101
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Tejada-Romero B, Carter JM, Mihaylova Y, Neumann B, Aboobaker AA. JNK signalling is necessary for a Wnt- and stem cell-dependent regeneration programme. Development 2015; 142:2413-24. [PMID: 26062938 DOI: 10.1242/dev.115139] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2014] [Accepted: 06/03/2015] [Indexed: 12/23/2022]
Abstract
Regeneration involves the integration of new and old tissues in the context of an adult life history. It is clear that the core conserved signalling pathways that orchestrate development also play central roles in regeneration, and further study of conserved signalling pathways is required. Here we have studied the role of the conserved JNK signalling cascade during planarian regeneration. Abrogation of JNK signalling by RNAi or pharmacological inhibition blocks posterior regeneration and animals fail to express posterior markers. While the early injury-induced expression of polarity markers is unaffected, the later stem cell-dependent phase of posterior Wnt expression is not established. This defect can be rescued by overactivation of the Hh or Wnt signalling pathway to promote posterior Wnt activity. Together, our data suggest that JNK signalling is required to establish stem cell-dependent Wnt expression after posterior injury. Given that Jun is known to be required in vertebrates for the expression of Wnt and Wnt target genes, we propose that this interaction may be conserved and is an instructive part of planarian posterior regeneration.
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Affiliation(s)
- Belen Tejada-Romero
- Department of Zoology, Tinbergen Building, South Parks Road, University of Oxford, Oxford OX1 3PS, UK
| | - Jean-Michel Carter
- Department of Zoology, Tinbergen Building, South Parks Road, University of Oxford, Oxford OX1 3PS, UK
| | - Yuliana Mihaylova
- Department of Zoology, Tinbergen Building, South Parks Road, University of Oxford, Oxford OX1 3PS, UK
| | - Bjoern Neumann
- Department of Zoology, Tinbergen Building, South Parks Road, University of Oxford, Oxford OX1 3PS, UK
| | - A Aziz Aboobaker
- Department of Zoology, Tinbergen Building, South Parks Road, University of Oxford, Oxford OX1 3PS, UK
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102
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Reactive Oxygen Species in Planarian Regeneration: An Upstream Necessity for Correct Patterning and Brain Formation. OXIDATIVE MEDICINE AND CELLULAR LONGEVITY 2015; 2015:392476. [PMID: 26180588 PMCID: PMC4477255 DOI: 10.1155/2015/392476] [Citation(s) in RCA: 74] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/11/2014] [Revised: 04/30/2015] [Accepted: 05/04/2015] [Indexed: 12/12/2022]
Abstract
Recent research highlighted the impact of ROS as upstream regulators of tissue regeneration. We investigated their role and targeted processes during the regeneration of different body structures using the planarian Schmidtea mediterranea, an organism capable of regenerating its entire body, including its brain. The amputation of head and tail compartments induces a ROS burst at the wound site independently of the orientation. Inhibition of ROS production by diphenyleneiodonium (DPI) or apocynin (APO) causes regeneration defaults at both the anterior and posterior wound sites, resulting in reduced regeneration sites (blastemas) and improper tissue homeostasis. ROS signaling is necessary for early differentiation and inhibition of the ROS burst results in defects on the regeneration of the nervous system and on the patterning process. Stem cell proliferation was not affected, as indicated by histone H3-P immunostaining, fluorescence-activated cell sorting (FACS), in situ hybridization of smedwi-1, and transcript levels of proliferation-related genes. We showed for the first time that ROS modulate both anterior and posterior regeneration in a context where regeneration is not limited to certain body structures. Our results indicate that ROS are key players in neuroregeneration through interference with the differentiation and patterning processes.
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103
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Inferring regulatory networks from experimental morphological phenotypes: a computational method reverse-engineers planarian regeneration. PLoS Comput Biol 2015; 11:e1004295. [PMID: 26042810 PMCID: PMC4456145 DOI: 10.1371/journal.pcbi.1004295] [Citation(s) in RCA: 57] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2014] [Accepted: 04/21/2015] [Indexed: 01/18/2023] Open
Abstract
Transformative applications in biomedicine require the discovery of complex regulatory networks that explain the development and regeneration of anatomical structures, and reveal what external signals will trigger desired changes of large-scale pattern. Despite recent advances in bioinformatics, extracting mechanistic pathway models from experimental morphological data is a key open challenge that has resisted automation. The fundamental difficulty of manually predicting emergent behavior of even simple networks has limited the models invented by human scientists to pathway diagrams that show necessary subunit interactions but do not reveal the dynamics that are sufficient for complex, self-regulating pattern to emerge. To finally bridge the gap between high-resolution genetic data and the ability to understand and control patterning, it is critical to develop computational tools to efficiently extract regulatory pathways from the resultant experimental shape phenotypes. For example, planarian regeneration has been studied for over a century, but despite increasing insight into the pathways that control its stem cells, no constructive, mechanistic model has yet been found by human scientists that explains more than one or two key features of its remarkable ability to regenerate its correct anatomical pattern after drastic perturbations. We present a method to infer the molecular products, topology, and spatial and temporal non-linear dynamics of regulatory networks recapitulating in silico the rich dataset of morphological phenotypes resulting from genetic, surgical, and pharmacological experiments. We demonstrated our approach by inferring complete regulatory networks explaining the outcomes of the main functional regeneration experiments in the planarian literature; By analyzing all the datasets together, our system inferred the first systems-biology comprehensive dynamical model explaining patterning in planarian regeneration. This method provides an automated, highly generalizable framework for identifying the underlying control mechanisms responsible for the dynamic regulation of growth and form. Developmental and regenerative biology experiments are producing a huge number of morphological phenotypes from functional perturbation experiments. However, existing pathway models do not generally explain the dynamic regulation of anatomical shape due to the difficulty of inferring and testing non-linear regulatory networks responsible for appropriate form, shape, and pattern. We present a method that automates the discovery and testing of regulatory networks explaining morphological outcomes directly from the resultant phenotypes, producing network models as testable hypotheses explaining regeneration data. Our system integrates a formalization of the published results in planarian regeneration, an in silico simulator in which the patterning properties of regulatory networks can be quantitatively tested in a regeneration assay, and a machine learning module that evolves networks whose behavior in this assay optimally matches the database of planarian results. We applied our method to explain the key experiments in planarian regeneration, and discovered the first comprehensive model of anterior-posterior patterning in planaria under surgical, pharmacological, and genetic manipulations. Beyond the planarian data, our approach is readily generalizable to facilitate the discovery of testable regulatory networks in developmental biology and biomedicine, and represents the first developmental model discovered de novo from morphological outcomes by an automated system.
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104
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Werner S, Stückemann T, Beirán Amigo M, Rink JC, Jülicher F, Friedrich BM. Scaling and regeneration of self-organized patterns. PHYSICAL REVIEW LETTERS 2015; 114:138101. [PMID: 25884138 DOI: 10.1103/physrevlett.114.138101] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/10/2014] [Indexed: 06/04/2023]
Abstract
Biological patterns generated during development and regeneration often scale with organism size. Some organisms, e.g., flatworms, can regenerate a rescaled body plan from tissue fragments of varying sizes. Inspired by these examples, we introduce a generalization of Turing patterns that is self-organized and self-scaling. A feedback loop involving diffusing expander molecules regulates the reaction rates of a Turing system, thereby adjusting pattern length scales proportional to system size. Our model captures essential features of body plan regeneration in flatworms as observed in experiments.
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Affiliation(s)
- Steffen Werner
- Max Planck Institute for the Physics of Complex Systems, Nöthnitzer Straße 38, 01187 Dresden, Germany
| | - Tom Stückemann
- Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstr. 108, 01307 Dresden, Germany
| | - Manuel Beirán Amigo
- Max Planck Institute for the Physics of Complex Systems, Nöthnitzer Straße 38, 01187 Dresden, Germany
- Universidad Autónoma de Madrid, Ciudad Universitaria de Cantoblanco, 28049 Madrid, Spain
| | - Jochen C Rink
- Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstr. 108, 01307 Dresden, Germany
| | - Frank Jülicher
- Max Planck Institute for the Physics of Complex Systems, Nöthnitzer Straße 38, 01187 Dresden, Germany
| | - Benjamin M Friedrich
- Max Planck Institute for the Physics of Complex Systems, Nöthnitzer Straße 38, 01187 Dresden, Germany
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105
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Owen JH, Wagner DE, Chen CC, Petersen CP, Reddien PW. teashirt is required for head-versus-tail regeneration polarity in planarians. Development 2015; 142:1062-72. [PMID: 25725068 DOI: 10.1242/dev.119685] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Regeneration requires that the identities of new cells are properly specified to replace missing tissues. The Wnt signaling pathway serves a central role in specifying posterior cell fates during planarian regeneration. We identified a gene encoding a homolog of the Teashirt family of zinc-finger proteins in the planarian Schmidtea mediterranea to be a target of Wnt signaling in intact animals and at posterior-facing wounds. Inhibition of Smed-teashirt (teashirt) by RNA interference (RNAi) resulted in the regeneration of heads in place of tails, a phenotype previously observed with RNAi of the Wnt pathway genes β-catenin-1, wnt1, Dvl-1/2 or wntless. teashirt was required for β-catenin-1-dependent activation of posterior genes during regeneration. These findings identify teashirt as a transcriptional target of Wnt signaling required for Wnt-mediated specification of posterior blastemas.
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Affiliation(s)
- Jared H Owen
- Howard Hughes Medical Institute, MIT Biology and Whitehead Institute for Biomedical Research, 9 Cambridge Center, Cambridge, MA 02142, USA
| | - Daniel E Wagner
- Howard Hughes Medical Institute, MIT Biology and Whitehead Institute for Biomedical Research, 9 Cambridge Center, Cambridge, MA 02142, USA
| | - Chun-Chieh Chen
- Howard Hughes Medical Institute, MIT Biology and Whitehead Institute for Biomedical Research, 9 Cambridge Center, Cambridge, MA 02142, USA
| | - Christian P Petersen
- Howard Hughes Medical Institute, MIT Biology and Whitehead Institute for Biomedical Research, 9 Cambridge Center, Cambridge, MA 02142, USA Department of Molecular Biosciences, Northwestern University, 2205 Tech Drive, Hogan Hall Room 2-144, Evanston, IL 60208, USA
| | - Peter W Reddien
- Howard Hughes Medical Institute, MIT Biology and Whitehead Institute for Biomedical Research, 9 Cambridge Center, Cambridge, MA 02142, USA
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106
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Protein expression profiling in head fragments during planarian regeneration after amputation. Dev Genes Evol 2015; 225:79-93. [PMID: 25697422 DOI: 10.1007/s00427-015-0494-3] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2014] [Accepted: 02/09/2015] [Indexed: 10/24/2022]
Abstract
Following amputation, a planarian tail fragment can regrow into a complete organism including a well-organized brain within about 2-3 weeks, thus restoring the structure and function to presurgical levels. Despite the enormous potential of these animals for regenerative medicine, our understanding of the exact mechanism of planarian regeneration is incomplete. To better understand the molecular nature of planarian head regeneration, we applied two-dimensional electrophoresis (2-DE)/matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF)/time-of-flight mass spectrometry (TOF MS) technique to analyze the dynamic proteomic expression profiles over the course of 6 to 168 h post-decapitation. This approach identified a total of 141 differentially expressed proteins, 47 of which exhibited exceptionally high fold changes (≥3-fold change). Of these, Rx protein, an important regulator of head and brain development, was considered to be closely related to planarian head regeneration because of its exceptional high expression almost throughout the time course of regeneration process. Functional annotation analysis classified the 141 proteins into eight categories: (1) signaling, (2) Ca(2+) binding and translocation, (3) transcription and translation, (4) cytoskeleton, (5) metabolism, (6) cell protection, (7) tissue differentiation, and (8) cell cycle. Signaling pathway analysis indicated that Wnt1/Ca(2+) signaling pathway was activated during head regeneration. Integrating the analyses of proteome expression profiling, functional annotation, and signaling pathway, amputation-induced head reformation requires some mechanisms to promote cell proliferation and differentiation, including differential regulation of proapoptotic and antiapoptotic proteins, and the regulation of proliferation and differentiation-related proteins. Importantly, Wnt1/Ca(2+) signaling pathway upregulates Rx expression, finally facilitating the differentiation of neoblasts into various cell types. Taken together, our study demonstrated that proteomic analysis approach used by us is a powerful tool in understanding molecular process related to head regeneration of planarian.
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107
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Roberts-Galbraith RH, Newmark PA. On the organ trail: insights into organ regeneration in the planarian. Curr Opin Genet Dev 2015; 32:37-46. [PMID: 25703843 DOI: 10.1016/j.gde.2015.01.009] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2014] [Revised: 01/25/2015] [Accepted: 01/27/2015] [Indexed: 11/28/2022]
Abstract
Advances in stem cell biology have led to the derivation of diverse cell types, yet challenges remain in creating complex tissues and functional organs. Unlike humans, some animals regenerate all missing tissues and organs successfully after dramatic injuries. Studies of organisms with exceptional regenerative capacity, like planarians, could complement in vitro studies and reveal mechanistic themes underlying regeneration on the scale of whole organs and tissues. In this review, we outline progress in understanding planarian organ regeneration, with focus on recent studies of the nervous, digestive, and excretory systems. We further examine molecular mechanisms underlying establishment of diverse cell fates from the planarian stem cell pool. Finally, we explore conceptual directions for future studies of organ regeneration in planarians.
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Affiliation(s)
- Rachel H Roberts-Galbraith
- Howard Hughes Medical Institute and Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, United States
| | - Phillip A Newmark
- Howard Hughes Medical Institute and Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, United States.
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108
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Β-catenin-dependent control of positional information along the AP body axis in planarians involves a teashirt family member. Cell Rep 2014; 10:253-65. [PMID: 25558068 DOI: 10.1016/j.celrep.2014.12.018] [Citation(s) in RCA: 54] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2014] [Revised: 11/07/2014] [Accepted: 12/09/2014] [Indexed: 11/21/2022] Open
Abstract
Wnt/β-catenin signaling regulates tissue homeostasis and regeneration in metazoans. In planarians-flatworms with high regenerative potential-Wnt ligands are thought to control tissue polarity by shaping a β-catenin activity gradient along the anterior-posterior axis, yet the downstream mechanisms are poorly understood. We performed an RNA sequencing (RNA-seq)-based screen and identified hundreds of β-catenin-dependent transcripts, of which several were expressed in muscle tissue and stem cells in a graded fashion. In particular, a teashirt (tsh) ortholog was induced in a β-catenin-dependent manner during regeneration in planarians and zebrafish, and RNAi resulted in two-headed planarians. Strikingly, intact planarians depleted of tsh induced anterior markers and slowly transformed their tail into a head, reminiscent of β-catenin RNAi phenotypes. Given that β-catenin RNAi enhanced the formation of muscle cells expressing anterior determinants in tail regions, our study suggests that this pathway controls tissue polarity through regulating the identity of differentiating cells during homeostasis and regeneration.
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109
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Abstract
Recent studies in Drosophila, Hydra, planarians, zebrafish, mice, indicate that cell death can open paths to regeneration in adult animals. Indeed injury can induce cell death, itself triggering regeneration following an immediate instructive mechanism, whereby the dying cells release signals that induce cellular responses over short and/or long-range distances. Cell death can also provoke a sustained derepressing response through the elimination of cells that suppress regeneration in homeostatic conditions. Whether common properties support what we name "regenerative cell death," is currently unclear. As key parameters, we review here the injury proapoptotic signals, the signals released by the dying cells, the cellular responses, and their respective timing. ROS appears as a common signal triggering cell death through MAPK and/or JNK pathway activation. But the modes of ROS production vary, from a brief pulse upon wounding, to repeated waves as observed in the zebrafish fin where ROS supports two peaks of cell death. Indeed regenerative cell death can be restricted to the injury phase, as in Hydra, Drosophila, or biphasic, immediate, and delayed, as in planarians and zebrafish. The dying cells release in a caspase-dependent manner a variety of signaling molecules, cytokines, growth factors, but also prostaglandins or ATP as recorded in Drosophila, Hydra, mice, and zebrafish, respectively. Interestingly, the ROS-producing cells often resist to cell death, implying a complex paracrine mode of signaling to launch regeneration, involving ROS-producing cells, ROS-sensing cells that release signaling molecules upon caspase activation, and effector cells that respond to these signals by proliferating, migrating, and/or differentiating.
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Affiliation(s)
- Sophie Vriz
- Collège de France, Center for Interdisciplinary Research in Biology (CIRB), Paris, France; University Paris-Diderot, Paris, France
| | - Silke Reiter
- Department of Genetics and Evolution, University of Geneva, Switzerland
| | - Brigitte Galliot
- Department of Genetics and Evolution, University of Geneva, Switzerland.
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110
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Vásquez-Doorman C, Petersen CP. zic-1 Expression in Planarian neoblasts after injury controls anterior pole regeneration. PLoS Genet 2014; 10:e1004452. [PMID: 24992682 PMCID: PMC4081000 DOI: 10.1371/journal.pgen.1004452] [Citation(s) in RCA: 54] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2013] [Accepted: 05/07/2014] [Indexed: 11/24/2022] Open
Abstract
Mechanisms that enable injury responses to prompt regenerative outgrowth are not well understood. Planarians can regenerate essentially any tissue removed by wounding, even after decapitation, due to robust regulation of adult pluripotent stem cells of the neoblast population. Formation of pole signaling centers involving Wnt inhibitors or Wnt ligands promotes head or tail regeneration, respectively, and this process requires the use of neoblasts early after injury. We used expression profiling of purified neoblasts to identify factors needed for anterior pole formation. Using this approach, we identified zic-1, a Zic-family transcription factor, as transcriptionally activated in a subpopulation of neoblasts near wound sites early in head regeneration. As head regeneration proceeds, the Wnt inhibitor notum becomes expressed in the newly forming anterior pole in zic-1-expressing cells descended from neoblasts. Inhibition of zic-1 by RNAi resulted in a failure to express notum at the anterior pole and to regenerate a head, but did not affect tail regeneration. Both injury and canonical Wnt signaling inhibition are required for zic-1 expression, and double-RNAi experiments suggest zic-1 inhibits Wnt signaling to allow head regeneration. Analysis of neoblast fate determinants revealed that zic-1 controls specification of notum-expressing cells from foxD-expressing neoblasts to form the anterior pole, which organizes subsequent outgrowth. Specialized differentiation programs may in general underlie injury-dependent formation of tissue organizing centers used for regenerative outgrowth. Some animals are capable of regenerating organs damaged or removed by injury, and this ability likely requires precise control of secreted proteins that promote growth. Planarians are flatworms that can regenerate any missing tissues by regulating the activity of adult stem cells that can produce any specialized cell type. We identify the zic-1 gene as activated in planarian stem cells by injury and needed for head regeneration after decapitation. This gene's product likely acts as a transcription factor to produce cells that secrete a growth-promoting protein, NOTUM, at the tip of the regenerating tissue outgrowth to organize and enable head regeneration. These results suggest that regeneration requires specialized uses of stem cell descendants to orchestrate new tissue production following injury.
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Affiliation(s)
- Constanza Vásquez-Doorman
- Department of Molecular Biosciences, Northwestern University, Evanston, Illinois, United States of America
| | - Christian P. Petersen
- Department of Molecular Biosciences, Northwestern University, Evanston, Illinois, United States of America
- Robert Lurie Comprehensive Cancer Center, Northwestern University, Evanston, Illinois, United States of America
- * E-mail:
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111
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Sánchez Alvarado A, Yamanaka S. Rethinking differentiation: stem cells, regeneration, and plasticity. Cell 2014; 157:110-9. [PMID: 24679530 DOI: 10.1016/j.cell.2014.02.041] [Citation(s) in RCA: 186] [Impact Index Per Article: 18.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2014] [Revised: 02/20/2014] [Accepted: 02/24/2014] [Indexed: 12/30/2022]
Abstract
Cell differentiation is an essential process for the development, growth, reproduction, and longevity of all multicellular organisms, and its regulation has been the focus of intense investigation for the past four decades. The study of natural and induced stem cells has ushered an age of re-examination of what it means to be a stem or a differentiated cell. Past and recent discoveries in plants and animals, as well as novel experimental manipulations, are beginning to erode many of these established concepts and are forcing a re-evaluation of the experimental systems and paradigms presently being used to explore these and other biological process.
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Affiliation(s)
| | - Shinya Yamanaka
- Center for iPS Cell Research and Application (CiRA), Kyoto University, Kyoto 606-8507, Japan; Gladstone Institute of Cardiovascular Disease, San Francisco, CA 94158, USA.
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112
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Almuedo-Castillo M, Crespo X, Seebeck F, Bartscherer K, Salò E, Adell T. JNK controls the onset of mitosis in planarian stem cells and triggers apoptotic cell death required for regeneration and remodeling. PLoS Genet 2014; 10:e1004400. [PMID: 24922054 PMCID: PMC4055413 DOI: 10.1371/journal.pgen.1004400] [Citation(s) in RCA: 74] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2013] [Accepted: 04/09/2014] [Indexed: 01/18/2023] Open
Abstract
Regeneration of lost tissues depends on the precise interpretation of molecular signals that control and coordinate the onset of proliferation, cellular differentiation and cell death. However, the nature of those molecular signals and the mechanisms that integrate the cellular responses remain largely unknown. The planarian flatworm is a unique model in which regeneration and tissue renewal can be comprehensively studied in vivo. The presence of a population of adult pluripotent stem cells combined with the ability to decode signaling after wounding enable planarians to regenerate a complete, correctly proportioned animal within a few days after any kind of amputation, and to adapt their size to nutritional changes without compromising functionality. Here, we demonstrate that the stress-activated c-jun-NH2-kinase (JNK) links wound-induced apoptosis to the stem cell response during planarian regeneration. We show that JNK modulates the expression of wound-related genes, triggers apoptosis and attenuates the onset of mitosis in stem cells specifically after tissue loss. Furthermore, in pre-existing body regions, JNK activity is required to establish a positive balance between cell death and stem cell proliferation to enable tissue renewal, remodeling and the maintenance of proportionality. During homeostatic degrowth, JNK RNAi blocks apoptosis, resulting in impaired organ remodeling and rescaling. Our findings indicate that JNK-dependent apoptotic cell death is crucial to coordinate tissue renewal and remodeling required to regenerate and to maintain a correctly proportioned animal. Hence, JNK might act as a hub, translating wound signals into apoptotic cell death, controlled stem cell proliferation and differentiation, all of which are required to coordinate regeneration and tissue renewal.
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Affiliation(s)
- María Almuedo-Castillo
- Department of Genetics and Institute of Biomedicine, University of Barcelona, Barcelona, Catalonia, Spain
| | - Xenia Crespo
- Department of Genetics and Institute of Biomedicine, University of Barcelona, Barcelona, Catalonia, Spain
| | - Florian Seebeck
- Max Planck Research Group Stem Cells and Regeneration, Max Planck Institute for Molecular Biomedicine, Münster, Germany
- Faculty of Medicine, University of Münster, Münster, Germany
| | - Kerstin Bartscherer
- Max Planck Research Group Stem Cells and Regeneration, Max Planck Institute for Molecular Biomedicine, Münster, Germany
- Faculty of Medicine, University of Münster, Münster, Germany
| | - Emili Salò
- Department of Genetics and Institute of Biomedicine, University of Barcelona, Barcelona, Catalonia, Spain
| | - Teresa Adell
- Department of Genetics and Institute of Biomedicine, University of Barcelona, Barcelona, Catalonia, Spain
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113
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Hou J, Luo X, Wang S, Yin C, Zhang S, Zhu X, Dou Y, Cai X. Sequence analysis and molecular characterization of Wnt4 gene in metacestodes of Taenia solium. THE KOREAN JOURNAL OF PARASITOLOGY 2014; 52:163-8. [PMID: 24850959 PMCID: PMC4028453 DOI: 10.3347/kjp.2014.52.2.163] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/24/2013] [Revised: 02/04/2014] [Accepted: 02/24/2014] [Indexed: 11/23/2022]
Abstract
Wnt proteins are a family of secreted glycoproteins that are evolutionarily conserved and considered to be involved in extensive developmental processes in metazoan organisms. The characterization of wnt genes may improve understanding the parasite's development. In the present study, a wnt4 gene encoding 491amino acids was amplified from cDNA of metacestodes of Taenia solium using reverse transcription PCR (RT-PCR). Bioinformatics tools were used for sequence analysis. The conserved domain of the wnt gene family was predicted. The expression profile of Wnt4 was investigated using real-time PCR. Wnt4 expression was found to be dramatically increased in scolex evaginated cysticerci when compared to invaginated cysticerci. In situ hybridization showed that wnt4 gene was distributed in the posterior end of the worm along the primary body axis in evaginated cysticerci. These findings indicated that wnt4 may take part in the process of cysticerci evagination and play a role in scolex/bladder development of cysticerci of T. solium.
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Affiliation(s)
- Junling Hou
- State Key Laboratory of Veterinary Etiological Biology, Key Laboratory of Veterinary Parasitology of Gansu Province, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, Gansu, P. R. China
| | - Xuenong Luo
- State Key Laboratory of Veterinary Etiological Biology, Key Laboratory of Veterinary Parasitology of Gansu Province, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, Gansu, P. R. China
| | - Shuai Wang
- State Key Laboratory of Veterinary Etiological Biology, Key Laboratory of Veterinary Parasitology of Gansu Province, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, Gansu, P. R. China
| | - Cai Yin
- State Key Laboratory of Veterinary Etiological Biology, Key Laboratory of Veterinary Parasitology of Gansu Province, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, Gansu, P. R. China
| | - Shaohua Zhang
- State Key Laboratory of Veterinary Etiological Biology, Key Laboratory of Veterinary Parasitology of Gansu Province, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, Gansu, P. R. China
| | - Xueliang Zhu
- State Key Laboratory of Veterinary Etiological Biology, Key Laboratory of Veterinary Parasitology of Gansu Province, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, Gansu, P. R. China
| | - Yongxi Dou
- State Key Laboratory of Veterinary Etiological Biology, Key Laboratory of Veterinary Parasitology of Gansu Province, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, Gansu, P. R. China
| | - Xuepeng Cai
- State Key Laboratory of Veterinary Etiological Biology, Key Laboratory of Veterinary Parasitology of Gansu Province, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, Gansu, P. R. China
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114
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Adler CE, Seidel CW, McKinney SA, Sánchez Alvarado A. Selective amputation of the pharynx identifies a FoxA-dependent regeneration program in planaria. eLife 2014; 3:e02238. [PMID: 24737865 PMCID: PMC3985184 DOI: 10.7554/elife.02238] [Citation(s) in RCA: 97] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2014] [Accepted: 03/07/2014] [Indexed: 01/08/2023] Open
Abstract
Planarian flatworms regenerate every organ after amputation. Adult pluripotent stem cells drive this ability, but how injury activates and directs stem cells into the appropriate lineages is unclear. Here we describe a single-organ regeneration assay in which ejection of the planarian pharynx is selectively induced by brief exposure of animals to sodium azide. To identify genes required for pharynx regeneration, we performed an RNAi screen of 356 genes upregulated after amputation, using successful feeding as a proxy for regeneration. We found that knockdown of 20 genes caused a wide range of regeneration phenotypes and that RNAi of the forkhead transcription factor FoxA, which is expressed in a subpopulation of stem cells, specifically inhibited regrowth of the pharynx. Selective amputation of the pharynx therefore permits the identification of genes required for organ-specific regeneration and suggests an ancient function for FoxA-dependent transcriptional programs in driving regeneration. DOI: http://dx.doi.org/10.7554/eLife.02238.001.
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Affiliation(s)
- Carolyn E Adler
- Stowers Institute for Medical Research, Kansas City, United States
| | - Chris W Seidel
- Stowers Institute for Medical Research, Kansas City, United States
| | - Sean A McKinney
- Stowers Institute for Medical Research, Kansas City, United States
| | - Alejandro Sánchez Alvarado
- Stowers Institute for Medical Research, Kansas City, United States
- Howard Hughes Medical Institute, Stowers Institute for Medical Research, Kansas City, United States
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115
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Fraguas S, Barberán S, Iglesias M, Rodríguez-Esteban G, Cebrià F. egr-4, a target of EGFR signaling, is required for the formation of the brain primordia and head regeneration in planarians. Development 2014; 141:1835-47. [PMID: 24700819 DOI: 10.1242/dev.101345] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
During the regeneration of freshwater planarians, polarity and patterning programs play essential roles in determining whether a head or a tail regenerates at anterior or posterior-facing wounds. This decision is made very soon after amputation. The pivotal role of the Wnt/β-catenin and Hh signaling pathways in re-establishing anterior-posterior (AP) polarity has been well documented. However, the mechanisms that control the growth and differentiation of the blastema in accordance with its AP identity are less well understood. Previous studies have described a role of Smed-egfr-3, a planarian epidermal growth factor receptor, in blastema growth and differentiation. Here, we identify Smed-egr-4, a zinc-finger transcription factor belonging to the early growth response gene family, as a putative downstream target of Smed-egfr-3. Smed-egr-4 is mainly expressed in the central nervous system and its silencing inhibits anterior regeneration without affecting the regeneration of posterior regions. Single and combinatorial RNA interference to target different elements of the Wnt/β-catenin pathway, together with expression analysis of brain- and anterior-specific markers, revealed that Smed-egr-4: (1) is expressed in two phases - an early Smed-egfr-3-independent phase and a late Smed-egfr-3-dependent phase; (2) is necessary for the differentiation of the brain primordia in the early stages of regeneration; and (3) that it appears to antagonize the activity of the Wnt/β-catenin pathway to allow head regeneration. These results suggest that a conserved EGFR/egr pathway plays an important role in cell differentiation during planarian regeneration and indicate an association between early brain differentiation and the proper progression of head regeneration.
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Affiliation(s)
- Susanna Fraguas
- Departament de Genètica de la Universitat de Barcelona and Institut de Biomedicina de la Universitat de Barcelona (IBUB), Avenida Diagonal 643, Edifici Prevosti planta 1, Barcelona 08028, Spain
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116
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Vogg MC, Owlarn S, Pérez Rico YA, Xie J, Suzuki Y, Gentile L, Wu W, Bartscherer K. Stem cell-dependent formation of a functional anterior regeneration pole in planarians requires Zic and Forkhead transcription factors. Dev Biol 2014; 390:136-48. [PMID: 24704339 DOI: 10.1016/j.ydbio.2014.03.016] [Citation(s) in RCA: 65] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2013] [Revised: 03/24/2014] [Accepted: 03/25/2014] [Indexed: 11/20/2022]
Abstract
Planarians can regenerate their head within days. This process depends on the direction of adult stem cells to wound sites and the orchestration of their progenitors to commit to appropriate lineages and to arrange into patterned tissues. We identified a zinc finger transcription factor, Smed-ZicA, as a downstream target of Smed-FoxD, a Forkhead transcription factor required for head regeneration. Smed-zicA and Smed-FoxD are co-expressed with the Wnt inhibitor notum and the Activin inhibitor follistatin in a cluster of cells at the anterior-most tip of the regenerating head - the anterior regeneration pole - and in surrounding stem cell progeny. Depletion of Smed-zicA and Smed-FoxD by RNAi abolishes notum and follistatin expression at the pole and inhibits head formation downstream of initial polarity decisions. We suggest a model in which ZicA and FoxD transcription factors synergize to control the formation of Notum- and Follistatin-producing anterior pole cells. Pole formation might constitute an early step in regeneration, resulting in a signaling center that orchestrates cellular events in the growing tissue.
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Affiliation(s)
- Matthias C Vogg
- Max Planck Research Group Stem Cells & Regeneration, Max Planck Institute for Molecular Biomedicine, Von-Esmarch-Str. 54, 48149 Münster, Germany; Medical Faculty, University of Münster, Albert-Schweitzer-Campus 1, 48149 Münster, Germany
| | - Suthira Owlarn
- Max Planck Research Group Stem Cells & Regeneration, Max Planck Institute for Molecular Biomedicine, Von-Esmarch-Str. 54, 48149 Münster, Germany; Medical Faculty, University of Münster, Albert-Schweitzer-Campus 1, 48149 Münster, Germany; CiM-IMPRS Graduate School, Schlossplatz 5, 48149 Münster, Germany
| | - Yuvia A Pérez Rico
- Max Planck Research Group Stem Cells & Regeneration, Max Planck Institute for Molecular Biomedicine, Von-Esmarch-Str. 54, 48149 Münster, Germany; Medical Faculty, University of Münster, Albert-Schweitzer-Campus 1, 48149 Münster, Germany
| | - Jianlei Xie
- MOE Key Laboratory of Protein Science, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Yoko Suzuki
- CiM-IMPRS Graduate School, Schlossplatz 5, 48149 Münster, Germany; Planarian Stem Cell Laboratory, Max Planck Institute for Molecular Biomedicine, Von-Esmarch-Str. 54, 48149 Münster, Germany
| | - Luca Gentile
- Planarian Stem Cell Laboratory, Max Planck Institute for Molecular Biomedicine, Von-Esmarch-Str. 54, 48149 Münster, Germany
| | - Wei Wu
- MOE Key Laboratory of Protein Science, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Kerstin Bartscherer
- Max Planck Research Group Stem Cells & Regeneration, Max Planck Institute for Molecular Biomedicine, Von-Esmarch-Str. 54, 48149 Münster, Germany; Medical Faculty, University of Münster, Albert-Schweitzer-Campus 1, 48149 Münster, Germany.
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117
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Lin AYT, Pearson BJ. Planarian yorkie/YAP functions to integrate adult stem cell proliferation, organ homeostasis and maintenance of axial patterning. Development 2014; 141:1197-208. [PMID: 24523458 DOI: 10.1242/dev.101915] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
During adult homeostasis and regeneration, the freshwater planarian must accomplish a constant balance between cell proliferation and cell death, while also maintaining proper tissue and organ size and patterning. How these ordered processes are precisely modulated remains relatively unknown. Here we show that planarians use the downstream effector of the Hippo signaling cascade, yorkie (yki; YAP in vertebrates) to control a diverse set of pleiotropic processes in organ homeostasis, stem cell regulation, regeneration and axial patterning. We show that yki functions to maintain the homeostasis of the planarian excretory (protonephridial) system and to limit stem cell proliferation, but does not affect the differentiation process or cell death. Finally, we show that Yki acts synergistically with WNT/β-catenin signaling to repress head determination by limiting the expression domains of posterior WNT genes and that of the WNT-inhibitor notum. Together, our data show that yki is a key gene in planarians that integrates stem cell proliferation control, organ homeostasis, and the spatial patterning of tissues.
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Affiliation(s)
- Alexander Y T Lin
- The Hospital for Sick Children, Program in Developmental and Stem Cell Biology, Toronto, ON M5G 1X8, Canada
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118
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Scimone ML, Lapan SW, Reddien PW. A forkhead transcription factor is wound-induced at the planarian midline and required for anterior pole regeneration. PLoS Genet 2014; 10:e1003999. [PMID: 24415944 PMCID: PMC3886891 DOI: 10.1371/journal.pgen.1003999] [Citation(s) in RCA: 66] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2013] [Accepted: 10/19/2013] [Indexed: 11/30/2022] Open
Abstract
Planarian regeneration requires positional information to specify the identity of tissues to be replaced as well as pluripotent neoblasts capable of differentiating into new cell types. We found that wounding elicits rapid expression of a gene encoding a Forkhead-family transcription factor, FoxD. Wound-induced FoxD expression is specific to the ventral midline, is regulated by Hedgehog signaling, and is neoblast-independent. FoxD is subsequently expressed within a medial subpopulation of neoblasts at wounds involving head regeneration. Ultimately, FoxD is co-expressed with multiple anterior markers at the anterior pole. Inhibition of FoxD with RNA interference (RNAi) results in the failure to specify neoblasts expressing anterior markers (notum and prep) and in anterior pole formation defects. FoxD(RNAi) animals fail to regenerate a new midline and to properly pattern the anterior blastema, consistent with a role for the anterior pole in organizing pattern of the regenerating head. Our results suggest that wound signaling activates a forkhead transcription factor at the midline and, if the head is absent, FoxD promotes specification of neoblasts at the prior midline for anterior pole regeneration. Regeneration is widespread in the animal kingdom. Planarians are able to regenerate entire bodies from almost any fragment type. This ability requires a cell population called neoblasts, which include pluripotent stem cells, for the production of all missing tissues, as well as the information to form and pattern correct new tissue types. Two discrete regions of the body, called poles, are found at the anterior and posterior ends of the animal. Here we investigate the role of a gene encoding a Forkhead-family transcription factor, FoxD, in formation of the anterior pole. FoxD is expressed at the anterior pole and following injury, FoxD expression is induced in a restricted midline region of the animal. Next, FoxD is expressed in a subset of neoblasts at the midline. Inhibition of FoxD with RNA interference results in defective anterior pole regeneration, and subsequent failure to regenerate an organized head pattern around a new midline. FoxD is specifically required for anterior regeneration. These results suggest that there is a regenerative connection between the midline and the anterior pole.
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Affiliation(s)
- M Lucila Scimone
- Howard Hughes Medical Institute, MIT Biology and Whitehead Institute for Biomedical Research, Cambridge, Massachusetts, United States of America
| | - Sylvain W Lapan
- Howard Hughes Medical Institute, MIT Biology and Whitehead Institute for Biomedical Research, Cambridge, Massachusetts, United States of America
| | - Peter W Reddien
- Howard Hughes Medical Institute, MIT Biology and Whitehead Institute for Biomedical Research, Cambridge, Massachusetts, United States of America
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119
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Kao D, Felix D, Aboobaker A. The planarian regeneration transcriptome reveals a shared but temporally shifted regulatory program between opposing head and tail scenarios. BMC Genomics 2013; 14:797. [PMID: 24238224 PMCID: PMC4046745 DOI: 10.1186/1471-2164-14-797] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2013] [Accepted: 11/11/2013] [Indexed: 12/31/2022] Open
Abstract
BACKGROUND Planarians can regenerate entire animals from a small fragment of the body. The regenerating fragment is able to create new tissues and remodel existing tissues to form a complete animal. Thus different fragments with very different starting components eventually converge on the same solution. In this study, we performed an extensive RNA-seq time-course on regenerating head and tail fragments to observe the differences and similarities of the transcriptional landscape between head and tail fragments during regeneration. RESULTS We have consolidated existing transcriptomic data for S. mediterranea to generate a high confidence set of transcripts for use in genome wide expression studies. We performed a RNA-seq time-course on regenerating head and tail fragments from 0 hours to 3 days. We found that the transcriptome profiles of head and tail regeneration were very different at the start of regeneration; however, an unexpected convergence of transcriptional profiles occurred at 48 hours when head and tail fragments are still morphologically distinct. By comparing differentially expressed transcripts at various time-points, we revealed that this divergence/convergence pattern is caused by a shared regulatory program that runs early in heads and later in tails.Additionally, we also performed RNA-seq on smed-prep(RNAi) tail fragments which ultimately fail to regenerate anterior structures. We find the gene regulation program in response to smed-prep(RNAi) to display the opposite regulatory trend compared to the previously mentioned share regulatory program during regeneration. Using annotation data and comparative approaches, we also identified a set of approximately 4,800 triclad specific transcripts that were enriched amongst the genes displaying differential expression during the regeneration time-course. CONCLUSION The regeneration transcriptome of head and tail regeneration provides us with a rich resource for investigating the global expression changes that occurs during regeneration. We show that very different regenerative scenarios utilize a shared core regenerative program. Furthermore, our consolidated transcriptome and annotations allowed us to identity triclad specific transcripts that are enriched within this core regulatory program. Our data support the hypothesis that both conserved aspects of animal developmental programs and recent evolutionarily innovations work in concert to control regeneration.
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Affiliation(s)
- Damian Kao
- />School of Life Sciences, University of Nottingham, University Park, Nottingham, NG7 2RD UK
| | - Daniel Felix
- />Fundación CNIC Carlos III- Centro Nacional de Investigaciones Cardiovasculares, Melchor Fernández Almagro, 3, Madrid, Código Postal 28029 Spain
| | - Aziz Aboobaker
- />Department of Zoology, University of Oxford, The Tinbergen Building, South Parks Road, Oxford, OX1 3PS UK
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120
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Gaviño MA, Wenemoser D, Wang IE, Reddien PW. Tissue absence initiates regeneration through follistatin-mediated inhibition of activin signaling. eLife 2013; 2:e00247. [PMID: 24040508 PMCID: PMC3771573 DOI: 10.7554/elife.00247] [Citation(s) in RCA: 76] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2012] [Accepted: 08/07/2013] [Indexed: 12/22/2022] Open
Abstract
Regeneration is widespread, but mechanisms that activate regeneration remain mysterious. Planarians are capable of whole-body regeneration and mount distinct molecular responses to wounds that result in tissue absence and those that do not. A major question is how these distinct responses are activated. We describe a follistatin homolog (Smed-follistatin) required for planarian regeneration. Smed-follistatin inhibition blocks responses to tissue absence but does not prevent normal tissue turnover. Two activin homologs (Smed-activin-1 and Smed-activin-2) are required for the Smed-follistatin phenotype. Finally, Smed-follistatin is wound-induced and expressed at higher levels following injuries that cause tissue absence. These data suggest that Smed-follistatin inhibits Smed-Activin proteins to trigger regeneration specifically following injuries involving tissue absence and identify a mechanism critical for regeneration initiation, a process important across the animal kingdom. DOI:http://dx.doi.org/10.7554/eLife.00247.001.
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Affiliation(s)
- Michael A Gaviño
- Department of Biology, Howard Hughes Medical Institute, Whitehead Institute, Massachusetts Institute of Technology, Cambridge, United States
| | - Danielle Wenemoser
- Department of Biology, Howard Hughes Medical Institute, Whitehead Institute, Massachusetts Institute of Technology, Cambridge, United States
| | - Irving E Wang
- Department of Biology, Howard Hughes Medical Institute, Whitehead Institute, Massachusetts Institute of Technology, Cambridge, United States
| | - Peter W Reddien
- Department of Biology, Howard Hughes Medical Institute, Whitehead Institute, Massachusetts Institute of Technology, Cambridge, United States
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121
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Witchley JN, Mayer M, Wagner DE, Owen JH, Reddien PW. Muscle cells provide instructions for planarian regeneration. Cell Rep 2013; 4:633-41. [PMID: 23954785 PMCID: PMC4101538 DOI: 10.1016/j.celrep.2013.07.022] [Citation(s) in RCA: 163] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2013] [Revised: 06/24/2013] [Accepted: 07/17/2013] [Indexed: 12/11/2022] Open
Abstract
Regeneration requires both potential and instructions for tissue replacement. In planarians, pluripotent stem cells have the potential to produce all new tissue. The identities of the cells that provide regeneration instructions are unknown. Here, we report that position control genes (PCGs) that control regeneration and tissue turnover are expressed in a subepidermal layer of nonneoblast cells. These subepidermal cells coexpress many PCGs. We propose that these subepidermal cells provide a system of body coordinates and positional information for regeneration, and identify them to be muscle cells of the planarian body wall. Almost all planarian muscle cells express PCGs, suggesting a dual function: contraction and control of patterning. PCG expression is dynamic in muscle cells after injury, even in the absence of neoblasts, suggesting that muscle is instructive for regeneration. We conclude that planarian regeneration involves two highly flexible systems: pluripotent neoblasts that can generate any new cell type and muscle cells that provide positional instructions for the regeneration of any body region.
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Affiliation(s)
- Jessica N Witchley
- Howard Hughes Medical Institute, 4000 Jones Bridge Road, Chevy Chase, MD 20815, USA
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122
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Generation of hair cells in neonatal mice by β-catenin overexpression in Lgr5-positive cochlear progenitors. Proc Natl Acad Sci U S A 2013; 110:13851-6. [PMID: 23918377 DOI: 10.1073/pnas.1219952110] [Citation(s) in RCA: 139] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Mammalian hair cells do not regenerate, and their loss is a major cause of deafness. We recently identified leucine-rich repeat containing, G-protein-coupled receptor 5 (Lgr5)-expressing cochlear supporting cells with the capacity for self-renewal and hair cell differentiation in vitro. We found that these cells, a subset of cochlear supporting cells, were responsive to Wnt signaling. Here we asked whether these Lgr5-positive cells, despite their lack of contribution to hair cell replacement after degenerative loss, could be driven by forced expression of β-catenin to act as hair cell progenitors in vivo. We showed that forced stabilization of β-catenin in supporting cells in neonatal animals resulted in proliferation of supporting cells and generation of hair cells. Although β-catenin expression was increased by genetic means in all supporting cells, entry to the cell cycle and differentiation to hair cells of the normally postmitotic cells was restricted to the Lgr5-positive population. Our finding suggests that Wnt/β-catenin can drive Lgr5-positive cells to act as hair cell progenitors, even after their exit from the cell cycle and apparent establishment of cell fate.
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123
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Currie KW, Pearson BJ. Transcription factors lhx1/5-1 and pitx are required for the maintenance and regeneration of serotonergic neurons in planarians. Development 2013; 140:3577-88. [PMID: 23903188 DOI: 10.1242/dev.098590] [Citation(s) in RCA: 90] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
In contrast to most adult organisms, freshwater planarians can regenerate any injured body part, including their entire nervous system. This allows for the analysis of genes required for both the maintenance and regeneration of specific neural subtypes. In addition, the loss of specific neural subtypes may uncover previously unknown behavioral roles for that neural population in the context of the adult animal. Here we show that two homeodomain transcription factor homologs, Smed-lhx1/5-1 and Smed-pitx, are required for the maintenance and regeneration of serotonergic neurons in planarians. When either lhx1/5-1 or pitx was knocked down by RNA interference, the expression of multiple canonical markers for serotonergic neurons was lost. Surprisingly, the loss of serotonergic function uncovered a role for these neurons in the coordination of motile cilia on the ventral epidermis of planarians that are required for their nonmuscular gliding locomotion. Finally, we show that in addition to its requirement in serotonergic neurons, Smed-pitx is required for proper midline patterning during regeneration, when it is required for the expression of the midline-organizing molecules Smed-slit in the anterior and Smed-wnt1 in the posterior.
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Affiliation(s)
- Ko W Currie
- Hospital for Sick Children, Program in Developmental and Stem Cell Biology, Toronto, ON, Canada
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124
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Restoration of anterior regeneration in a planarian with limited regenerative ability. Nature 2013; 500:77-80. [PMID: 23883929 PMCID: PMC3812084 DOI: 10.1038/nature12403] [Citation(s) in RCA: 104] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2012] [Accepted: 06/21/2013] [Indexed: 12/12/2022]
Abstract
Variability of regenerative potential among animals has long perplexed biologists. On the basis of their exceptional regenerative abilities, planarians have become important models for understanding the molecular basis of regeneration. However, planarian species with limited regenerative abilities are also found. Despite the importance of understanding the differences between closely related, regenerating and non-regenerating organisms, few studies have focused on the evolutionary loss of regeneration, and the molecular mechanisms leading to such regenerative loss remain obscure. Here we examine Procotyla fluviatilis, a planarian with restricted ability to replace missing tissues, using next-generation sequencing to define the gene expression programs active in regeneration-permissive and regeneration-deficient tissues. We found that Wnt signalling is aberrantly activated in regeneration-deficient tissues. Notably, downregulation of canonical Wnt signalling in regeneration-deficient regions restores regenerative abilities: blastemas form and new heads regenerate in tissues that normally never regenerate. This work reveals that manipulating a single signalling pathway can reverse the evolutionary loss of regenerative potential.
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125
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Reactivating head regrowth in a regeneration-deficient planarian species. Nature 2013; 500:81-4. [PMID: 23883932 DOI: 10.1038/nature12414] [Citation(s) in RCA: 123] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2012] [Accepted: 06/25/2013] [Indexed: 12/11/2022]
Abstract
Species capable of regenerating lost body parts occur throughout the animal kingdom, yet close relatives are often regeneration incompetent. Why in the face of 'survival of the fittest' some animals regenerate but others do not remains a fascinating question. Planarian flatworms are well known and studied for their ability to regenerate from minute tissue pieces, yet species with limited regeneration abilities have been described even amongst planarians. Here we report the characterization of the regeneration defect in the planarian Dendrocoelum lacteum and its successful rescue. Tissue fragments cut from the posterior half of the body of this species are unable to regenerate a head and ultimately die. We find that this defect originates during the early stages of head specification, which require inhibition of canonical Wnt signalling in other planarian species. Notably, RNA interference (RNAi)-mediated knockdown of Dlac-β-catenin-1, the Wnt signal transducer, restored the regeneration of fully functional heads on tail pieces, rescuing D. lacteum's regeneration defect. Our results demonstrate the utility of comparative studies towards the reactivation of regenerative abilities in regeneration-deficient animals. Furthermore, the availability of D. lacteum as a regeneration-impaired planarian model species provides a first step towards elucidating the evolutionary mechanisms that ultimately determine why some animals regenerate and others do not.
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126
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Abstract
The cephalochordate amphioxus is now established as an important model system for understanding the evolution of vertebrate novelties from an invertebrate chordate ancestor. It is also emerging as a serious candidate for studies of organ regeneration. We extend here our previous observations on the European amphioxus´ extensive adult regenerative capacity. The expression of Wnt5 and the presence of β-catenin protein in the early bud-stage blastema support a role for Wnt signaling during tail regeneration in amphioxus. We also present data showing that Branchiostoma lanceolatum continues to regenerate well after repeated amputation of the post-anal tail. These results are discussed in relation to vertebrate regeneration and other stem cell systems, and in the context of regeneration decline with aging.
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Affiliation(s)
- Ildikó M L Somorjai
- Centre for Organismal Studies; University of Heidelberg; Heidelberg, Germany ; CNRS; UMR7232; Universite Pierre et Marie Curie Paris 06; Observatoire Oceanologique; Banyuls-sur-Mer; Paris, France ; Department de Genètica; Facultat de Biologia; Universitat de Barcelona; Barcelona, Spain
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127
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Elliott SA, Sánchez Alvarado A. The history and enduring contributions of planarians to the study of animal regeneration. WILEY INTERDISCIPLINARY REVIEWS. DEVELOPMENTAL BIOLOGY 2013; 2:301-26. [PMID: 23799578 PMCID: PMC3694279 DOI: 10.1002/wdev.82] [Citation(s) in RCA: 132] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Having an almost unlimited capacity to regenerate tissues lost to age and injury, planarians have long fascinated naturalists. In the Western hemisphere alone, their documented history spans more than 200 years. Planarians were described in the early 19th century as being 'immortal under the edge of the knife', and initial investigation of these remarkable animals was significantly influenced by studies of regeneration in other organisms and from the flourishing field of experimental embryology in the late 19th and early 20th centuries. This review strives to place the study of planarian regeneration into a broader historical context by focusing on the significance and evolution of knowledge in this field. It also synthesizes our current molecular understanding of the mechanisms of planarian regeneration uncovered since this animal's relatively recent entrance into the molecular-genetic age.
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Affiliation(s)
- Sarah A Elliott
- Howard Hughes Medical Institute and Stowers Institute for Medical Research, Kansas City, MO, USA.
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128
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Abstract
Planarians are members of the Platyhelminthes (flatworms). These animals have evolved a remarkable stem cell system. A single pluripotent adult stem cell type ("neoblast") gives rise to the entire range of cell types and organs in the planarian body plan, including a brain, digestive-, excretory-, sensory- and reproductive systems. Neoblasts are abundantly present throughout the mesenchyme and divide continuously. The resulting stream of progenitors and turnover of differentiated cells drive the rapid self-renewal of the entire animal within a matter of weeks. Planarians grow and literally de-grow ("shrink") by the food supply-dependent adjustment of organismal turnover rates, scaling body plan proportions over as much as a 50-fold size range. Their dynamic body architecture further allows astonishing regenerative abilities, including the regeneration of complete and perfectly proportioned animals even from tiny tissue remnants. Planarians as an experimental system, therefore, provide unique opportunities for addressing a spectrum of current problems in stem cell research, including the evolutionary conservation of pluripotency, the dynamic organization of differentiation lineages and the mechanisms underlying organismal stem cell homeostasis. The first part of this review focuses on the molecular biology of neoblasts as pluripotent stem cells. The second part examines the fascinating mechanistic and conceptual challenges posed by a stem cell system that epitomizes a universal design principle of biological systems: the dynamic steady state.
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Affiliation(s)
- Jochen C Rink
- Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, 01307 Dresden, Germany.
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129
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Chen CCG, Wang IE, Reddien PW. pbx is required for pole and eye regeneration in planarians. Development 2013; 140:719-29. [PMID: 23318641 DOI: 10.1242/dev.083741] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Planarian regeneration involves regionalized gene expression that specifies the body plan. After amputation, planarians are capable of regenerating new anterior and posterior poles, as well as tissues polarized along the anterior-posterior, dorsal-ventral and medial-lateral axes. Wnt and several Hox genes are expressed at the posterior pole, whereas Wnt inhibitory genes, Fgf inhibitory genes, and prep, which encodes a TALE-family homeodomain protein, are expressed at the anterior pole. We found that Smed-pbx (pbx for short), which encodes a second planarian TALE-family homeodomain transcription factor, is required for restored expression of these genes at anterior and posterior poles during regeneration. Moreover, pbx(RNAi) animals gradually lose pole gene expression during homeostasis. By contrast, pbx was not required for initial anterior-posterior polarized responses to wounds, indicating that pbx is required after wound responses for development and maintenance of poles during regeneration and homeostatic tissue turnover. Independently of the requirement for pbx in pole regeneration, pbx is required for eye precursor formation and, consequently, eye regeneration and eye replacement in homeostasis. Together, these data indicate that pbx promotes pole formation of body axes and formation of regenerative progenitors for eyes.
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Affiliation(s)
- Chun-Chieh G Chen
- Howard Hughes Medical Institute, MIT Biology, Whitehead Institute for Biomedical Research, Cambridge, MA 02142, USA.
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130
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Blassberg RA, Felix DA, Tejada-Romero B, Aboobaker AA. PBX/extradenticle is required to re-establish axial structures and polarity during planarian regeneration. Development 2013; 140:730-9. [PMID: 23318635 DOI: 10.1242/dev.082982] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Recent advances in a number of systems suggest many genes involved in orchestrating regeneration are redeployed from similar processes in development, with others being novel to the regeneration process in particular lineages. Of particular importance will be understanding the architecture of regenerative genetic regulatory networks and whether they are conserved across broad phylogenetic distances. Here, we describe the role of the conserved TALE class protein PBX/Extradenticle in planarians, a representative member of the Lophotrocozoa. PBX/Extradenticle proteins play central roles in both embryonic and post-embryonic developmental patterning in both vertebrates and insects, and we demonstrate a broad requirement during planarian regeneration. We observe that Smed-pbx has pleiotropic functions during regeneration, with a primary role in patterning the anterior-posterior (AP) axis and AP polarity. Smed-pbx is required for expression of polarity determinants notum and wnt1 and for correct patterning of the structures polarized along the AP axis, such as the brain, pharynx and gut. Overall, our data suggest that Smed-pbx functions as a central integrator of positional information to drive patterning of regeneration along the body axis.
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Affiliation(s)
- Robert A Blassberg
- Department of Zoology, Tinbergen Building, University of Oxford, South Parks Road, Oxford OX1 3PS, UK.
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131
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Follistatin antagonizes activin signaling and acts with notum to direct planarian head regeneration. Proc Natl Acad Sci U S A 2013; 110:1363-8. [PMID: 23297191 DOI: 10.1073/pnas.1214053110] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Animals establish their body plans in embryogenesis, but only a few animals can recapitulate this signaling milieu for regeneration after injury. In planarians, a pluripotent stem cell population and perpetual signaling of polarity axes collaborate to direct a steady replacement of cells during homeostasis and to power robust regeneration after even severe injuries. Several studies have documented the roles of conserved signaling pathways in maintaining and resetting axial polarity in planarians, but it is unclear how planarians reestablish polarity signaling centers after injury and whether these centers serve to influence identity decisions of stem cell progeny during their differentiation. Here we find that a planarian Follistatin homolog directs regeneration of anterior identity by opposing an Activin/ActR-1/Smad2/3 signaling pathway. Follistatin and Notum, a Wnt inhibitor, are mutually required to reestablish an anterior signaling center that expresses both cues. Furthermore, we show that the direction of cells down particular differentiation paths requires regeneration of this anterior signaling center. Just as its amphibian counterpart in the organizer signals body plan and cell fate during embryogenesis, planarian Follistatin promotes reestablishment of anterior polarity during regeneration and influences specification of cell types in the head and beyond.
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132
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Sánchez Alvarado A. Q&A: what is regeneration, and why look to planarians for answers? BMC Biol 2012; 10:88. [PMID: 23136835 PMCID: PMC3493261 DOI: 10.1186/1741-7007-10-88] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2012] [Accepted: 11/02/2012] [Indexed: 02/04/2023] Open
Affiliation(s)
- Alejandro Sánchez Alvarado
- Howard Hughes Medical Institute and Stowers Institute for Medical Research, 1000 E. 50th Street, Kansas City, MO 64110, USA.
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133
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Vij S, Rink JC, Ho HK, Babu D, Eitel M, Narasimhan V, Tiku V, Westbrook J, Schierwater B, Roy S. Evolutionarily ancient association of the FoxJ1 transcription factor with the motile ciliogenic program. PLoS Genet 2012; 8:e1003019. [PMID: 23144623 PMCID: PMC3493443 DOI: 10.1371/journal.pgen.1003019] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2011] [Accepted: 08/22/2012] [Indexed: 01/03/2023] Open
Abstract
It is generally believed that the last eukaryotic common ancestor (LECA) was a unicellular organism with motile cilia. In the vertebrates, the winged-helix transcription factor FoxJ1 functions as the master regulator of motile cilia biogenesis. Despite the antiquity of cilia, their highly conserved structure, and their mechanism of motility, the evolution of the transcriptional program controlling ciliogenesis has remained incompletely understood. In particular, it is presently not known how the generation of motile cilia is programmed outside of the vertebrates, and whether and to what extent the FoxJ1-dependent regulation is conserved. We have performed a survey of numerous eukaryotic genomes and discovered that genes homologous to foxJ1 are restricted only to organisms belonging to the unikont lineage. Using a mis-expression assay, we then obtained evidence of a conserved ability of FoxJ1 proteins from a number of diverse phyletic groups to activate the expression of a host of motile ciliary genes in zebrafish embryos. Conversely, we found that inactivation of a foxJ1 gene in Schmidtea mediterranea, a platyhelminth (flatworm) that utilizes motile cilia for locomotion, led to a profound disruption in the differentiation of motile cilia. Together, all of these findings provide the first evolutionary perspective into the transcriptional control of motile ciliogenesis and allow us to propose a conserved FoxJ1-regulated mechanism for motile cilia biogenesis back to the origin of the metazoans. Cilia are microtubule-based, hair-like organelles that project from the surfaces of eukaryotic cells. Protists use motile cilia for locomotion as well as for sensory perception. In metazoans, motile cilia also function in fluid transport over epithelia, such as in the mammalian lungs. Most vertebrate and some invertebrate cell-types differentiate non-motile primary cilia, which function exclusively in sensory transduction. It is believed that primary cilia arose from motile cilia through the loss of the motility apparatus. Cilia are complex organelles: a large number of proteins are involved in their assembly and maintenance. FoxJ1, a forkhead-domain transcription factor, is the master regulator of motile ciliogenesis in vertebrates. It is not known to what extent this transcriptional control is conserved and how it may have evolved. Here, we document the existence of FoxJ1 orthologs in several eukaryotic groups besides the vertebrates. FoxJ1 proteins from three representative phyla—Placozoa, Platyhelminthes, and Echinodermata—were able to activate the expression of ciliary genes when mis-expressed in zebrafish embryos. Moreover, inactivation of FoxJ1 in planaria (Platyhelminthes) abolished motile cilia differentiation. These results provide new insights into the transcriptional regulation of motile cilia biogenesis outside the vertebrates and demonstrate a remarkable conservation of the activity of FoxJ1.
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Affiliation(s)
- Shubha Vij
- Institute of Molecular and Cell Biology, Proteos, Singapore, Singapore
| | - Jochen C. Rink
- Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany
| | - Hao Kee Ho
- Institute of Molecular and Cell Biology, Proteos, Singapore, Singapore
| | - Deepak Babu
- Institute of Molecular and Cell Biology, Proteos, Singapore, Singapore
- Department of Biological Sciences, National University of Singapore, Singapore, Singapore
- NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore, Singapore, Singapore
| | - Michael Eitel
- ITZ Division of Ecology and Evolution, Stiftung Tierärztliche Hochschule, Hannover, Germany
| | | | - Varnesh Tiku
- Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany
| | - Jody Westbrook
- Department of Molecular and Cell Biology and Center for Integrative Genomics, University of California Berkeley, Berkeley, California, United States of America
| | - Bernd Schierwater
- ITZ Division of Ecology and Evolution, Stiftung Tierärztliche Hochschule, Hannover, Germany
| | - Sudipto Roy
- Institute of Molecular and Cell Biology, Proteos, Singapore, Singapore
- Department of Biological Sciences, National University of Singapore, Singapore, Singapore
- NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore, Singapore, Singapore
- School of Biological Sciences, Nanyang Technological University, Singapore, Singapore
- * E-mail:
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134
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Guedelhoefer OC, Sánchez Alvarado A. Amputation induces stem cell mobilization to sites of injury during planarian regeneration. Development 2012; 139:3510-20. [PMID: 22899852 DOI: 10.1242/dev.082099] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
How adult stem cell populations are recruited for tissue renewal and repair is a fundamental question of biology. Mobilization of stem cells out of their niches followed by correct migration and differentiation at a site of tissue turnover or injury are important requirements for proper tissue maintenance and regeneration. However, we understand little about the mechanisms that control this process, possibly because the best studied vertebrate adult stem cell systems are not readily amenable to in vivo observation. Furthermore, few clear examples of the recruitment of fully potent stem cells, compared with limited progenitors, are known. Here, we show that planarian stem cells directionally migrate to amputation sites during regeneration. We also show that during tissue homeostasis they are stationary. Our study not only uncovers the existence of specific recruitment mechanisms elicited by amputation, but also sets the stage for the systematic characterization of evolutionarily conserved stem cell regulatory processes likely to inform stem cell function and dysfunction in higher organisms, including humans.
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Affiliation(s)
- Otto C Guedelhoefer
- Department of Neurobiology and Anatomy, University of Utah School of Medicine, Salt Lake City, UT 84132, USA
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135
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Guedelhoefer OC, Sánchez Alvarado A. Planarian immobilization, partial irradiation, and tissue transplantation. J Vis Exp 2012:4015. [PMID: 23007410 DOI: 10.3791/4015] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
The planarian, a freshwater flatworm, has proven to be a powerful system for dissecting metazoan regeneration and stem cell biology. Planarian regeneration of any missing or damaged tissues is made possible by adult stem cells termed neoblasts. Although these stem cells have been definitively shown to be pluripotent and singularly capable of reconstituting an entire animal, the heterogeneity within the stem cell population and the dynamics of their cellular behaviors remain largely unresolved. Due to the large number and wide distribution of stem cells throughout the planarian body plan, advanced methods for manipulating subpopulations of stem cells for molecular and functional study in vivo are needed. Tissue transplantation and partial irradiation are two methods by which a subpopulation of planarian stem cells can be isolated for further study. Each technique has distinct advantages. Tissue transplantation allows for the introduction of stem cells, into a naïve host, that are either inherently genetically distinct or have been previously treated pharmacologically. Alternatively, partial irradiation allows for the isolation of stem cells within a host, juxtaposed to tissue devoid of stem cells, without the introduction of a wound or any breech in tissue integrity. Using these two methods, one can investigate the cell autonomous and non-autonomous factors that control stem cell functions, such as proliferation, differentiation, and migration. Both tissue transplantation and partial irradiation have been used historically in defining many of the questions about planarian regeneration that remain under study today. However, these techniques have remained underused due to the laborious and inconsistent nature of previous methods. The protocols presented here represent a large step forward in decreasing the time and effort necessary to reproducibly generate large numbers of grafted or partially irradiated animals with efficacies approaching 100 percent. We cover the culture of large animals, immobilization, preparation for partial irradiation, tissue transplantation, and the optimization of animal recovery. Furthermore, the work described here demonstrates the first application of the partial irradiation method for use with the most widely studied planarian, Schmidtea mediterranea. Additionally, efficient tissue grafting in planaria opens the door for the functional testing of subpopulations of naïve or treated stem cells in repopulation assays, which has long been the gold-standard method of assaying adult stem cell potential in mammals. Broad adoption of these techniques will no doubt lead to a better understanding of the cellular behaviors of adult stem cells during tissue homeostasis and regeneration.
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Affiliation(s)
- Otto C Guedelhoefer
- Department of Neurobiology and Anatomy, University of Utah School of Medicine, Utah, USA
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136
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Wenemoser D, Lapan SW, Wilkinson AW, Bell GW, Reddien PW. A molecular wound response program associated with regeneration initiation in planarians. Genes Dev 2012; 26:988-1002. [PMID: 22549959 DOI: 10.1101/gad.187377.112] [Citation(s) in RCA: 176] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Planarians are capable of regenerating any missing body part and present an attractive system for molecular investigation of regeneration initiation. The gene activation program that occurs at planarian wounds to coordinate regenerative responses remains unknown. We identified a large set of wound-induced genes during regeneration initiation in planarians. Two waves of wound-induced gene expression occurred in differentiated tissues. The first wave includes conserved immediate early genes. Many second-wave genes encode conserved patterning factors required for proper regeneration. Genes of both classes were generally induced by wounding, indicating that a common initial gene expression program is triggered regardless of missing tissue identity. Planarian regeneration uses a population of regenerative cells (neoblasts), including pluripotent stem cells. A class of wound-induced genes was activated directly within neoblasts, including the Runx transcription factor-encoding runt-1 gene. runt-1 was required for specifying different cell types during regeneration, promoting heterogeneity in neoblasts near wounds. Wound-induced gene expression in neoblasts, including that of runt-1, required SRF (serum response factor) and sos-1. Taken together, these data connect wound sensation to the activation of specific cell type regeneration programs in neoblasts. Most planarian wound-induced genes are conserved across metazoans, and identified genes and mechanisms should be important broadly for understanding wound signaling and regeneration initiation.
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Affiliation(s)
- Danielle Wenemoser
- Howard Hughes Medical Institute, Whitehead Institute, Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02142, USA
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137
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Abstract
Wnt genes are important regulators of embryogenesis and cell differentiation in vertebrates and insects. New data revealed by comparative genomics have now shown that members of the Wnt signaling pathway can be found in all clades of metazoans, but not in fungi, plants, or unicellular eukaryotes. This article focuses on new data from recent genomic analyses of several basal metazoan organisms, providing evidence that the Wnt pathway was a primordial signaling pathway during evolution. The formation of a Wnt signaling center at the site of gastrulation was instrumental for the formation of a primary, anterior-posterior body axis, which can be traced throughout animal evolution.
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Affiliation(s)
- Thomas W Holstein
- Department of Molecular Evolution and Genomics, Centre for Organismal Studies, Heidelberg University, D-69120 Heidelberg, Germany.
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138
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Abstract
Regeneration of complex structures after injury requires dramatic changes in cellular behavior. Regenerating tissues initiate a program that includes diverse processes such as wound healing, cell death, dedifferentiation, and stem (or progenitor) cell proliferation; furthermore, newly regenerated tissues must integrate polarity and positional identity cues with preexisting body structures. Gene knockdown approaches and transgenesis-based lineage and functional analyses have been instrumental in deciphering various aspects of regenerative processes in diverse animal models for studying regeneration.
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Affiliation(s)
- Ryan S King
- Howard Hughes Medical Institute, Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
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139
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Three decades of Wnts: a personal perspective on how a scientific field developed. EMBO J 2012; 31:2670-84. [PMID: 22617420 DOI: 10.1038/emboj.2012.146] [Citation(s) in RCA: 308] [Impact Index Per Article: 25.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2012] [Accepted: 04/24/2012] [Indexed: 12/13/2022] Open
Abstract
Wnt genes and components of Wnt signalling pathways have been implicated in a wide spectrum of important biological phenomena, ranging from early organismal development to cell behaviours to several diseases, especially cancers. Emergence of the field of Wnt signalling can be largely traced back to the discovery of the first mammalian Wnt gene in 1982. In this essay, we mark the thirtieth anniversary of that discovery by describing some of the critical scientific developments that led to the flowering of this field of research.
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140
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Abstract
A mechanistic understanding of robust self-assembly and repair capabilities of complex systems would have enormous implications for basic evolutionary developmental biology as well as for transformative applications in regenerative biomedicine and the engineering of highly fault-tolerant cybernetic systems. Molecular biologists are working to identify the pathways underlying the remarkable regenerative abilities of model species that perfectly regenerate limbs, brains, and other complex body parts. However, a profound disconnect remains between the deluge of high-resolution genetic and protein data on pathways required for regeneration, and the desired spatial, algorithmic models that show how self-monitoring and growth control arise from the synthesis of cellular activities. This barrier to progress in the understanding of morphogenetic controls may be breached by powerful techniques from the computational sciences-using non-traditional modeling approaches to reverse-engineer systems such as planaria: flatworms with a complex bodyplan and nervous system that are able to regenerate any body part after traumatic injury. Currently, the involvement of experts from outside of molecular genetics is hampered by the specialist literature of molecular developmental biology: impactful collaborations across such different fields require that review literature be available that presents the key functional capabilities of important biological model systems while abstracting away from the often irrelevant and confusing details of specific genes and proteins. To facilitate modeling efforts by computer scientists, physicists, engineers, and mathematicians, we present a different kind of review of planarian regeneration. Focusing on the main patterning properties of this system, we review what is known about the signal exchanges that occur during regenerative repair in planaria and the cellular mechanisms that are thought to underlie them. By establishing an engineering-like style for reviews of the molecular developmental biology of biomedically important model systems, significant fresh insights and quantitative computational models will be developed by new collaborations between biology and the information sciences.
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Affiliation(s)
| | | | - Michael Levin
- Center for Regenerative and Developmental Biology, and Department of Biology, Tufts University, Medford, Massachusetts, United States of America
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141
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Peiris TH, Oviedo NJ. Gap junction proteins: master regulators of the planarian stem cell response to tissue maintenance and injury. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2012; 1828:109-17. [PMID: 22450236 DOI: 10.1016/j.bbamem.2012.03.005] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/23/2011] [Revised: 02/24/2012] [Accepted: 03/09/2012] [Indexed: 11/26/2022]
Abstract
Gap junction (GJ) proteins are crucial mediators of cell-cell communication during embryogenesis, tissue regeneration and disease. GJ proteins form plasma membrane channels that facilitate passage of small molecules across cells and modulate signaling pathways and cellular behavior in different tissues. These properties have been conserved throughout evolution, and in most invertebrates GJ proteins are known as innexins. Despite their critical relevance for physiology and disease, the mechanisms by which GJ proteins modulate cell behavior are poorly understood. This review summarizes findings from recent work that uses planarian flatworms as a paradigm to analyze GJ proteins in the complexity of the whole organism. The planarian model allows access to a large pool of adult somatic stem cells (known as neoblasts) that support physiological cell turnover and tissue regeneration. Innexin proteins are present in planarians and play a fundamental role in controlling neoblast behavior. We discuss the possibility that GJ proteins participate as cellular sensors that inform neoblasts about local and systemic physiological demands. We believe that functional analyses of GJ proteins will bring a complementary perspective to studies that focus on the temporal expression of genes. Finally, integrating functional studies along with molecular genetics and epigenetic approaches would expand our understanding of cellular regulation in vivo and greatly enhance the possibilities for rationally modulating stem cell behavior in their natural environment. This article is part of a Special Issue entitled: The communicating junctions, roles and dysfunctions.
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Affiliation(s)
- T Harshani Peiris
- Department of Molecular and Cell Biology, University of California, Merced, CA 95343, USA
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142
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Peiris TH, Weckerle F, Ozamoto E, Ramirez D, Davidian D, García-Ojeda ME, Oviedo NJ. TOR signaling regulates planarian stem cells and controls localized and organismal growth. J Cell Sci 2012; 125:1657-65. [PMID: 22427692 DOI: 10.1242/jcs.104711] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
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.
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Affiliation(s)
- T Harshani Peiris
- Department of Molecular and Cell Biology, School of Natural Sciences, University of California at Merced, Merced, CA 95343, USA
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143
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TORC1 is required to balance cell proliferation and cell death in planarians. Dev Biol 2012; 365:458-69. [PMID: 22445864 PMCID: PMC3367000 DOI: 10.1016/j.ydbio.2012.03.010] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2012] [Revised: 02/24/2012] [Accepted: 03/11/2012] [Indexed: 11/24/2022]
Abstract
Multicellular organisms are equipped with cellular mechanisms that enable them to replace differentiated cells lost to normal physiological turnover, injury, and for some such as planarians, even amputation. This process of tissue homeostasis is generally mediated by adult stem cells (ASCs), tissue-specific stem cells responsible for maintaining anatomical form and function. To do so, ASCs must modulate the balance between cell proliferation, i.e. in response to nutrients, and that of cell death, i.e. in response to starvation or injury. But how these two antagonistic processes are coordinated remains unclear. Here, we explore the role of the core components of the TOR pathway during planarian tissue homeostasis and regeneration and identified an essential function for TORC1 in these two processes. RNAi-mediated silencing of TOR in intact animals resulted in a significant increase in cell death, whereas stem cell proliferation and stem cell maintenance were unaffected. Amputated animals failed to increase stem cell proliferation after wounding and displayed defects in tissue remodeling. Together, our findings suggest two distinct roles for TORC1 in planarians. TORC1 is required to modulate the balance between cell proliferation and cell death during normal cell turnover and in response to nutrients. In addition, it is required to initiate appropriate stem cell proliferation during regeneration and for proper tissue remodeling to occur to maintain scale and proportion.
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144
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Opposing roles of voltage-gated Ca2+ channels in neuronal control of regenerative patterning. J Neurosci 2011; 31:15983-95. [PMID: 22049441 DOI: 10.1523/jneurosci.3029-11.2011] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
There is intense interest in developing methods to regulate proliferation and differentiation of stem cells into neuronal fates for the purposes of regenerative medicine. One way to do this is through in vivo pharmacological engineering using small molecules. However, a key challenge is identification of relevant signaling pathways and therein druggable targets to manipulate stem cell behavior efficiently in vivo. Here, we use the planarian flatworm as a simple chemical-genetic screening model for nervous system regeneration to show that the isoquinoline drug praziquantel (PZQ) acts as a small molecule neurogenic to produce two-headed animals with integrated CNSs following regeneration. Characterization of the entire family of planarian voltage-operated Ca(2+) channel α subunits (Ca(v)α), followed by in vivo RNAi of specific Ca(v) subunits, revealed that PZQ subverted regeneration by activation of a specific voltage-gated Ca(2+) channel isoform (Ca(v)1A). PZQ-evoked Ca(2+) entry via Ca(v)1A served to inhibit neuronally derived Hedgehog signals, as evidenced by data showing that RNAi of Ca(v)1A prevented PZQ-evoked bipolarity, Ca(2+) entry, and decreases in wnt1 and wnt11-5 levels. Surprisingly, the action of PZQ was opposed by Ca(2+) influx through a closely related neuronal Ca(v) isoform (Ca(v)1B), establishing a novel interplay between specific Ca(v)1 channel isoforms, Ca(2+) entry, and neuronal Hedgehog signaling. These data map PZQ efficacy to specific neuronal Ca(v) complexes in vivo and underscore that both activators (Ca(v)1A) and inhibitors (Ca(v)1B) of Ca(2+) influx can act as small molecule neurogenics in vivo on account of the unique coupling of Ca(2+) channels to neuronally derived polarity cues.
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145
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Evans DJ, Owlarn S, Tejada Romero B, Chen C, Aboobaker AA. Combining classical and molecular approaches elaborates on the complexity of mechanisms underpinning anterior regeneration. PLoS One 2011; 6:e27927. [PMID: 22125640 PMCID: PMC3220713 DOI: 10.1371/journal.pone.0027927] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2011] [Accepted: 10/27/2011] [Indexed: 01/26/2023] Open
Abstract
The current model of planarian anterior regeneration evokes the establishment of low levels of Wnt signalling at anterior wounds, promoting anterior polarity and subsequent elaboration of anterior fate through the action of the TALE class homeodomain PREP. The classical observation that decapitations positioned anteriorly will regenerate heads more rapidly than posteriorly positioned decapitations was among the first to lead to the proposal of gradients along an anteroposterior (AP) axis in a developmental context. An explicit understanding of this phenomenon is not included in the current model of anterior regeneration. This raises the question what the underlying molecular and cellular basis of this temporal gradient is, whether it can be explained by current models and whether understanding the gradient will shed light on regenerative events. Differences in anterior regeneration rate are established very early after amputation and this gradient is dependent on the activity of Hedgehog (Hh) signalling. Animals induced to produce two tails by either Smed-APC-1(RNAi) or Smed-ptc(RNAi) lose anterior fate but form previously described ectopic anterior brain structures. Later these animals form peri-pharyngeal brain structures, which in Smed-ptc(RNAi) grow out of the body establishing a new A/P axis. Combining double amputation and hydroxyurea treatment with RNAi experiments indicates that early ectopic brain structures are formed by uncommitted stem cells that have progressed through S-phase of the cell cycle at the time of amputation. Our results elaborate on the current simplistic model of both AP axis and brain regeneration. We find evidence of a gradient of hedgehog signalling that promotes posterior fate and temporarily inhibits anterior regeneration. Our data supports a model for anterior brain regeneration with distinct early and later phases of regeneration. Together these insights start to delineate the interplay between discrete existing, new, and then later homeostatic signals in AP axis regeneration.
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Affiliation(s)
- Deborah J. Evans
- Centre for Genetics and Genomics, Queen's Medical Centre, University of Nottingham, Nottingham, United Kingdom
| | - Suthira Owlarn
- Centre for Genetics and Genomics, Queen's Medical Centre, University of Nottingham, Nottingham, United Kingdom
| | - Belen Tejada Romero
- Centre for Genetics and Genomics, Queen's Medical Centre, University of Nottingham, Nottingham, United Kingdom
| | - Chen Chen
- Centre for Genetics and Genomics, Queen's Medical Centre, University of Nottingham, Nottingham, United Kingdom
| | - A. Aziz Aboobaker
- Centre for Genetics and Genomics, Queen's Medical Centre, University of Nottingham, Nottingham, United Kingdom
- * E-mail:
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146
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Mii Y, Taira M. Secreted Wnt "inhibitors" are not just inhibitors: regulation of extracellular Wnt by secreted Frizzled-related proteins. Dev Growth Differ 2011; 53:911-23. [PMID: 21995331 DOI: 10.1111/j.1440-169x.2011.01299.x] [Citation(s) in RCA: 80] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Gradient formation and signaling ranges of secreted proteins are crucial problems to understand how morphogens work for positional information and patterning in animal development. Yet, extracellular behaviors of secreted signaling molecules remain unexplored compared to their downstream pathways inside the cell. Recent advances in bioimaging make it possible to directly visualize morphogen molecules, and this simple strategy has, at least partly, succeeded in uncovering molecular behaviors of morphogens, such as Wnt (wingless-type MMTV integration site family member) and BMP (bone morphogenetic protein) as well as secreted Wnt binding proteins, sFRPs (secreted Frizzled-related proteins), in embryonic tissues. Here, we review the regulation of Wnt signaling by sFRPs, focusing on extracellular regulation of Wnt ligands in comparison with other morphogens. We also discuss evolutionary aspects with comprehensive syntenic and phylogenetic information about vertebrate sfrp genes. We newly annotated several sfrp genes including sfrp2-like 1 (sfrp2l1) in frogs and fishes and crescent in mammals.
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Affiliation(s)
- Yusuke Mii
- Department of Biological Sciences, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
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147
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Hayashi T, Motoishi M, Yazawa S, Itomi K, Tanegashima C, Nishimura O, Agata K, Tarui H. A LIM-homeobox gene is required for differentiation of Wnt-expressing cells at the posterior end of the planarian body. Development 2011; 138:3679-88. [PMID: 21828095 DOI: 10.1242/dev.060194] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Planarians have high regenerative ability, which is dependent on pluripotent adult somatic stem cells called neoblasts. Recently, canonical Wnt/β-catenin signaling was shown to be required for posterior specification, and Hedgehog signaling was shown to control anterior-posterior polarity via activation of the Djwnt1/P-1 gene at the posterior end of planarians. Thus, various signaling molecules play an important role in planarian stem cell regulation. However, the molecular mechanisms directly involved in stem cell differentiation have remained unclear. Here, we demonstrate that one of the planarian LIM-homeobox genes, Djislet, is required for the differentiation of Djwnt1/P-1-expressing cells from stem cells at the posterior end. RNA interference (RNAi)-treated planarians of Djislet [Djislet(RNAi)] show a tail-less phenotype. Thus, we speculated that Djislet might be involved in activation of the Wnt signaling pathway in the posterior blastema. When we carefully examined the expression pattern of Djwnt1/P-1 by quantitative real-time PCR during posterior regeneration, we found two phases of Djwnt1/P-1 expression: the first phase was detected in the differentiated cells in the old tissue in the early stage of regeneration and then a second phase was observed in the cells derived from stem cells in the posterior blastema. Interestingly, Djislet is expressed in stem cell-derived DjPiwiA- and Djwnt1/P-1-expressing cells, and Djislet(RNAi) only perturbed the second phase. Thus, we propose that Djislet might act to trigger the differentiation of cells expressing Djwnt1/P-1 from stem cells.
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Affiliation(s)
- Tetsutaro Hayashi
- Genome Resource and Analysis Unit, RIKEN Center for Developmental Biology, 2-2-3 Minatojima-minamimachi, Chuo-ku, Kobe, Hyogo 650-0047, Japan.
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148
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Tanaka EM, Reddien PW. The cellular basis for animal regeneration. Dev Cell 2011; 21:172-85. [PMID: 21763617 DOI: 10.1016/j.devcel.2011.06.016] [Citation(s) in RCA: 363] [Impact Index Per Article: 27.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2011] [Revised: 06/02/2011] [Accepted: 06/10/2011] [Indexed: 10/18/2022]
Abstract
The ability of animals to regenerate missing parts is a dramatic and poorly understood aspect of biology. The sources of new cells for these regenerative phenomena have been sought for decades. Recent advances involving cell fate tracking in complex tissues have shed new light on the cellular underpinnings of regeneration in Hydra, planarians, zebrafish, Xenopus, and Axolotl. Planarians accomplish regeneration with use of adult pluripotent stem cells, whereas several vertebrates utilize a collection of lineage-restricted progenitors from different tissues. Together, an array of cellular strategies-from pluripotent stem cells to tissue-specific stem cells and dedifferentiation-are utilized for regeneration.
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Affiliation(s)
- Elly M Tanaka
- Technical University of Dresden, DFG Center for Regenerative Therapies Dresden, c/o Max Planck Institute of Cell Biology and Genetics, Pfotenhauerstrasse 108, Dresden, Germany.
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149
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Abstract
Wnt genes encode secreted glycoproteins that act in cell-cell signalling to regulate a wide array of developmental processes, ranging from cellular differentiation to axial patterning. Discovery that canonical Wnt/β-catenin signalling is responsible for regulating head/tail specification in planarian regeneration has recently highlighted their importance in flatworm (phylum Platyhelminthes) development, but examination of their roles in the complex development of the diverse parasitic groups has yet to be conducted. Here, we characterise Wnt genes in the model tapeworm Hymenolepis microstoma and mine genomic resources of free-living and parasitic species for the presence of Wnts and downstream signalling components. We identify orthologs through a combination of BLAST and phylogenetic analyses, showing that flatworms have a highly reduced and dispersed complement that includes orthologs of only five subfamilies (Wnt1, Wnt2, Wnt4, Wnt5 and Wnt11) and fewer paralogs in parasitic flatworms (5-6) than in planarians (9). All major signalling components are identified, including antagonists and receptors, and key binding domains are intact, indicating that the canonical (Wnt/β-catenin) and non-canonical (planar cell polarity and Wnt/Ca(2+)) pathways are functional. RNA-Seq data show expression of all Hymenolepis Wnts and most downstream components in adults and larvae with the notable exceptions of wnt1, expressed only in adults, and wnt2 expressed only in larvae. The distribution of Wnt subfamilies in animals corroborates the idea that the last common ancestor of the Cnidaria and Bilateria possessed all contemporary Wnts and highlights the extent of gene loss in flatworms.
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Affiliation(s)
- Nick Riddiford
- Department of Zoology, The Natural History Museum, Cromwell Road, London SW7 5BD, UK
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150
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Forsthoefel DJ, Park AE, Newmark PA. Stem cell-based growth, regeneration, and remodeling of the planarian intestine. Dev Biol 2011; 356:445-59. [PMID: 21664348 PMCID: PMC3490491 DOI: 10.1016/j.ydbio.2011.05.669] [Citation(s) in RCA: 92] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2011] [Accepted: 05/24/2011] [Indexed: 10/18/2022]
Abstract
Although some animals are capable of regenerating organs, the mechanisms by which this is achieved are poorly understood. In planarians, pluripotent somatic stem cells called neoblasts supply new cells for growth, replenish tissues in response to cellular turnover, and regenerate tissues after injury. For most tissues and organs, however, the spatiotemporal dynamics of stem cell differentiation and the fate of tissue that existed prior to injury have not been characterized systematically. Utilizing in vivo imaging and bromodeoxyuridine pulse-chase experiments, we have analyzed growth and regeneration of the planarian intestine, the organ responsible for digestion and nutrient distribution. During growth, we observe that new gut branches are added along the entire anteroposterior axis. We find that new enterocytes differentiate throughout the intestine rather than in specific growth zones, suggesting that branching morphogenesis is achieved primarily by remodeling of differentiated intestinal tissues. During regeneration, we also demonstrate a previously unappreciated degree of intestinal remodeling, in which pre-existing posterior gut tissue contributes extensively to the newly formed anterior gut, and vice versa. By contrast to growing animals, differentiation of new intestinal cells occurs at preferential locations, including within newly generated tissue (the blastema), and along pre-existing intestinal branches undergoing remodeling. Our results indicate that growth and regeneration of the planarian intestine are achieved by co-ordinated differentiation of stem cells and the remodeling of pre-existing tissues. Elucidation of the mechanisms by which these processes are integrated will be critical for understanding organogenesis in a post-embryonic context.
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Affiliation(s)
- David J. Forsthoefel
- Howard Hughes Medical Institute, Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, Urbana-Champaign, IL, 61801, USA
| | - Amanda E. Park
- Howard Hughes Medical Institute, Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, Urbana-Champaign, IL, 61801, USA
| | - Phillip A. Newmark
- Howard Hughes Medical Institute, Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, Urbana-Champaign, IL, 61801, USA
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