A role for maternal β-catenin in early mesoderm induction in Xenopus

Mesoderm formation results from an inducing process that requires maternal and zygotic FGF/MAPK and TGFβ activities, while maternal activation of the Wnt/β‐catenin pathway determines the anterior–dorsal axis. Here, we show a new role of Wnt/β‐catenin signaling in mesoderm induction. We find that maternal β‐catenin signaling is not only active dorsally but also all around the equatorial region, coinciding with the prospective mesoderm. Maternal β‐catenin function is required both for expression of dorsal genes and for activation of MAPK and the mesodermal markers Xbra and eomesodermin. β‐catenin acts in a non‐ cell‐autonomous manner upstream of zygotic FGF and nodal signals. The Wnt/β‐catenin activity in the equatorial region of the early embryo is the first example of a maternally provided mesoderm inducer restricted to the prospective mesoderm.