Requirement for beta-catenin in anterior-posterior axis formation in mice

The anterior-posterior axis of the mouse embryo is defined before formation of the primitive streak, and axis specification and subsequent anterior de velopment involves signaling from both embryonic ectoderm and visceral endo derm. The Wnt signaling pathway is essential for various developmental proc esses, but a role in anterior-posterior axis formation in the mouse has not been previously established. beta-Catenin is a central player in the Wnt p athway and in cadherin-mediated cell adhesion. We generated beta-catenin-de ficient mouse embryos and observed a defect in anterior-posterior axis form ation at embryonic day 5.5, as visualized by the absence of Hex and Hesx1 a nd the mislocation of cerberus-like and Lim1 expression. Subsequently, no m esoderm and head structures are generated. Intercellular adhesion is mainta ined since plakoglobin substitutes for beta-catenin. Our data demonstrate t hat beta-catenin function is essential in anterior-posterior axis formation in the mouse, and experiments with chimeric embryos show that this functio n is required in the embryonic ectoderm.