Adult pancreatic beta-cells are formed by self-duplication rather than stem-cell differentiation.
TL;DR: This work introduces a method for genetic lineage tracing to determine the contribution of stem cells to a tissue of interest and suggests that terminally differentiated β-cells retain a significant proliferative capacity in vivo and casts doubt on the idea that adult stem cells have a significant role in β-cell replenishment.
Abstract: How tissues generate and maintain the correct number of cells is a fundamental problem in biology. In principle, tissue turnover can occur by the differentiation of stem cells, as is well documented for blood, skin and intestine, or by the duplication of existing differentiated cells. Recent work on adult stem cells has highlighted their potential contribution to organ maintenance and repair. However, the extent to which stem cells actually participate in these processes in vivo is not clear. Here we introduce a method for genetic lineage tracing to determine the contribution of stem cells to a tissue of interest. We focus on pancreatic beta-cells, whose postnatal origins remain controversial. Our analysis shows that pre-existing beta-cells, rather than pluripotent stem cells, are the major source of new beta-cells during adult life and after pancreatectomy in mice. These results suggest that terminally differentiated beta-cells retain a significant proliferative capacity in vivo and cast doubt on the idea that adult stem cells have a significant role in beta-cell replenishment.
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TL;DR: This study identifies a specific combination of three transcription factors (Ngn3) Pdx1 and Mafa that reprograms differentiated pancreatic exocrine cells in adult mice into cells that closely resemble β-cells, and suggests a general paradigm for directing cell reprogramming without reversion to a pluripotent stem cell state.
Abstract: One goal of regenerative medicine is to instructively convert adult cells into other cell types for tissue repair and regeneration. Although isolated examples of adult cell reprogramming are known, there is no general understanding of how to turn one cell type into another in a controlled manner. Here, using a strategy of re-expressing key developmental regulators in vivo, we identify a specific combination of three transcription factors (Ngn3 (also known as Neurog3) Pdx1 and Mafa) that reprograms differentiated pancreatic exocrine cells in adult mice into cells that closely resemble beta-cells. The induced beta-cells are indistinguishable from endogenous islet beta-cells in size, shape and ultrastructure. They express genes essential for beta-cell function and can ameliorate hyperglycaemia by remodelling local vasculature and secreting insulin. This study provides an example of cellular reprogramming using defined factors in an adult organ and suggests a general paradigm for directing cell reprogramming without reversion to a pluripotent stem cell state.
1,990 citations
TL;DR: The path to meaningful clinical progress has never been clearer to improve PDAC patient survival and a deeper understanding of cancer cell biology, particularly altered cancer cell metabolism and impaired DNA repair processes, is providing novel therapeutic strategies that show strong preclinical activity.
Abstract: With 5-year survival rates remaining constant at 6% and rising incidences associated with an epidemic in obesity and metabolic syndrome, pancreatic ductal adenocarcinoma (PDAC) is on track to become the second most common cause of cancer-related deaths by 2030. The high mortality rate of PDAC stems primarily from the lack of early diagnosis and ineffective treatment for advanced tumors. During the past decade, the comprehensive atlas of genomic alterations, the prominence of specific pathways, the preclinical validation of such emerging targets, sophisticated preclinical model systems, and the molecular classification of PDAC into specific disease subtypes have all converged to illuminate drug discovery programs with clearer clinical path hypotheses. A deeper understanding of cancer cell biology, particularly altered cancer cell metabolism and impaired DNA repair processes, is providing novel therapeutic strategies that show strong preclinical activity. Elucidation of tumor biology principles, most notably a deeper understanding of the complexity of immune regulation in the tumor microenvironment, has provided an exciting framework to reawaken the immune system to attack PDAC cancer cells. While the long road of translation lies ahead, the path to meaningful clinical progress has never been clearer to improve PDAC patient survival.
1,220 citations
TL;DR: The data provide the first direct evidence for the source of proliferating cardiomyocytes during zebrafish heart regeneration and indicate that stem or progenitor cells are not significantly involved in this process.
Abstract: Although mammalian hearts show almost no ability to regenerate, there is a growing initiative to determine whether existing cardiomyocytes or progenitor cells can be coaxed into eliciting a regenerative response. In contrast to mammals, several non-mammalian vertebrate species are able to regenerate their hearts, including the zebrafish, which can fully regenerate its heart after amputation of up to 20% of the ventricle. To address directly the source of newly formed cardiomyocytes during zebrafish heart regeneration, we first established a genetic strategy to trace the lineage of cardiomyocytes in the adult fish, on the basis of the Cre/lox system widely used in the mouse. Here we use this system to show that regenerated heart muscle cells are derived from the proliferation of differentiated cardiomyocytes. Furthermore, we show that proliferating cardiomyocytes undergo limited dedifferentiation characterized by the disassembly of their sarcomeric structure, detachment from one another and the expression of regulators of cell-cycle progression. Specifically, we show that the gene product of polo-like kinase 1 (plk1) is an essential component of cardiomyocyte proliferation during heart regeneration. Our data provide the first direct evidence for the source of proliferating cardiomyocytes during zebrafish heart regeneration and indicate that stem or progenitor cells are not significantly involved in this process.
1,195 citations
TL;DR: The results indicate that electrically coupled cardiac muscle regenerates after resection injury, primarily through activation and expansion of cardiomyocyte populations, which have implications for promoting regeneration of the injured human heart.
Abstract: Recent studies indicate that mammals, including humans, maintain some capacity to renew cardiomyocytes throughout postnatal life. Yet, there is little or no significant cardiac muscle regeneration after an injury such as acute myocardial infarction. By contrast, zebrafish efficiently regenerate lost cardiac muscle, providing a model for understanding how natural heart regeneration may be blocked or enhanced. In the absence of lineage-tracing technology applicable to adult zebrafish, the cellular origins of newly regenerated cardiac muscle have remained unclear. Using new genetic fate-mapping approaches, here we identify a population of cardiomyocytes that become activated after resection of the ventricular apex and contribute prominently to cardiac muscle regeneration. Through the use of a transgenic reporter strain, we found that cardiomyocytes throughout the subepicardial ventricular layer trigger expression of the embryonic cardiogenesis gene gata4 within a week of trauma, before expression localizes to proliferating cardiomyocytes surrounding and within the injury site. Cre-recombinase-based lineage-tracing of cells expressing gata4 before evident regeneration, or of cells expressing the contractile gene cmlc2 before injury, each labelled most cardiac muscle in the ensuing regenerate. By optical voltage mapping of surface myocardium in whole ventricles, we found that electrical conduction is re-established between existing and regenerated cardiomyocytes between 2 and 4 weeks post-injury. After injury and prolonged fibroblast growth factor receptor inhibition to arrest cardiac regeneration and enable scar formation, experimental release of the signalling block led to gata4 expression and morphological improvement of the injured ventricular wall without loss of scar tissue. Our results indicate that electrically coupled cardiac muscle regenerates after resection injury, primarily through activation and expansion of cardiomyocyte populations. These findings have implications for promoting regeneration of the injured human heart.
969 citations
TL;DR: The genetic data support the view that an age-induced increase of p16INK4a expression limits the regenerative capacity of β-cells with ageing and constrains islet proliferation and regeneration in anAge-dependent manner.
Abstract: In this issue, three separate labs report the discovery of a protein that regulates ageing specifically in stem cells. This helps answer a fundamental question: why do mammalian progenitor cells gradually lose their ability to divide and generate new cells as they grow old? Norman Sharpless and colleagues generated a knockout mouse lacking tumour suppressor p16INK4a, a protein involved in cell cycle control and known to be expressed in an age-dependent manner. Studying its role in regeneration of the blood, pancreas and brain, the three groups separately found that p16INK4a is not only a biomarker, but an effector of ageing. By comparing the effect of elevated or reduced p16INK4a expression in mice, they found that p16INK4a halts proliferation of stem cells, but only in older mice. Taken together, the work suggests that p16INK4a reduces cancer incidence via its tumour suppressor action, at the same time contributing to ageing by reducing stem cell function. The work also suggests that type 2 diabetes might be linked to the failure of the pancreatic islets to renew, and that blocking this protein in certain tissues might combat some effects of ageing. Three separate labs report that p16INK4a, a protein known to be expressed in an age-dependent manner regulates ageing specifically in stem cells. Studying its role in regeneration of three different tissues, the blood, pancreas, and brain, the three groups separately found that p16INK4a is not only a biomarker, but an effector of ageing. The p16INK4a tumour suppressor accumulates in many tissues as a function of advancing age1,2,3. p16INK4a is an effector of senescence4,5 and a potent inhibitor of the proliferative kinase Cdk4 (ref. 6), which is essential for pancreatic β-cell proliferation in adult mammals7,8. Here we show that p16INK4a constrains islet proliferation and regeneration in an age-dependent manner. Expression of the p16INK4a transcript is enriched in purified islets compared with the exocrine pancreas, and islet-specific expression of p16INK4a, but not other cyclin-dependent kinase inhibitors, increases markedly with ageing. To determine the physiological significance of p16INK4a accumulation on islet function, we assessed the impact of p16INK4a deficiency and overexpression with increasing age and in the regenerative response after exposure to a specific β-cell toxin. Transgenic mice that overexpress p16INK4a to a degree seen with ageing demonstrated decreased islet proliferation. Similarly, islet proliferation was unaffected by p16INK4a deficiency in young mice, but was relatively increased in p16INK4a-deficient old mice. Survival after toxin-mediated ablation of β-cells, which requires islet proliferation, declined with advancing age; however, mice lacking p16INK4a demonstrated enhanced islet proliferation and survival after β-cell ablation. These genetic data support the view that an age-induced increase of p16INK4a expression limits the regenerative capacity of β-cells with ageing.
966 citations
References
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Book•
01 Jan 1983
TL;DR: Biology of Cultured Cells, Design and Layout, and Organotypic Culture: Problems Solving.
Abstract: The most complete resource on the techniques, equipment,principles, and practices of animal cell culture
Since publication of the previous edition of this benchmark text, numerous groundbreaking advances have occurred in stem cell research, cloning, tissue engineering, and in vitro toxicity testing. These and other developments have been incorporated into this fully revised and expanded Fifth Edition of Culture of Animal Cells. In addition, to answer the needs of the exponential increase in newcomers to cell culture, particularly in the biopharmaceutical industry, a completely new chapter on training in cell culture technology has been introduced.
The most complete resource on the techniques, equipment, principles, and practices of animal cell culture, this text offers a complete background related to growth of animal cells in culture. Beginning with laboratory design, safety, validation and bioethics, then continuing with preparation of media, primary culture and cell lines, through to characterization and authentication, contamination, specialized techniques, and troubleshooting, the coverage includes:
* An all-new section of training exercises, separated into basic, intermediate, and advanced procedures, cross-referenced to the relevant protocols
* New coverage of stem cells, bioethics, validation, cloning, cell signaling, in vitro toxicity testing, and tissue engineering
* An expanded full-color atlas section, with images of primary culture, cell lines, subculture, differentiation, cancer cells and transformation, three-dimensional culture, contamination, and specialized equipment
* Enhanced treatment of troubleshooting, with full cross-referencing to the relevant protocols and sections of text
* Fully updated references
* The clearest, most consistent presentation of step-by-step protocols available
* Numerous diagrams, photographs, tables, and charts
* Detailed and up-to-date information on reagent preparation and sourcing of materials and equipment, including a fully updated list of suppliers and other resources with Web sites
Indispensable for clinical and biopharmaceutical researchers and scientists, students, trainees, and technicians, this landmark text presents the most accessible and comprehensive introduction available to the culture and experimental manipulation of animal cells.
5,543 citations
"Adult pancreatic beta-cells are for..." refers methods in this paper
...Pancreases were dissociated to a single-cell suspension essentially as describe...
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TL;DR: Molecular insights into the formation of new blood vessels are being generated at a rapidly increasing pace, offering new therapeutic opportunities that are currently being evaluated.
Abstract: Blood vessels constitute the first organ in the embryo and form the largest network in our body but, sadly, are also often deadly. When dysregulated, the formation of new blood vessels contributes to numerous malignant, ischemic, inflammatory, infectious and immune disorders. Molecular insights into these processes are being generated at a rapidly increasing pace, offering new therapeutic opportunities that are currently being evaluated.
4,137 citations
"Adult pancreatic beta-cells are for..." refers background in this paper
...A similar process is thought to occur during angiogenesis, in which differentiated endothelial cells give rise to ‘activated endothelium’, which then proliferates and organizes into new blood vessel...
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Book•
17 Sep 2010
2,236 citations
TL;DR: The results provide direct evidence that NGN3+ cells are islet progenitors during embryogenesis and in adult mice, and suggest that lineages for exocrine, endocrine islet and duct progenitor are committed at mid-gestation.
Abstract: The location and lineage of cells that give rise to endocrine islets during embryogenesis has not been established nor has the origin or identity of adult islet stem cells. We have employed an inducible Cre-ER(TM)-LoxP system to indelibly mark the progeny of cells expressing either Ngn3 or Pdx1 at different stages of development. The results provide direct evidence that NGN3+ cells are islet progenitors during embryogenesis and in adult mice. In addition, we find that cells expressing Pdx1 give rise to all three types of pancreatic tissue: exocrine, endocrine and duct. Furthermore, exocrine and endocrine cells are derived from Pdx1-expressing progenitors throughout embryogenesis. By contrast, the pancreatic duct arises from PDX1+ progenitors that are set aside around embryonic day 10.5 (E9.5-E11.5). These findings suggest that lineages for exocrine, endocrine islet and duct progenitors are committed at mid-gestation.
1,507 citations
TL;DR: Following the transfer into fertilized mouse eggs of recombinant genes composed of the upstream region of the rat insulin II gene linked to sequences coding for the large-T antigen of simian virus 40, large- T antigen is detected exclusively in the β-Cells of the endocrine pancreas of transgenic mice.
Abstract: Following the transfer into fertilized mouse eggs of recombinant genes composed of the upstream region of the rat insulin II gene linked to sequences coding for the large-T antigen of simian virus 40, large-T antigen is detected exclusively in the beta-cells of the endocrine pancreas of transgenic mice. The alpha- and delta-cells normally found in the islets of Langerhans are rare and disordered. Well-vascularized beta-cell tumours arise in mice harbouring and inheriting these hybrid oncogenes.
1,383 citations
"Adult pancreatic beta-cells are for..." refers methods in this paper
...We generated a transgenic mouse strain in which the insulin promote...
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