| Popis: |
Evidence is given against the view that the “eutetrapods”(anurans and amniotes) have a common prechondrogenic chondrogenic pattern of skeletal development of the limb which repeats the pattern of the ancestral adult limb of primitive tetrapods. In the chick wing and leg buds, isotopic sulphate labelling of chondroitin sulphate reveals instead a prechondrogenic pattern which is already specialized. The leg bud pattern is consistent with the theory of Shubin & Alberch that tetrapods have a similar common process of asymmetric postaxial branching and segmentation. The paper proposes that the asymmetry is controlled by the zone of polarising activity (ZPA) localised along the postaxial border acting as a signal source imposing asymmetry on a primitive branching property of the limb bud mesenchyme. This is proposed as a general model for the generation of the limb skeletal pattern in anurans and amniotes. |
