ABSTRACT
Planarians (freshwater fl atworms) are able to regenerate a complete animal, including the brain and reproductive system, after any kind of amputation. Although their striking regenerative capacity has attracted generations of biologists, recent years have seen them transformed into an essential model for the study of regeneration and stem cell biology using modern molecular and genomic tools. The impressive plasticity of planarians is based upon the presence in adult animals of a unique type of totipotent stem cells named neoblasts. In this chapter, we review current understanding of the molecular mechanisms that direct body patterning and control neoblast maintenance and differentiation in planarians. We provide an overview of the large volume of data obtained mainly in the last 5 years on the molecular mechanisms underlying the establishment and maintenance of axial polarity by the Wnt and BMP signalling pathways. We also review recent approaches to elucidate the mechanism of neoblast differentiation into specifi c cell types and organs.
