Cellular contribution to supernumerary limbs in the axolotl, Ambystoma mexicanum.

Ken Muneoka,Susan V Bryant

doi:10.1016/0012-1606(84)90272-0

Abstract

Using the triploid cell marker, the cellular contribution from graft and stump to the supernumerary limbs which result from controlateral grafts of limb buds and regeneration blastemas in the axolotl has been analyzed. Grafts were made so as to appose anterior and posterior limb positions. Overall, the contribution from graft and stump tissue was found to be approximately equal although the position of the boundary between the two was variable from limb to limb. This result is consistent with models which suggest that intercalary regeneration is the driving force for patterning of the vertebrate limb. In addition, the pattern of cellular contribution to supernumerary limbs was consistently found to be asymmetrical in the dorsal-ventral axis. Hence, posterior limb tissue predominantly contributed cells to the posterior and dorsal part of the supernumerary limb whereas anterior limb tissue predominantly contributed cells to the anterior and ventral part of the supernumerary limb. The reason for this asymmetrical pattern remains unknown, but we suggest that it might result from a directional bias in intercalary regeneration, similar to that observed during intercalation in the proximal-distal axis of the urodele limb. Using the triploid cell marker in conjunction with a black/white pigmentation marker, the relationship between the cellular contribution boundary and the pigmentation boundary in supernumerary limbs has also been analyzed. It has been found that the positions of the two boundaries do not coincide, a result which suggests that the eventual location of pigment cells is not a good indicator of the location of nonpigment cells derived from graft and stump.

Highlights

IntroductionSupernumerary limbs can result from a number of different experimental grafting manipulations of the regeneration blastema and the developing limb bud (regeneration-reviewed in Tank and Holder, 1981; development-Maden and Goodwin, 1980; Thorns and Fallon, 1980; Muneoka and Bryant, 1982)
In urodeles, supernumerary limbs can result from a number of different experimental grafting manipulations of the regeneration blastema and the developing limb bud
The majority (29/40) of the supernumerary limbs were classified as complete supernumerary limbs, i.e., they possessed four digits (1’7/20 forelimb blastema grafts) or five digits (12/20 hindlimb bud grafts)

Summary

Introduction

Supernumerary limbs can result from a number of different experimental grafting manipulations of the regeneration blastema and the developing limb bud (regeneration-reviewed in Tank and Holder, 1981; development-Maden and Goodwin, 1980; Thorns and Fallon, 1980; Muneoka and Bryant, 1982). The polar coordinate model (French et ab, 1976; Bryant et al, 1981) has in recent years provided a framework for exploring epimorphic pattern regulation. This model proposes that cells behave as if they possess positional information (Wolpert, 1969) about both their location along the proximal-distal axis of the limb and their location around the limb circumference. An alternative view proposes that positional information is specified with respect to the local concentration of a diffusible morphogen produced at a specialized region (polarizing zone) of the limb bud or blastema (Tickle et al, 1975; Meinhardt, 1982, 1983; see Tank and Holder, 1981)

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Conclusion