title: Gradients of signalling in the developing limb.
abstract: The developing limb is one of the first systems where it was proposed that a signalling gradient is involved in pattern formation. This gradient for specifying positional information across the antero-posterior axis is based on Sonic hedgehog signalling from the polarizing region. Recent evidence suggests that Sonic hedgehog signalling also specifies positional information across the antero-posterior axis by a timing mechanism acting in parallel with graded signalling. The progress zone model for specifying proximo-distal pattern, involving timing to provide cells with positional information, continues to be challenged, and there is further evidence that graded signalling by retinoic acid specifies the proximal part of the limb. Other recent papers present the first evidence that gradients of signalling by Wnt5a and FGFs govern cell behaviour involved in outgrowth and morphogenesis of the developing limb.
authors.affiliation: MRC Centre for Developmental and Biomedical Genetics, University of Sheffield, Sheffield, UK.
authors.forename: Matthew
authors.initials: M
authors.lastname: Towers
authors.forename: Lewis
authors.initials: L
authors.lastname: Wolpert
authors.forename: Cheryll
authors.initials: C
authors.lastname: Tickle
mesh_terms: D000818:Animals; D019521:Body Patterning; D002450:Cell Communication; D005121:Extremities / Q000196:embryology*; D005346:Fibroblast Growth Factors / Q000378:metabolism; D053823:Hedgehog Proteins / Q000378:metabolism; D015398:Signal Transduction; D014212:Tretinoin / Q000378:metabolism; D051153:Wnt Proteins / Q000378:metabolism
chemical_list: D053823:Hedgehog Proteins; D051153:Wnt Proteins; D014212:Tretinoin; D005346:Fibroblast Growth Factors