenin complex, where vinculin is recruited to take a role in indirect association with actin cytoskeleton. However, cadherin-catenin complex can also bind directly to the actin without the help of vinculin. Moreover, the strength of cadherin adhesion can increase by dephosphorylation of p120 catenin and the binding of -catenin and vinculin. Function Development Cadherins behave as both receptors and ligands for other molecules. During development, their behavior assists at properly positioning cells: they are responsible for the separation of the different tissue layers and for cellular migration. In the very early stages of development, E-cadherins (epithelial cadherin) are most greatly expressed. Many cadherins are specified for specific functions in the cell, and they are differentially expressed in a developing embryo. For example, during neurulation, when a neural plate forms in an embryo, the tissues residing near the cranial neural folds have decreased N-cadherin expression. Conversely, the expression of the N-cadherins remains unchanged in other regions of the neural tube that is located on the anterior-posterior