Vertebrate limb development.
The recent identification of Wnt-7a as a signalling molecule in dorsal/ventral patterning means that we now have a known signal for control of each of the three limb axes. Fibroblast growth factors can allow proximal/distal patterning and Sonic hedgehog gene expression signals anterior/posterior patterning. Networks of these signals not only coordinate cell responses, but also mutually maintain each other. A positive feedback loop is established which coordinates expression of Sonic hedgehog in mesenchyme cells of the polarizing region and Fgf-4 expression in overlying apical ridge ectoderm. Wnt-7a expression in dorsal ectoderm also influences Sonic hedgehog expression in the polarizing region. Initiation of development of a complete limb can be achieved with just one signal, a growth factor.
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Department of Anatomy and Developmental Biology, University College and Middlesex School of Medicine, University College London, UK.
D000818:Animals; D004627:Embryonic Induction; D005121:Extremities / Q000196:embryology / Q000254:growth & development*; D018507:Gene Expression Regulation, Developmental; D053823:Hedgehog Proteins; D018878:Limb Buds / Q000196:embryology; D011506:Proteins / Q000502:physiology; D015398:Signal Transduction; D015534:Trans-Activators; D014714:Vertebrates / Q000196:embryology*
D053823:Hedgehog Proteins; D011506:Proteins; D015534:Trans-Activators