Molecular analysis of a classic experiment

Jenna Galloway and Cliff Tabin have revisited a classical set of experiments designed to test the ‘progress zone’ model of limb bud pattering along the long axis. 30 years ago, researchers observed that chick embryos exposed to x-irradiation developed a limb deformity referred to as phocomelia - a progressive distalization of the limb structure resulting, in the worst case, to a distal “hand” element, attached directly to the shoulder girdle.  This original observation provided the strongest evidence for the progress zone model of limb patterning.  
In their paper, Gallaway and Tabin conduct a thorough molecular analysis of the results of x-irradiation and demonstrate that the phocomelia seen is a result of a time-dependant ablation of skeletal progenetor cells rather than a defect in patterning as previously assumed.
Their work is published in the 24 June issue of Nature.