Bryant, S.V.: REGENERATION: SOMETHING OLD; SOMETHING NEW

Urodeles are unique among vertebrates in their ability to regenerate lost appendages as adults. Evidence from numerous studies indicates that regeneration is a biphasic process, with the first phase involving the transition to a blastema, and the second involving the control of growth and pattern formation within the regeneration blastema. Patterns of gene expression in the first phase mark it as unique and distinct from limb development. In the second phase, patterns of gene expression and tests of gene function, suggest mechanisms that are common to both development and regeneration. It is the genes expressed during the early, unique phase that transform differentiated limb cells into a blastema with similar properties to that of an embryonic limb bud, thereby making regeneration possible. Recent advances in somatic cell transgenesis in the axolotl are allowing for the functional analysis of the molecules controlling the transition into dedifferentiation, and will eventually lead to therapeutic interventions to stimulate human regeneration.