Adult somatic stem cells can play critical roles in
postembryonic developmental processes such as tissue
renewal, growth, repair, and regeneration [1].
Understanding how such cells are maintained and
produce differentiated progeny is thus of general interest
in developmental biology, in addition to being of clear
biomedical relevance. Invertebrate models have great
potential for elucidating the cellular and molecular basis
of stem-cell function. However, in the main invertebrate
models used for dissecting the details of animal
development, including Drosophila and Caenorhabditis,
adult somatic tissues are primarily post-mitotic and are
largely or entirely devoid of adult stem cells, which limits
the use of these established models for stem-cell research.
Representatives of two groups of soft-bodied worms, the
Acoela and the Platyhelminthes, possess large pools of
adult somatic stem cells, making them useful invertebrate
models for stem-cell biology. These organisms are now
beginning to provide new insights into the cellular and
molecular basis of adult stem-cell function.