Description
During limb development, fibroblast growth factors (FGFs) govern proximal-distal outgrowth and patterning. FGFs also synchronize developmental patterning between the proximal-distal and anterior-posterior axes by maintaining sonic hedgehog (SHH) expression in cells of the zone of polarizing activity (ZPA) in the distal posterior mesoderm. SHH, in turn, maintains FGFs in the apical ectodermal ridge (AER) which caps the distal tip of the limb bud. Crosstalk between FGF and SHH signaling is critical for patterned limb development, but the mechanisms underlying this feedback loop are not well characterized.