Cut a planarian in half and it forms two new flatworms, a remarkable feat of regeneration. But what controls pattern formation in the newly formed tissues? According to Cebrià and Newmark, during anterior regeneration in the planarian Schmidtea mediterranea, the answer may involve the nervous system (see ). The proper rewiring of the nervous system is a crucial event in regeneration,so the researchers began their study by identifying a planarian ortholog of the axonguidance receptor roundabout (Smed-roboA). Unexpectedly, RNAi knockdown of Smed-roboA led to the development of an extra pharynx (the worm's feeding organ) and to ectopic head structures during anterior regeneration. The researchers report that the regenerating brain in these animals did not reestablish proper connections with the ventral nerve cords and that this defect preceded the development of ectopic structures. They therefore propose that, as in annelids and amphibians, the nervous system may be an important source of the signals needed for proper morphogenesis during planarian regeneration.
