Amputations trigger a molecular response that determines if a head or tail will be regrown in planaria, a flatworm commonly studied for its regenerative capabilities. Until now, no molecular connection between wounding and the decision to regenerate either a head or tail in planaria had been identified.
Whitehead Institute scientists report this finding in the September 15-28 issue of PNAS Early Edition.
Regeneration is the regrowth of part of an organism's body after it has been damaged or removed. Although animals such as planaria and starfish can regrow virtually any part of their bodies, humans have restricted regenerative capabilities. A better understanding of regeneration, including how the body decides which organs or tissues should be regrown after an injury, may eventually benefit patients with traumatic injuries, such as amputations or nerve damage.
To study how planaria regrow their bodies from a sliver of tissue, Christian Petersen, a postdoctoral fellow in Whitehead Member Peter Reddien's lab, looked at two of the planaria's genes, wntP-1 and wntP-2. These genes act to control cell to cell communication in a process called the Wnt signaling pathway, which is involved in many biological events, including development and growth. Petersen and Reddien had theorized that at least some portion of the Wnt pathway plays a role in regeneration.
In earlier work with planaria, Petersen and Reddien showed that a Wnt-related gene, called Smed-beta-catenin-1 (beta catenin), is necessary for planaria to regenerate a tail instead of a head after tail amputation. This ability to grow a head when the head is cut off and grow a tail when the tail is cut off is known as "regeneration polarity". In this experiment, Petersen cut the head, tail or both the head and tail off of planaria and observed where wntP-1 gene expression occurred.
Because previous experiments linked the Wnt-related gene beta catenin to proper tail regrowth, Petersen and Reddien expected that only the worms with amputated tails would express the wntP-1 gene. However, shortly after wounding the worms, a number of cells near both the head-facing and tail-facing wound sites expressed the wntP-1 gene.