Anteroposterior axis formation in Xenopus limb bud recombinants: a model of pattern formation during limb regeneration.

We previously showed that recombinant limb buds with dissociated and reaggregated mesenchyme develop more than 30 digits in Xenopus laevis, which exhibits different capacities for limb regeneration at different developmental stages (Yokoyama et al. [1998] Dev Biol 196:1-10). Cell-cell contact among anterior- and posterior-derived mesenchymal cells is required for anteroposterior (AP) axis formation of recombinant limbs in an intercalary manner. However, whether one-way induction from posterior cells to anterior cells as proposed by the polarizing zone model or interactions between anterior and posterior cells evoke the AP axis formation in recombinant limbs remains unclear. In this study, we found, by a combination of X-ray irradiation and a recombinant limb technique, that not one-way induction but interactions between anterior and posterior cells accompanied by cell contribution are indispensable for AP axis formation in recombinant limbs. Shh was expressed in posterior-derived not anterior-derived cells. We propose that the recombinant limb is an excellent model for examining the axis formation mechanism in regenerating limbs because, as in recombinant limbs, cell-cell contact among cells derived from different positions of an amputation plane occurs in the blastema of regenerating limbs.