Trends in Cell Biology
ReviewPlanarian stem cells: a simple paradigm for regeneration
Section snippets
What can we learn from a regenerative life history? The tale of a stem cell
Currently, the molecular mechanisms behind regenerative phenomena remain obscure, largely because highly regenerative organisms do not have the short lifecycles and high fecundity suited to classical genetics; therefore, the amount of genetic, and subsequent molecular, research on these species has been relatively small.
Regenerative phenomena in various organisms are now proving to be molecularly tractable 1, 2. Among the bilaterians, planarians probably represent the most prodigious
A growing catalog of neoblast-associated genes: telling mother and daughter apart
An important starting point for investigating neoblast biology is the identification of actively expressed genes. These serve as candidate genes for regulating important aspects of neoblast biology and as markers of neoblasts and their undifferentiated progeny. One simple but important tool in planarian biology has been the use of gamma irradiation to remove proliferative neoblasts. Microarray-based expression analyses in two different species comparing normal and irradiated worms produced a
Neoblast maintenance and RNA metabolism: what happens in the chromatoid body (CB)?
Functional studies have revealed that many genes with roles in stem cells and germ cells in other animals have functions in neoblasts and early neoblast progeny 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38. Many of these genes are associated with RNA binding and metabolism and are localized in neoblast CBs or the CBs or germ plasm of other animals.
CBs are characteristic electron-dense perinuclear structures that resemble the germ granules associated with the germline lineages of animal
Chromatin organizers are implicated in regulating early stages of neoblast differentiation
Perhaps surprisingly, little progress has been made in identifying the genes required for neoblasts to differentiate down particular lineages. As mentioned above, the regeneration and differentiation of germline stem cells from neoblasts requires Smed-nanos [26], and a microarray expression-based functional genomic screen utilizing the Smed-nanos(RNAi) phenotype has identified the genes required for the differentiation of germline stem cells [52]. But little is known about the cell autonomous
Directing stem cell differentiation in time and space to reestablish polarity, fate and function: old favorites in new packages
Perhaps the most rapid progress in the planarian model system has been made in understanding how the signals that pattern the positional identities of the planarian body plan are reestablished during regeneration. These signals direct neoblast progeny to replace distal missing tissues and remodel existing tissues to ensure the restoration and integration of all body systems. A detailed understanding of these processes provides a simple paradigm for how this might be achieved in contexts where
Concluding remarks
Considerable progress has been made in understanding the biology of the previously enigmatic neoblast stem cells, their progeny and the fundamentals of the regenerative process. We now have several clues about how early events in neoblast differentiation and maintenance are controlled (Figure 1) as well as a working model of how axial polarity and fate might be determined during regeneration (Figure 2). Nonetheless, detailed mechanistic descriptions are still missing. These will come to light
Acknowledgments
I would like to thank Deborah Evans and Jordi Solana for help with figures and ongoing discussions regarding planarian stem cells and regeneration. I also thank members of my laboratory and the EuroPlanNet community (www.europlannet.org) for stimulating discussions and ideas. Planarian research in the author's laboratory is supported by grants from the MRC, BBSRC, Wellcome Trust and the University of Nottingham.
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WTAP regulates stem cells via TRAF6 to maintain planarian homeostasis and regeneration
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2023, Biochemical and Biophysical Research CommunicationsCitation Excerpt :These stem cells provide the cellular basis for all new tissue production in planarian regeneration [18–20]. The neoblasts can migrate toward the wound site after injury and differentiate into any planarian cell type [20–22]. To correctly replace the missing tissue, the neoblasts must receive proper positional instructions [13].
Exposure to polystyrene microplastics reduces regeneration and growth in planarians
2022, Journal of Hazardous Materials