Nick Barker

The University of Edinburgh, Edinburgh, Scotland, United Kingdom

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Publications (95)1300.54 Total impact

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  • Annie Ng · Nick Barker ·
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    ABSTRACT: The mammalian ovary is covered by a single-layered epithelium that undergoes rupture and remodelling following each ovulation. Although resident stem cells are presumed to be crucial for this cyclic regeneration, their identity and mode of action have been elusive. Surrogate stemness assays and in vivo fate-mapping studies using recently discovered stem cell markers have identified stem cell pools in the ovary and fimbria that ensure epithelial homeostasis. Recent findings provide insights into intrinsic mechanisms and local extrinsic cues that govern the function of ovarian and fimbrial stem cells. These discoveries have advanced our understanding of stem cell biology in the ovary and fimbria, and lay the foundations for evaluating the contribution of resident stem cells to the initiation and progression of human epithelial ovarian cancer.
    Nature Reviews Molecular Cell Biology 09/2015; 16(10). DOI:10.1038/nrm4056 · 37.81 Impact Factor
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    ABSTRACT: Wnt pathway deregulation is a common characteristic of many cancers. Only colorectal cancer predominantly harbours mutations in APC, whereas other cancer types (hepatocellular carcinoma, solid pseudopapillary tumours of the pancreas) have activating mutations in β-catenin (CTNNB1). We have compared the dynamics and the potency of β-catenin mutations in vivo. Within the murine small intestine (SI), an activating mutation of β-catenin took much longer to achieve Wnt deregulation and acquire a crypt-progenitor cell (CPC) phenotype than Apc or Gsk3 loss. Within the colon, a single activating mutation of β-catenin was unable to drive Wnt deregulation or induce the CPC phenotype. This ability of β-catenin mutation to differentially transform the SI versus the colon correlated with higher expression of E-cadherin and a higher number of E-cadherin:β-catenin complexes at the membrane. Reduction in E-cadherin synergised with an activating mutation of β-catenin resulting in a rapid CPC phenotype within the SI and colon. Thus, there is a threshold of β-catenin that is required to drive transformation, and E-cadherin can act as a buffer to sequester mutated β-catenin. © 2015 Cancer Research UK Beatson Institute. Published under the terms of the CC BY 4.0 license.
    The EMBO Journal 08/2015; 34(18). DOI:10.15252/embj.201591739 · 10.43 Impact Factor
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    ABSTRACT: The tumour suppressor p53 is regulated primarily at the protein level. In normal tissues its levels are maintained at a very low level by the action of specific E3 ligases and the ubiquitin proteosome pathway. The mutant p53 protein contributes to transformation, metastasis and drug resistance. High levels of mutant p53 can be found in tumours and the accumulation of mutant p53 has previously been reported in pathologically normal cells in human skin. We show for the first time that similarly elevated levels of mutant p53 can be detected in apparently normal cells in a mutant p53 knock-in mouse model. In fact, in the small intestine, mutant p53 spontaneously accumulates in a manner dependent on gene dosage and cell type. Mutant p53 protein is regulated similarly to wild type p53, which can accumulate rapidly after induction by ionising radiation or Mdm2 inhibitors, however, the clearance of mutant p53 protein is much slower than wild type p53. The accumulation of the protein in the murine small intestine is limited to the cycling, crypt base columnar cells and proliferative zone and is lost as the cells differentiate and exit the cell cycle. Loss of Mdm2 results in even higher levels of p53 expression but p53 is still restricted to proliferating cells in the small intestine. Therefore, the small intestine of these p53 mutant mice is an experimental system in which we can dissect the molecular pathways leading to p53 accumulation, which has important implications for cancer prevention and therapy. Link:
    Oncotarget 07/2015; 6(20):17968-17980. DOI:10.18632/oncotarget.4956 · 6.36 Impact Factor
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    ABSTRACT: The mammalian adult small intestinal epithelium is a rapidly self-renewing tissue that is maintained by a pool of cycling stem cells intermingled with Paneth cells at the base of crypts. These crypt base stem cells exclusively express Lgr5 and require Wnt3 or, in its absence, Wnt2b. However, the Frizzled (Fzd) receptor that transmits these Wnt signals is unknown. We determined the expression profile of Fzd receptors in Lgr5(+) stem cells, their immediate daughter cells, and Paneth cells. Here we show Fzd7 is enriched in Lgr5(+) stem cells and binds Wnt3 and Wnt2b. Conditional deletion of the Fzd7 gene in adult intestinal epithelium leads to stem cell loss in vivo and organoid death in vitro. Crypts of conventional Fzd7 knockout mice show decreased basal Wnt signaling and impaired capacity to regenerate the epithelium following deleterious insult. These observations indicate that Fzd7 is required for robust Wnt-dependent processes in Lgr5(+) intestinal stem cells. Copyright © 2015 The Authors. Published by Elsevier Inc. All rights reserved.
    Stem Cell Reports 04/2015; 4(5). DOI:10.1016/j.stemcr.2015.03.003 · 5.37 Impact Factor
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    ABSTRACT: Snail family members regulate epithelial-to-mesenchymal transition (EMT) during invasion of intestinal tumours, but their role in normal intestinal homeostasis is unknown. Studies in breast and skin epithelia indicate that Snail proteins promote an undifferentiated state. Here, we demonstrate that conditional knockout of Snai1 in the intestinal epithelium results in apoptotic loss of crypt base columnar stem cells and bias towards differentiation of secretory lineages. In vitro organoid cultures derived from Snai1 conditional knockout mice also undergo apoptosis when Snai1 is deleted. Conversely, ectopic expression of Snai1 in the intestinal epithelium in vivo results in the expansion of the crypt base columnar cell pool and a decrease in secretory enteroendocrine and Paneth cells. Following conditional deletion of Snai1, the intestinal epithelium fails to produce a proliferative response following radiation-induced damage indicating a fundamental requirement for Snai1 in epithelial regeneration. These results demonstrate that Snai1 is required for regulation of lineage choice, maintenance of CBC stem cells and regeneration of the intestinal epithelium following damage. © 2015 The Authors.
    The EMBO Journal 03/2015; 34(10). DOI:10.15252/embj.201490881 · 10.43 Impact Factor
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    ABSTRACT: The ovary surface epithelium (OSE) undergoes ovulatory tear and remodelling throughout life. Resident stem cells drive such tissue homeostasis in many adult epithelia, but their existence in the ovary has not been definitively proven. Lgr5 marks stem cells in multiple epithelia. Here we use reporter mice and single-molecule fluorescent in situ hybridization to document candidate Lgr5(+) stem cells in the mouse ovary and associated structures. Lgr5 is broadly expressed during ovary organogenesis, but becomes limited to the OSE in neonate life. In adults, Lgr5 expression is predominantly restricted to proliferative regions of the OSE and mesovarian-fimbria junctional epithelia. Using in vivo lineage tracing, we identify embryonic and neonate Lgr5(+) populations as stem/progenitor cells contributing to the development of the OSE cell lineage, as well as epithelia of the mesovarian ligament and oviduct/fimbria. Adult Lgr5(+) populations maintain OSE homeostasis and ovulatory regenerative repair in vivo. Thus, Lgr5 marks stem/progenitor cells of the ovary and tubal epithelia.
    Nature Cell Biology 07/2014; 16(8). DOI:10.1038/ncb3000 · 19.68 Impact Factor
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    ABSTRACT: Lgr5 is a marker for proliferating stem cells in adult intestine, stomach, and hair follicle. However, Lgr5 is not expressed in adult hematopoietic stem and progenitor cells (HSPCs). Whether Lgr5 is expressed in the embryonic and fetal HSPCs that undergo rapid proliferation is unknown. Here we report the detection of Lgr5 expression in HSPCs in the aorta-gonad-mesonephros (AGM) and fetal liver. We also found that a portion of Lgr5+ cells expressed the Runx1 gene that is critical for the ontogeny of HSPCs. A small portion of Lgr5+ cells also expressed HSPC surface markers c-Kit and CD34 in AGM or CD41 in fetal liver. Furthermore, the majority of Lgr5+ cells expressed Ki67, indicating their proliferating state. Transplantation of fetal liver-derived Lgr5-GFP+ cells (E12.5) demonstrated that Lgr5-GFP+ cells were able to reconstitute myeloid and lymphoid lineages in adult recipients, but the engraftment was short-term (4–8 weeks) and 20-fold lower compared with the Lgr5-GFP− control. Our data show that Lgr5-expressing cells mark short-term hematopoietic stem and progenitor cells, consistent with the role of Lgr5 in supporting HSPCs rapid proliferation during embryonic and fetal development.
    Journal of Biological Chemistry 06/2014; 289(34). DOI:10.1074/jbc.M114.568170 · 4.57 Impact Factor
  • Marc Leushacke · Nick Barker ·
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    ABSTRACT: Limited pools of resident adult stem cells are critical effectors of epithelial renewal in the intestine throughout life. Recently, significant progress has been made regarding the isolation and in vitro propagation of fetal and adult intestinal stem cells in mammals. It is now possible to generate ever-expanding, three-dimensional epithelial structures in culture that closely parallel the in vivo epithelium of the intestine. Growing such organotypic epithelium ex vivo facilitates a detailed description of endogenous niche factors or stem-cell characteristics, as they can be monitored in real time. Accordingly, this technology has already greatly contributed to our understanding of intestinal adult stem-cell renewal and differentiation. Transplanted organoids have also been proven to readily integrate into, and effect the long-term repair of, mouse colonic epithelia in vivo, establishing the organoid culture as a promising tool for adult stem cell/gene therapy. In another exciting development, novel genome-editing techniques have been successfully employed to functionally repair disease loci in cultured intestinal stem cells from human patients with a hereditary defect. It is anticipated that this technology will be instrumental in exploiting the regenerative medicine potential of human intestinal stem cells for treating human disorders in the intestinal tract and for creating near-physiological ex vivo models of human gastrointestinal disease.
    Gut 05/2014; 63(8). DOI:10.1136/gutjnl-2014-307204 · 14.66 Impact Factor
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    ABSTRACT: The different branches of the Wnt signaling pathway were first characterized in developmental contexts, but in recent times, each branch has been implicated in tumor growth and progression. This chapter exemplifies this link between development and cancer by focusing on two Wnt-driven cancers, colorectal cancer (CRC) and hepatocellular carcinoma (HCC). It focuses on the processes of epithelial-to-mesenchymal transition (EMT) and the reverse transition, mesenchymal-to-epithelial transition (MET), both fundamental mechanisms of tumor metastasis and morphogenesis. HCC shares many parallels with CRC with respect to the involvement of Wnt signaling in cancer initiation and progression.
    Wnt Signaling in Development and Disease, 03/2014: pages 315-328; , ISBN: 9781118444160
  • Shawna Tan · Nick Barker ·
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    ABSTRACT: The mammalian intestine is comprised of an epithelial layer that serves multiple functions in order to maintain digestive activity as well as intestinal homeostasis. This epithelial layer contains highly proliferative stem cells which facilitate its characteristic rapid regeneration. How these stem cells contribute to tissue repair and normal homeostasis are actively studied, and while we have a greater understanding of the molecular mechanisms and cellular locations that underlie stem cell regulation in this tissue, much still remains undiscovered. This review describes epithelial stem cells in both intestinal and non-intestinal tissues, as well as the strategies that have been used to further characterize the cells. Through a discussion of the current understanding of intestinal self-renewal and tissue regeneration in response to injury, we focus on how dysregulation of critical signaling pathways results in potentially oncogenic aberrations, and highlight issues that should be addressed in order for effective intestinal cancer therapies to be devised.
    Seminars in Cancer Biology 02/2014; 32. DOI:10.1016/j.semcancer.2014.02.005 · 9.33 Impact Factor
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    ABSTRACT: Leucine-rich repeat-containing G-protein-coupled receptor 5 (Lgr5) is expressed in many organs, including female reproductive organs, and is a stem cell marker in the stomach and intestinal epithelium, hair follicles, and ovarian surface epithelium. Despite ongoing studies, the definitive physiological functions of Lgr5 remain unclear. We utilized mice with conditional deletion of Lgr5 (Lgr5(d/d)) in the female reproductive organs by progesterone receptor-Cre (Pgr(Cre)) to determine Lgr5's functions during pregnancy. Only 30% of plugged Lgr5(d/d) females delivered live pups, and their litter sizes were lower. We found that pregnancy failure in Lgr5(d/d) females was due to insufficient ovarian progesterone (P4) secretion that compromised decidualization, terminating pregnancy. The drop in P4 levels was reflected in elevated levels of P4-metabolizing enzyme 20α-hydroxysteroid dehydrogenase in corpora lutea (CL) inactivated of Lgr5. Of interest, P4 supplementation rescued decidualization failure and supported pregnancy to full term in Lgr5(d/d) females. These results provide strong evidence that Lgr5 is critical to normal CL function, unveiling a new role of LGR5 in the ovary.-Sun, X., Terakawa, J., Clevers, H., Barker, N., Daikoku, T., Dey, S. K. Ovarian LGR5 is critical for successful pregnancy.
    The FASEB Journal 01/2014; 28(5). DOI:10.1096/fj.13-248344 · 5.04 Impact Factor
  • David Wei-Min Tan · Nick Barker ·
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    ABSTRACT: The intestinal epithelium is a classic example of a rapidly self-renewing tissue fueled by dedicated resident stem cells. These stem cells reside at the crypt base, generating committed progeny that mature into the various functional epithelial lineages while following a rapid migratory path toward the villi. Two models of intestinal stem cell location were proposed half a century ago and data have been presented in support of both models, dividing the scientific community. Molecular markers have been identified and validated using new techniques such as in vivo lineage tracing and ex vivo organoid culture. The intestinal stem cell niche comprises both epithelial cells, in particular the Paneth cell, and the stromal compartment, where cell-associated ligands and soluble factors regulate stem cell behavior. This review highlights the recent advances in identifying and characterizing the intestinal stem cells and their defining niche.
    Current Topics in Developmental Biology 01/2014; 107C:77-107. DOI:10.1016/B978-0-12-416022-4.00003-2 · 4.68 Impact Factor
  • Nick Barker ·
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    ABSTRACT: Small populations of adult stem cells are responsible for the remarkable ability of the epithelial lining of the intestine to be efficiently renewed and repaired throughout life. The recent discovery of specific markers for these stem cells, together with the development of new technologies to track endogenous stem cell activity in vivo and to exploit their ability to generate new epithelia ex vivo, has greatly improved our understanding of stem cell-driven homeostasis, regeneration and cancer in the intestine. These exciting new insights into the biology of intestinal stem cells have the potential to accelerate the development of stem cell-based therapies and ameliorate cancer treatments.
    Nature Reviews Molecular Cell Biology 12/2013; 15(1). DOI:10.1038/nrm3721 · 37.81 Impact Factor
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    ABSTRACT: Like normal colorectal epithelium, colorectal carcinomas (CRC) are organized hierarchically and include populations of cells with stem-like properties. Leucine-rich-repeat-containing G-protein-coupled receptor 5 (LGR5) is associated with these stem cells in normal colorectal epithelium, however the precise function of LGR5 in CRC remains largely unknown. Here, we analyzed the functional and molecular consequences of short hairpin RNA-mediated silencing of LGR5 in CRC cell lines SW480 and HT-29. Additionally, we exposed Lgr5-EGFP-IRES-CreERT2 mice to azoxymethane/dextrane sodium sulfate (AOM/DSS) which induces inflammation-driven colon tumors. Tumors were then flow-sorted into fractions of epithelial cells that expressed high or low levels of Lgr5 and were molecularly characterized using gene expression profiling and array comparative genomic hybridization. Silencing of LGR5 in SW480 CRC cells resulted in a depletion of spheres but did not affect adherently growing cells. Spheres expressed higher levels of several stem cell-associated genes than adherent cells, including LGR5. Silencing of LGR5 reduced proliferation, migration and colony formation in vitro, and tumorigenicity in vivo. In accordance with these results, NOTCH signaling was down-regulated upon LGR5 silencing. In AOM/DSS-induced colon tumors Lgr5 high cells showed higher levels of several stem cell-associated genes and higher Wnt signaling than Lgr5 low tumor cells and Lgr5 high normal colon cells. Array comparative genomic hybridization revealed no genomic imbalances in either tumor cell fraction. Our data elucidate mechanisms that define the role of LGR5 as a marker for stem-like cells in CRC.
    Carcinogenesis 11/2013; 35(4). DOI:10.1093/carcin/bgt377 · 5.33 Impact Factor
  • Marc Leushacke · Annie Ng · Joerg Galle · Markus Loeffler · Nick Barker ·
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    ABSTRACT: The pyloric epithelium continuously self-renews throughout life, driven by limited reservoirs of resident Lgr5(+) adult stem cells. Here, we characterize the population dynamics of these stem cells during epithelial homeostasis. Using a clonal fate-mapping strategy, we demonstrate that multiple Lgr5(+) cells routinely contribute to epithelial renewal in the pyloric gland and, similar to what was previously observed in the intestine, a balanced homeostasis of the glandular epithelium and stem cell pools is predominantly achieved via neutral competition between symmetrically dividing Lgr5(+) stem cells. Additionally, we document a lateral expansion of stem cell clones via gland fission under nondamage conditions. These findings represent a major advance in our basic understanding of tissue homeostasis in the stomach and form the foundation for identifying altered stem cell behavior during gastric disease.
    Cell Reports 10/2013; 9(2). DOI:10.1016/j.celrep.2013.09.025 · 8.36 Impact Factor

  • Cancer Research 08/2013; 73(8 Supplement):5023-5023. DOI:10.1158/1538-7445.AM2013-5023 · 9.33 Impact Factor

Publication Stats

17k Citations
1,300.54 Total Impact Points

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  • 2013-2015
    • The University of Edinburgh
      • MRC Centre for Regenerative Medicine
      Edinburgh, Scotland, United Kingdom
  • 2014
    • Institute for Stem Cell Biology and Regenerative Medicine
      Bengalūru, Karnataka, India
  • 1997-2012
    • University Medical Center Utrecht
      • Department of Immunology
      Utrecht, Utrecht, Netherlands
  • 2011
    • Institute of Medical Biology
      Tumasik, Singapore
  • 2007-2011
    • Hubrecht Institute
      Utrecht, Utrecht, Netherlands
  • 2003-2010
    • Netherlands Institute for Space Research, Utrecht
      Utrecht, Utrecht, Netherlands
  • 2008
    • Koninklijke Nederlandse Akademie van Wetenschappen
      • Hubrecht Institute for Developmental Biology and Stem Cell Research
      Amsterdamo, North Holland, Netherlands
  • 2001
    • Erasmus MC
      • Department of Medical Oncology
      Rotterdam, South Holland, Netherlands
  • 1998-2000
    • Utrecht University
      • Division of Immunology
      Utrecht, Utrecht, Netherlands