An additional function for Sonic hedgehog (Shh) in the limb bud is identified, namely the control of expression of cell cycle regulators, thereby controlling growth and specifying the size of the field in which the digit specification gradient operates. It is found that when Shh signalling was inhibited in chick limb buds, all the digit precursors formed anterior structures. In contrast, when cell proliferation was inhibited, all the anterior structures were lost and all the digit-precursors formed posterior structures.
- Matthew Towers
- Ruth Mahood
- Cheryll Tickle
