Practice question

In axolotl limb regeneration studies, fibroblast growth factors supplied alone via beads or transgenes promote distal outgrowth. FGF8, FGF10 secreted by apical epidermal cap and nerves maintain distal blastema identity expressing HoxA13 and distal proliferation while failing to activate proximal program Meis. Therefore implantation of FGF alone leads to regeneration of distal structures only, such as hand elements, with poor proximal restoration unless exogenous retinoic acid provides proximalizing cue. Combined RA plus FGF signaling is required for complete limb pattern, but FGFs alone distalize, mirroring developmental AER FGF role in maintaining distal progressive zone during outgrowth.