Pattern discontinuity, polarity and directional intercalation in axolotl limbs.

Axolotl limb stumps with dorsal-ventral confrontations between digits 2 and 3 but with a normal anterior-posterior pattern were created by grafting between contralateral limbs. Graft and host differed in ploidy to permit a determination of the origin of cells in the regenerated limb. After regeneration, limbs were analysed for skeletal and muscle patterns and for the distribution of marked cells in the regenerate. Regenerated limbs showed varying degrees of abnormality in their dorsal-ventral organization. Following regeneration, the original dorsal-ventral discontinuities were in some cases maintained and in others resolved. The maintenance or resolution of pattern discontinuities occurred in a position-dependent manner. Cell marker analysis indicates a relationship between the resolution of discontinuities and the extent to which cells become displaced across the original graft-host interface. These data lend support to the suggestion that circumferential intercalation is directionally biased.