DOCSLIB.ORG

DNA Damage Checkpoint Control in Cells Exposed to Ionizing Radiation

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
DNA Damage Checkpoint Control in Cells Exposed to Ionizing Radiation Oncogene (2003) 22, 5834–5847 & 2003 Nature Publishing Group All rights reserved 0950-9232/03 $25.00 www.nature.com/onc DNA damage checkpoint control in cells exposed to ionizing radiation George Iliakis*,1, Ya Wang2, Jun Guan2 and Huichen Wang2 1Institute of Medical Radiation Biology, University of Essen Medical School, Hufelanstrasse 55, 45122 Essen, Germany; 2Department of Radiation Oncology, Kimmel Cancer Center, Jefferson Medical College, Philadelphia, PA 19107, USA Damage induced in the DNA after exposure of cells to Lu¨ cke-Huhle, 1982). Strong support for this alternative ionizing radiation activates checkpoint pathways that came with the observation that cells from ataxia inhibit progression of cells through the G1 and G2 phases telagiectasia (AT) patients have significantly reduced and induce a transient delay in the progression through delays in their progression through the cell cycle and are, S phase.Checkpoints together with repair and apoptosis at the same time, sensitive to killing after exposure to IR are integrated in a circuitry that determines the ultimate (Houldsworth and Lavin, 1980; Painter and Young, response of a cell to DNA damage.Checkpoint activation 1980; Painter, 1981, 1986; Lavin and Schroeder, 1988). typically requires sensors and mediators of DNA damage, Decisive in the further development of the field was signal transducers and effectors.Here, we review the the isolation, first in the budding and later in the fission current state of knowledge regarding mechanisms of yeast, of repair-proficient, radiation-sensitive mutants checkpoint activation and proteins involved in the different showing defects in radiation-induced cell cycle delays steps of the process.Emphasis is placed on the role of (Lee and Nurse, 1988; Hartwell and Weinert, 1989; ATM and ATR, as well on CHK1 and CHK2 kinases in Nurse, 1990; Norbury and Nurse, 1992; Hartwell and checkpoint response.The roles of downstream effectors, Kastan, 1994; Paulovich et al., 1997). Extensive genetic such as P53 and the CDC25 family of proteins, are also studies with these organisms uncovered a complex described, and connections between repair and checkpoint network of genes that cooperate to delay the normal activation are attempted.The role of checkpoints in progression through the cycle as soon as damage is genomic stability and the potential of improving the registered in the genome. We now know that in these treatment of cancer by DNA damage inducing agents genome-surveillance mechanisms, delay in cell cycle through checkpoint abrogation are also briefly outlined. progression is but one manifestation, captured by the Oncogene (2003) 22, 5834–5847. doi:10.1038/sj.onc.1206682 term DNA damage checkpoint. The present state of knowledge allows the integration of delays induced after Keywords: checkpoints; DNA repair; DNA double- irradiation in the different phases of the cell cycle under strand breaks; ionizing radiation the rubric of a single checkpoint activated by damage in the DNA (Elledge, 1996; Zhou and Elledge, 2000). A parallel development that proved essential for the molecular understanding of the DNA damage check- point was the delineation of events underlying progres- Introduction sion of cells through the cycle. It is now established that the cell cycle is controlled by interdependent regulatory It has been known for over 50 years that exposure of transitions that bring the DNA to a state competent for cells to ionizing radiation (IR) delays the normal duplication and division (Nurse, 1994; Elledge, 1996; progression through the cell cycle (Maity et al., 1994; Sherr, 1996; Stillman, 1996). These transitions are Bernhard et al., 1995; Iliakis, 1997). While a delay in G2 achieved by the activation of cyclin-dependent kinases is the most evident, significant delays also occur in G1, (CDKs), the operation of proteolytic pathways and as well as throughout S phase. These cell cycle delays alterations in the state of chromatin. CDKs are essential were initially interpreted as passive cellular responses components of the cell cycle machinery and are subject resulting from the induction by IR of damage in the to strict regulation by independent mechanisms includ- DNA. However, these early studies also provided ing association with cognate cyclins, phosphorylation at circumstantial evidence that the delays actually reflect specific serine/threonine or tyrosine residues and the induction of cellular processes assisting the irradiated association with specific inhibitory proteins. Not sur- cell to cope with the induced damage by somehow prisingly, CDKs turn out to also function as key targets facilitating repair (Walters et al., 1974; Tobey, 1975; of the checkpoint response. Progression through the cycle mediated by the above cell cycle machinery is ‘checked’ by surveillance mechanisms to ensure that cells will not progress to the next phase of the cell cycle *Correspondence: Professor Dr G Iliakis; before events of the preceding phase have been E-mail: [email protected] completed (Hartwell and Weinert, 1989; Hartwell and DNA damage checkpoint control in cells G Iliakis et al 5835 Kastan, 1994; Nurse, 1997; Paulovich et al., 1997). Conceptual Organization of These surveillance mechanisms, known as cell cycle DNA Damage Checkpoint Response checkpoints, are conceptually distinct from the DNA damage checkpoint. However, as our understanding of Signal the molecular mechanisms underlying the different DNA Damage checkpoints increases important similarities become (Before or after processing) apparent. Here, we briefly outline the current state of knowledge of the DNA damage checkpoint. The progress made since the initial radiobiological observations is specta- Sensors cular and represents the combined achievements of genetics and biochemistry in yeast, Xenopus and REPAIR Signal mammalian cell systems. The review mainly focuses on Transduction the DNA damage checkpoint as presently delineated in Transducers higher eukaryotes exposed to IR. Studies with other systems are only mentioned when the results have direct relevance to higher eukaryotes. Despite the recent dramatic accumulation of knowledge, key issues of Effectors checkpoint response remain unresolved and are dis- cussed briefly. Apoptosis Like many fields in modern biology, the field of checkpoints is nurtured by the conviction that detailed Interphase to Cell Cycle, or Transcription knowledge of the molecular mechanisms will enable a better understanding of the processes underlying geno- Figure 1 Conceptual organization of the essential components mic instability and cancer. Virtually every gene im- and the outcomes of checkpoint responses plicated in the DNA damage checkpoint contributes to genomic stability or is associated with genetic disorders Table 1 or predisposition to cancer development. Moreover, because checkpoint abrogation seems to be an impor- Function Class Gene tant feature of the cancer cell, considerable effort is Sensors/mediators RFC1-like RAD17 presently placed towards the development of com- RFC2-5 pounds that specifically abrogate the remaining check- PCNA-like RAD9 point responses in cancer cells. It is hoped that these RAD1 reagents will significantly improve our ability to combat HUS1 BRCT-containing BRCA1 cancer, alone or in combination with other treatment 53BP1 modalities such as IR. TopBP1 MDC1 DSB recognition/repair Mre11 General concepts and key players RAD50 NBS1 The DNA damage checkpoint can be defined as a network of interacting pathways operating in concert to Transducers PI3 kinases like protein ATR recognize damage in the DNA and elicit the response ATM (Elledge, 1996; Zhou and Elledge, 2000; Nyberg et al., PIKK binding proteins ATRIP Effector kinases CHK1 2002). It shares characteristics of a signal transduction CHK2 pathway, and the participating proteins can be formally divided into sensors, transducers and effectors (Figure 1). Sensor proteins recognize DNA damages, detailed mechanisms of signal transmission and arrest in directly or indirectly, and function to signal the presence the different phases of the cell cycle are described in the of these abnormalities and initiate the biochemical subsequent sections. cascade. Transducers are typically protein kinases that It comes as a surprise that from the basic steps of the relay and amplify the damage signal from the sensors by DNA damage checkpoint, the one involved in the initial phosphorylating other kinases or downstream target sensing of abnormal DNA structures is the less well proteins. Effector proteins include the ultimate down- understood. Two proteins were initially considered good stream targets of the transducer protein kinases. candidates as sensors owing to their ability to be directly Modification of effector proteins by upstream kinases, activated by single- and double-strand breaks (DSBs), directly or indirectly, mediates the inhibition in cell cycle respectively, poly(ADP-ribose) polymerase (PARP) and progression. The effector stage is where the DNA DNA-dependent protein kinase (DNA-PK) (Lu¨ cke- damage checkpoint, interphases with the cell cycle Huhle, 1982; Anderson and Carter, 1996; Lees-Miller, machinery. Proteins presently implicated as sensors 1996; Jeggo, 1997; D’Amours et al., 1999; Smith and and signal transducers are summarized in Table 1, and Jackson, 1999; Smith, 2001; Ziegler and Oei, 2001). key players are described next. Effector proteins and However, they do not seem to be required for the Oncogene DNA damage checkpoint control in cells G Iliakis et al 5836 initiation
Load more

Recommended publications
  • Calcium Lability of Cytoplasmic Microtubules and Its Modulation By
    Proc. Natl. Acad. Sci. USA Vol. 78, No. 2, pp. 1037-1041, February 1981 Cell Biology Calcium lability of cytoplasmic microtubules and its modulation by microtubule-associated proteins (detergent extraction/calmodulin/calmodulin inhibitors/immunofluorescence microscopy) MANFRED SCHLIWA*, URSULA EUTENEUER*, JEANNETTE CHLOE BULINSKItt, AND JONATHAN G. IZANT* *Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, Colorado 80309; and tLaboratory of Molecular Biology, University of Wisconsin, Madison, Wisconsin 53706 Communicated by Keith R. Porter, October 31, 1980 ABSTRACT Detergent-extracted BSC-1 monkey cells have The discovery that calmodulin, a ubiquitous Ca2+-binding been used as a model system to study the Ca2+ sensitivity of in vivo protein that regulates a number of Ca2+-dependent functions polymerized microtubules under in vitro conditions. The effects (for reviews, see refs. 9 and 10), influences microtubule assem- of various experimental treatments were observed by immuno- has the fluorescence microscopy. Whereas microtubules are completely bly in vitro in a Ca2+-dependent manner (11) opened stable at Ca2+ concentrations below 1 pM, Ca2+ at greater than possibility that Ca2+ effects on microtubules are mediated by 1-4 ,uM induces microtubule disassembly that begins in the cell this protein. Immunofluorescence microscopy with antibodies periphery and proceeds towards the cell center. At concentrations against calmodulin further showed an association of this protein of up to 500 jiM, both the pattern and time course of disassembly with certain components of the mitotic spindle (12, 13), sug- are not markedly altered, suggesting that, within this concentra- gesting an important role in Ca2+-dependent functions during tion range, Ca2+ effects are catalytic rather than stoichiometric.
    [Show full text]
  • Molecules Involved in Proliferation of Normal and Cancer Cells: Presidential Address1
    [CANCER RESEARCH 47. 1488-1491, March 15, 1987] Molecules Involved in Proliferation of Normal and Cancer Cells: Presidential Address1 Arthur B. Pardee Division of Cell Growth and Regulation, Dana-Farber Cancer Institute, Boston, Massachusetts 02115 Overview may permit the escape of cells from growth control. The proposal that a labile protein is necessary for prolifera All definitions of cancer stress the defective regulation of cell tion of normal cells and that its levels are altered in tumorigenic growth and differentiation because such physiological aberra cells led us to examine proteins on two-dimensional gels. A tions underlie the gross derangements of the disease. An im candidate protein which was unstable in normal cells but rela portant goal of basic cancer biology is to provide molecular tively stabilized in tumorigenic cells was indeed identified. It explanations for these defective cellular processes. With recent has been shown to possess a molecular weight of 68,000. This developments in molecular and cellular biology, investigators protein is one of a very small number closely linked to cell have obtained penetrating insights into cell processes and their proliferation during G|. Our work in progress is designed to respective derangements. These are being investigated at four further identify this protein, clone its gene, and study its prop experimental levels: genes and their mRNAs; growth factors erties in normal cells that have been transfected with this gene. and their receptors; biochemical regulation; and cell biology in We are also investigating events following the restriction culture. The results are interrelated and integrated within the point. The rather long time interval (about 2 h) between the framework of the classical cell proliferation cycle.
    [Show full text]
  • P53 Regulates Biosynthesis Through Direct Inactivation of Glucose-6-Phosphate Dehydrogenase
    LETTERS p53 regulates biosynthesis through direct inactivation of glucose-6-phosphate dehydrogenase Peng Jiang1,2,4, Wenjing Du1,2,4, Xingwu Wang1, Anthony Mancuso2, Xiang Gao3, Mian Wu1,5 and Xiaolu Yang2,5 Cancer cells consume large quantities of glucose and primarily link to glycolysis, the regulation of the PPP in tumour cells use glycolysis for ATP production, even in the presence of remains unclear. adequate oxygen1,2. This metabolic signature (aerobic To investigate whether p53 modulates the PPP, we compared the glycolysis or the Warburg effect) enables cancer cells to direct oxidative PPP flux in isogenic p53C=C and p53−=− human colon glucose to biosynthesis, supporting their rapid growth and cancer HCT116 cells11. Cells were cultured in medium containing proliferation3,4. However, both causes of the Warburg effect [2-13C]glucose, and the glucose metabolites were measured by nuclear and its connection to biosynthesis are not well understood. magnetic resonance (NMR) spectroscopy. As shown in Fig. 1a, the Here we show that the tumour suppressor p53, the most absence of p53 resulted in a strong enhancement (∼50%) in oxidative frequently mutated gene in human tumours, inhibits the PPP flux, indicating that p53 suppresses the PPP. The absence of p53 pentose phosphate pathway5 (PPP). Through the PPP, p53 concomitantly led to a strong increase in glucose consumption, and this suppresses glucose consumption, NADPH production and was observed in both HCT116 and mouse embryonic fibroblast (MEF) biosynthesis. The p53 protein binds to glucose-6-phosphate cells (Fig. 1b,c). Inhibition of G6PD using either small interfering RNA dehydrogenase (G6PD), the first and rate-limiting enzyme of (siRNA) or dehydroepiandrosterone (DHEA) reversed the increase in the PPP, and prevents the formation of the active dimer.
    [Show full text]
  • Control of Cell Division: Models from Microorganisms
    [CANCER RESEARCH 28, 1802-1809,September 1968] Control of Cell Division: Models from Microorganisms Arthur B. Pardee Program in Biochemical Sciences, Moffett Laboratory, Princeton University, Princeton, New Jersey 08540 Control of Cell Division of a few years ago on the bacterial division cycle are sum One approach to the discovery of a difference between nor marized (12). The reviews furnish a guide to the literature mal and malignant cells is to investigate the regulation of cell before 1966. division. Normal tissues are regulated so that their cells are in a steady-state balance between duplication and destruction. Bacterial Division Malignant cells appear to duplicate unceasingly and are not Most investigations of bacterial division have been carried out with the closely related Gram-negative staining organisms in balance with the rest of the organism; they appear to have lost a control mechanism for cell division. Our problem is to Escherichia coli and Salmonella typhimurium. These organisms are implied unless otherwise stated. Gram-positive Bacillus determine how normal control mechanisms function, how they are deranged in malignant cells, and how they can be restored. species have been used for some fundamental studies on chro The working hypothesis of this article is that the funda mosome replication and for morphologic investigations. It is mental biochemical events which regulate cell division are too early to say whether important differences of cell division similar in both bacteria and higher organisms. This hypothesis regulation exist between different bacteria. Major points of will be useful at present to the extent that bacteria provide bacterial division and chromosomal duplication are illustrated a logical framework for ideas and experiments regarding an schematically in Chart 1.
    [Show full text]
  • Restriction Point Control of Cell Growth by a Labile Protein
    Proc. NatL Acad. Sci. USA Vol. 79, pp. 436-440, January 1982 Cell Biology Restriction point control of cell growth by a labile protein: Evidence for increased stability in transformed cells (animal cells/transformation/protein degradation/cell cycle/growth control) JUDITH CAMPISI, ESTELA E. MEDRANO*, GAIL MORREO, AND ARTHUR B. PARDEEt Department of Pharmacology, Harvard Medical School, and Division ofCell Growth and Regulation, Sidney Farber Cancer Institute, 44 Binney Street, Boston, Massachusetts 02115 Contributed by Arthur B. Pardee, September 14, 1981 ABSTRACT It has been proposed that animal cells must ac- mouse 3T3 cells at 2-3 hr prior to the onset of DNA synthesis cumulate a labile protein(s) before they can pass the restriction (7, 8). (R) point in the G1 phase ofthe cell cycle [Rossow, P. W., Riddle, What is the biochemical nature of the R point? Two types of V. G. H. & Pardee, A. B. (1979) Proc NatL Acad Sci USA 76, experiments have led to the hypothesis that afunctionally short- 4446-4450]. Here, we present evidence that this R protein ac- lived (labile) regulatory protein(s) (R protein), whose synthesis quires increased stability in transformed 3T3 cells, thereby allow- is sensitive to environmental conditions, need accumulate to a ing these cells to continue growth under conditions that arrest critical amount before a cell can pass the R point and proceed untransformed cells. Low doses of cycloheximide or histidinol towards DNA synthesis. First, pulses ofhigh concentrations of drastically reduced the rate at which normal 3T3 (A31) fibroblasts cycloheximide (CHM), administered to synchronized cultures, in early G, could enter DNA synthesis.
    [Show full text]
  • The Role of Metals in Enzyme Activity*
    ANNALS OF CLINICAL AND LABORATORY SCIENCE, Vol. 7, No. 2 Copyright © 1977, Institute for Clinical Science The Role of Metals in Enzyme Activity* JAMES F. RIORDAN, Ph.D. Biophysics Research Laboratory, Department of Biological Chemistry, Harvard Medical School, and Division of Medical Biology, Veter Bent Brigham Hospital, Boston, MA 02115 ABSTRACT Metal ions play important roles in the biological function of many en­ zymes. The various modes of metal-protein interaction include metal-, ligand-, and enzyme-bridge complexes. Metals can serve as electron donors or acceptors, Lewis acids or structural regulators. Those that participate directly in the catalytic mechanism usually exhibit anomalous physicochemical characteristics reflecting their entatic state. Carboxypep- tidase A, liver alcohol dehydrogenase, aspartate transcarbamoylase and al­ kaline phosphatase exemplify the different roles of metals in metalloen- zymes while the nucleotide polymerases point to the essential role of zinc in maintaining normal growth and development. Introduction At present, reliable measurements of small concentrations of metals present in Certain metals have long been recog­ tissues, cells, subcellular particles, body nized to have important biological func­ fluids and biomacromolecules can be tions primarily as a consequence of nu­ performed by colorimetry, fluorimetry, tritional investigations.14,15,22 Thus, the polarography, emission spectrometry absence of a specific, essential metal with spark, flame or plasma excitation from the diet of an organism
    [Show full text]
  • Poly(ADP-Ribosyl)Ation of P53 During Apoptosis in Human Osteosarcoma Cells1
    [CANCER RESEARCH 59, 2190–2194, May 1, 1999] Poly(ADP-ribosyl)ation of p53 during Apoptosis in Human Osteosarcoma Cells1 Cynthia M. Simbulan-Rosenthal, Dean S. Rosenthal, RuiBai Luo, and Mark E. Smulson2 Department of Biochemistry and Molecular Biology, Georgetown University School of Medicine, Washington, DC 20007 ABSTRACT separation of its DNA binding domain from its catalytic site essentially inactivates the enzyme. PARP has also been implicated in the induction Spontaneous apoptosis in human osteosarcoma cells was observed to be of p53 expression during apoptosis (25) The specific proteolytic cleavage associated with a marked increase in the intracellular abundance of p53. of PARP by caspase-3 is a key apoptotic event because PARP cleavage Immunoprecipitation and immunoblot analysis revealed that, together with a variety of other nuclear proteins, p53 undergoes extensive poly- and inactivation as well as subsequent apoptotic events are blocked by a (ADP-ribosyl)ation early during the apoptotic program in these cells. peptide inhibitor of this protease (23, 26). Subsequent degradation of poly(ADP-ribose) (PAR), attached to p53 pre- We have shown recently that a transient poly(ADP-ribosyl)ation of sumably by PAR glycohydrolase, the only reported enzyme to degrade nuclear proteins in intact human osteosarcoma cells occurs early in PAR, was apparent concomitant with the onset of proteolytic processing apoptosis, prior to commitment to cell death, and is subsequently and activation of caspase-3, caspase-3-mediated cleavage of poly(ADP- followed by cleavage and inactivation of PARP (24). No PAR is ribose) polymerase (PARP), and internucleosomal DNA fragmentation synthesized at the later stages of apoptosis, despite the presence of a during the later stages of cell death.
    [Show full text]
  • University of California, San Diego
    UNIVERSITY OF CALIFORNIA, SAN DIEGO Design and Characterization of an Allosteric Metalloprotein Assembly A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Chemistry by Lewis Anthony Churchfield Committee in charge: Professor F. Akif Tezcan, Chair Professor Michael D. Burkart Professor Neal K. Devaraj Professor Tracy M. Handel Professor Valerie A. Schmidt 2018 Copyright Lewis Anthony Churchfield, 2018 All rights reserved. Signature Page This Dissertation of Lewis Anthony Churchfield is approved, and it is acceptable in quality and form for publication on microfilm and electronically: Chair University of California, San Diego 2018 iii EPIGRAPH Epigraph Sometimes science is more art than science. Dr. Rick Sanchez iv TABLE OF CONTENTS Table of Contents Signature Page ................................................................................................................... iii Epigraph ............................................................................................................................. iv Table of Contents ................................................................................................................ v List of Abbreviations ........................................................................................................ vii List of Figures .................................................................................................................... ix List of Tables ..................................................................................................................
    [Show full text]
  • Downstream Processing of Cell Culture-Derived Animal Viruses
    Downstream processing of cell culture-derived animal viruses Dina de Jesus Marinheiro Antunes Thesis to obtain the Master of Science Degree in Biotechnology Supervisors: Prof. Maria Raquel Murias dos Santos Aires Barros Dr. Miguel Agostinho Sousa Pinto de Torres Fevereiro Examination Committee Chairperson: Prof. Luís Joaquim Pina da Fonseca Supervisor: Dr. Miguel Agostinho Sousa Pinto de Torres Fevereiro Member of the Committee: Dr. Ana Margarida Ferreira Henriques de Oliveira Mourão July, 2014 2 Dedicated to Querida Mãe e Pai (Dear Mom and Dad) "Nós nunca nos realizamos. Somos dois abismos - um poço fitando o céu." Fernando Pessoa 3 Acknowledgments All my friends say that one of my major defects, which I totally disagree (I am a little bit stubborn…), is saying “Obrigada” (Thank you) too often. This word has its origin from the latim obligatus, participle of the verb obligare, which means connect, attach. When we mention it, we feel connected, even for a moment, to some favor someone did. And I am glad to have a section in my Dissertation where I can finally say this beautiful word how many times I want. And tie me to the people. “Obrigada” This dissertation would not have been possible without the guidance and cooperation of several people who contributed with their invaluable assistance in the formulation, development and completion of this study. First and foremost, I would like to show my greatest gratitude to Dr. Miguel Fevereiro, who provided an inspiring environment to work in and taught me the real sense of “negative thinking”. He showed that it is possible (believe me!) to be an exceptional Director, teacher, researcher and vet, with a LOT of work, love and engagement.
    [Show full text]
  • Familial Dysautonomia Model Reveals Ikbkap Deletion Causes Apoptosis Of
    Familial dysautonomia model reveals Ikbkap deletion + causes apoptosis of Pax3 progenitors and peripheral neurons Lynn Georgea,b,1, Marta Chaverraa,1, Lindsey Wolfea, Julian Thornea, Mattheson Close-Davisa, Amy Eibsa, Vickie Riojasa, Andrea Grindelandc, Miranda Orrc, George A. Carlsonc, and Frances Lefcorta,2 aDepartment of Cell Biology and Neuroscience, Montana State University, Bozeman, MT 59717; bDepartment of Biological and Physical Sciences, Montana State University Billings, Billings, MT 59101; and cMcLaughlin Research Institute, Great Falls, MT 59405 Edited by Qiufu Ma, Dana-Farber Cancer Institute, Boston, MA, and accepted by the Editorial Board October 7, 2013 (received for review May 8, 2013) Familial dysautonomia (FD) is a devastating developmental and thermoreceptors, mechanoreceptors and proprioceptors. With progressive peripheral neuropathy caused by a mutation in the gene the completion of neural crest migration, multiple steps ensue inhibitor of kappa B kinase complex-associated protein (IKBKAP). that are essential for normal PNS development, including pro- To identify the cellular and molecular mechanisms that cause FD, liferation of discrete sets of neuronal progenitor cells that derive we generated mice in which Ikbkap expression is ablated in the from different waves of migrating neural crest cells, neuronal peripheral nervous system and identify the steps in peripheral differentiation, axonogenesis, target innervation, and circuit nervous system development that are Ikbkap-dependent. We formation. FD could theoretically result from failure in any or show that Ikbkap is not required for trunk neural crest migration several of these key developmental processes. or pathfinding, nor for the formation of dorsal root or sympathetic Insight into the mechanisms that cause FD have been com- ganglia, or the adrenal medulla.
    [Show full text]
  • Cell-Size Dependent Progression of the Cell Cycle Creates Homeostasis and flexibility of Plant Cell Size
    ARTICLE Received 21 Nov 2016 | Accepted 23 Feb 2017 | Published 27 Apr 2017 DOI: 10.1038/ncomms15060 OPEN Cell-size dependent progression of the cell cycle creates homeostasis and flexibility of plant cell size Angharad R. Jones1, Manuel Forero-Vargas1,w, Simon P. Withers1, Richard S. Smith2, Jan Traas3, Walter Dewitte1,* & James A.H. Murray1,* Mean cell size at division is generally constant for specific conditions and cell types, but the mechanisms coupling cell growth and cell cycle control with cell size regulation are poorly understood in intact tissues. Here we show that the continuously dividing fields of cells within the shoot apical meristem of Arabidopsis show dynamic regulation of mean cell size dependent on developmental stage, genotype and environmental signals. We show cell size at division and cell cycle length is effectively predicted using a two-stage cell cycle model linking cell growth and two sequential cyclin dependent kinase (CDK) activities, and experimental results concur in showing that progression through both G1/S and G2/M is size dependent. This work shows that cell-autonomous co-ordination of cell growth and cell division previously observed in unicellular organisms also exists in intact plant tissues, and that cell size may be an emergent rather than directly determined property of cells. 1 Division of Molecular Biosciences, Cardiff School of Biosciences, Cardiff University, Cardiff, Wales CF10 3AX, UK. 2 Department of Comparative Development and Genetics, Max Planck Institute for Plant Breeding Research, 50829 Cologne, Germany. 3 Laboratoire de Reproduction de de´veloppement des plantes, INRA, CNRS, ENS Lyon, UCB Lyon 1, Universite´ de Lyon, 69364 Lyon Cedex 07, France.
    [Show full text]
  • Cell Cycle : Information Can Be Found in Red Print on Either Side of the Divider
    Using this book: This book is designed to be used in both introductory and advanced cell biology courses. The primary text is generally on the left side of the vertical divider, and printed in black. Details that are usually left to an advanced course are printed in blue and found on the right side of the divider. Finally, additional biomedically relevant Cell Cycle : information can be found in red print on either side of the divider. Life cycle of the cell and Gametogenesis The Prokaryotic Cell Cycle Cells, whether prokaryotic or eukaryotic, eventually reproduce or die. For prokaryotes, the mechanism of reproduction is relatively simple, since there are no internal organ- elles. The process consists of three distinct but short phases: first, a growth phase in which the mass of the cell is increased, then the chromosomal replication phase, and finally the chromosomes are separated and the cells are physically split into two inde- pendent new cells. In bacteria, these are referred to as the B, C, and D periods, respec- tively. Initiation of the reproductive process appears to be primarily a function of cell size. The length of the overall cell cycle is determined by the B period, as the C and D periods have relatively fixed time constraints. The length of B is determined, in part, by environmental conditions and the gain in cell mass. Generation times for bacteria can vary from under half an hour to several days, although most bacterial cultures in laboratory settings and nutrient-rich media have generation times under a day. DNA replication has already been covered in detail in chapter 7.
    [Show full text]