Practice question

Capability of Wnt signaling to initiate limbs was demonstrated by gain-of-function manipulation of canonical pathway. Overexpression of Wnt3a or stabilized beta-catenin or constitutive Tcf in lateral plate mesoderm of chick embryos induced ectopic expression of FGF10 and its downstream cascade, formation of additional apical ridge and ectopic limbs from flank with DV polarity. This proved Wnt signals operate upstream of FGF10 to establish limb fields and permit FGF10-FGF8 loop initiation, interacting with Tbx5. Knockout of FGF8 truncates limbs, AER removal time-course reveals PD specification, ZPA transplant duplicates anterior-posterior. Thus Wnt overexpression demonstrates limb-inducing ability.