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Progressive Specification Rather than Intercalation of Segments During Limb Regeneration

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Science  13 Dec 2013:
Vol. 342, Issue 6164, pp. 1375-1379
DOI: 10.1126/science.1241796

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Limb Regeneration Mirrors Development

Salamanders regenerate the right amount of limb after cutting anywhere along its length. A long-discussed explanation suggests that the regenerating tissue first sets the fingertips as a boundary and then regenerates everything in between. However, Roensch et al. (p. 1375) report that the limb regenerates in the opposite order. Similar to the processes followed during development, the regenerating salamander limb first establishes a field of cells with the identity of the cut site, and then cells progressively commit to alternate fates as they grow closer to the tip of the regenerated limb.

Abstract

An amputated salamander limb regenerates the correct number of segments. Models explaining limb regeneration were largely distinct from those for limb development, despite the presence of common patterning molecules. Intercalation has been an important concept to explain salamander limb regeneration, but clear evidence supporting or refuting this model was lacking. In the intercalation model, the first blastema cells acquire fingertip identity, creating a gap in positional identity that triggers regeneration of the intervening region from the stump. We used HOXA protein analysis and transplantation assays to show that axolotl limb blastema cells acquire positional identity in a proximal-to-distal sequence. Therefore, intercalation is not the primary mechanism for segment formation during limb regeneration in this animal. Patterning in development and regeneration uses similar mechanisms.

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