LRP4 is required for Wnt-induced AChR clusters. A, Wnt9a and Wnt11 fail to stimulate AChR clustering in LRP4mitt muscle cells. Primary muscle cells were cultured from wt and mt mice and assayed for AChR clusters as in Figure 1. Histogram shows quantitative analysis of AChR clusters. B, Wnts bind to ectodomain of LRP4. Flag-tagged Wnt7a, Wnt9a or Wnt11 were immobilized with beads and incubated with LRP4N-Myc. Interactions were determined by precipitation and Western blot using anti-Myc antibody.