DOCSLIB.ORG

Meiotic Prophase Regulation and Achiasmate Chromosome Segregation in Caenorhabditis Elegans

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Meiotic Prophase Regulation and Achiasmate Chromosome Segregation in Caenorhabditis Elegans Meiotic prophase regulation and achiasmate chromosome segregation in Caenorhabditis elegans By Christina Marie Glazier A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Molecular and Cell Biology in the Graduate Division of the University of California, Berkeley Committee in Charge: Professor Abby Dernburg, Chair Professor Georjana Barnes Professor Rebecca Heald Professor Marvalee Wake Spring 2015 Abstract Meiotic prophase regulation and achiasmate chromosome segregation in Caenorhabditis elegans by Christina Marie Glazier Doctor of Philosophy in Molecular and Cell Biology University of California, Berkeley Professor Abby Dernburg, Chair Meiosis is the specialized cell division by which sexually reproducing organisms produce haploid gametes. In order to reduce the chromosome complement by half, chromosomes must undergo pairing, synapsis, and crossover formation, followed by two rounds of chromosome division. All of these mechanisms depend on the proper establishment, maintenance, and remodeling of sister chromatid cohesion. Sister chromatid cohesion is mediated by cohesin complexes, which associate with newly replicated sister chromatids. Cohesion is required for all major aspects of meiosis: formation of the synaptonemal complex, induction of DNA double- strand breaks, and the repair of breaks to form crossovers, in addition to the regulated release of cohesion to enable segregation. During meiosis, cohesin complexes incorporate specialized subunits and are subject to different regulation, compared to mitotically dividing cells. The functions and regulation of cohesion during meiosis remain poorly characterized, and a major goal of my thesis work has been to address these important questions. Wapl is a widely conserved regulator of cohesin. It has been implicated in antagonizing the association of cohesin complexes with DNA to facilitate cohesin removal during mitosis. However, its role in meiotic chromosome dynamics has not been investigated in any detail. To better understand the roles and regulation of sister chromatid cohesion in meiosis, I have focused on the Caenorhabditis elegans Wapl homolog, WAPL-1. I found that C. elegans WAPL-1 promotes faithful mitotic chromosome segregation, as in other organisms. I also found that WAPL-1 affects cohesin dynamics during meiosis, contributes to DNA double-strand break repair, and is regulated by the meiosis-specific kinase, CHK-2. A second component of my thesis work examines the behavior of achiasmate chromosomes during meiosis. When early meiotic events fail to establish the requisite crossovers, the resulting achiasmate chromosomes often missegregate, or nondisjoin. Chromosome nondisjunction can result in aneuploid gametes, which has disastrous consequences for the developing embryo. To accurately detect autosomal nondisjunction in single embryos, I developed a fragment length polymorphism (FLP) assay. I used this approach to analyze chromosome segregation in oocyte meiosis in wildtype animals at different ages, and in mutants with elevated frequencies of achiasmate chromosomes. I found that nondisjunction occurred asymmetrically, yielding a higher frequency of monosomic than trisomic embryos. I also found evidence that germline apoptosis protects C. elegans hermaphrodites from increased nondisjunction as they age. Together, the results of these studies further illuminate meiotic prophase regulation and achiasmate chromosome segregation. 1 . Dedicated to those who imparted on me four pieces of advice required for the successful completion of this dissertation. To my father, who, through his own actions and stories of my Nana and Papa, reminds me to work hard. To my mother, who teaches me to stand up for others, as well as myself. To my sweet brother, who reminds me to be kind. And to my Lola and Lolo, who taught me that happiness is sadness. i Table of Contents Chapter 1: Introduction ............................................................................................................... 1 1.1 Meiosis, a specialized cell division ....................................................................................... 1 1.2 Early meiotic processes ensure proper chromosome segregation ......................................... 2 1.3 Chromosome nondisjunction and its affects on human health ............................................. 8 1.4 The model organism Caenorhabditis elegans ....................................................................... 9 Chapter 2: WAPL-1 is regulated by the meiotic kinase, CHK-2, during meiotic prophase 13 2.1 Introduction and summary of results .................................................................................. 13 2.2 Results ................................................................................................................................. 14 2.3 Discussion ........................................................................................................................... 23 2.4 Materials and Methods ........................................................................................................ 25 Chapter 3: Achiasmate chromosome segregation .................................................................... 39 3.1 Introduction and summary of results .................................................................................. 39 3.2 Results ................................................................................................................................. 41 3.3 Discussion ........................................................................................................................... 49 3.4 Materials and Methods ........................................................................................................ 51 Chapter 4: Concluding remarks and future perspectives ....................................................... 57 4.1 Review of findings .............................................................................................................. 57 4.2 Implication of findings ........................................................................................................ 59 4.3 Remaining questions ........................................................................................................... 60 References .................................................................................................................................... 63 Appendix A C. elegans strains and plasmids ............................................................................ 68 Appendix B Mass spectrometry data tables ............................................................................. 70 ii List of Tables Table 1 List of C. elegans strains. ................................................................................................ 68 Table 2 List of plasmids. .............................................................................................................. 69 Table 3 C. elegans proteins identified by mass spectrometry following immunoprecipitation of endogenous WAPL-1. ........................................................................................................... 70 Table 4 List of phosphorylated amino acids identified by mass spectrometry following in vitro phosphorylation of recombinant WAPL-1. ........................................................................... 82 Table 5 List of phosphorylated amino acids identified by mass spectrometry following purification of WAPL-1 from wildtype C. elegans lysate .................................................. 104 iii List of Figures Figure 1.1 Schematic of restoration of diploidy through sexual reproduction and early meiotic events .................................................................................................................................... 11 Figure 1.2 Schematic of chromosome nondisjunction at Meiosis I ............................................. 12 Figure 2.1 The WAPL-1 isoform A is the primary transcribed and translated isoform .............. 29 Figure 2.2 WAPL-1 localizes to mitotically dividing nuclei by immunofluorescence ............... 30 Figure 2.3 WAPL-1 is present during meiotic prophase, but sensitive to immunofluorescence protocol ................................................................................................................................. 31 Figure 2.4 wapl-1 mutants display phenotypes associated with mitotic defects ......................... 32 Figure 2.5 Immunoprecipitation of WAPL-1 identifies mitotic cohesin complex proteins and DNA repair proteins as WAPL-1 interactors ........................................................................ 33 Figure 2.6 wapl-1 mutants display defects in DNA DSB repair .................................................. 34 Figure 2.7 wapl-1 mutants display defects in inhibition of SCC-1 .............................................. 35 Figure 2.8 A candidate screen identified CHK-2 as a WAPL-1 regulator .................................. 36 Figure 2.9 Misregulation of WAPL-1 in chk-2 causes defects in COH-3/4 loading ................... 37 Figure 2.10 Mutation of WAPL-1 CHK-2 consensus motifs reduces WAPL-1 phosphorylation in vitro, but does not affect WAPL-1 regulation in the germline ......................................... 38 Figure 3.1 Schematic of fragment length polymorphism protocol and mating scheme .............. 53 Figure 3.2 The fragment length polymorphism assay assesses autosomal nondisjunction
Load more

Recommended publications
  • Sumoylation Regulates Protein Dynamics During Meiotic Chromosome Segregation in C
    © 2019. Published by The Company of Biologists Ltd | Journal of Cell Science (2019) 132, jcs232330. doi:10.1242/jcs.232330 RESEARCH ARTICLE Sumoylation regulates protein dynamics during meiotic chromosome segregation in C. elegans oocytes Federico Pelisch*, Laura Bel Borja, Ellis G. Jaffray and Ronald T. Hay ABSTRACT studies of MT-dependent chromosome movement focused on Oocyte meiotic spindles in most species lack centrosomes and pulling forces generated by kinetochore MTs (kMTs) making the mechanisms that underlie faithful chromosome segregation end-on contacts with chromosomes (Cheeseman, 2014), there is in acentrosomal meiotic spindles are not well understood. In also evidence for pushing forces that are exerted on the segregating C. elegans oocytes, spindle microtubules exert a poleward force on chromosomes (Khodjakov et al., 2004; Nahaboo et al., 2015; š ́ chromosomes that is dependent on the microtubule-stabilising Laband et al., 2017; Vuku ic et al., 2017; Yu et al., 2019 preprint). protein CLS-2, the orthologue of the mammalian CLASP proteins. The nematode Caenorhabditis elegans contains holocentric The checkpoint kinase BUB-1 and CLS-2 localise in the central chromosomes (Maddox et al., 2004) and has served as an spindle and display a dynamic localisation pattern throughout extremely useful system to uncover mechanisms of meiosis and anaphase, but the signals regulating their anaphase-specific mitosis for almost 20 years (Oegema et al., 2001; Desai et al., 2003; localisation remains unknown. We have shown previously that Cheeseman et al., 2004, 2005; Monen et al., 2005). Meiosis is a SUMO regulates BUB-1 localisation during metaphase I. Here, we specialised cell division with two successive rounds of chromosome found that SUMO modification of BUB-1 is regulated by the SUMO E3 segregation that reduce the ploidy and generates haploid gametes ligase GEI-17 and the SUMO protease ULP-1.
    [Show full text]
  • Chapter 3 Characterization of Meiotic Chromosome Organization and the Distribution of Dsbs and Crossovers
    UC Berkeley UC Berkeley Electronic Theses and Dissertations Title Quantitative characterization of meiotic chromosome organization Permalink https://escholarship.org/uc/item/5mr0c0kp Author Cheveralls, Keith Charles Publication Date 2016 Peer reviewed|Thesis/dissertation eScholarship.org Powered by the California Digital Library University of California Quantitative characterization of meiotic chromosome organization By Keith Charles Cheveralls A Dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Biophysics in the Graduate Division of the University of California, Berkeley Committee in charge: Professor Abby F. Dernburg, Chair Professor David Drubin Professor Barbara Meyer Professor Eva Nogales Spring 2016 Abstract Quantitative characterization of meiotic chromosome organization by Keith Charles Cheveralls Doctor of Philosophy in Biophysics University of California, Berkeley Professor Abby F. Dernburg, Chair Sexual reproduction relies on a specialized program of cell division called meiosis to generate haploid gametes from diploid germ cells. In order for chromosome segregation to occur accurately, homologous chromosomes must pair, synapse, and undergo crossover recombination. These physical and biochemical interactions occur in coordination with large-scale reorganization of meiotic chromosomes. To understand the relationship between chromosome organization and the regulation of recombination, we developed an automated image analysis pipeline that combines the throughput of population-based
    [Show full text]
  • BIOLOGY 639 SCIENCE ONLINE the Unexpected Brains Behind Blood Vessel Growth 641 THIS WEEK in SCIENCE 668 U.K
    4 February 2005 Vol. 307 No. 5710 Pages 629–796 $10 07%.'+%#%+& 2416'+0(70%6+10 37#06+6#6+8' 51(69#4' #/2.+(+%#6+10 %'..$+1.1); %.10+0) /+%41#44#;5 #0#.;5+5 #0#.;5+5 2%4 51.76+105 Finish first with a superior species. 50% faster real-time results with FullVelocity™ QPCR Kits! Our FullVelocity™ master mixes use a novel enzyme species to deliver Superior Performance vs. Taq -Based Reagents FullVelocity™ Taq -Based real-time results faster than conventional reagents. With a simple change Reagent Kits Reagent Kits Enzyme species High-speed Thermus to the thermal profile on your existing real-time PCR system, the archaeal Fast time to results FullVelocity technology provides you high-speed amplification without Enzyme thermostability dUTP incorporation requiring any special equipment or re-optimization. SYBR® Green tolerance Price per reaction $$$ • Fast, economical • Efficient, specific and • Probe and SYBR® results sensitive Green chemistries Need More Information? Give Us A Call: Ask Us About These Great Products: Stratagene USA and Canada Stratagene Europe FullVelocity™ QPCR Master Mix* 600561 Order: (800) 424-5444 x3 Order: 00800-7000-7000 FullVelocity™ QRT-PCR Master Mix* 600562 Technical Services: (800) 894-1304 Technical Services: 00800-7400-7400 FullVelocity™ SYBR® Green QPCR Master Mix 600581 FullVelocity™ SYBR® Green QRT-PCR Master Mix 600582 Stratagene Japan K.K. *U.S. Patent Nos. 6,528,254, 6,548,250, and patents pending. Order: 03-5159-2060 Purchase of these products is accompanied by a license to use them in the Polymerase Chain Reaction (PCR) Technical Services: 03-5159-2070 process in conjunction with a thermal cycler whose use in the automated performance of the PCR process is YYYUVTCVCIGPGEQO covered by the up-front license fee, either by payment to Applied Biosystems or as purchased, i.e., an authorized thermal cycler.
    [Show full text]
  • The Many Facets of SC Function During C. Elegans Meiosis
    Chromosoma DOI 10.1007/s00412-006-0061-9 REVIEW Mónica P. Colaiácovo The many facets of SC function during C. elegans meiosis Received: 7 December 2005 / Revised: 15 February 2006 / Accepted: 16 February 2006 # Springer-Verlag 2006 Abstract Sexually reproducing organisms rely on meiosis halving in chromosome number is the result of one round for the formation of haploid gametes. This is achieved of DNA replication followed by two rounds of cell through two consecutive rounds of cell division (meiosis I division: meiosis I (a reductional division) and meiosis II and II) after one round of DNA replication. During the (an equational division). While meiosis II proceeds meiotic divisions, chromosomes face several challenges to similarly to a mitotic division, unique events unfold during ultimately ensure proper chromosome segregation. Unique meiosis I. In particular, during prophase I, homologous events unfold during meiosis I to overcome these chromosomes have to identify each other and pair, challenges. Homologous chromosomes pair, synapse, and followed by the formation of a proteinaceous structure recombine. A remarkable feature throughout this process is known as the synaptonemal complex (SC) between the formation of an evolutionarily conserved tripartite homologs, and completion of meiotic recombination proteinaceous structure known as the synaptonemal com- leading to physical attachments between homologs. plex (SC). It is comprised of two lateral elements, These events ultimately ensure proper chromosome segre- assembled along each axis of a pair of homologous gation upon the first meiotic division. Succeeding in this chromosomes, and a central region consisting of transverse outcome is crucial given that chromosome nondisjunction filaments bridging the gap between lateral elements.
    [Show full text]
  • Homologous Chromosome Pairing in Drosophila Melanogaster Proceeds Through Multiple Independent Initiations Jennifer C
    Homologous Chromosome Pairing in Drosophila melanogaster Proceeds through Multiple Independent Initiations Jennifer C. Fung,* Wallace F. Marshall,‡ Abby Dernburg,‡ David A. Agard,‡i and John W. Sedat‡ *Graduate Group in Biophysics and ‡Department of Biochemistry and Biophysics, University of California, San Francisco, California 94143-0554; and iThe Howard Hughes Medical Institute, San Franciso, California 94143 Abstract. The dynamics by which homologous chro- pairing kinetics of histone loci during nuclear cycle 14. mosomes pair is currently unknown. Here, we use fluo- By measuring changes of nuclear length and correlating rescence in situ hybridization in combination with these changes with progression of time during cycle 14, three-dimensional optical microscopy to show that ho- we were able to express the pairing frequency and dis- mologous pairing of the somatic chromosome arm 2L tance between homologous loci as a function of time. in Drosophila occurs by independent initiation of pair- Comparing the experimentally determined dynamics of ing at discrete loci rather than by a processive zippering pairing to simulations based on previously proposed Downloaded from of sites along the length of chromosome. By evaluating models of pairing motion, we show that the observed the pairing frequencies of 11 loci on chromosome arm pairing kinetics are most consistent with a constrained 2L over several timepoints during Drosophila embry- random walk model and not consistent with a directed onic development, we show that all 11 loci are paired motion model. Thus, we conclude that simple random very early in Drosophila development, within 13 h after contacts through diffusion could suffice to allow pairing egg deposition.
    [Show full text]
  • Laboratory Directed Research and Development Program FY 2002
    LBNL/PUB -54 8 5 Laboratory Directed Research and Development Program FY 2002 March 2003 Disclaimer This document wlls prepared as an account or work sponsored by the United Stales Government. While this document is believed ta contain correct inrormution, neither the United Stntes Government nor any agcncy thereof, nor The Regents orthe University of California, nor any of their employees, makes any wmnty, express or implied. or assumes any legal linbility or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product or process disclased, or represents that its use would not infringc privately awned rights. Reference herein to any specific commcrcial product, process, or service by its tradc name, trademark, manufacturer, or otherwise, does not necessnrily constitute or imply its endoaemcnt, recommendation, or favoring by the United States Government or any ogency thereof, ar The Regcnls of the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of ihe United Siates Gwernment or any agency thercol or The Regents of the University of Caliktmia nnd shall not be used lor advertising or product endorsement purposes. Ernest Orlnndo hwrence Berkeley National Laboratory is an equal opportunity employer. Report on Ernest Orlando Lawrence Berkeley National Laboratory Laboratory Directed Research and Development Program FY 2002 Ernest Orlando Lawrence Berkeley National Laboratory Berkeley, California 94720 Off ice of Science USDepartment
    [Show full text]
  • Cell Biology's Journal
    BoothStop #1203 By More Imaging With Molecular Devices’ complete turnkey solutions for high-content screening, expect more imaging from your screening, more easily and affordably than ever before. More Imaging Systems ULTRA New ImageXpress ™ confocal high-content screening system INSTRUMENTS MICRO ImageXpress ™ high-content screening system ASSAYS ImageXpress® 5000A for live-cell and kinetic assays SOFTWARE INFORMATICS More Software DATA MANAGEMENT MetaXpress™ for uniform image acquisition, processing and analysis Application Modules for validated turnkey analysis of high- content images AcuityXpress™ database-driven cellular informatics software for efficient yet powerful data mining and statistical capabilities MetaMorph®: the gold standard for research microscopy More Assays Transfluor® high-content assays for GPCR activation Expect more. We’ll do our very best to exceed your expectations. now part of MDS Analytical Technologies tel. +1-800-635-5577 | www.moleculardevices.com www.roche-applied-science.com FuGENE® HD Transfection Reagent Measure the results of your transfection, not your transfection reagent. Are you confident that the cellular effects you observe are the result of your 2000 transfected plasmid? Or are your results due to differential gene expression caused ■ 1741 Genes affected by only this reagent by the transfection reagent you use? 1500 ■ Genes affected by Rely on FuGENE® HD Transfection Reagent to avoid the high levels of nonspecific, both reagents off-target effects that can be generated with other transfection reagents (Figure 1). 1000 1505 ■ Generate physiologically relevant data you can trust with a unique non- 500 liposomal formulation. 282 46 ■ Achieve greater cell survival 236 236 when transfecting with this low-cytotoxicity Number of differentially expressed genes 0 reagent that is sterile filtered and free of animal-derived components.
    [Show full text]
  • Profile of R. Scott Hawley
    PROFILE Profile of R. Scott Hawley eiosis sets the stage for sexual younger Pauling told Hawley that if he reproduction through a tri- really wanted to do something about Mfold and tightly choreogra- birth defects, he should learn about phed dance: Chromosomes what caused them. So Hawley enrolled from the mother and father form pairs, in a genetics course. Suddenly every- exchange genetic material, and then sep- thing Ellison had written about in the arate from their partners. Geneticist R. Ticktockman story clicked. Growing up, Scott Hawley, who has studied these three Hawley says, all he knew was that “being steps for the better part of his career, has different was bad and there was a price dubbed the sequence a “meiotic ballet.” to be paid for it. Then I took genetics Although the dance steps have been and I realized that the whole point of known for more than a century, major genetics was to cherish the exceptions. By questions remain unanswered. How do looking at the things that are different, chromosomes find their partners or ho- you can figure out how things work.” mologs? What controls the exchange of By his sophomore year Hawley had genetic material? And what happens be- begun work in the laboratory of fly ge- hind the scenes when paired chromosomes neticist Dean Parker, where he began his first divide? earliest research into meiosis. Hawley Studying meiosis is both a biological and published a paper in his senior year on a philosophical pursuit, says Hawley, how radiation impairs the segregation of a researcher at the Stowers Institute for homologous chromosomes (2).
    [Show full text]
  • 1 a Single Unpaired and Transcriptionally Silenced X
    Genetics: Published Articles Ahead of Print, published on December 14, 2009 as 10.1534/genetics.109.110338 A single unpaired and transcriptionally silenced X chromosome locally precludes checkpoint signaling in the Caenorhabditis elegans germ line Aimee Jaramillo-Lambert and JoAnne Engebrecht Department of Molecular and Cellular Biology, Genetics Graduate Group, University of California, Davis, CA 95616 Running title: Sex chromosomes and checkpoint signaling Key words: apoptosis, checkpoint, DSBs, germ line, meiosis Corresponding author: JoAnne Engebrecht, MCB, 1 Shields Ave; UC, Davis; Davis, CA. 95616 1 ABSTRACT In many organisms, female and male meiosis display extensive sexual dimorphism in the temporal meiotic program, the number and location of recombination events, sex chromosome segregation and checkpoint function. We show here that both meiotic prophase timing and germ-line apoptosis, one output of checkpoint signaling, are dictated by the sex of the germ line (oogenesis vs. spermatogenesis) in Caenorhabditis elegans. During oogenesis in feminized animals (fem-3), a single pair of asynapsed autosomes elicits a checkpoint response yet an unpaired X chromosome fails to induce checkpoint activation. The single X in males and fem-3 worms is a substrate for the meiotic recombination machinery and repair of the resulting double strand breaks appears to be delayed compared with worms carrying paired X chromosomes. Synaptonemal complex axial HORMA domain proteins, implicated in repair of meiotic double strand breaks and checkpoint function, are assembled and disassembled on the single X similarly to paired chromosomes, but the central region component, SYP-1, is not loaded on the X chromosome in males. In fem-3 worms some X chromosomes achieve nonhomologous self- synapsis; however, germ cells with SYP-1-positive X chromosomes are not preferentially protected from apoptosis.
    [Show full text]
  • Polo-Like Kinase Cdc5 Drives Exit from Pachytene During Budding Yeast Meiosis
    Downloaded from genesdev.cshlp.org on September 29, 2021 - Published by Cold Spring Harbor Laboratory Press RESEARCH COMMUNICATION molog connections that later ensure proper homolog Polo-like kinase Cdc5 drives alignment on the metaphase I spindle and thus their ac- exit from pachytene during curate segregation at anaphase I. The exit from pachytene is a crucial transition, since it budding yeast meiosis is associated with the resolution of JMs as COs, SC dis- assembly, and kinetochore modification so that sister 1 Anuradha Sourirajan and Michael Lichten kinetochores orient toward the same spindle pole (mono- orientation), and the separation of duplicated spindle Laboratory of Biochemistry and Molecular Biology, Center for pole bodies (SPBs), the fungal centrosome equivalents Cancer Research, National Cancer Institute, (Shuster and Byers 1989; Xu et al. 1995, 1997; Clyne et al. Bethesda, Maryland 20892, USA 2003; Lee and Amon 2003b). Failure in any of these pro- In budding yeast, exit from the pachytene stage of meio- cesses can result in chromosome nondisjunction and the production of aneuploid progeny. Consequently, check- sis requires the mid-meiosis transcription factor Ndt80, ∼ point systems monitor synapsis and recombination and which promotes expression of 200 genes. Ndt80 is re- prevent exit from pachytene unless these processes are quired for meiotic function of polo-like kinase (PLK, complete (Roeder and Bailis 2000). Cdc5) and cyclin-dependent kinase (CDK), two cell cycle Ndt80, a transcription factor first expressed in late kinases previously implicated in pachytene exit. We pachytene, is a central target of these checkpoint sys- show that ongoing CDK activity is dispensable for two tems (Xu et al.
    [Show full text]
  • Centromere Dynamics Kerry Bloom
    Centromere dynamics Kerry Bloom At the foundation of all eukaryotic kinetochores is a This review explores recent studies that extend our unique histone variant, known as CenH3 (centromere understanding of how the site of CenH3 is specified, histone H3). We are starting to identify the histone how the pericentric chromatin is organized and how this chaperones responsible for CenH3 deposition at centromere chromatin resists mitotic forces. DNA, and the mechanisms that restrict CenH3 from chromosome arms. The specialized nucleosome that Centromere DNA and the ubiquitous contains CenH3 in place of canonical histone H3 lies centromere histone H3 variant at the interface between microtubules and chromosomes Centromere DNA is specified by 125 bp in S. cerevisiae and and directs kinetochore protein assembly. By contrast, Kluyveromyces lactis, 3–4kb in Candida albicans, 40–60kb in pericentric chromatin is highly elastic and can stretch S. pombe and 1–4 Mb in mammalian cells. The 125 bp or recoil in response to microtubule shortening or growth in centromeres are referred to as point centromeres, versus mitosis. The variety in histone modification is likely to play a regional centromeres that are characteristic of most other key role in regulating the behavior of these distinct chromatin eukaryotes [4]. Interestingly, all yeasts with point centro- domains. meres have a CenH3 END (essential N-terminal domain) Addresses homology in the N terminus [5 ]. Centromere DNA Department of Biology, University of North Carolina at Chapel Hill, does not cross species boundaries, even when sequences Chapel Hill, NC 27599-3280, USA from species with similar organization, such as S. cerevisiae and K.
    [Show full text]
  • History of Research on C. Elegans and Other Free-Living Nematodes As
    History of research on C. elegans and other free-living nematodes as model organisms* Victor Marc Nigon1 and Marie-Anne Félix2§ 1Université de Lyon 1, France 2Ecole Normale Supérieure, Paris, France Table of Contents 1. Introduction ............................................................................................................................3 2. Methods .................................................................................................................................5 2.1. Culture ........................................................................................................................5 2.2. Cytological methods ...................................................................................................... 7 3. Hermaphroditism: selfing and crossing with males ......................................................................... 7 3.1. Protandric hermaphroditism as a modification of the female .................................................. 8 3.2. Variation in hermaphroditism among different species .......................................................... 9 3.3. Crosses in hermaphroditic species .................................................................................... 9 3.4. Biological species test through crosses: C. briggsae discovery ............................................. 10 3.5. Evolution of selfing from male-female ancestors ............................................................... 11 4. Sex determination and meiosis in sexual species .........................................................................
    [Show full text]