Uncoupling the Role of Sonic Hedgehog in Limb Development: Growth and Specification

Philippa Francis-West^1* and Robert Hill^2*

¹Department of Craniofacial Development, King’s College London, Guy’s Tower, Floor 27, London Bridge, London SE1 9RT, UK.
²Medical Research Council Human Genetics Unit, Western General Hospital, Crewe Road, Edinburgh EH4 2XU, UK.

Abstract: Sonic hedgehog (Shh) signaling is essential for the anterior-posterior (A-P) patterning of the embryonic limb bud. An additional role for Shh has now been identified in the mouse and chick, in which Shh promotes the proliferation of limb mesenchymal cells, which increases the number of digits that form. Surprisingly, these data are not consistent with any of the previous models in the mouse that described roles for Shh and the zone of polarizing activity in the patterning of the A-P axis. Therefore, new light is shed on the mechanisms of Shh action, which both challenges our understanding of limb development and gives insights into the evolutionary changes that result in digit reductions.

*Corresponding authors. E-mail: philippa.francis-west{at}kcl.ac.uk (P.F.-W.); bob.hill{at}hgu.mrc.ac.uk (R.H.)

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