Enhanced c-myc gene expression during forelimb regenerative outgrowth in the young Xenopus laevis.

Analysis of the expression of the c-myc protooncogene has been carried out in the forelimb regenerate of the Xenopus laevis froglet. Northern blot hybridization analysis revealed the presence of a 2.5-kilobase c-myc transcript in the regenerate forelimb at a level at least 7-fold more than the one found in nonregenerating forelimbs or stumps of regenerating forelimbs. In situ hybridization analyses confirmed the relative abundance of c-myc RNA in the regenerate forelimb and provided evidence of spatial localization of high levels of c-myc RNA in specific cell layers. The deepest layers of the wound epithelium of epidermal origin showed a strong signal, whereas virtually no c-myc RNA was detected in the outermost layers. Labeling was also observed in mesenchymal cells of the blastema where it was relatively evenly distributed. This pattern of c-myc RNA in the regenerate might indicate that the expression of c-myc plays a role in the regulation of the continued proliferation of specific cells of the regenerate, whereas repression of this gene in the epidermis correlates with terminal differentiation of keratinocytes.