A somitic contribution to the apical ectodermal ridge is essential for fin formation

Invasion of a somite-derived cell population into the apical ectodermal ridge in zebrafish regulates apical fold induction during fin formation; ablation of these cells inhibits formation of the apical fold and increases the size of the underlying fin bud mesenchyme, suggesting that somite-derived cells play a key part in the evolutionary transition from fins to limbs.