Molecular aspects of regeneration in developing vertebrate limbs.

We review embryological as well as molecular evidence that emphasizes the idea that both the regenerate and the developing vertebrate limb bud utilize a similar set of signals that regulate pattern formation. Evidence is presented to implicate the Hox-7.1 gene in the developmental regulation of growth, differentiation, and positional assignment during limb outgrowth and the proposal is made that the expression of this gene governs the cellular activities within the progress zone during limb outgrowth. Finally, we review the limited information known about the regenerative capabilities of limb buds in organisms that cannot regenerate as adults. We content that a solution to the problem of regenerative failure among higher vertebrates will come progressively through a stepwise analysis of impaired regeneration associated with increasing developmental age.