Practice question

Classic sufficiency test placed FGF10 beads into interlimb flank where normally no limb forms due to absence of Tbx expression and inhibitory cues. Ectopic FGF10 activated FGFR2b, beta-catenin and induced a new AER expressing FGF8 and Wnt3a, initiating progress zone proliferation and complete supernumerary limb containing all three segments stylopod zeugopod autopod and digits with dorsal-ventral polarity. This demonstrated FGF10 as potent limb inducer and sufficient for de novo limb initiation, distinct from inhibition of growth, dorsalization of mesenchyme or homeotic transformation of forelimb to hindlimb fate.