The highly conserved Wnt signaling proteins play critical roles in guiding pattern formation, cell fate decision, and morphogenetic movement during animal development. They bind to the Frizzled family of seven-pass transmembrane proteins and initiate at least three different intracellular signaling pathways, resulting in regulation of gene expression and/or changes in cell behavior. A single transmembrane protein from the low-density-lipoprotein family functions as a co-receptor in the canonical/beta-catenin pathway. The specificity of Wnt signaling depends in part on the affinities between various Wnt-Frizzled pairs. A Wnt-dependent receptor dimerization or clustering step has been hypothesized as the step that initiates the canonical signaling cascade in cells.