Wnt3a Plays a Major Role in the Segmentation Clock Controlling Somitogenesis

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The vertebral column derives from somites generated by segmentation of presomitic mesoderm (PSM). Somitogenesis involves a molecular oscillator, the segmentation clock, controlling periodic Notch signaling in the PSM. Here, we establish a novel link between Wnt/β-catenin signaling and the segmentation clock. Axin2, a negative regulator of the Wnt pathway, is directly controlled by Wnt/β-catenin and shows oscillating expression in the PSM, even when Notch signaling is impaired, alternating with Lfng expression. Moreover, Wnt3a is required for oscillating Notch signaling activity in the PSM. We propose that the segmentation clock is established by Wnt/β-catenin signaling via a negative-feedback mechanism and that Wnt3a controls the segmentation process in vertebrates.