An Introduction to Planarians and Their Stem Cells

Abstract

Of all animals, it is perhaps planarians that have the greatest ability to regenerate. These once classical classroom organisms have now become the subject of advanced molecular genetic studies that have the potential to inform us about our own biology. Regeneration relies upon a population of pluripotent adult stem cells, called neoblasts. These collectively pluripotent stem cells underpin the regenerative capacity of planarians. The underlying molecular mechanisms controlling their proliferation, self‐renewal and differentiation are now being described. In particular, progress has been made in describing the expression profile of these cells and identifying some of the molecular mechanisms that regulate their behaviour leading to a better understanding of how these cells power regeneration. Key Concepts Planarians are bilaterians and share many cell and tissue types with other animals including vertebrates. Planarians are able to mount a profound regenerative response to wounding allowing even small fragments to regenerate whole new worms. Planarian regeneration requires the proliferation and differentiation of a population of pluripotent stem cell population called neoblasts. Expression profiling of the neoblast population shows they are a heterogeneous population and express gene regulatory networks in common with both somatic and germline stem cells Many cell biological and molecular genetic approaches can be used to study gene function in planarians allowing novel biological insights to be made, relevant to our own biology. Current research has uncovered many important regulatory processes that regulate stem cells, including those regulated by transcription factors, chromatin modification and RNA binding proteins. Future work will uncover the detailed mechanisms that control stem cell proliferation, self‐renewal and differentiation as well as how missing structures are accurately restored.

Feedback Control in Planarian Stem Cell Systems

“…A growing body of co-expression data shows that sub-populations of cycling neoblasts express lineage specifc mRNA markers [13]. Some of these co-expressed markers are functionally required for production of both the neoblast sub-population and the differentiated cell lineage in question; reviewed in [14]. This provides evidence for the existence of committed proliferating cells amongst the neoblast population, but this awaits definitive experimental proof.…”