51
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Roles of Germline Stem Cells and Somatic Multipotent Stem Cells in Hydra Sexual Reproduction. DIVERSITY AND COMMONALITY IN ANIMALS 2018. [DOI: 10.1007/978-4-431-56609-0_7] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
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52
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He X, Lindsay-Mosher N, Li Y, Molinaro AM, Pellettieri J, Pearson BJ. FOX and ETS family transcription factors regulate the pigment cell lineage in planarians. Development 2017; 144:4540-4551. [PMID: 29158443 DOI: 10.1242/dev.156349] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2017] [Accepted: 11/03/2017] [Indexed: 12/16/2022]
Abstract
Many pigment cells acquire unique structural properties and gene expression profiles during animal development. The underlying differentiation pathways have been well characterized in cells formed during embryogenesis, such as the neural crest-derived melanocyte. However, much less is known about the developmental origins of pigment cells produced in adult organisms during tissue homeostasis and repair. Here we report a lineage analysis of ommochrome- and porphyrin-producing cells in the brown, freshwater planarian Schmidtea mediterranea Using an RNA-sequencing approach, we identified two classes of markers expressed in sequential fashion when new pigment cells are generated during regeneration or in response to pigment cell ablation. We also report roles for FOXF-1 and ETS-1 transcription factors, as well as for an FGFR-like molecule, in the specification and maintenance of this cell type. Together, our results provide insights into mechanisms of adult pigment cell development in the strikingly colorful Platyhelminthes phylum.
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Affiliation(s)
- Xinwen He
- Hospital for Sick Children, Program in Developmental and Stem Cell Biology, Toronto, Ontario M5G0A4, Canada.,Department of Molecular Genetics, University of Toronto, Toronto, Ontario M5G0A4, Canada
| | - Nicole Lindsay-Mosher
- Hospital for Sick Children, Program in Developmental and Stem Cell Biology, Toronto, Ontario M5G0A4, Canada.,Department of Molecular Genetics, University of Toronto, Toronto, Ontario M5G0A4, Canada
| | - Yan Li
- Hospital for Sick Children, Program in Developmental and Stem Cell Biology, Toronto, Ontario M5G0A4, Canada.,Ontario Institute for Cancer Research, Toronto, Ontario M5G0A4, Canada
| | - Alyssa M Molinaro
- Hospital for Sick Children, Program in Developmental and Stem Cell Biology, Toronto, Ontario M5G0A4, Canada.,Department of Molecular Genetics, University of Toronto, Toronto, Ontario M5G0A4, Canada
| | | | - Bret J Pearson
- Hospital for Sick Children, Program in Developmental and Stem Cell Biology, Toronto, Ontario M5G0A4, Canada .,Department of Molecular Genetics, University of Toronto, Toronto, Ontario M5G0A4, Canada.,Ontario Institute for Cancer Research, Toronto, Ontario M5G0A4, Canada
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53
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Cellular, ultrastructural and molecular analyses of epidermal cell development in the planarian Schmidtea mediterranea. Dev Biol 2017; 433:357-373. [PMID: 29100657 DOI: 10.1016/j.ydbio.2017.08.030] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2017] [Revised: 08/23/2017] [Accepted: 08/26/2017] [Indexed: 12/20/2022]
Abstract
The epidermis is essential for animal survival, providing both a protective barrier and cellular sensor to external environments. The generally conserved embryonic origin of the epidermis, but the broad morphological and functional diversity of this organ across animals is puzzling. We define the transcriptional regulators underlying epidermal lineage differentiation in the planarian Schmidtea mediterranea, an invertebrate organism that, unlike fruitflies and nematodes, continuously replaces its epidermal cells. We find that Smed-p53, Sox and Pax transcription factors are essential regulators of epidermal homeostasis, and act cooperatively to regulate genes associated with early epidermal precursor cell differentiation, including a tandemly arrayed novel gene family (prog) of secreted proteins. Additionally, we report on the discovery of distinct and previously undescribed secreted organelles whose production is dependent on the transcriptional activity of soxP-3, and which we term Hyman vesicles.
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54
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Sahu S, Dattani A, Aboobaker AA. Secrets from immortal worms: What can we learn about biological ageing from the planarian model system? Semin Cell Dev Biol 2017; 70:108-121. [PMID: 28818620 DOI: 10.1016/j.semcdb.2017.08.028] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2017] [Revised: 08/07/2017] [Accepted: 08/09/2017] [Indexed: 12/12/2022]
Abstract
Understanding how some animals are immortal and avoid the ageing process is important. We currently know very little about how they achieve this. Research with genetic model systems has revealed the existence of conserved genetic pathways and molecular processes that affect longevity. Most of these established model organisms have relatively short lifespans. Here we consider the use of planarians, with an immortal life-history that is able to entirely avoid the ageing process. These animals are capable of profound feats of regeneration fueled by a population of adult stem cells called neoblasts. These cells are capable of indefinite self-renewal that has underpinned the evolution of animals that reproduce only by fission, having disposed of the germline, and must therefore be somatically immortal and avoid the ageing process. How they do this is only now starting to be understood. Here we suggest that the evidence so far supports the hypothesis that the lack of ageing is an emergent property of both being highly regenerative and the evolution of highly effective mechanisms for ensuring genome stability in the neoblast stem cell population. The details of these mechanisms could prove to be very informative in understanding how the causes of ageing can be avoided, slowed or even reversed.
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Affiliation(s)
- Sounak Sahu
- Department of Zoology, South Parks Road, University of Oxford, Oxford OX1 3PS, UK
| | - Anish Dattani
- Department of Zoology, South Parks Road, University of Oxford, Oxford OX1 3PS, UK
| | - A Aziz Aboobaker
- Department of Zoology, South Parks Road, University of Oxford, Oxford OX1 3PS, UK.
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55
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Lin AYT, Pearson BJ. Yorkie is required to restrict the injury responses in planarians. PLoS Genet 2017; 13:e1006874. [PMID: 28686611 PMCID: PMC5515462 DOI: 10.1371/journal.pgen.1006874] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2017] [Revised: 07/18/2017] [Accepted: 06/15/2017] [Indexed: 12/30/2022] Open
Abstract
Regeneration requires the precise integration of cues that initiate proliferation, direct differentiation, and ultimately re-pattern tissues to the proper size and scale. Yet how these processes are integrated with wounding responses remains relatively unknown. The freshwater planarian, Schmidtea mediterranea, is an ideal model to study the stereotyped proliferative and transcriptional responses to injury due to its high capacity for regeneration. Here, we characterize the effector of the Hippo signalling cascade, yorkie, during planarian regeneration and its role in restricting early injury responses. In yki(RNAi) regenerating animals, wound responses are hyper-activated such that both stem cell proliferation and the transcriptional wound response program are heighted and prolonged. Using this observation, we also uncovered novel wound-induced genes by RNAseq that were de-repressed in yki(RNAi) animals compared with controls. Additionally, we show that yki(RNAi) animals have expanded epidermal and muscle cell populations, which we hypothesize are the increased sources of wound-induced genes. Finally, we show that in yki(RNAi) animals, the sensing of the size of an injury by eyes or the pharynx is not appropriate, and the brain, gut, and midline cannot remodel or scale correctly to the size of the regenerating fragment. Taken together, our results suggest that yki functions as a key molecule that can integrate multiple aspects of the injury response including proliferation, apoptosis, injury-induced transcription, and patterning. The planarian displays a remarkable ability to regenerate any tissue from mere fragments of its original size. This high capacity to regenerate is attributed to the abundant population of pluripotent adult stem cells. In response to an injury, such as an amputation, stem cells proliferate and replace the lost tissues de novo (epimorphosis), whereas existing tissue must rescale to the correct proportions in relation to the new fragment size (morphallaxis). Currently, the molecules that control either the responses to injury or the ones that mediate size and scaling are not well understood. For instance, how are the injury responses precisely activated and shut down to ensure regenerating tissues are not under- or overgrown? Here, we find that Yki, the effector of the Hippo signalling cascade, is a critical molecule that influences several injury processes during regeneration. Loss of Yki function in regenerating animals resulted in increased and temporally dysregulated expression of wound-induced genes, proliferation, and apoptosis. Genes that are injury induced were mis-expressed in yki(RNAi) animals, which also showed increases in the epidermal and muscle cell populations. Taken together, our findings suggest that the injury responses must be restricted to ensure proper regenerative outcomes of correct scale, and that Yki is a key regulator in these processes.
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Affiliation(s)
- Alexander Y. T. Lin
- Hospital for Sick Children, Program in Developmental and Stem Cell Biology, Toronto, ON, Canada
- Department of Molecular Genetics, University of Toronto, Toronto, ON, Canada
| | - Bret J. Pearson
- Hospital for Sick Children, Program in Developmental and Stem Cell Biology, Toronto, ON, Canada
- Department of Molecular Genetics, University of Toronto, Toronto, ON, Canada
- Ontario Institute for Cancer Research, Toronto, ON, Canada
- * E-mail:
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56
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Wurtzel O, Oderberg IM, Reddien PW. Planarian Epidermal Stem Cells Respond to Positional Cues to Promote Cell-Type Diversity. Dev Cell 2017; 40:491-504.e5. [PMID: 28292427 DOI: 10.1016/j.devcel.2017.02.008] [Citation(s) in RCA: 64] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2016] [Revised: 12/08/2016] [Accepted: 02/10/2017] [Indexed: 11/25/2022]
Abstract
Successful regeneration requires that progenitors of different lineages form the appropriate missing cell types. However, simply generating lineages is not enough. Cells produced by a particular lineage often have distinct functions depending on their position within the organism. How this occurs in regeneration is largely unexplored. In planarian regeneration, new cells arise from a proliferative cell population (neoblasts). We used the planarian epidermal lineage to study how the location of adult progenitor cells results in their acquisition of distinct functional identities. Single-cell RNA sequencing of epidermal progenitors revealed the emergence of distinct spatial identities as early in the lineage as the epidermal neoblasts, with further pre-patterning occurring in their post-mitotic migratory progeny. Establishment of dorsal-ventral epidermal identities and functions, in response to BMP signaling, required neoblasts. Our work identified positional signals that activate regionalized transcriptional programs in the stem cell population and subsequently promote cell-type diversity in the epidermis.
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Affiliation(s)
- Omri Wurtzel
- Whitehead Institute for Biomedical Research, Cambridge, MA 02142, USA; Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA; Howard Hughes Medical Institute, Chevy Chase, MD 20815, USA
| | - Isaac M Oderberg
- Whitehead Institute for Biomedical Research, Cambridge, MA 02142, USA; Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA; Howard Hughes Medical Institute, Chevy Chase, MD 20815, USA
| | - Peter W Reddien
- Whitehead Institute for Biomedical Research, Cambridge, MA 02142, USA; Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA; Howard Hughes Medical Institute, Chevy Chase, MD 20815, USA.
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57
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Brown DDR, Pearson BJ. A Brain Unfixed: Unlimited Neurogenesis and Regeneration of the Adult Planarian Nervous System. Front Neurosci 2017; 11:289. [PMID: 28588444 PMCID: PMC5441136 DOI: 10.3389/fnins.2017.00289] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2017] [Accepted: 05/08/2017] [Indexed: 11/25/2022] Open
Abstract
Powerful genetic tools in classical laboratory models have been fundamental to our understanding of how stem cells give rise to complex neural tissues during embryonic development. In contrast, adult neurogenesis in our model systems, if present, is typically constrained to one or a few zones of the adult brain to produce a limited subset of neurons leading to the dogma that the brain is primarily fixed post-development. The freshwater planarian (flatworm) is an invertebrate model system that challenges this dogma. The planarian possesses a brain containing several thousand neurons with very high rates of cell turnover (homeostasis), which can also be fully regenerated de novo from injury in just 7 days. Both homeostasis and regeneration depend on the activity of a large population of adult stem cells, called neoblasts, throughout the planarian body. Thus, much effort has been put forth to understand how the flatworm can continually give rise to the diversity of cell types found in the adult brain. Here we focus on work using single-cell genomics and functional analyses to unravel the cellular hierarchies from stem cell to neuron. In addition, we will review what is known about how planarians utilize developmental signaling to maintain proper tissue patterning, homeostasis, and cell-type diversity in their brains. Together, planarians are a powerful emerging model system to study the dynamics of adult neurogenesis and regeneration.
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Affiliation(s)
- David D R Brown
- Program in Developmental and Stem Cell Biology, The Hospital for Sick ChildrenToronto, ON, Canada.,Department of Molecular Genetics, University of TorontoToronto, ON, Canada
| | - Bret J Pearson
- Program in Developmental and Stem Cell Biology, The Hospital for Sick ChildrenToronto, ON, Canada.,Department of Molecular Genetics, University of TorontoToronto, ON, Canada.,Ontario Institute for Cancer ResearchToronto, ON, Canada
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58
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Ross KG, Currie KW, Pearson BJ, Zayas RM. Nervous system development and regeneration in freshwater planarians. WILEY INTERDISCIPLINARY REVIEWS-DEVELOPMENTAL BIOLOGY 2017; 6. [DOI: 10.1002/wdev.266] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/28/2016] [Revised: 01/10/2017] [Accepted: 01/20/2017] [Indexed: 01/22/2023]
Affiliation(s)
- Kelly G. Ross
- Department of Biology San Diego State University San Diego CA USA
| | - Ko W. Currie
- Program in Developmental and Stem Cell Biology The Hospital for Sick Children Toronto Canada
- Department of Molecular Genetics University of Toronto Toronto Canada
- Ontario Institute for Cancer Research Toronto Canada
| | - Bret J. Pearson
- Program in Developmental and Stem Cell Biology The Hospital for Sick Children Toronto Canada
- Department of Molecular Genetics University of Toronto Toronto Canada
- Ontario Institute for Cancer Research Toronto Canada
| | - Ricardo M. Zayas
- Department of Biology San Diego State University San Diego CA USA
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59
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Seebeck F, März M, Meyer AW, Reuter H, Vogg MC, Stehling M, Mildner K, Zeuschner D, Rabert F, Bartscherer K. Integrins are required for tissue organization and restriction of neurogenesis in regenerating planarians. Development 2017; 144:795-807. [PMID: 28137894 PMCID: PMC5374344 DOI: 10.1242/dev.139774] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2016] [Accepted: 01/11/2017] [Indexed: 12/13/2022]
Abstract
Tissue regeneration depends on proliferative cells and on cues that regulate cell division, differentiation, patterning and the restriction of these processes once regeneration is complete. In planarians, flatworms with high regenerative potential, muscle cells express some of these instructive cues. Here, we show that members of the integrin family of adhesion molecules are required for the integrity of regenerating tissues, including the musculature. Remarkably, in regenerating β1-integrin RNAi planarians, we detected increased numbers of mitotic cells and progenitor cell types, as well as a reduced ability of stem cells and lineage-restricted progenitor cells to accumulate at wound sites. These animals also formed ectopic spheroid structures of neural identity in regenerating heads. Interestingly, those polarized assemblies comprised a variety of neural cells and underwent continuous growth. Our study indicates that integrin-mediated cell adhesion is required for the regenerative formation of organized tissues and for restricting neurogenesis during planarian regeneration. Highlighted article: Integrin signaling acts to recruit and localize progenitor cells following injury, thereby promoting the correct organization of regenerating planarian tissue.
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Affiliation(s)
- Florian Seebeck
- Max Planck Research Group Stem Cells & Regeneration, Max Planck Institute for Molecular Biomedicine, Von-Esmarch-Str. 54, Münster 48149, Germany.,Medical Faculty, University of Münster, Albert-Schweitzer-Campus 1, 48149 Münster, Germany
| | - Martin März
- Max Planck Research Group Stem Cells & Regeneration, Max Planck Institute for Molecular Biomedicine, Von-Esmarch-Str. 54, Münster 48149, Germany.,Medical Faculty, University of Münster, Albert-Schweitzer-Campus 1, 48149 Münster, Germany
| | - Anna-Wiebke Meyer
- Max Planck Research Group Stem Cells & Regeneration, Max Planck Institute for Molecular Biomedicine, Von-Esmarch-Str. 54, Münster 48149, Germany.,Medical Faculty, University of Münster, Albert-Schweitzer-Campus 1, 48149 Münster, Germany
| | - Hanna Reuter
- Max Planck Research Group Stem Cells & Regeneration, Max Planck Institute for Molecular Biomedicine, Von-Esmarch-Str. 54, Münster 48149, Germany.,Medical Faculty, University of Münster, Albert-Schweitzer-Campus 1, 48149 Münster, Germany
| | - Matthias C Vogg
- Max Planck Research Group Stem Cells & Regeneration, Max Planck Institute for Molecular Biomedicine, Von-Esmarch-Str. 54, Münster 48149, Germany.,Medical Faculty, University of Münster, Albert-Schweitzer-Campus 1, 48149 Münster, Germany
| | - Martin Stehling
- Flow Cytometry Unit, Max Planck Institute for Molecular Biomedicine, Röntgenstrasse 20, Münster 48149, Germany
| | - Karina Mildner
- Electron Microscopy Unit, Max Planck Institute for Molecular Biomedicine, Röntgenstrasse 20, Münster 48149, Germany
| | - Dagmar Zeuschner
- Electron Microscopy Unit, Max Planck Institute for Molecular Biomedicine, Röntgenstrasse 20, Münster 48149, Germany
| | - Franziska Rabert
- Max Planck Research Group Stem Cells & Regeneration, Max Planck Institute for Molecular Biomedicine, Von-Esmarch-Str. 54, Münster 48149, Germany.,Medical Faculty, University of Münster, Albert-Schweitzer-Campus 1, 48149 Münster, Germany
| | - Kerstin Bartscherer
- Max Planck Research Group Stem Cells & Regeneration, Max Planck Institute for Molecular Biomedicine, Von-Esmarch-Str. 54, Münster 48149, Germany .,Medical Faculty, University of Münster, Albert-Schweitzer-Campus 1, 48149 Münster, Germany
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60
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Davies EL, Lei K, Seidel CW, Kroesen AE, McKinney SA, Guo L, Robb SM, Ross EJ, Gotting K, Alvarado AS. Embryonic origin of adult stem cells required for tissue homeostasis and regeneration. eLife 2017; 6:21052. [PMID: 28072387 PMCID: PMC5293490 DOI: 10.7554/elife.21052] [Citation(s) in RCA: 50] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2016] [Accepted: 01/04/2017] [Indexed: 11/13/2022] Open
Abstract
Planarian neoblasts are pluripotent, adult somatic stem cells and lineage-primed progenitors that are required for the production and maintenance of all differentiated cell types, including the germline. Neoblasts, originally defined as undifferentiated cells residing in the adult parenchyma, are frequently compared to embryonic stem cells yet their developmental origin remains obscure. We investigated the provenance of neoblasts during Schmidtea mediterranea embryogenesis, and report that neoblasts arise from an anarchic, cycling piwi-1+ population wholly responsible for production of all temporary and definitive organs during embryogenesis. Early embryonic piwi-1+ cells are molecularly and functionally distinct from neoblasts: they express unique cohorts of early embryo enriched transcripts and behave differently than neoblasts in cell transplantation assays. Neoblast lineages arise as organogenesis begins and are required for construction of all major organ systems during embryogenesis. These subpopulations are continuously generated during adulthood, where they act as agents of tissue homeostasis and regeneration.
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Affiliation(s)
- Erin L Davies
- Howard Hughes Medical Institute, Stowers Institute for Medical Research, Kansas City, United States
| | - Kai Lei
- Howard Hughes Medical Institute, Stowers Institute for Medical Research, Kansas City, United States
| | - Christopher W Seidel
- Howard Hughes Medical Institute, Stowers Institute for Medical Research, Kansas City, United States
| | - Amanda E Kroesen
- Howard Hughes Medical Institute, Stowers Institute for Medical Research, Kansas City, United States
| | - Sean A McKinney
- Howard Hughes Medical Institute, Stowers Institute for Medical Research, Kansas City, United States
| | - Longhua Guo
- Howard Hughes Medical Institute, Stowers Institute for Medical Research, Kansas City, United States
| | - Sofia Mc Robb
- Howard Hughes Medical Institute, Stowers Institute for Medical Research, Kansas City, United States
| | - Eric J Ross
- Howard Hughes Medical Institute, Stowers Institute for Medical Research, Kansas City, United States
| | - Kirsten Gotting
- Howard Hughes Medical Institute, Stowers Institute for Medical Research, Kansas City, United States
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61
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Lobo D, Levin M. Computing a Worm: Reverse-Engineering Planarian Regeneration. EMERGENCE, COMPLEXITY AND COMPUTATION 2017. [DOI: 10.1007/978-3-319-33921-4_24] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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62
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Currie KW, Molinaro AM, Pearson BJ. Neuronal sources of hedgehog modulate neurogenesis in the adult planarian brain. eLife 2016; 5:19735. [PMID: 27864883 PMCID: PMC5153250 DOI: 10.7554/elife.19735] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2016] [Accepted: 11/18/2016] [Indexed: 12/13/2022] Open
Abstract
The asexual freshwater planarian is a constitutive adult, whose central nervous system (CNS) is in a state of constant homeostatic neurogenesis. However, very little is known about the extrinsic signals that act on planarian stem cells to modulate rates of neurogenesis. We have identified two planarian homeobox transcription factors, Smed-nkx2.1 and Smed-arx, which are required for the maintenance of cholinergic, GABAergic, and octopaminergic neurons in the planarian CNS. These very same neurons also produce the planarian hedgehog ligand (Smed-hh), which appears to communicate with brain-adjacent stem cells to promote normal levels of neurogenesis. Planarian stem cells nearby the brain express core hh signal transduction genes, and consistent hh signaling levels are required to maintain normal production of neural progenitor cells and new mature cholinergic neurons, revealing an important mitogenic role for the planarian hh signaling molecule in the adult CNS. DOI:http://dx.doi.org/10.7554/eLife.19735.001 Most animals can continue to generate and add new neurons in their nervous system into adulthood, though the process is often tightly regulated. In adult humans, only a small number of neurons are made or lost, such that the fewer than 2% of the neurons in the nervous will change over, or “turnover”, the course of a year. The turnover of neurons in some other animals is much higher than it is in humans. A freshwater flatworm, called Schmidtea mediterranea, is one example of such an animal that can even regenerate an entirely new brain if its head is decapitated. These flatworms have a large population of adult stem cells, which makes these high rates of neuron production and regeneration possible. However, it is largely unknown if this population contains stem cells that can only become new neurons, in other words “dedicated neuronal stem cells”. Moreover, it is also not clear what kinds of signals communicate with these stem cells to promote the production of new neurons. In animals from flies to humans, a signaling molecule encoded by a gene called hedgehog forms part of a signaling pathway that can promote neuron production during development. Therefore, Currie et al. asked if the hedgehog signaling molecule might communicate with the stem cells in adult flatworms to control how many new neurons they produce. The experiments revealed that the hedgehog signaling molecule is almost exclusively produced by the flatworm’s brain and the pair of nerve cords that run the length of the flatworm. Currie et al. then found a smaller group of cells close to the flatworm’s brain that looked like dedicated neural stem cells. These cells can receive the hedgehog signals, and further experiments showed that flatworm’s brain requires hedgehog signaling to be able to produce new neurons at its normal level. The hedgehog signaling molecule is likely only one of many signaling molecules that regulate the production of new neurons in flatworms. It will be important to uncover these additional signals and understand how they work in concert. In the future, a better understanding of this process will help efforts to devise ways to induce humans to replace neurons that are lost following injury or neurodegenerative diseases. DOI:http://dx.doi.org/10.7554/eLife.19735.002
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Affiliation(s)
- Ko W Currie
- Program in Developmental and Stem Cell Biology, Hospital for Sick Children, Toronto, Canada.,Department of Molecular Genetics, University of Toronto, Toronto, Canada
| | - Alyssa M Molinaro
- Program in Developmental and Stem Cell Biology, Hospital for Sick Children, Toronto, Canada.,Department of Molecular Genetics, University of Toronto, Toronto, Canada
| | - Bret J Pearson
- Program in Developmental and Stem Cell Biology, Hospital for Sick Children, Toronto, Canada.,Department of Molecular Genetics, University of Toronto, Toronto, Canada.,Ontario Institute for Cancer Research, Toronto, Canada
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63
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Collins JNR, Collins JJ. Tissue Degeneration following Loss of Schistosoma mansoni cbp1 Is Associated with Increased Stem Cell Proliferation and Parasite Death In Vivo. PLoS Pathog 2016; 12:e1005963. [PMID: 27812220 PMCID: PMC5094730 DOI: 10.1371/journal.ppat.1005963] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2016] [Accepted: 09/29/2016] [Indexed: 01/06/2023] Open
Abstract
Schistosomiasis is second only to malaria in terms of the global impact among diseases caused by parasites. A striking feature of schistosomes are their ability to thrive in their hosts for decades. We have previously demonstrated that stem cells, called neoblasts, promote homeostatic tissue maintenance in adult schistosomes and suggested these cells likely contribute to parasite longevity. Whether these schistosome neoblasts have functions independent of homeostatic tissue maintenance, for example in processes such as tissue regeneration following injury, remains unexplored. Here we characterize the schistosome CBP/p300 homolog, Sm-cbp1. We found that depleting cbp1 transcript levels with RNA interference (RNAi) resulted in increased neoblast proliferation and cell death, eventually leading to organ degeneration. Based on these observations we speculated this increased rate of neoblast proliferation may be a response to mitigate tissue damage due to increased cell death. Therefore, we tested if mechanical injury was sufficient to stimulate neoblast proliferation. We found that mechanical injury induced both cell death and neoblast proliferation at wound sites, suggesting that schistosome neoblasts are capable of mounting proliferative responses to injury. Furthermore, we observed that the health of cbp1(RNAi) parasites progressively declined during the course of our in vitro experiments. To determine the fate of cbp1(RNAi) parasites in the context of a mammalian host, we coupled RNAi with an established technique to transplant schistosomes into the mesenteric veins of uninfected mice. We found transplanted cbp1(RNAi) parasites were cleared from vasculature of recipient mice and were incapable of inducing measurable pathology in their recipient hosts. Together our data suggest that injury is sufficient to induce neoblast proliferation and that cbp1 is essential for parasite survival in vivo. These studies present a new methodology to study schistosome gene function in vivo and highlight a potential role for schistosome neoblasts in promoting tissue repair following injury.
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Affiliation(s)
| | - James J. Collins
- Department of Pharmacology, UT Southwestern Medical Center, Dallas, Texas
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64
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Lei K, Thi-Kim Vu H, Mohan RD, McKinney SA, Seidel CW, Alexander R, Gotting K, Workman JL, Sánchez Alvarado A. Egf Signaling Directs Neoblast Repopulation by Regulating Asymmetric Cell Division in Planarians. Dev Cell 2016; 38:413-29. [PMID: 27523733 DOI: 10.1016/j.devcel.2016.07.012] [Citation(s) in RCA: 55] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2015] [Revised: 06/01/2016] [Accepted: 07/15/2016] [Indexed: 12/27/2022]
Abstract
A large population of proliferative stem cells (neoblasts) is required for physiological tissue homeostasis and post-injury regeneration in planarians. Recent studies indicate that survival of a few neoblasts after sublethal irradiation results in the clonal expansion of the surviving stem cells and the eventual restoration of tissue homeostasis and regenerative capacity. However, the precise mechanisms regulating the population dynamics of neoblasts remain largely unknown. Here, we uncovered a central role for epidermal growth factor (EGF) signaling during in vivo neoblast expansion mediated by Smed-egfr-3 (egfr-3) and its putative ligand Smed-neuregulin-7 (nrg-7). Furthermore, the EGF receptor-3 protein localizes asymmetrically on the cytoplasmic membrane of neoblasts, and the ratio of asymmetric to symmetric cell divisions decreases significantly in egfr-3(RNAi) worms. Our results not only provide the first molecular evidence of asymmetric stem cell divisions in planarians, but also demonstrate that EGF signaling likely functions as an essential regulator of neoblast clonal expansion.
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Affiliation(s)
- Kai Lei
- Stowers Institute for Medical Research, Kansas City, MO 64110, USA.
| | - Hanh Thi-Kim Vu
- Stowers Institute for Medical Research, Kansas City, MO 64110, USA
| | - Ryan D Mohan
- Division of Cell Biology and Biophysics, School of Biological Sciences, University of Missouri-Kansas City, Kansas City, MO 64110, USA
| | - Sean A McKinney
- Stowers Institute for Medical Research, Kansas City, MO 64110, USA
| | - Chris W Seidel
- Stowers Institute for Medical Research, Kansas City, MO 64110, USA
| | | | - Kirsten Gotting
- Stowers Institute for Medical Research, Kansas City, MO 64110, USA
| | - Jerry L Workman
- Stowers Institute for Medical Research, Kansas City, MO 64110, USA
| | - Alejandro Sánchez Alvarado
- Stowers Institute for Medical Research, Kansas City, MO 64110, USA; Howard Hughes Medical Institute, Stowers Institute for Medical Research, Kansas City, MO 64110, USA.
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65
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Solana J, Irimia M, Ayoub S, Orejuela MR, Zywitza V, Jens M, Tapial J, Ray D, Morris Q, Hughes TR, Blencowe BJ, Rajewsky N. Conserved functional antagonism of CELF and MBNL proteins controls stem cell-specific alternative splicing in planarians. eLife 2016; 5. [PMID: 27502555 PMCID: PMC4978528 DOI: 10.7554/elife.16797] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2016] [Accepted: 07/07/2016] [Indexed: 12/11/2022] Open
Abstract
In contrast to transcriptional regulation, the function of alternative splicing (AS) in stem cells is poorly understood. In mammals, MBNL proteins negatively regulate an exon program specific of embryonic stem cells; however, little is known about the in vivo significance of this regulation. We studied AS in a powerful in vivo model for stem cell biology, the planarian Schmidtea mediterranea. We discover a conserved AS program comprising hundreds of alternative exons, microexons and introns that is differentially regulated in planarian stem cells, and comprehensively identify its regulators. We show that functional antagonism between CELF and MBNL factors directly controls stem cell-specific AS in planarians, placing the origin of this regulatory mechanism at the base of Bilaterians. Knockdown of CELF or MBNL factors lead to abnormal regenerative capacities by affecting self-renewal and differentiation sets of genes, respectively. These results highlight the importance of AS interactions in stem cell regulation across metazoans. DOI:http://dx.doi.org/10.7554/eLife.16797.001 Stem cells are specialized cells found in all animals that can develop into several different types of mature cells. Stem cells are therefore well suited for maintaining organs that are in heavy use, such as the intestine, and for regenerating tissues that are prone to injury, like the skin. One reason why stem cells differ from mature cell types is because they activate, or “express”, different sets of genes. In addition, many genes can be expressed as one of several versions. These variants, also known as isoforms, are generated by a process called alternative splicing. In mature cells in mammals, a group of proteins called the MBNL proteins help to prevent the expression of gene isoforms that are characteristic to stem cells. The adult flatworm Schmidtea mediterranea contains stem cells that can regenerate any part of the body. Solana, Irimia et al. have now investigated whether alternative splicing is important for controlling how the worm’s stem cells behave. After establishing which gene isoforms are expressed in the stem cells and the mature cells, the levels of different sets of proteins that control alternative splicing were experimentally reduced. The results indicate that just as seen in mammals, the MBNL proteins reduce the expression of stem cell-related gene isoforms in the flatworms. Furthermore, Solana, Irimia et al. found that another protein called CELF counteracts MBNL proteins by helping to express gene isoforms that are active in stem cells. The interplay between the MBNL and CELF proteins has also been observed in human cells. Thus, it appears that this way of controlling alternative splicing is common to flatworms and mammals and is therefore evolutionarily ancient. This suggests that other similar ways of controlling stem cells by interactions between regulatory proteins might be working in all animal stem cells. Further studies are now needed to investigate these control proteins. DOI:http://dx.doi.org/10.7554/eLife.16797.002
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Affiliation(s)
- Jordi Solana
- Systems Biology of Gene Regulatory Elements, Berlin Institute for Medical Systems Biology, Max-Delbrück Center for Molecular Medicine, Berlin, Germany
| | - Manuel Irimia
- Centre for Genomic Regulation, Barcelona Institute of Science and Technology (BIST), Barcelona, Spain.,Universitat Pompeu Fabra, Barcelona, Spain
| | - Salah Ayoub
- Systems Biology of Gene Regulatory Elements, Berlin Institute for Medical Systems Biology, Max-Delbrück Center for Molecular Medicine, Berlin, Germany
| | - Marta Rodriguez Orejuela
- Systems Biology of Gene Regulatory Elements, Berlin Institute for Medical Systems Biology, Max-Delbrück Center for Molecular Medicine, Berlin, Germany
| | - Vera Zywitza
- Systems Biology of Gene Regulatory Elements, Berlin Institute for Medical Systems Biology, Max-Delbrück Center for Molecular Medicine, Berlin, Germany
| | - Marvin Jens
- Systems Biology of Gene Regulatory Elements, Berlin Institute for Medical Systems Biology, Max-Delbrück Center for Molecular Medicine, Berlin, Germany
| | - Javier Tapial
- Centre for Genomic Regulation, Barcelona Institute of Science and Technology (BIST), Barcelona, Spain.,Universitat Pompeu Fabra, Barcelona, Spain
| | - Debashish Ray
- Donnelly Centre, University of Toronto, Toronto, Canada
| | - Quaid Morris
- Donnelly Centre, University of Toronto, Toronto, Canada.,Department of Molecular Genetics, University of Toronto, Toronto, Canada
| | - Timothy R Hughes
- Donnelly Centre, University of Toronto, Toronto, Canada.,Department of Molecular Genetics, University of Toronto, Toronto, Canada
| | - Benjamin J Blencowe
- Donnelly Centre, University of Toronto, Toronto, Canada.,Department of Molecular Genetics, University of Toronto, Toronto, Canada
| | - Nikolaus Rajewsky
- Systems Biology of Gene Regulatory Elements, Berlin Institute for Medical Systems Biology, Max-Delbrück Center for Molecular Medicine, Berlin, Germany
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66
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(Neo)blast from the past: new insights into planarian stem cell lineages. Curr Opin Genet Dev 2016; 40:74-80. [PMID: 27379899 DOI: 10.1016/j.gde.2016.06.007] [Citation(s) in RCA: 49] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2016] [Revised: 05/18/2016] [Accepted: 06/16/2016] [Indexed: 12/20/2022]
Abstract
Collectively, planarian stem cells (neoblasts) are totipotent and are required for tissue homeostasis and regeneration. Recent work has begun to test the long-standing question of whether all neoblasts have the same potential, or whether they actually represent molecularly distinct subpopulations with distinct tissue restriction. Here, we summarize the current state of the field in neoblast lineage organization. It is clear that at least some neoblasts are totipotent, whereas other neoblasts represent functionally distinct molecular subclasses with restricted potential. In addition to neoblast subclasses, tissue-specific progenitors have also been identified, though their ability to proliferate is largely unknown. Together, neoblast lineage development, subclasses, and cell hierarchies are becoming elucidated, showing the complex regulation required for proper tissue homeostasis and regeneration in planarians.
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67
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Owlarn S, Bartscherer K. Go ahead, grow a head! A planarian's guide to anterior regeneration. ACTA ACUST UNITED AC 2016; 3:139-55. [PMID: 27606065 PMCID: PMC5011478 DOI: 10.1002/reg2.56] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2016] [Revised: 04/08/2016] [Accepted: 04/15/2016] [Indexed: 12/12/2022]
Abstract
The unique ability of some planarian species to regenerate a head de novo, including a functional brain, provides an experimentally accessible system in which to study the mechanisms underlying regeneration. Here, we summarize the current knowledge on the key steps of planarian head regeneration (head‐versus‐tail decision, anterior pole formation and head patterning) and their molecular and cellular basis. Moreover, instructive properties of the anterior pole as a putative organizer and in coordinating anterior midline formation are discussed. Finally, we highlight that regeneration initiation occurs in a two‐step manner and hypothesize that wound‐induced and existing positional cues interact to detect tissue loss and together determine the appropriate regenerative outcomes.
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Affiliation(s)
- Suthira Owlarn
- Max Planck Research Group Stem Cells and Regeneration Max Planck Institute for Molecular Biomedicine Von-Esmarch-Str. 5448149 Münster Germany; Medical Faculty University of Münster Albert-Schweitzer-Campus 148149 Münster Germany; CiM-IMPRS Graduate School Schlossplatz 548149 Münster Germany
| | - Kerstin Bartscherer
- Max Planck Research Group Stem Cells and Regeneration Max Planck Institute for Molecular Biomedicine Von-Esmarch-Str. 5448149 Münster Germany; Medical Faculty University of Münster Albert-Schweitzer-Campus 148149 Münster Germany
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68
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Stubenhaus BM, Dustin JP, Neverett ER, Beaudry MS, Nadeau LE, Burk-McCoy E, He X, Pearson BJ, Pellettieri J. Light-induced depigmentation in planarians models the pathophysiology of acute porphyrias. eLife 2016; 5. [PMID: 27240733 PMCID: PMC4887210 DOI: 10.7554/elife.14175] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2016] [Accepted: 04/25/2016] [Indexed: 12/12/2022] Open
Abstract
Porphyrias are disorders of heme metabolism frequently characterized by extreme photosensitivity. This symptom results from accumulation of porphyrins, tetrapyrrole intermediates in heme biosynthesis that generate reactive oxygen species when exposed to light, in the skin of affected individuals. Here we report that in addition to producing an ommochrome body pigment, the planarian flatworm Schmidtea mediterranea generates porphyrins in its subepithelial pigment cells under physiological conditions, and that this leads to pigment cell loss when animals are exposed to intense visible light. Remarkably, porphyrin biosynthesis and light-induced depigmentation are enhanced by starvation, recapitulating a common feature of some porphyrias – decreased nutrient intake precipitates an acute manifestation of the disease. Our results establish planarians as an experimentally tractable animal model for research into the pathophysiology of acute porphyrias, and potentially for the identification of novel pharmacological interventions capable of alleviating porphyrin-mediated photosensitivity or decoupling dieting and fasting from disease pathogenesis. DOI:http://dx.doi.org/10.7554/eLife.14175.001 Porphyrias are rare diseases that involve ring-shaped molecules called porphyrins accumulating in various parts of the body. Porphyrins are produced as part of the normal process that makes an important molecule called heme, which is required to transport oxygen. However, high levels of porphyrins can be toxic. For example, porphyrins deposited in the skin can cause swelling and blistering when the skin is exposed to bright light. Other disease symptoms include neurological issues ranging from anxiety and confusion to seizures or paralysis. It has been speculated that porphyrias may have affected several historical figures, including the artist Vincent van Gogh. In addition to their role in heme production, porphyrins also have other roles. For example, they are used as pigments in the wing feathers of some owls. Researchers are trying to understand more about how organisms regulate porphyrin production so that it might be possible to develop more effective treatments for porphyria in humans. Here, Stubenhaus et al. studied how a flatworm called Schmidtea mediterranea makes porphyrins. A group of undergraduate students noticed that these animals – which are normally brown in color – turned white when they were exposed to sunlight for several days. Stubenhaus et al. found that S. mediterranea makes porphyrins in the pigment cells of its skin using the same genes that make porphyrins in humans. Together with other molecules called ommochromes, the porphyrins give rise to the normal color of this flatworm. However, when the animals are exposed to intense light for extended periods of time, which is unlikely to occur in the wild, porphyrin production leads to loss of the pigment cells. The experiments also show that starvation increases the rate of pigment cell loss in light-exposed flatworms, which mirrors the worsening of disease symptoms some porphyria patients experience when they diet or fast. Stubenhaus et al. propose that flatworms are useful models in which to study the molecular processes that are responsible for porphyrias in humans. Further research is required to determine the exact chemical structure of the porphyrin and ommochrome molecules produced in different flatworm species. Stubenhaus et al. also plan to use flatworms to screen for drugs that could potentially be developed into new treatments for porphyria. DOI:http://dx.doi.org/10.7554/eLife.14175.002
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Affiliation(s)
| | - John P Dustin
- Department of Biology, Keene State College, Keene, United States
| | - Emily R Neverett
- Department of Biology, Keene State College, Keene, United States
| | - Megan S Beaudry
- Department of Biology, Keene State College, Keene, United States
| | - Leanna E Nadeau
- Department of Biology, Keene State College, Keene, United States
| | - Ethan Burk-McCoy
- Department of Biology, Keene State College, Keene, United States
| | - Xinwen He
- The Hospital for Sick Children, Toronto, Canada.,Department of Molecular Genetics, University of Toronto, Toronto, Canada
| | - Bret J Pearson
- The Hospital for Sick Children, Toronto, Canada.,Department of Molecular Genetics, University of Toronto, Toronto, Canada.,Ontario Institute for Cancer Research, Toronto, Canada
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69
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Barberán S, Fraguas S, Cebrià F. The EGFR signaling pathway controls gut progenitor differentiation during planarian regeneration and homeostasis. Development 2016; 143:2089-102. [PMID: 27122174 DOI: 10.1242/dev.131995] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2015] [Accepted: 04/12/2016] [Indexed: 12/19/2022]
Abstract
The planarian Schmidtea mediterranea maintains and regenerates all its adult tissues through the proliferation and differentiation of a single population of pluripotent adult stem cells (ASCs) called neoblasts. Despite recent advances, the mechanisms regulating ASC differentiation into mature cell types are poorly understood. Here, we show that silencing of the planarian EGF receptor egfr-1 by RNA interference (RNAi) impairs gut progenitor differentiation into mature cells, compromising gut regeneration and maintenance. We identify a new putative EGF ligand, nrg-1, the silencing of which phenocopies the defects observed in egfr-1(RNAi) animals. These findings indicate that egfr-1 and nrg-1 promote gut progenitor differentiation, and are thus essential for normal cell turnover and regeneration in the planarian gut. Our study demonstrates that the EGFR signaling pathway is an important regulator of ASC differentiation in planarians.
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Affiliation(s)
- Sara Barberán
- Department of Genetics, Faculty of Biology, University of Barcelona and Institute of Biomedicine of the University of Barcelona (IBUB), Av. Diagonal 643, Edifici Prevosti, Planta 1, Barcelona, Catalunya 08028, Spain
| | - Susanna Fraguas
- Department of Genetics, Faculty of Biology, University of Barcelona and Institute of Biomedicine of the University of Barcelona (IBUB), Av. Diagonal 643, Edifici Prevosti, Planta 1, Barcelona, Catalunya 08028, Spain
| | - Francesc Cebrià
- Department of Genetics, Faculty of Biology, University of Barcelona and Institute of Biomedicine of the University of Barcelona (IBUB), Av. Diagonal 643, Edifici Prevosti, Planta 1, Barcelona, Catalunya 08028, Spain
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70
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Molinaro AM, Pearson BJ. In silico lineage tracing through single cell transcriptomics identifies a neural stem cell population in planarians. Genome Biol 2016; 17:87. [PMID: 27150006 PMCID: PMC4858873 DOI: 10.1186/s13059-016-0937-9] [Citation(s) in RCA: 70] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2016] [Accepted: 04/08/2016] [Indexed: 12/01/2022] Open
Abstract
Background The planarian Schmidtea mediterranea is a master regenerator with a large adult stem cell compartment. The lack of transgenic labeling techniques in this animal has hindered the study of lineage progression and has made understanding the mechanisms of tissue regeneration a challenge. However, recent advances in single-cell transcriptomics and analysis methods allow for the discovery of novel cell lineages as differentiation progresses from stem cell to terminally differentiated cell. Results Here we apply pseudotime analysis and single-cell transcriptomics to identify adult stem cells belonging to specific cellular lineages and identify novel candidate genes for future in vivo lineage studies. We purify 168 single stem and progeny cells from the planarian head, which were subjected to single-cell RNA sequencing (scRNAseq). Pseudotime analysis with Waterfall and gene set enrichment analysis predicts a molecularly distinct neoblast sub-population with neural character (νNeoblasts) as well as a novel alternative lineage. Using the predicted νNeoblast markers, we demonstrate that a novel proliferative stem cell population exists adjacent to the brain. Conclusions scRNAseq coupled with in silico lineage analysis offers a new approach for studying lineage progression in planarians. The lineages identified here are extracted from a highly heterogeneous dataset with minimal prior knowledge of planarian lineages, demonstrating that lineage purification by transgenic labeling is not a prerequisite for this approach. The identification of the νNeoblast lineage demonstrates the usefulness of the planarian system for computationally predicting cellular lineages in an adult context coupled with in vivo verification. Electronic supplementary material The online version of this article (doi:10.1186/s13059-016-0937-9) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Alyssa M Molinaro
- Hospital for Sick Children, Program in Developmental and Stem Cell Biology, Toronto, ON, Canada.,Department of Molecular Genetics, University of Toronto, Toronto, ON, Canada
| | - Bret J Pearson
- Hospital for Sick Children, Program in Developmental and Stem Cell Biology, Toronto, ON, Canada. .,Department of Molecular Genetics, University of Toronto, Toronto, ON, Canada. .,Ontario Institute for Cancer Research, Toronto, ON, M5G0A4, Canada.
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71
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Currie KW, Brown DDR, Zhu S, Xu C, Voisin V, Bader GD, Pearson BJ. HOX gene complement and expression in the planarian Schmidtea mediterranea. EvoDevo 2016; 7:7. [PMID: 27034770 PMCID: PMC4815179 DOI: 10.1186/s13227-016-0044-8] [Citation(s) in RCA: 55] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2015] [Accepted: 03/09/2016] [Indexed: 12/21/2022] Open
Abstract
Background Freshwater planarians are well known for their regenerative abilities. Less well known is how planarians maintain spatial patterning in long-lived adult animals or how they re-pattern tissues during regeneration. HOX genes are good candidates to regulate planarian spatial patterning, yet the full complement or genomic clustering of planarian HOX genes has not yet been described, primarily because only a few have been detectable by in situ hybridization, and none have given morphological phenotypes when knocked down by RNAi. Results Because the planarian Schmidteamediterranea (S. mediterranea) is unsegmented, appendage less, and morphologically simple, it has been proposed that it may have a simplified HOX gene complement. Here, we argue against this hypothesis and show that S. mediterranea has a total of 13 HOX genes, which represent homologs to all major axial categories, and can be detected by whole-mount in situ hybridization using a highly sensitive method. In addition, we show that planarian HOX genes do not cluster in the genome, yet 5/13 have retained aspects of axially restricted expression. Finally, we confirm HOX gene axial expression by RNA deep-sequencing 6 anterior–posterior “zones” of the animal, which we provide as a dataset to the community to discover other axially restricted transcripts. Conclusions Freshwater planarians have an unappreciated HOX gene complexity, with all major axial categories represented. However, we conclude based on adult expression patterns that planarians have a derived body plan and their asexual lifestyle may have allowed for large changes in HOX expression from the last common ancestor between arthropods, flatworms, and vertebrates. Using our in situ method and axial zone RNAseq data, it should be possible to further understand the pathways that pattern the anterior–posterior axis of adult planarians. Electronic supplementary material The online version of this article (doi:10.1186/s13227-016-0044-8) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Ko W Currie
- Program in Developmental and Stem Cell Biology, Hospital for Sick Children, Toronto, ON M5G10A4 Canada ; Department of Molecular Genetics, University of Toronto, Toronto, ON M5G10A4 Canada
| | - David D R Brown
- Program in Developmental and Stem Cell Biology, Hospital for Sick Children, Toronto, ON M5G10A4 Canada ; Department of Molecular Genetics, University of Toronto, Toronto, ON M5G10A4 Canada
| | - Shujun Zhu
- Program in Developmental and Stem Cell Biology, Hospital for Sick Children, Toronto, ON M5G10A4 Canada ; Department of Molecular Genetics, University of Toronto, Toronto, ON M5G10A4 Canada
| | - ChangJiang Xu
- Donnelly Centre for Cellular and Biomolecular Research, Toronto, ON M5G10A4 Canada
| | - Veronique Voisin
- Donnelly Centre for Cellular and Biomolecular Research, Toronto, ON M5G10A4 Canada
| | - Gary D Bader
- Department of Molecular Genetics, University of Toronto, Toronto, ON M5G10A4 Canada ; Donnelly Centre for Cellular and Biomolecular Research, Toronto, ON M5G10A4 Canada
| | - Bret J Pearson
- Program in Developmental and Stem Cell Biology, Hospital for Sick Children, Toronto, ON M5G10A4 Canada ; Department of Molecular Genetics, University of Toronto, Toronto, ON M5G10A4 Canada ; Ontario Institute for Cancer Research, Toronto, ON M5G10A4 Canada
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72
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Collins JJ, Wendt GR, Iyer H, Newmark PA. Stem cell progeny contribute to the schistosome host-parasite interface. eLife 2016; 5:e12473. [PMID: 27003592 PMCID: PMC4841766 DOI: 10.7554/elife.12473] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2015] [Accepted: 03/03/2016] [Indexed: 12/14/2022] Open
Abstract
Schistosomes infect more than 200 million of the world's poorest people. These parasites live in the vasculature, producing eggs that spur a variety of chronic, potentially life-threatening, pathologies exacerbated by the long lifespan of schistosomes, that can thrive in the host for decades. How schistosomes maintain their longevity in this immunologically hostile environment is unknown. Here, we demonstrate that somatic stem cells in Schistosoma mansoni are biased towards generating a population of cells expressing factors associated exclusively with the schistosome host-parasite interface, a structure called the tegument. We show cells expressing these tegumental factors are short-lived and rapidly turned over. We suggest that stem cell-driven renewal of this tegumental lineage represents an important strategy for parasite survival in the context of the host vasculature. DOI:http://dx.doi.org/10.7554/eLife.12473.001 Schistosomes are parasitic worms that infect and cause chronic disease in hundreds of millions of people in the developing world. A major reason these parasites are so damaging is that they are capable of living and reproducing in the human bloodstream for decades. Previous research had shown that schistosomes have a population of stem cells that are proposed to promote the parasite’s survival inside the host’s bloodstream. However, it was not clear what role these cells play in the worms. Collins et al. have now found that, in a parasitic worm called Schistosoma mansoni, a large number of these stem cells are destined to become cells that generate the parasite’s skin. This unique tissue is known as the tegument, and had long been thought to have evolved in parasitic flatworms to help them survive in their host and evade its immune defenses. Therefore, Collins et al.’s findings suggest a new mechanism by which stem cells can promote the survival of a parasite inside its host. In the long-term, these findings could lead to new treatments for parasitic infections and may shed light on the evolution of parasitic flatworms. An important future challenge will be to determine if disrupting these parasites’ stem cells, and their ability to generate new tegumental cells, has any effect on the parasite inside its host. DOI:http://dx.doi.org/10.7554/eLife.12473.002
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Affiliation(s)
- James J Collins
- Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, Urbana, United States.,Department of Pharmacology, UT Southwestern Medical Center, Dallas, United States.,Howard Hughes Medical Institute, University of Illinois at Urbana-Champaign, Urbana, United States
| | - George R Wendt
- Department of Pharmacology, UT Southwestern Medical Center, Dallas, United States
| | - Harini Iyer
- Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, Urbana, United States.,Howard Hughes Medical Institute, University of Illinois at Urbana-Champaign, Urbana, United States
| | - Phillip A Newmark
- Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, Urbana, United States.,Howard Hughes Medical Institute, University of Illinois at Urbana-Champaign, Urbana, United States
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73
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Peiris TH, García-Ojeda ME, Oviedo NJ. Alternative flow cytometry strategies to analyze stem cells and cell death in planarians. ACTA ACUST UNITED AC 2016; 3:123-35. [PMID: 27307993 PMCID: PMC4895324 DOI: 10.1002/reg2.53] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2015] [Revised: 01/11/2016] [Accepted: 01/18/2016] [Indexed: 12/13/2022]
Abstract
Planarians possess remarkable stem cell populations that continuously support cellular turnover and are instrumental in the regeneration of tissues upon injury. Cellular turnover and tissue regeneration in planarians rely on the proper integration of local and systemic signals that regulate cell proliferation and cell death. Thus, understanding the signals controlling cellular proliferation and cell death in planarians could provide valuable insights for maintenance of adult body homeostasis and the biology of regeneration. Flow cytometry techniques have been utilized widely to identify, isolate, and characterize planarian stem cell populations. We developed alternative flow cytometry strategies that reduce the number of reagents and the time of sample preparation to analyze stem cells and cell death in planarians. The sensitivity of these methods is validated with functional studies using RNA interference and treatment with γ irradiation or stressful conditions that are known to trigger cell death. Altogether, we provide a community resource intended to minimize adverse effects during ex vivo studies of stem cells and cell death in planarians.
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Affiliation(s)
- Tanuja Harshani Peiris
- Department of Molecular and Cell Biology, School of Natural Sciences University of California Merced California 95343 USA; Quantitative and Systems Biology Graduate Program University of California Merced California 95343 USA
| | - Marcos E García-Ojeda
- Department of Molecular and Cell Biology, School of Natural Sciences University of California Merced California 95343 USA; Quantitative and Systems Biology Graduate Program University of California Merced California 95343 USA; Health Sciences Research Institute University of California Merced California 95343 USA
| | - Néstor J Oviedo
- Department of Molecular and Cell Biology, School of Natural Sciences University of California Merced California 95343 USA; Quantitative and Systems Biology Graduate Program University of California Merced California 95343 USA; Health Sciences Research Institute University of California Merced California 95343 USA
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74
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Brandl H, Moon H, Vila-Farré M, Liu SY, Henry I, Rink JC. PlanMine--a mineable resource of planarian biology and biodiversity. Nucleic Acids Res 2015; 44:D764-73. [PMID: 26578570 PMCID: PMC4702831 DOI: 10.1093/nar/gkv1148] [Citation(s) in RCA: 117] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2015] [Accepted: 10/19/2015] [Indexed: 11/13/2022] Open
Abstract
Planarian flatworms are in the midst of a renaissance as a model system for regeneration and stem cells. Besides two well-studied model species, hundreds of species exist worldwide that present a fascinating diversity of regenerative abilities, tissue turnover rates, reproductive strategies and other life history traits. PlanMine (http://planmine.mpi-cbg.de/) aims to accomplish two primary missions: First, to provide an easily accessible platform for sharing, comparing and value-added mining of planarian sequence data. Second, to catalyze the comparative analysis of the phenotypic diversity amongst planarian species. Currently, PlanMine houses transcriptomes independently assembled by our lab and community contributors. Detailed assembly/annotation statistics, a custom-developed BLAST viewer and easy export options enable comparisons at the contig and assembly level. Consistent annotation of all transcriptomes by an automated pipeline, the integration of published gene expression information and inter-relational query tools provide opportunities for mining planarian gene sequences and functions. For inter-species comparisons, we include transcriptomes of, so far, six planarian species, along with images, expert-curated information on their biology and pre-calculated cross-species sequence homologies. PlanMine is based on the popular InterMine system in order to make the rich biology of planarians accessible to the general life sciences research community.
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Affiliation(s)
- Holger Brandl
- Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, 01307 Dresden, Germany
| | - HongKee Moon
- Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, 01307 Dresden, Germany
| | - Miquel Vila-Farré
- Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, 01307 Dresden, Germany
| | - Shang-Yun Liu
- Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, 01307 Dresden, Germany
| | - Ian Henry
- Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, 01307 Dresden, Germany
| | - Jochen C Rink
- Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, 01307 Dresden, Germany
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75
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Tu KC, Cheng LC, T K Vu H, Lange JJ, McKinney SA, Seidel CW, Sánchez Alvarado A. Egr-5 is a post-mitotic regulator of planarian epidermal differentiation. eLife 2015; 4:e10501. [PMID: 26457503 PMCID: PMC4716842 DOI: 10.7554/elife.10501] [Citation(s) in RCA: 74] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2015] [Accepted: 10/10/2015] [Indexed: 02/06/2023] Open
Abstract
Neoblasts are an abundant, heterogeneous population of adult stem cells (ASCs) that facilitate the maintenance of planarian tissues and organs, providing a powerful system to study ASC self-renewal and differentiation dynamics. It is unknown how the collective output of neoblasts transit through differentiation pathways to produce specific cell types. The planarian epidermis is a simple tissue that undergoes rapid turnover. We found that as epidermal progeny differentiate, they progress through multiple spatiotemporal transition states with distinct gene expression profiles. We also identified a conserved early growth response family transcription factor, egr-5, that is essential for epidermal differentiation. Disruption of epidermal integrity by egr-5 RNAi triggers a global stress response that induces the proliferation of neoblasts and the concomitant expansion of not only epidermal, but also multiple progenitor cell populations. Our results further establish the planarian epidermis as a novel paradigm to uncover the molecular mechanisms regulating ASC specification in vivo.
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Affiliation(s)
- Kimberly C Tu
- Stowers Institute for Medical Research, Kansas City, United States
| | - Li-Chun Cheng
- Stowers Institute for Medical Research, Kansas City, United States
| | - Hanh T K Vu
- Stowers Institute for Medical Research, Kansas City, United States
| | - Jeffrey J Lange
- Stowers Institute for Medical Research, Kansas City, United States
| | - Sean A McKinney
- Stowers Institute for Medical Research, Kansas City, United States
| | - Chris W Seidel
- 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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Adler CE, Sánchez Alvarado A. Types or States? Cellular Dynamics and Regenerative Potential. Trends Cell Biol 2015; 25:687-696. [PMID: 26437587 DOI: 10.1016/j.tcb.2015.07.008] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2015] [Revised: 07/13/2015] [Accepted: 07/29/2015] [Indexed: 01/31/2023]
Abstract
Many of our organs can maintain and repair themselves during homeostasis and injury, as a result of the action of tissue-specific, multipotent stem cells. However, recent evidence from mammalian systems suggests that injury stimulates dramatic plasticity, or transient changes in cell potential, in both stem cells and more differentiated cells. Planarian flatworms possess abundant stem cells, making them an exceptional model for understanding the cellular behavior underlying homeostasis and regeneration. Recent discoveries of cell lineages and regeneration-specific events provide an initial framework for unraveling the complex cellular contributions to regeneration. In this review, we discuss the concept of cellular plasticity in the context of planarian regeneration, and consider the possibility that pluripotency may be a transient, probabilistic state exhibited by stem cells.
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Affiliation(s)
- Carolyn E Adler
- Stowers Institute for Medical Research, 1000 E. 50th Street, Kansas City, MO 64110, USA; Current address: Department of Molecular Medicine, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA.
| | - Alejandro Sánchez Alvarado
- Stowers Institute for Medical Research, 1000 E. 50th Street, Kansas City, MO 64110, USA; Howard Hughes Medical Institute, 4000 Jones Bridge Road, Chevy Chase, MD 20815-6789, USA.
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