Fig. 6. Wnt3a-dependent transcriptional networks coordinate mesoderm formation with segment boundary determination. Schematic of selected target genes and pathways activated in the PSM by Wnt3a, see text for details. The red color represents the expression domain of the Wnt3a and β-catenin target genes (Dll1, T, Tbx6) in the PSM. T and Tbx6 are grouped together for the sake of simplicity. Yellow indicates a representative oscillating negative-feedback loop in the Notch (N) pathway in the segmentation clock. Expression of the segment boundary determination genes Ripply2 and Mesp2 (black hatching) in S-I, overlap with the anterior domain of Tbx6 expression. The proposed Wnt3a/β-catenin target repressor (?) is expressed in the posterior PSM where it ensures that boundary determination gene expression is repressed. A, anterior; P, posterior.