FGF4 and Skeletal Morphogenesis

Of vertebrate organ systems, the developing limb has been especially well characterized. Embryological studies combined with molecular manipulations have yielded a wealth of information about the control of pattern formation during limb outgrowth. A number of key signaling pathways have been implicated in the control of numerous aspects of limb development, including the establishment of the early limb field, determination of limb identity, elongation of the limb bud, specification of digit pattern, and sculpting of the digits. Although there is clear evidence that specific signaling pathways that operate in the limb field and early limb bud control the specification of pattern, little is known about how these signals interface with the cell biology of limb development (1). One instance where some progress has been made concerns the role of FGF4 signaling by the apical ectodermal ridge (AER) in the limb bud.