Fig. 6. A sequential recruitment and amplification model for Wnt-induced Lrp6 phosphorylation. (A) Initiation. Wnt-induced Fz-Lrp6 complex formation promotes initial Lrp6 phosphorylation via Dvl recruitment of the axin-Gsk3 complex. (B) Amplification. Initial Lrp6 phosphorylation provides docking sites and thereby recruits additional Axin-Gsk3 complex to promote further Lrp6 phosphorylation in cis and possibly in trans if/when Lrp6 multimerizes. See Discussion for details. For clarity, β-catenin, CK1 and other proteins are omitted from the axin complex, the protein composition of which may be different with and without Wnt stimulation.