Related Experiment Video
Updated: May 24, 2026
Pharmacological and Functional Genetic Assays to Manipulate Regeneration of the Planarian Dugesia japonica
Published on: August 31, 2011
TOR signaling regulates planarian stem cells and controls localized and organismal growth
T Harshani Peiris1, Frank Weckerle, Elyse Ozamoto
1Department of Molecular and Cell Biology, School of Natural Sciences, University of California at Merced, Merced, CA 95343, USA.
Abstract:
Target of Rapamycin (TOR) controls an evolutionarily conserved signaling pathway that modulates cellular growth and division by sensing levels of nutrients, energy and stress. As such, TOR signaling is a crucial component of tissues and organs that translates systemic signals into cellular behavior. The ubiquitous nature of TOR signaling, together with the difficulty of analyzing tissue during cellular turnover and repair, have limited our understanding of how this kinase operates throughout the body. Here, we use the planarian model system to address TOR regulation at the organismal level. The planarian TOR homolog (Smed-TOR) is ubiquitously expressed, including stem cells (neoblasts) and differentiated tissues. Inhibition of TOR with RNA interference severely restricts cell proliferation, allowing the study of neoblasts with restricted proliferative capacity during regeneration and systemic cell turnover. Strikingly, TOR signaling is required for neoblast response to amputation and localized growth (blastema). However, in the absence of TOR signaling, regeneration takes place only within differentiated tissues. In addition, TOR is essential for maintaining the balance between cell division and cell death, and its dysfunction leads to tissue degeneration and lack of organismal growth in the presence of nutrients. Finally, TOR function is likely to be mediated through TOR Complex 1 as its disruption recapitulates signs of the TOR phenotype. Our data reveal novel roles for TOR signaling in controlling adult stem cells at a systemic level and suggest a new paradigm for studying TOR function during physiological turnover and regeneration.
Insights
Target of Rapamycin (TOR) signaling regulates cellular growth and division. In planarians, TOR is essential for adult stem cell function, regeneration, and maintaining tissue homeostasis.
Area of Science:
- Cell Biology
- Developmental Biology
- Regenerative Medicine
Background:
- Target of Rapamycin (TOR) signaling is a conserved pathway regulating cellular growth, division, and response to nutrients, energy, and stress.
- Understanding TOR's systemic role is challenging due to its ubiquitous nature and difficulties in studying tissue turnover and repair.
- The planarian flatworm is a powerful model for studying organismal-level biological processes due to its regenerative capabilities and simple anatomy.
Purpose of the Study:
- To investigate the role of Target of Rapamycin (TOR) signaling in regulating adult stem cells and regeneration at the organismal level.
- To elucidate how TOR signaling integrates systemic cues to control cellular behavior in tissues and organs.
- To explore the function of Smed-TOR in planarian stem cell (neoblast) proliferation, regeneration, and tissue homeostasis.
Main Methods:
- Utilized the planarian model system to study Smed-TOR (the planarian TOR homolog) expression and function.
- Employed RNA interference (RNAi) to inhibit TOR signaling and observe its effects on cell proliferation and regeneration.
- Analyzed the impact of TOR inhibition on neoblast behavior, blastema formation, tissue repair, and the balance between cell division and cell death.
Main Results:
- Smed-TOR is ubiquitously expressed in planarian stem cells (neoblasts) and differentiated tissues.
- TOR inhibition severely restricted cell proliferation, impacting neoblast response to amputation and blastema formation.
- While regeneration was impaired systemically, it occurred within differentiated tissues in the absence of TOR signaling.
- TOR dysfunction led to tissue degeneration, imbalanced cell division/death, and lack of growth despite nutrient availability.
- Disruption of TOR Complex 1 mimicked the observed TOR inhibition phenotype.
Conclusions:
- TOR signaling plays a critical, previously unrecognized role in controlling adult stem cell function at a systemic level.
- TOR is essential for neoblast proliferation, response to injury, and overall organismal homeostasis.
- This study establishes a new framework for investigating TOR function in physiological turnover and regeneration using the planarian model.
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