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Summary: Regeneration -- the regrowth or repair of cells, tissues
and organs -- is widely but non-uniformly represented
among all animal phyla1
(FIG. 1a). The diverse modes by
which regeneration is accomplished is a topic of as much
interest as its distribution among taxonomic groups2
.
Regenerative strategies include the rearrangement of
pre-existing tissue, the use of adult somatic stem cells
and the dedifferentiation and/or transdifferentiation of
cells (FIG. 2), and more than one mode can operate in
different tissues of the same animal. All these strategies
result in the re-establishment of appropriate tissue polar-
ity, structure and form. Therefore, the key questions in
regeneration research relate to the evolutionary and bio-
logical reasons that distinct modes are used in different
cases, the molecular pathways that are involved and the
differences and similarities between regeneration and
normal development.
As well as being a fascinating biological problem,
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