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. 2010 Feb;2(2):a000869. doi: 10.1101/cshperspect.a000869

Figure 3.

Figure 3.

A β-catenin protein gradient controls PSM differentiation and somite formation. (A) ISH for Wnt3a mRNA in 9.5 days postcoitum (dpc) mouse embryo shows site of localized ligand production in the posterior PSM/tail bud. (B) ISH for β-catenin mRNA shows ubiquitous expression in the PSM of mouse embryos. (C) In contrast, β-catenin immunofluorescent detection (green) reveals a posterior-anterior nuclear protein gradient within the PSM. DAPI staining is shown in blue. (D) Scanning electron microscopy image of a control 9.0 dpc mouse embryo showing the periodic arrangement of formed somites. (E) Scanning electron microscopy image of mutant embryo in which a stabilized isoform of β-catenin has been conditionally expressed in mesodermal cells. Note that disruption of the β-catenin protein gradient leads to an expanded, undifferentiated PSM and an absence of somite formation. In D and E, the ectoderm was removed, which allows a direct view of the mesodermal layer.