Fig. 6. Canonical Wnt pathway inhibition in AP patterning. (A) Epistatic hierarchy of Wnt/ß-catenin signalling pathway components involved in vertebrate AP patterning. Components in red represent factors for which loss-of-function studies have provided direct evidence for a role in AP neural patterning: Dkk1 (Glinka et al., 1998; Mukhopadhyay et al., 2001), Krm (present study), Wnt8 (Erter et al., 2001; Levken et al., 2001), LRP6 (Pinson et al., 2000), Axin (Heisenberg et al., 2001; van de Water et al., 2001), ß-catenin (Heasman et al., 2000) and Tcf3 (Kim et al., 2000). For clarity, some components of the pathway have been omitted. (B,C) Proposed molecular interactions for membrane linked Wnt pathway components. Krm, Dkk1 and LRP6 form a ternary complex (B), which disrupts Wnt/LRP6 signalling (C). Proteoglycans have been omitted for simplicity.