Figure 4.
Roles of Wnt/β-catenin pathways in mice embryo somitogenesis and left–right axis determination. The expression of canonical Wnt3a molecules along the primitive streak upregulates the transcription factor T which sustains mesoderm production. In addition, the canonical Wnt3a pathway initiates the expression of the Notch pathway ligand Dll1 to regulate somitogenesis in the adjacent PSM. The expression of Dll1 in the PSM also mediates Nodal expression at the periphery of the node by activating the Notch signaling pathway. The leftward flow generated by rotating nodal cilia leads to left side Nodal accumulation to eventually enhance Nodal signaling on the left side for left–right body axis determination. (A color version of this figure is available in the online journal.) Source: Figure modified from Barker et al.85 and Wang et al.86
LPM: lateral plate mesoderm; PSM: paraxial presomitic mesoderm.