Formation of proximal and anterior limb skeleton requires early function of Irx3 and Irx5 and is negatively regulated by Shh signaling

Dev Cell. 2014 Apr 28;29(2):233-40. doi: 10.1016/j.devcel.2014.03.001. Epub 2014 Apr 10.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Body Patterning / physiology
  • Bone Development / physiology*
  • Femur / embryology
  • Femur / physiology
  • Gene Expression Regulation, Developmental
  • Hedgehog Proteins / genetics
  • Hedgehog Proteins / metabolism*
  • Hindlimb / embryology
  • Hindlimb / physiology
  • Homeodomain Proteins / genetics
  • Homeodomain Proteins / metabolism*
  • Limb Buds / embryology*
  • Limb Buds / metabolism*
  • Mice
  • Mice, Knockout
  • Mutation
  • Signal Transduction / physiology
  • Tibia / embryology
  • Tibia / physiology
  • Toes / embryology
  • Toes / physiology
  • Transcription Factors / genetics
  • Transcription Factors / metabolism*


  • Hedgehog Proteins
  • Homeodomain Proteins
  • Irx3 protein, mouse
  • Irx5 protein, mouse
  • Shh protein, mouse
  • Transcription Factors