title: An intrinsic timer specifies distal structures of the vertebrate limb.
abstract: How the positional values along the proximo-distal axis (stylopod-zeugopod-autopod) of the limb are specified is intensely debated. Early work suggested that cells intrinsically change their proximo-distal positional values by measuring time. Recently, however, it is suggested that instructive extrinsic signals from the trunk and apical ectodermal ridge specify the stylopod and zeugopod/autopod, respectively. Here, we show that the zeugopod and autopod are specified by an intrinsic timing mechanism. By grafting green fluorescent protein-expressing cells from early to late chick wing buds, we demonstrate that distal mesenchyme cells intrinsically time Hoxa13 expression, cell cycle parameters and the duration of the overlying apical ectodermal ridge. In addition, we reveal that cell affinities intrinsically change in the distal mesenchyme, which we suggest results in a gradient of positional values along the proximo-distal axis. We propose a complete model in which a switch from extrinsic signalling to intrinsic timing patterns the vertebrate limb.
authors.affiliation: Instituto de Biomedicina y Biotecnología de Cantabria, IBBTEC (CSIC-Universidad de Cantabria), Santander 39011, Spain.
authors.forename: Patricia
authors.initials: P
authors.lastname: Saiz-Lopez
authors.affiliation: Bateson Centre, Department of Biomedical Sciences, University of Sheffield, Western Bank, Sheffield S10 2TN, UK.
authors.forename: Kavitha
authors.initials: K
authors.lastname: Chinnaiya
authors.affiliation: Instituto de Biomedicina y Biotecnología de Cantabria, IBBTEC (CSIC-Universidad de Cantabria), Santander 39011, Spain.
authors.forename: Victor M
authors.initials: VM
authors.lastname: Campa
authors.affiliation: Instituto de Biomedicina y Biotecnología de Cantabria, IBBTEC (CSIC-Universidad de Cantabria), Santander 39011, Spain.
authors.forename: Irene
authors.initials: I
authors.lastname: Delgado
authors.affiliation: Instituto de Biomedicina y Biotecnología de Cantabria, IBBTEC (CSIC-Universidad de Cantabria), Santander 39011, Spain.|Departamento de Anatomía y Biología Celular, Facultad de Medicina, Universidad de Cantabria, Santander 39011, Spain.
authors.forename: Maria A
authors.initials: MA
authors.lastname: Ros
authors.affiliation: Bateson Centre, Department of Biomedical Sciences, University of Sheffield, Western Bank, Sheffield S10 2TN, UK.
authors.forename: Matthew
authors.initials: M
authors.lastname: Towers
mesh_terms: D000818:Animals; D001133:Bones of Upper Extremity / Q000196:embryology / Q000378:metabolism; D002453:Cell Cycle; D002642:Chick Embryo; D004475:Ectoderm / Q000196:embryology / Q000378:metabolism; D005121:Extremities / Q000196:embryology; D005346:Fibroblast Growth Factors / Q000378:metabolism*; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D018507:Gene Expression Regulation, Developmental; D049452:Green Fluorescent Proteins; D018398:Homeodomain Proteins / Q000235:genetics* / Q000378:metabolism; D017403:In Situ Hybridization; D020287:In Situ Nick-End Labeling; D008648:Mesoderm / Q000196:embryology / Q000378:metabolism; D013997:Time Factors; D014921:Wings, Animal / Q000196:embryology* / Q000378:metabolism
chemical_list: D018398:Homeodomain Proteins; C485192:green fluorescent protein, Aequorea victoria; C099959:homeobox protein HOXA13; D049452:Green Fluorescent Proteins; D005346:Fibroblast Growth Factors