Fig. 1.

Norrin is a ligand for LGR4. (A) Phylogenetic relationship of norrin, burs, pburs, gremlin, and DAN. Genes with cystine-knot structures homologous to burs and pburs were categorized into three subfamilies by the ClustalW program (Thompson et al., 1994). The phylogenetic tree was built with Mega 4 (Tamura et al., 2007) using the Neighbor-Joining method and 1000 bootstrap replications. The numbers at interior branches refer to the bootstrap values (in percentages). Sk, Saccoglossus kowalevskii; Ce, Caenorhabditis elegans; Hm, Hydra magnipapillata; Dm, Drosophila melanogaster; Nv, Nematostella vectensis; Xt, Xenopus tropicalis (Silurana); Mm, Mus musculus; Hs, Homo sapiens; Ap, Acyrthosiphon pisum; Tc, Tribolium castaneum. (B) Norrin, but not gremlin or DAN, stimulated Wnt signaling in HEK293T cells expressing LGR4. HEK293T cells were transfected with TOPFLASH, LGR4, together with increasing amounts of plasmids encoding norrin, gremlin, gremlin2 or DAN before luciferase assays.