title: Formation of proximal and anterior limb skeleton requires early function of Irx3 and Irx5 and is negatively regulated by Shh signaling.
abstract: Limb skeletal pattern relies heavily on graded Sonic hedgehog (Shh) signaling. As a morphogen and growth cue, Shh regulates identities of posterior limb elements, including the ulna/fibula and digits 2 through 5. In contrast, proximal and anterior structures, including the humerus/femur, radius/tibia, and digit 1, are regarded as Shh independent, and mechanisms governing their specification are unclear. Here, we show that patterning of the proximal and anterior limb skeleton involves two phases. Irx3 and Irx5 (Irx3/5) are essential in the initiating limb bud to specify progenitors of the femur, tibia, and digit 1. However, these skeletal elements can be restored in Irx3/5 null mice when Shh signaling is diminished, indicating that Shh negatively regulates their formation after initiation. Our data provide genetic evidence supporting the concept of early specification and progressive determination of anterior limb pattern.
authors.affiliation: Program in Developmental & Stem Cell Biology, The Hospital for Sick Children, Toronto, ON M5G 1L7, Canada; Department of Molecular Genetics, University of Toronto, Toronto, ON MS5 1A8, Canada.
authors.forename: Danyi
authors.initials: D
authors.lastname: Li
authors.affiliation: Program in Developmental & Stem Cell Biology, The Hospital for Sick Children, Toronto, ON M5G 1L7, Canada.
authors.forename: Rui
authors.initials: R
authors.lastname: Sakuma
authors.affiliation: Program in Developmental & Stem Cell Biology, The Hospital for Sick Children, Toronto, ON M5G 1L7, Canada; Department of Molecular Genetics, University of Toronto, Toronto, ON MS5 1A8, Canada.
authors.forename: Niki A
authors.initials: NA
authors.lastname: Vakili
authors.affiliation: Program in Developmental & Stem Cell Biology, The Hospital for Sick Children, Toronto, ON M5G 1L7, Canada.
authors.forename: Rong
authors.initials: R
authors.lastname: Mo
authors.affiliation: Program in Developmental & Stem Cell Biology, The Hospital for Sick Children, Toronto, ON M5G 1L7, Canada.
authors.forename: Vijitha
authors.initials: V
authors.lastname: Puviindran
authors.affiliation: Program in Developmental & Stem Cell Biology, The Hospital for Sick Children, Toronto, ON M5G 1L7, Canada.
authors.forename: Steven
authors.initials: S
authors.lastname: Deimling
authors.affiliation: Program in Developmental & Stem Cell Biology, The Hospital for Sick Children, Toronto, ON M5G 1L7, Canada.
authors.forename: Xiaoyun
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Program in Developmental & Stem Cell Biology, The Hospital for Sick Children, Toronto, ON M5G 1L7, Canada; Department of Molecular Genetics, University of Toronto, Toronto, ON MS5 1A8, Canada; Division of Orthopaedics, The Hospital for Sick Children, Toronto, ON M5G 1L7, Canada; Department of Surgery, University of Toronto, Toronto, ON M5G 1X8, Canada. Electronic address: sevan.hopyan@sickkids.ca.
authors.forename: Sevan
authors.initials: S
authors.lastname: Hopyan
authors.affiliation: Program in Developmental & Stem Cell Biology, The Hospital for Sick Children, Toronto, ON M5G 1L7, Canada; Department of Molecular Genetics, University of Toronto, Toronto, ON MS5 1A8, Canada. Electronic address: cchui@sickkids.ca.
authors.forename: Chi-chung
authors.initials: CC
authors.lastname: Hui
mesh_terms: D000818:Animals; D019521:Body Patterning / Q000502:physiology; D001846:Bone Development / Q000502:physiology*; D005269:Femur / Q000196:embryology / Q000502:physiology; D018507:Gene Expression Regulation, Developmental; D053823:Hedgehog Proteins / Q000235:genetics / Q000378:metabolism*; D006614:Hindlimb / Q000196:embryology / Q000502:physiology; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D018878:Limb Buds / Q000196:embryology* / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D009154:Mutation; D015398:Signal Transduction / Q000502:physiology; D013977:Tibia / Q000196:embryology / Q000502:physiology; D014034:Toes / Q000196:embryology / Q000502:physiology; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: D053823:Hedgehog Proteins; D018398:Homeodomain Proteins; C501599:Irx3 protein, mouse; C501601:Irx5 protein, mouse; C465570:Shh protein, mouse; D014157:Transcription Factors