Abstract
We investigated cellular contributions to intercalary regenerates and 180o supernumerary limbs during axolotl limb regeneration using the cell autonomous green fluorescent protein marker and exchanged blastemas between white and green fluorescent protein animals. After distal blastemas were grafted to proximal levels tissues of the intercalary regenerate behaved independently with regard to the law of distal transformation; graft epidermis was replaced by stump epidermis, muscle‐derived cells, blood vessels, and Schwann cells of the distal blastema moved proximally to the stylopodium and cartilage and dermal cells conformed to the law. After 180o rotation, blastemas showed contributions from stump tissues which failed to alter patterning of the blastema. Supernumerary limbs were composed of stump and graft tissues and extensive contributions of stump tissues generated inversions or duplications of polarity to produce limbs of mixed handedness. Tail skeletal muscle and cardiac muscle broke the law with cells derived from these tissues exhibiting an apparent anteroposterior polarity as they migrated to the anterior side of the blastema. We attribute this behavior to the possible presence of a chemotactic factor from the wound epidermis.
Highlights
The concept of positional information (Wolpert 1969) has been thoroughly studied in regenerating systems such as the amphibian and insect limb to formulate laws that can explain how cells determine their position during morphogenesis (e.g., French et al 1976; Meinhardt 1983)
The green fluorescent protein (GFP) blastemas were removed and transplanted to corresponding white limb stumps that had been freshly amputated through the mid-humerus/femur level thereby generating a large disparity in proximodistal level between the graft and stump (Fig. 1A)
This study was designed with the intention of re-investigating earlier experiments on positional interactions in the regenerating limb such as the analysis of proximodistal positional information by grafting distal blastemas to proximal levels (Iten & Bryant 1975; Stocum 1975; Maden 1980a; Pescitelli & Stocum 1980) or rotating blastemas 180o on their stumps to analyze the relative contribution of stump and graft cells to the regenerates (Maden 1980b; Maden & Mustafa 1984)
Summary
The concept of positional information (Wolpert 1969) has been thoroughly studied in regenerating systems such as the amphibian and insect limb to formulate laws that can explain how cells determine their position (relative to other cells) during morphogenesis (e.g., French et al 1976; Meinhardt 1983). The elaboration of such laws is a prerequisite to a complete cellular and molecular understanding of organ regeneration and, as such, theoretical models for pattern formation represent important generalizations. It has been proposed that cells comprising the blastema possess molecular coding of their global position within the limb in order to correctly regenerate the precise structures which were removed by amputation
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