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Yamashita YM. Asymmetric Stem Cell Division and Germline Immortality. Annu Rev Genet 2023; 57:181-199. [PMID: 37552892 DOI: 10.1146/annurev-genet-022123-040039] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/10/2023]
Abstract
Germ cells are the only cell type that is capable of transmitting genetic information to the next generation, which has enabled the continuation of multicellular life for the last 1.5 billion years. Surprisingly little is known about the mechanisms supporting the germline's remarkable ability to continue in this eternal cycle, termed germline immortality. Even unicellular organisms age at a cellular level, demonstrating that cellular aging is inevitable. Extensive studies in yeast have established the framework of how asymmetric cell division and gametogenesis may contribute to the resetting of cellular age. This review examines the mechanisms of germline immortality-how germline cells reset the aging of cells-drawing a parallel between yeast and multicellular organisms.
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Affiliation(s)
- Yukiko M Yamashita
- Whitehead Institute for Biomedical Research, Howard Hughes Medical Institute, and Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA;
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Nelson JO, Kumon T, Yamashita YM. rDNA magnification is a unique feature of germline stem cells. Proc Natl Acad Sci U S A 2023; 120:e2314440120. [PMID: 37967216 PMCID: PMC10666004 DOI: 10.1073/pnas.2314440120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2023] [Accepted: 10/16/2023] [Indexed: 11/17/2023] Open
Abstract
Ribosomal DNA (rDNA) encodes ribosomal RNA and exists as tandem repeats of hundreds of copies in the eukaryotic genome to meet the high demand of ribosome biogenesis. Tandemly repeated DNA elements are inherently unstable; thus, mechanisms must exist to maintain rDNA copy number (CN), in particular in the germline that continues through generations. A phenomenon called rDNA magnification was discovered over 50 y ago in Drosophila as a process that recovers the rDNA CN on chromosomes that harbor minimal CN. Our recent studies indicated that rDNA magnification is the mechanism to maintain rDNA CN under physiological conditions to counteract spontaneous CN loss that occurs during aging. Our previous studies that explored the mechanism of rDNA magnification implied that asymmetric division of germline stem cells (GSCs) may be particularly suited to achieve rDNA magnification. However, it remains elusive whether GSCs are the unique cell type that undergoes rDNA magnification or differentiating germ cells are also capable of magnification. In this study, we provide empirical evidence that suggests that rDNA magnification operates uniquely in GSCs, but not in differentiating germ cells. We further provide computer simulation that suggests that rDNA magnification is only achievable through asymmetric GSC divisions. We propose that despite known plasticity and transcriptomic similarity between GSCs and differentiating germ cells, GSCs' unique ability to divide asymmetrically serves a critical role of maintaining rDNA CN through generations, supporting germline immortality.
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Affiliation(s)
- Jonathan O Nelson
- Whitehead Institute for Biomedical Research, Cambridge, MA 02142
- HHMI, Chevy Chase, MD 20815
| | - Tomohiro Kumon
- Whitehead Institute for Biomedical Research, Cambridge, MA 02142
- HHMI, Chevy Chase, MD 20815
| | - Yukiko M Yamashita
- Whitehead Institute for Biomedical Research, Cambridge, MA 02142
- HHMI, Chevy Chase, MD 20815
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02142
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3
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Nelson JO, Watase GJ, Warsinger-Pepe N, Yamashita YM. Mechanisms of rDNA Copy Number Maintenance. Trends Genet 2019; 35:734-742. [PMID: 31395390 DOI: 10.1016/j.tig.2019.07.006] [Citation(s) in RCA: 54] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2019] [Revised: 06/28/2019] [Accepted: 07/12/2019] [Indexed: 12/21/2022]
Abstract
rDNA, the genes encoding the RNA components of ribosomes (rRNA), are highly repetitive in all eukaryotic genomes, containing 100s to 1000s of copies, to meet the demand for ribosome biogenesis. rDNA genes are arranged in large stretches of tandem repeats, forming loci that are highly susceptible to copy loss due to their repetitiveness and active transcription throughout the cell cycle. Despite this inherent instability, rDNA copy number is generally maintained within a particular range in each species, pointing to the presence of mechanisms that maintain rDNA copy number in a homeostatic range. In this review, we summarize the current understanding of these maintenance mechanisms and how they sustain rDNA copy number throughout populations.
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Affiliation(s)
- Jonathan O Nelson
- Life Sciences Institute, University of Michigan, Ann Arbor, MI, USA; Howard Hughes Medical Institute, University of Michigan, Ann Arbor, MI, USA
| | - George J Watase
- Life Sciences Institute, University of Michigan, Ann Arbor, MI, USA; Howard Hughes Medical Institute, University of Michigan, Ann Arbor, MI, USA
| | - Natalie Warsinger-Pepe
- Life Sciences Institute, University of Michigan, Ann Arbor, MI, USA; Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI, USA
| | - Yukiko M Yamashita
- Life Sciences Institute, University of Michigan, Ann Arbor, MI, USA; Cell and Developmental Biology, University of Michigan, Ann Arbor, MI, USA; Howard Hughes Medical Institute, University of Michigan, Ann Arbor, MI, USA.
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Lu KL, Nelson JO, Watase GJ, Warsinger-Pepe N, Yamashita YM. Transgenerational dynamics of rDNA copy number in Drosophila male germline stem cells. eLife 2018; 7:32421. [PMID: 29436367 PMCID: PMC5811208 DOI: 10.7554/elife.32421] [Citation(s) in RCA: 44] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2017] [Accepted: 01/19/2018] [Indexed: 02/02/2023] Open
Abstract
rDNA loci, composed of hundreds of tandemly duplicated arrays of rRNA genes, are known to be among the most unstable genetic elements due to their repetitive nature. rDNA instability underlies aging (replicative senescence) in yeast cells, however, its contribution to the aging of multicellular organisms is poorly understood. In this study, we investigate the dynamics of rDNA loci during aging in the Drosophila male germline stem cell (GSC) lineage, and show that rDNA copy number decreases during aging. Our study further reveals that this age-dependent decrease in rDNA copy number is heritable from generation to generation, yet GSCs in young animals that inherited reduced rDNA copy number are capable of recovering normal rDNA copy number. Based on these findings, we propose that rDNA loci are dynamic genetic elements, where rDNA copy number changes dynamically yet is maintained through a recovery mechanism in the germline.
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Affiliation(s)
- Kevin L Lu
- Life Sciences Institute, University of Michigan, Ann Arbor, United States.,Cellular and Molecular Biology Program, University of Michigan, Ann Arbor, United States.,Medical Scientist Training Program, University of Michigan, Ann Arbor, United States
| | - Jonathan O Nelson
- Life Sciences Institute, University of Michigan, Ann Arbor, United States.,Howard Hughes Medical Institute, University of Michigan, Ann Arbor, United States
| | - George J Watase
- Life Sciences Institute, University of Michigan, Ann Arbor, United States.,Howard Hughes Medical Institute, University of Michigan, Ann Arbor, United States
| | - Natalie Warsinger-Pepe
- Life Sciences Institute, University of Michigan, Ann Arbor, United States.,Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, United States
| | - Yukiko M Yamashita
- Life Sciences Institute, University of Michigan, Ann Arbor, United States.,Cellular and Molecular Biology Program, University of Michigan, Ann Arbor, United States.,Howard Hughes Medical Institute, University of Michigan, Ann Arbor, United States.,Department of Cell and Developmental Biology, University of Michigan, Ann Arbor, United States
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6
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Tritto P, Palumbo V, Micale L, Marzulli M, Bozzetti MP, Specchia V, Palumbo G, Pimpinelli S, Berloco M. Loss of Pol32 in Drosophila melanogaster causes chromosome instability and suppresses variegation. PLoS One 2015; 10:e0120859. [PMID: 25826374 PMCID: PMC4380491 DOI: 10.1371/journal.pone.0120859] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2014] [Accepted: 01/27/2015] [Indexed: 11/29/2022] Open
Abstract
Pol32 is an accessory subunit of the replicative DNA Polymerase δ and of the translesion Polymerase ζ. Pol32 is involved in DNA replication, recombination and repair. Pol32’s participation in high- and low-fidelity processes, together with the phenotypes arising from its disruption, imply multiple roles for this subunit within eukaryotic cells, not all of which have been fully elucidated. Using pol32 null mutants and two partial loss-of-function alleles pol32rd1 and pol32rds in Drosophila melanogaster, we show that Pol32 plays an essential role in promoting genome stability. Pol32 is essential to ensure DNA replication in early embryogenesis and it participates in the repair of mitotic chromosome breakage. In addition we found that pol32 mutantssuppress position effect variegation, suggesting a role for Pol32 in chromatin architecture.
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Affiliation(s)
- Patrizia Tritto
- Dipartimento di Biologia, Università degli Studi di Bari “Aldo Moro”, 70125 Bari, Italy
| | - Valeria Palumbo
- Dipartimento di Biologia e Biotecnologie “C. Darwin”, Università degli Studi di Roma “La Sapienza”, 00185 Roma, Italy
| | - Lucia Micale
- IRCCS Casa Sollievo Della Sofferenza Hospital, 71013 San Giovanni Rotondo, Italy
| | - Marco Marzulli
- Department of Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine, Pittsburgh, PA 15219, United States of America
| | - Maria Pia Bozzetti
- Dipartimento di Scienze e Tecnologie Biologiche ed Ambientali, Università del Salento, 73100 Lecce, Italy
| | - Valeria Specchia
- Dipartimento di Scienze e Tecnologie Biologiche ed Ambientali, Università del Salento, 73100 Lecce, Italy
| | - Gioacchino Palumbo
- Dipartimento di Biologia, Università degli Studi di Bari “Aldo Moro”, 70125 Bari, Italy
| | - Sergio Pimpinelli
- Istituto Pasteur—Fondazione Cenci Bolognetti and Dipartimento di Biologia e Biotecnologie “C. Darwin”, Università degli Studi di Roma “La Sapienza”, 00185 Roma, Italy
| | - Maria Berloco
- Dipartimento di Biologia, Università degli Studi di Bari “Aldo Moro”, 70125 Bari, Italy
- * E-mail:
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8
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The Drosophila HP1 homolog Rhino is required for transposon silencing and piRNA production by dual-strand clusters. Cell 2009; 138:1137-49. [PMID: 19732946 DOI: 10.1016/j.cell.2009.07.014] [Citation(s) in RCA: 314] [Impact Index Per Article: 20.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2009] [Revised: 05/07/2009] [Accepted: 07/02/2009] [Indexed: 01/06/2023]
Abstract
Piwi-interacting RNAs (piRNAs) silence transposons and maintain genome integrity during germline development. In Drosophila, transposon-rich heterochromatic clusters encode piRNAs either on both genomic strands (dual-strand clusters) or predominantly one genomic strand (uni-strand clusters). Primary piRNAs derived from these clusters are proposed to drive a ping-pong amplification cycle catalyzed by proteins that localize to the perinuclear nuage. We show that the HP1 homolog Rhino is required for nuage organization, transposon silencing, and ping-pong amplification of piRNAs. rhi mutations virtually eliminate piRNAs from the dual-strand clusters and block production of putative precursor RNAs from both strands of the major 42AB dual-strand cluster, but not of transcripts or piRNAs from the uni-strand clusters. Furthermore, Rhino protein associates with the 42AB dual-strand cluster,but does not bind to uni-strand cluster 2 or flamenco. Rhino thus appears to promote transcription of dual-strand clusters, leading to production of piRNAs that drive the ping-pong amplification cycle.
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Veiko NN, Shubaeva NO, Malashenko AM, Beskova TB, Agapova RK, Lyapunova NA. Ribosomal genes in inbred mouse strains: Interstrain and intrastrain variation of copy number and extent of methylation. RUSS J GENET+ 2007. [DOI: 10.1134/s1022795407090086] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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10
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Klattenhoff C, Bratu DP, McGinnis-Schultz N, Koppetsch BS, Cook HA, Theurkauf WE. Drosophila rasiRNA pathway mutations disrupt embryonic axis specification through activation of an ATR/Chk2 DNA damage response. Dev Cell 2007; 12:45-55. [PMID: 17199040 DOI: 10.1016/j.devcel.2006.12.001] [Citation(s) in RCA: 235] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2006] [Revised: 11/10/2006] [Accepted: 12/02/2006] [Indexed: 11/20/2022]
Abstract
Small repeat-associated siRNAs (rasiRNAs) mediate silencing of retrotransposons and the Stellate locus. Mutations in the Drosophila rasiRNA pathway genes armitage and aubergine disrupt embryonic axis specification, triggering defects in microtubule polarization as well as asymmetric localization of mRNA and protein determinants in the developing oocyte. Mutations in the ATR/Chk2 DNA damage signal transduction pathway dramatically suppress these axis specification defects, but do not restore retrotransposon or Stellate silencing. Furthermore, rasiRNA pathway mutations lead to germline-specific accumulation of gamma-H2Av foci characteristic of DNA damage. We conclude that rasiRNA-based gene silencing is not required for axis specification, and that the critical developmental function for this pathway is to suppress DNA damage signaling in the germline.
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Affiliation(s)
- Carla Klattenhoff
- Program in Molecular Medicine and Program in Cell Dynamics, University of Massachusetts Medical School, Worcester, MA 01605, USA
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11
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Grushcow JM, Holzen TM, Park KJ, Weinert T, Lichten M, Bishop DK. Saccharomyces cerevisiae checkpoint genes MEC1, RAD17 and RAD24 are required for normal meiotic recombination partner choice. Genetics 1999; 153:607-20. [PMID: 10511543 PMCID: PMC1460798 DOI: 10.1093/genetics/153.2.607] [Citation(s) in RCA: 117] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Checkpoint gene function prevents meiotic progression when recombination is blocked by mutations in the recA homologue DMC1. Bypass of dmc1 arrest by mutation of the DNA damage checkpoint genes MEC1, RAD17, or RAD24 results in a dramatic loss of spore viability, suggesting that these genes play an important role in monitoring the progression of recombination. We show here that the role of mitotic checkpoint genes in meiosis is not limited to maintaining arrest in abnormal meioses; mec1-1, rad24, and rad17 single mutants have additional meiotic defects. All three mutants display Zip1 polycomplexes in two- to threefold more nuclei than observed in wild-type controls, suggesting that synapsis may be aberrant. Additionally, all three mutants exhibit elevated levels of ectopic recombination in a novel physical assay. rad17 mutants also alter the fraction of recombination events that are accompanied by an exchange of flanking markers. Crossovers are associated with up to 90% of recombination events for one pair of alleles in rad17, as compared with 65% in wild type. Meiotic progression is not required to allow ectopic recombination in rad17 mutants, as it still occurs at elevated levels in ndt80 mutants that arrest in prophase regardless of checkpoint signaling. These observations support the suggestion that MEC1, RAD17, and RAD24, in addition to their proposed monitoring function, act to promote normal meiotic recombination.
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Affiliation(s)
- J M Grushcow
- Department of Radiation, University of Chicago, Chicago, Illinois 60637, USA
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Hanakahi LA, Dempsey LA, Li MJ, Maizels N. Nucleolin is one component of the B cell-specific transcription factor and switch region binding protein, LR1. Proc Natl Acad Sci U S A 1997; 94:3605-10. [PMID: 9108024 PMCID: PMC20487 DOI: 10.1073/pnas.94.8.3605] [Citation(s) in RCA: 110] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/1996] [Accepted: 01/16/1997] [Indexed: 02/04/2023] Open
Abstract
LR1 is a B cell-specific, sequence-specific DNA binding activity that regulates transcription in activated B cells. LR1 also binds Ig heavy chain switch region sequences and may function in class switch recombination. LR1 contains two polypeptides, of 106 kDa and 45 kDa, and here we report that the 106-kDa component of LR1 is nucleolin. This identification, initially made by microsequence analysis, was verified by showing that (i) LR1-DNA binding activity increased in B cells transfected with a nucleolin cDNA expression construct; (ii) LR1-DNA binding activity was recognized by antibodies raised against recombinant human nucleolin; and (iii) in B cells transfected with epitope-tagged nucleolin expression constructs, the LR1-DNA complex was recognized by the anti-tag antibody. Nucleolin is an abundant nucleolar protein which is believed to play a role in rDNA transcription or organization, or rRNA processing. Homology between nucleolin and histone H1 suggests that nucleolin may alter DNA organization in response to cell cycle controls, and the nucleolin component of LR1 may therefore function to organize switch regions before, during, or after switch recombination. The demonstration that nucleolin is a component of a B cell-specific complex that binds switch region sequences suggests that the G-rich switch regions may have evolved from rDNA.
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Affiliation(s)
- L A Hanakahi
- Department of Molecular Biophysics, Yale University, New Haven, CT 06520-8114, USA
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Hawley RS, Friend SH. Strange bedfellows in even stranger places: the role of ATM in meiotic cells, lymphocytes, tumors, and its functional links to p53. Genes Dev 1996; 10:2383-8. [PMID: 8843191 DOI: 10.1101/gad.10.19.2383] [Citation(s) in RCA: 50] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Affiliation(s)
- R S Hawley
- Department of Genetics, University of California at Davis, 95616, USA
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Banga SS, Yamamoto AH, Mason JM, Boyd JB. Molecular cloning of mei-41, a gene that influences both somatic and germline chromosome metabolism of Drosophila melanogaster. MOLECULAR & GENERAL GENETICS : MGG 1995; 246:148-55. [PMID: 7862085 DOI: 10.1007/bf00294677] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The mei-41 gene of Drosophila melanogaster plays an essential role in meiosis, in the maintenance of somatic chromosome stability, in postreplication repair and in DNA double-strand break repair. This gene has been cytogenetically localized to polytene chromosome bands 14C4-6 using available chromosomal aberrations. About 60 kb of DNA sequence has been isolated following a bidirectional chromosomal walk that extends over the cytogenetic interval 14C1-6. The breakpoints of chromosomal aberrations identified within that walk establish that the entire mei-41 gene has been cloned. Two independently derived mei-41 mutants have been shown to carry P insertions within a single 2.2 kb fragment of the walk. Since revertants of those mutants have lost the P element sequences, an essential region of the mei-41 gene is present in that fragment. A 10.5 kb genomic fragment that spans the P insertion sites has been found to restore methyl methanesulfonate resistance and female fertility of the mei-41D3 mutants. The results demonstrate that all the sequences required for the proper expression of the mei-41 gene are present on this genomic fragment. This study provides the foundation for molecular analysis of a function that is essential for chromosome stability in both the germline and somatic cells.
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Affiliation(s)
- S S Banga
- Section of Molecular and Cellular Biology, University of California Davis 95616
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Komma DJ, Glass SJ, Endow SA. Constitutive magnification by the Ybb- chromosome of Drosophila melanogaster. Genet Res (Camb) 1993; 62:205-12. [PMID: 8157172 DOI: 10.1017/s0016672300031918] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Ybb- is an rDNA-deficient chromosome of Drosophila that has often been used in magnification experiments to induce high-frequency reversion of bobbed (bb) chromosomes. We observed previously that Ybb- causes ring chromosome loss even when the rings are bb+, suggesting that Ybb- induces magnifying sister chromatid exchanges in bb+ rings. Here we show that the Ybb- chromosome causes low levels of bb magnification in bb+ flies. We refer to the ability of Ybb- to bypass the rDNA deficiency requirement for magnification as 'constitutive' magnification. We have magnified the ribosomal genes on the Ybb- chromosome and analysed the revertant chromosomes using genetic and molecular methods. We find that magnified Ybb- chromosomes also exhibit constitutive magnifier activity. Molecular analysis shows that both type 1 and type 2 intron+ ribosomal gene repeats are associated with magnified Ybb- chromosomes. Type 2 introns have been described previously in the rDNA of both X and Y chromosomes. However, type 1 intervening sequences are thought to be present only in X, but not Y, ribosomal genes. Some of the Ybb- type 1 insertions differ from those present in the rDNA of X chromosomes in that they contain an EcoRI site, and some may be present in tandem arrays. The constitutive magnifier activity of Ybb- may reside either in the structurally unusual ribosomal gene intervening sequences associated with the chromosome, or in the locus on YL that is required for magnification to occur.
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Affiliation(s)
- D J Komma
- Department of Microbiology, Duke University Medical Center, Durham, North Carolina 27710
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Butler DK, Metzenberg RL. Amplification of the nucleolus organizer region during the sexual phase of Neurospora crassa. Chromosoma 1993; 102:519-25. [PMID: 8243164 DOI: 10.1007/bf00368345] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Previously we have shown that the nucleolus organizer region (NOR) of Neurospora crassa displays frequent size changes during crosses. In these initial studies, we observed that decreases in NOR size are far more common than increases. Here, we have investigated the inheritance of NOR size in a strain with an unusually small NOR. We call this strain SNO for small nucleolus organizer. We found that progeny that inherit their rDNA from SNO receive either an NOR that is larger than that of SNO or, rarely, the same size, but never an NOR that is smaller than that of SNO. The number of progeny that inherit their NOR from SNO is not significantly different from the number that inherit their NOR from the other parent in the cross. This argues against the idea that the failure to find progeny with NORs smaller than that of SNO is due to inviability of spores carrying such an NOR, or that it is due to unconscious bias by the experimenter against isolating such spores. These results can most easily be explained by a combination of unequal sister chromatid exchanges in the rDNA, or sister chromatid conversion, coupled with selection against nuclei harboring small NORs during the premeiotic phase of the Neurospora life cycle. Other, less conventional, explanations are also possible, such as "directed" increase in the target NOR without corresponding loss at some other NOR.
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Affiliation(s)
- D K Butler
- Department of Biomolecular Chemistry, University of Wisconsin, Madison 53706
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Portin P, Rantanen M. A selective method for studying primary sex chromosome non-disjunction in females and males and X-Y exchange in males of Drosophila melanogaster including a demonstration of euchromatic X-Y exchange. Genetica 1992; 85:147-51. [PMID: 1624137 DOI: 10.1007/bf00120321] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
A selective method was developed, based on negative complementation of the Abruptex alleles of the Notch locus, for studying primary sex chromosome non-disjunction in females and males of Drosophila melanogaster and X-Y exchange in males. The results show that the frequency of primary non-disjunction of structurally normal X chromosomes was lower than the frequency of X-derY non-disjunction in males. Double exchange between the X and the derY chromosome in the male occurs with a frequency of at least 0.091%. Single exchanges are naturally expected to occur with even higher frequency. Exchanges were interestingly at least partly of euchromatic nature. The origin of these exchanges is at least partly of gonial origin.
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Affiliation(s)
- P Portin
- Department of Biology, University of Turku, Finland
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Komma DJ, Graves H, Endow SA. Mutant alleles of the meiotic locus, mei-9, differ in degree of effects on rod chromosome magnification and ring chromosome transmission in Drosophila. Genet Res (Camb) 1989; 53:155-61. [PMID: 2504645 DOI: 10.1017/s0016672300028111] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Two mutant alleles of the meiotic locus, mei-9, have been examined for their effect on magnification of a rod Xbb chromosome and transmission of a ring Xbb chromosome under magnifying conditions. Our results indicate that the effects of these two mutations are allele-specific: mei-9a strongly inhibits both rod chromosome magnification and ring chromosome loss under magnifying conditions, while mei-9b has a smaller inhibitory effect on rod chromosome magnification and on the transmission of ring chromosomes under magnifying conditions. These observations can be explained by a difference in leakiness between the two alleles. Our results demonstrate that mutants defective in excision repair and repair replication inhibit ribosomal gene magnification. This suggests that a component of the excision repair pathway is involved in the process of magnification.
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Malynn BA, Blackwell TK, Fulop GM, Rathbun GA, Furley AJ, Ferrier P, Heinke LB, Phillips RA, Yancopoulos GD, Alt FW. The scid defect affects the final step of the immunoglobulin VDJ recombinase mechanism. Cell 1988; 54:453-60. [PMID: 3135938 DOI: 10.1016/0092-8674(88)90066-9] [Citation(s) in RCA: 246] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Abelson murine leukemia virus-transformed precursor B lymphocytes from scid (severe combined immunodeficient) mice, like A-MuLV transformants from normal mice, actively rearrange segments of their Ig heavy chain variable region gene locus during growth in culture. Targeting of recombination to appropriate segments appears normal in these lines as evidenced by initial rearrangement of sequences from within the D and JH locus to form aberrant "DJH" rearrangements and secondary rearrangement of sequences from within the VH locus to the aberrant "DJH" intermediates. A detailed analysis of the joints in these rearrangements indicates that the VDJ recombinase in scid pre-B cells can correctly recognize heptamernonamer signal sequences and perform precise endonucleolytic scissions at these sequences. We propose that the scid defect involves the inability of scid precursor lymphocytes to join correctly the cleaved ends of the coding strands of variable region gene segments.
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Marcus CH, Zitron AE, Wright DA, Hawley RS. Autosomal modifiers of the bobbed phenotype are a major component of the rDNA magnification paradox in Drosophila melanogaster. Genetics 1986; 113:305-19. [PMID: 3087814 PMCID: PMC1202840 DOI: 10.1093/genetics/113.2.305] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
rDNA magnification in Drosophila melanogaster is defined experimentally as the ability of bb/Ybb- males to produce exceptional progeny that are wild type with respect to rDNA associated phenotypes. Here, we show that some of these bobbed-plus progeny result not from genetic reversion at the bb locus but rather from variants at two or more autosomal loci that ameliorate the bobbed phenotype of rDNA deficient males in Drosophila. In doing so we resolve several aspects of a long-standing paradox concerning the phenomenon of rDNA magnification. This problem arose from the use of two genetic assays, which were presumed to be identical, but paradoxically, produced conflicting data on both the kinetics of reversion and the stability of magnified bb+ chromosomes. We resolve this problem by demonstrating that in one assay bobbed-plus progeny arise primarily by genetic reversion at the bobbed locus, whereas in the other assay bobbed-plus progeny arise both by reversion and by an epistatic effect of autosomal modifiers on the bobbed phenotype. We further show that such modifiers can facilitate the appearance of phenotypically bobbed-plus progeny even under conditions where genetic reversion is blocked by magnification defective mutants. Finally, we present a speculative model relating the action of these modifiers to the large increases in rDNA content observed in males undergoing magnification.
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Hawley RS, Marcus CH, Cameron ML, Schwartz RL, Zitron AE. Repair-defect mutations inhibit rDNA magnification in Drosophila and discriminate between meiotic and premeiotic magnification. Proc Natl Acad Sci U S A 1985; 82:8095-9. [PMID: 3934666 PMCID: PMC391449 DOI: 10.1073/pnas.82.23.8095] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
We have examined rDNA magnification in Drosophila melanogaster males carrying one of 11 recombination- or repair-defective mutations representing seven loci. We show that mutations defined by a defect in postreplication repair (mus-101, mei-41, and mus-108) are also defective in rDNA magnification, whereas mutations that do not affect postreplication repair have little or no effect on magnification. mei-41 inhibits only premeiotic magnification events, while mus-108 blocks both premeiotic and meiotic events. This suggests that meiotic and premeiotic events share some but not all functions. A molecular analysis of rDNA magnification reveals that in mus-108 males, changes in the rDNA restriction pattern can occur within one or a few generations under magnifying conditions. We interpret these data in terms of the role of DNA repair systems in rDNA magnification and in terms of stable maintenance of tandemly repeated genes.
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Shaffer JB, Bewley GC. Genetic determination of sn-glycerol-3-phosphate dehydrogenase synthesis in Drosophila melanogaster. A cis-acting controlling element. J Biol Chem 1983. [DOI: 10.1016/s0021-9258(17)44601-1] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
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