Practice question

Hindlimb field stabilization within posterior lateral plate mesoderm depends on caudalizing Wnt signaling that fortifies hindlimb program. Wnt8c expressed in tailbud and posterior lateral plate activates canonical beta-catenin pathway, stabilizing FGF10 transcription in presumptive hindlimb mesenchyme and permitting subsequent activation of Tbx4, Pitx1, and hindlimb enhancers. Forelimb equivalent is Wnt3a-Wnt2b upstream of Tbx5, beta-catenin serves as common intracellular transducer in both, retinoic acid provides permissive flank environment. Localized Wnt8c thus designates lumbosacral competence zone positioning hindlimbs correctly and ensuring outgrowth.