Regeneration of axolotl hindlimbs bearing surgically created discontinuities in the anterior-posterior axis.

The pattern regulation process in amphibian limbs has been examined with respect to the presence of discontinuities in the anterior-posterior (a-p) axis. Limbs bearing such discontinuities were surgically created by contralateral exchange of either dorsal or ventral half thighs and these limbs were then amputated immediately after surgery. The results demonstrate that a-p discontinuities lead to the formation of extra limb structures during distal outgrowth in contrast to the mosaic behaviour of comparable limb stumps which contain dorsal-ventral (d-v) discontinuities (Holder & Weekes, 1984). It is evident, therefore, that pattern regulation in the transverse limb axes is accomplished by basically different mechanisms. The structure of the limbs in the present study was examined in Victoria-blue-stained wholemounts and serial sections. The results allow some discussion of the basic mechanisms for pattern regulation in the two transverse limb axes and the relationship between them.