For those of you with some memory of high school biology, the Planaria should be familiar. It's a flat worm with a couple of eyespots; an unremarkable creature in most ways. Until you try to kill it, that is. Cut off a part, and it grows back. Slice it in half, and you eventually get two complete Planaria. Slice it most of the way down its main axis and you get the two headed beastlet shown at the right. A biological curiosity, right?
In these days of molecular biology and genome completion, no. The Planaria genome is well on its way to being done, and its compact nature has enabled molecular exploration of this regenerative ability. Some scientists at the University of Utah have been doing just that. Using an RNA interference technique, they've blocked the expression of over 1000 genes, and found that many of these contribute to the regenerative ability. In the latest issue of Science, they focus on one such gene. The gene chosen is part of a family that interacts with double-stranded RNA, and may even be involved in RNA interference itself. In animals that do not express the gene, stem cells form, proliferate, and migrate to the point of injury, but don't replace damaged cells once there.
What might this mean for medical applications of regeneration? It's hard to say right now. Humans already have a version of this gene (in fact, they have 4, relative to Planaria's 2), so it's clear that simply having the gene isn't enough. But the ability to both identify genes involved in specific steps in regeneration and to observe the cellular processes that go into this ability may provide insights that may eventually be applicable to directing human stem cells to aid in tissue repair.