1
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Functional characterization of the TERRA transcriptome at damaged telomeres. Nat Commun 2014; 5:5379. [PMID: 25359189 DOI: 10.1038/ncomms6379] [Citation(s) in RCA: 182] [Impact Index Per Article: 18.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2014] [Accepted: 09/25/2014] [Indexed: 12/19/2022] Open
Abstract
Telomere deprotection occurs during tumorigenesis and aging upon telomere shortening or loss of the telomeric shelterin component TRF2. Deprotected telomeres undergo changes in chromatin structure and elicit a DNA damage response (DDR) that leads to cellular senescence. The telomeric long noncoding RNA TERRA has been implicated in modulating the structure and processing of deprotected telomeres. Here, we characterize the human TERRA transcriptome at normal and TRF2-depleted telomeres and demonstrate that TERRA upregulation is occurring upon depletion of TRF2 at all transcribed telomeres. TRF2 represses TERRA transcription through its homodimerization domain, which was previously shown to induce chromatin compaction and to prevent the early steps of DDR activation. We show that TERRA associates with SUV39H1 H3K9 histone methyltransferase, which promotes accumulation of H3K9me3 at damaged telomeres and end-to-end fusions. Altogether our data elucidate the TERRA landscape and defines critical roles for this RNA in the telomeric DNA damage response.
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2
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Abstract
The study of MYC has led to pivotal discoveries in cancer biology, induced pluripotency, and transcriptional regulation. In this review, continuing advances in our understanding of the function of MYC as a transcription factor and how its transcriptional activity controls normal vertebrate development and contributes to developmental disorders is discussed.
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Affiliation(s)
- Peter J Hurlin
- Shriners Hospitals for Children Portland, Portland, Oregon 97239
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3
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Kharazmi J, Moshfegh C. Investigation of dmyc Promoter and Regulatory Regions. GENE REGULATION AND SYSTEMS BIOLOGY 2013; 7:85-102. [PMID: 23761963 PMCID: PMC3663572 DOI: 10.4137/grsb.s10751] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Products of the myc gene family integrate extracellular signals by modulating a wide range of their targets involved in cellular biogenesis and metabolism; the purpose of this integration is to regulate cell death, proliferation, and differentiation. However, understanding the regulation of myc at the transcription level remains a challenge. We performed rapid amplification of dmyc cDNA ends (5' RACE) and mapped the transcription start site at P1 promoter, 18 base pairs upstream of the start of the known EST GM01143 and within the 5' UTR. Our data show that the first TATA box, previously computationally predicted, is utilized to generate dmyc full length mRNA. The largest transcript contains all three exons, generated after the removal of the introns by constitutively regulated splicing events. Further investigation of Downstream Promoter Element (DPE) was achieved by studying lacZ reporter activity; investigation revealed that this element and its upstream cluster of binding sites are required for the dmyc intron 2 activity. These findings may provide valuable tools for further analysis of dmyc cis-elements.
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Affiliation(s)
- Jasmine Kharazmi
- Bio-Technopark Zurich, Molecular Biology Laboratory, Zurich, Switzerland. ; Institute of Molecular Life Sciences, University of Zurich-Irchel, Zurich, Switzerland
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4
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Evidence for an RNA polymerization activity in axolotl and Xenopus egg extracts. PLoS One 2010; 5:e14411. [PMID: 21203452 PMCID: PMC3009717 DOI: 10.1371/journal.pone.0014411] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2010] [Accepted: 11/24/2010] [Indexed: 01/09/2023] Open
Abstract
We have previously reported a post-transcriptional RNA amplification observed in vivo following injection of in vitro synthesized transcripts into axolotl oocytes, unfertilized (UFE) or fertilized eggs. To further characterize this phenomenon, low speed extracts (LSE) from axolotl and Xenopus UFE were prepared and tested in an RNA polymerization assay. The major conclusions are: i) the amphibian extracts catalyze the incorporation of radioactive ribonucleotide in RNase but not DNase sensitive products showing that these products correspond to RNA; ii) the phenomenon is resistant to α-amanitin, an inhibitor of RNA polymerases II and III and to cordycepin (3′dAMP), but sensitive to cordycepin 5′-triphosphate, an RNA elongation inhibitor, which supports the existence of an RNA polymerase activity different from polymerases II and III; the detection of radiolabelled RNA comigrating at the same length as the exogenous transcript added to the extracts allowed us to show that iii) the RNA polymerization is not a 3′ end labelling and that iv) the radiolabelled RNA is single rather than double stranded. In vitro cell-free systems derived from amphibian UFE therefore validate our previous in vivo results hypothesizing the existence of an evolutionary conserved enzymatic activity with the properties of an RNA dependent RNA polymerase (RdRp).
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5
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Molecular dissection of telomeric repeat-containing RNA biogenesis unveils the presence of distinct and multiple regulatory pathways. Mol Cell Biol 2010; 30:4808-17. [PMID: 20713443 DOI: 10.1128/mcb.00460-10] [Citation(s) in RCA: 168] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Telomeres are transcribed into telomeric repeat-containing RNA (TERRA), large, heterogeneous, noncoding transcripts which form part of the telomeric heterochromatin. Despite a large number of functions that have been ascribed to TERRA, little is known about its biogenesis. Here, we present the first comprehensive analysis of the molecular structure of TERRA. We identify biochemically distinct TERRA complexes, and we describe TERRA regulation during the cell cycle. Moreover, we demonstrate that TERRA 5' ends contain 7-methylguanosine cap structures and that the poly(A) tail, present on a fraction of TERRA transcripts, contributes to their stability. Poly(A)(-) TERRA, but not poly(A)(+) TERRA, is associated with chromatin, possibly reflecting distinct biological roles of TERRA ribonucleoprotein complexes. In support of this idea, poly(A)(-) and poly(A)(+) TERRA molecules end with distinct sequence registers. We also determine that the bulk of 3'-terminal UUAGGG repeats have an average length of 200 bases, indicating that the length heterogeneity of TERRA likely stems from its subtelomeric regions. Finally, we find that TERRA is regulated during the cell cycle, being lowest in late S phase and peaking in early G(1). Our analyses offer the basis for investigating multiple regulatory pathways that affect TERRA synthesis, processing, turnover, and function.
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6
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Montreau N, Vaur S, Dautry F, Andéol Y. Coupled amplification and degradation of exogenous RNA injected in amphibian oocytes. Nucleic Acids Res 2004; 32:2957-65. [PMID: 15161959 PMCID: PMC419618 DOI: 10.1093/nar/gkh620] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The early development of amphibians takes place in the absence of significant transcription and is controlled at the post-transcriptional level. We have reported that in vitro synthesized transcripts injected into axolotl fertilized eggs or oocytes were not continuously degraded as their abundance apparently fluctuated over time, with detected amounts sometimes higher than initial injected amounts. To further characterize this phenomenon, we have co-injected RNA chain terminators to prevent RNA synthesis. This led to the suppression of fluctuations and to a regular decrease in the amount of transcripts that appeared to be more stable in the presence of inhibitors. These observations indicate a coupling between RNA synthesis and an accelerated degradation. Throughout the time course, cRNA molecules could be detected, and their abundance increased in the early phase of the kinetics, supporting the implication of an RNA-dependent RNA polymerase in an asymmetric amplification process. Finally, when the fate of the injected transcripts was investigated in individual oocytes, we observed an absolute increase in abundance in some but not all oocytes, supporting the existence of a limiting step in the initiation of the RNA amplification stochastic process.
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MESH Headings
- Ambystoma mexicanum/metabolism
- Animals
- Deoxyadenosines/pharmacology
- Deoxyuracil Nucleotides/pharmacology
- Female
- Genes, myc/genetics
- Kinetics
- Oocytes/drug effects
- Oocytes/metabolism
- Proto-Oncogene Proteins/genetics
- RNA Stability/drug effects
- RNA, Complementary/biosynthesis
- RNA, Complementary/genetics
- RNA, Complementary/metabolism
- RNA, Messenger/biosynthesis
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- RNA, Messenger/pharmacology
- RNA-Dependent RNA Polymerase/metabolism
- Stochastic Processes
- Transcription, Genetic/drug effects
- Transcription, Genetic/genetics
- Wnt Proteins
- Xenopus/genetics
- Zebrafish Proteins
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Affiliation(s)
- Nicole Montreau
- Laboratoire de Biologie du Développement, Université P. et M. Curie, CNRS, UMR 7622, 9 Quai St Bernard, 75251 Paris Cedex 05 France
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7
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Gregory MA, Hann SR. c-Myc proteolysis by the ubiquitin-proteasome pathway: stabilization of c-Myc in Burkitt's lymphoma cells. Mol Cell Biol 2000; 20:2423-35. [PMID: 10713166 PMCID: PMC85426 DOI: 10.1128/mcb.20.7.2423-2435.2000] [Citation(s) in RCA: 351] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
The c-Myc oncoprotein is a transcription factor which is a critical regulator of cellular proliferation. Deregulated expression of c-Myc is associated with many human cancers, including Burkitt's lymphoma. The c-Myc protein is normally degraded very rapidly with a half-life of 20 to 30 min. Here we demonstrate that proteolysis of c-Myc in vivo is mediated by the ubiquitin-proteasome pathway. Inhibition of proteasome activity blocks c-Myc degradation, and c-Myc is a substrate for ubiquitination in vivo. Furthermore, an increase in c-Myc stability occurs in mitotic cells and is associated with inhibited c-Myc ubiquitination. Deletion analysis was used to identify regions of the c-Myc protein which are required for rapid proteolysis. We found that a centrally located PEST sequence, amino acids 226 to 270, is necessary for rapid c-Myc degradation, but not for ubiquitination. Also, N-terminal sequences, located within the first 158 amino acids of c-Myc, are necessary for both efficient c-Myc ubiquitination and subsequent degradation. We found that c-Myc is significantly stabilized (two- to sixfold) in many Burkitt's lymphoma-derived cell lines, suggesting that aberrant c-Myc proteolysis may play a role in the pathogenesis of Burkitt's lymphoma. Finally, mutation of Thr-58, a major phosphorylation site in c-Myc and a mutational hot spot in Burkitt's lymphoma, increases c-Myc stability; however, mutation of c-Myc is not essential for stabilization in Burkitt's lymphoma cells.
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Affiliation(s)
- M A Gregory
- Department of Cell Biology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-2175, USA
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8
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Spotts GD, Patel SV, Xiao Q, Hann SR. Identification of downstream-initiated c-Myc proteins which are dominant-negative inhibitors of transactivation by full-length c-Myc proteins. Mol Cell Biol 1997; 17:1459-68. [PMID: 9032273 PMCID: PMC231871 DOI: 10.1128/mcb.17.3.1459] [Citation(s) in RCA: 99] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
The c-myc gene has been implicated in multiple cellular processes including proliferation, differentiation, and apoptosis. In addition to the full-length c-Myc 1 and 2 proteins, we have found that human, murine, and avian cells express smaller c-Myc proteins arising from translational initiation at conserved downstream AUG codons. These c-Myc short (c-Myc S) proteins lack most of the N-terminal transactivation domain but retain the C-terminal protein dimerization and DNA binding domains. As with full-length c-Myc proteins, the c-Myc S proteins appear to be localized to the nucleus, are relatively unstable, and are phosphorylated. Significant levels of c-Myc S, often approaching the levels of full-length c-Myc, are transiently observed during the rapid growth phase of several different types of cells. Optimization of the upstream initiation codons resulted in greatly reduced synthesis of the c-Myc S proteins, suggesting that a "leaky scanning" mechanism leads to the translation of these proteins. In some hematopoietic tumor cell lines having altered c-myc genes, the c-Myc S proteins are constitutively expressed at levels equivalent to that of full-length c-Myc. As predicted, the c-Myc S proteins are unable to activate transcription and inhibited transactivation by full-length c-Myc proteins, suggesting a dominant-negative inhibitory function. While these transcriptional inhibitors would not be expected to function as full-length c-Myc, the occurrence of tumors which express constitutive high levels of c-Myc S and their transient synthesis during rapid cell growth suggest that these proteins do not interfere with the growth-promoting functions of full-length c-Myc.
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Affiliation(s)
- G D Spotts
- Department of Cell Biology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-2175, USA
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9
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Differential stability of Xenopus c-myc RNA during oogenesis in axolotl Involvement of the 3' untranslated region in vivo. ACTA ACUST UNITED AC 1995; 205:182-191. [PMID: 28306079 DOI: 10.1007/bf00357764] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/1995] [Accepted: 08/17/1995] [Indexed: 10/26/2022]
Abstract
We have used the axolotl oocyte (Ambystoma mexicanum Shaw) to study the stability of exogenously injected Xenopus RNAs. Three different cellular developmental stages have been analysed: (1) the growing oocyte (stage III-IV of vitellogenesis), (2) the full-grown oocyte at the end of vitellogenesis (stage VI) and (3) the progesterone-matured stage VI oocyte. Three exogenous RNAs have been synthesized in vitro from a c-myc Xenopus cDNA clone. One transcript is 2.3 kb long (full length), the second is 1.5 kb long, with most of the 3' untranslated region (3'UTR) removed, and the third corresponds to the 3'UTR (0.8 kb). After injection or coinjection of these exogenous Xenopus RNAs into axolotl oocytes, the stability of the molecules was studied after 5 min, 6 h and 21 h by extraction of total RNA and Northern blot analysis.Results show a difference in Xenopus RNA stability during axolotl oogenesis. In growing oocytes, the three synthetic transcripts are gradually degraded. The absence of the 3'UTR is not therefore sufficient to stabilize the transcript during early oogenesis. No degradation is observed in full-grown oocytes, suggesting the existence of stabilizing factors at the end of oogenesis. When stage VI oocytes are induced to mature by progesterone, only the 2.3 and 1.5 kb Xenopus RNAs disappear. This suggests a role for germinal vesicle breakdown in this degradation process as well as the existence of a factor present in the nucleus and involved in the specific destabilization of these RNAs after oocyte maturation. This degradation might implicate several destabilizing sequences localized in the coding or in the 3'UTR of the c-myc gene. In contrast, the 0.8 kb transcript (3'UTR) is not degraded during this period and remains very stable. Therefore, degradation appears distinct from one transcript to another and from one region to another within the same molecule. During maturation, the behaviour of the 2.3 and 1.5 kb transcripts is different when coinjected with the 3'UTR, suggesting a role in trans of this untranslated molecule in c-myc stability. Our approach allows us to analyse the role of the coding and 3'UTR regions of the c-myc RNA in the control of mRNA degradation in vivo.
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10
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Affiliation(s)
- D A Jans
- Division for Biochemistry and Molecular Biology, John Curtin School of Medical Research, Australian National University, Canberra, Australia
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11
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Lemaitre JM, Bocquet S, Buckle R, Mechali M. Selective and rapid nuclear translocation of a c-Myc-containing complex after fertilization of Xenopus laevis eggs. Mol Cell Biol 1995; 15:5054-62. [PMID: 7651422 PMCID: PMC230752 DOI: 10.1128/mcb.15.9.5054] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
We report here unusual features of c-Myc specific to early embryonic development in Xenopus laevis, a period characterized by generalized transcriptional quiescence and rapid biphasic cell cycles. Two c-Myc protein forms, p61 and p64, are present in large amounts in the oocyte as well as during early development. In contrast, only p64 c-Myc is present in Xenopus somatic cells. p61 c-Myc is the direct translation product from both endogenous c-myc mRNAs and c-myc recombinant DNA. It is converted to the p64 c-Myc form after introduction into an egg extract, in the presence of phosphatase inhibitors. p61 and p64 belong to two distinct complexes localized in the cytoplasm of the oocyte. A 15S complex contains p64 c-Myc, and a 17.4S complex contains p61 c-Myc. Fertilization triggers the selective and total entry of only p64 c-Myc into the nucleus. This translocation occurs in a nonprogressive manner and is completed during the first cell cycles. This phenomenon results in an exceptionally high level of c-Myc in the nucleus, which returns to a somatic cell-like level only at the end of the blastulation period. During early development, when the entire embryonic genome is transcriptionally inactive, c-Myc does not exhibit a DNA binding activity with Max. Moreover, embryonic nuclei not only prevent the formation of c-Myc/Max complexes but also dissociate such preformed complexes. These peculiar aspects of c-Myc behavior suggest a function that could be linked to the rapid DNA replication cycles occurring during the early cell cycles rather than a function involving transcriptional activity.
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Affiliation(s)
- J M Lemaitre
- Unité d'Embryologie Moléculaire, Institut Jacques Monod, Paris, France
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12
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Abstract
The product of the c-myc gene (c-Myc) is a sequence-specific DNA-binding protein that has previously been demonstrated to be required for cell cycle progression. Here we report that the c-Myc DNA binding site confers cell cycle regulation to a reporter gene in Chinese hamster ovary cells. The observed transactivation was biphasic with a small increase in G1 and a marked increase during the S-to-G2/M transition of the cell cycle. This cell cycle regulation of transactivation potential is accounted for, in part, by regulatory phosphorylation of the c-Myc transactivation domain. Together, these data demonstrate that c-Myc may have an important role in the progression of cells through both the G1 and G2 phases of the cell cycle.
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13
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Abstract
The product of the c-myc gene (c-Myc) is a sequence-specific DNA-binding protein that has previously been demonstrated to be required for cell cycle progression. Here we report that the c-Myc DNA binding site confers cell cycle regulation to a reporter gene in Chinese hamster ovary cells. The observed transactivation was biphasic with a small increase in G1 and a marked increase during the S-to-G2/M transition of the cell cycle. This cell cycle regulation of transactivation potential is accounted for, in part, by regulatory phosphorylation of the c-Myc transactivation domain. Together, these data demonstrate that c-Myc may have an important role in the progression of cells through both the G1 and G2 phases of the cell cycle.
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Affiliation(s)
- A Seth
- Department of Biochemistry and Molecular Biology, University of Massachusetts Medical School, Worcester 01605
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14
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Comparative analysis of the expression and oncogenic activities of Xenopus c-, N-, and L-myc homologs. Mol Cell Biol 1993. [PMID: 8455622 DOI: 10.1128/mcb.13.4.2456] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A polymerase chain reaction-based cloning strategy allowed for the isolation of two distinct Xenopus L-myc genes, as well as previously isolated xc- and xN-myc genes, thus demonstrating that these three well-defined members of the mammalian myc gene family are present in lower vertebrates as well. Comparison of the Xenopus and mammalian Myc families revealed a high degree of structural relatedness at the gene and protein levels; this homology was consistent with the ability of the xc-myc1 and xN-myc1 genes to function as oncogenes in primary mammalian cells. In contrast, the xL-myc1 gene was found to be incapable of transforming rat embryo fibroblast cells, and this inactivity may relate to localized but significant differences in its putative transactivation domain. Analysis of xc-, xN-, and xL-myc gene expression demonstrated that (i) all three genes were highly expressed during oogenesis and their transcripts accumulated as abundant maternal mRNAs, (ii) each gene exhibited a distinctive pattern of expression during embryogenesis and in adult tissues, and (iii) the xL-myc1 and xL-myc2 genes were coordinately expressed in the maternal and zygotic genomes. The markedly high expression of the Xenopus myc gene family in differentiated tissues, such as the central nervous system and kidney, contrasts sharply with the low levels observed in mammalian adult tissues. These differences may reflect unique functions of the Myc family proteins in processes specific to amphibians, such as tissue regeneration.
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15
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Schreiber-Agus N, Torres R, Horner J, Lau A, Jamrich M, DePinho RA. Comparative analysis of the expression and oncogenic activities of Xenopus c-, N-, and L-myc homologs. Mol Cell Biol 1993; 13:2456-68. [PMID: 8455622 PMCID: PMC359566 DOI: 10.1128/mcb.13.4.2456-2468.1993] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
A polymerase chain reaction-based cloning strategy allowed for the isolation of two distinct Xenopus L-myc genes, as well as previously isolated xc- and xN-myc genes, thus demonstrating that these three well-defined members of the mammalian myc gene family are present in lower vertebrates as well. Comparison of the Xenopus and mammalian Myc families revealed a high degree of structural relatedness at the gene and protein levels; this homology was consistent with the ability of the xc-myc1 and xN-myc1 genes to function as oncogenes in primary mammalian cells. In contrast, the xL-myc1 gene was found to be incapable of transforming rat embryo fibroblast cells, and this inactivity may relate to localized but significant differences in its putative transactivation domain. Analysis of xc-, xN-, and xL-myc gene expression demonstrated that (i) all three genes were highly expressed during oogenesis and their transcripts accumulated as abundant maternal mRNAs, (ii) each gene exhibited a distinctive pattern of expression during embryogenesis and in adult tissues, and (iii) the xL-myc1 and xL-myc2 genes were coordinately expressed in the maternal and zygotic genomes. The markedly high expression of the Xenopus myc gene family in differentiated tissues, such as the central nervous system and kidney, contrasts sharply with the low levels observed in mammalian adult tissues. These differences may reflect unique functions of the Myc family proteins in processes specific to amphibians, such as tissue regeneration.
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Affiliation(s)
- N Schreiber-Agus
- Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, New York 10461
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16
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King MW. Developmentally regulated alternative splicing in the Xenopus laevis c-Myc gene creates an intron-1 containing c-Myc RNA present only in post-midblastula embryos. Nucleic Acids Res 1991; 19:5777-83. [PMID: 1945855 PMCID: PMC328990 DOI: 10.1093/nar/19.20.5777] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Two distinct c-Myc RNA classes have been identified in Xenopus laevis, presumably expressed from the duplicated c-Myc locus (1, 6). The major Xenopus c-Myc transcripts arise from sites termed P1 and P2 similarly to those of the mammalian c-Myc genes. I have used a cloned Xenopus c-Myc gene to examine the regulated pattern of expression from this gene during early Xenopus embryogenesis. Analysis of the pattern of transcript processing indicates that not only are P1 and P2 differentially active during early development but alternatively spliced c-Myc RNAs are generated which contain sequences of the first intron. These intron-1 containing c-Myc RNAs are generated by alternative splicing of transcripts initiated from the major transcription start site, P2, and are observed only in RNA samples from post-midblastula embryos or Xenopus tissue culture cells. Xenopus tissue culture cells synthesize two major c-Myc proteins (p61 and p64). Xenopus RNAs that do not contain intron-1 sequences synthesize only the p61 species. Two closely spaced ATG codons at the 5' end of exon-2 are utilized equivalently to generate a p61 doublet. Intron-1 containing RNAs utilize an ATG codon in the intron sequences to synthesize the p64 species as well as the exon-2 ATG codons to synthesize the p61 doublet.
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Affiliation(s)
- M W King
- Indiana University School of Medicine, Department of Biochemistry and Molecular Biology, Terre Haute Center for Medical Sciences, IN 47809
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17
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Principaud E, Spohr G. Xenopus laevis c-myc I and II genes: molecular structure and developmental expression. Nucleic Acids Res 1991; 19:3081-8. [PMID: 2057364 PMCID: PMC328274 DOI: 10.1093/nar/19.11.3081] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
The structure of the two Xenopus laevis c-myc I and c-myc II genes has been investigated by isolating and sequencing genomic and cDNAs clones. In oocytes, c-myc I mRNAs represent 80-90% of the overall amount of c-myc transcripts. The c-myc I expression is controlled primarily by two differentially regulated tandem promoters P1 and P2 which are separated by 50 bases. During oogenesis, maternal c-myc I mRNAs, are transcribed from both promoters whereas zygotic transcripts seem to initiate only from the P2 promoter. Sequence comparison between the promoter regions of c-myc I and II genes reveals the insertion in the c-myc I promoter region, between positions -831 and -389 relative to the P1 start site of a repetitive element. Comparison of X.laevis and mammalian c-myc promoter sequences reveals furthermore the conservation of cis-regulatory elements, including a motif known to be a negative regulator of the human c-myc transcription, a purine rich region, a binding site for the E2-F transcription factor and three SP1 binding sites. Finally, we report characterization of a new c-myc I mRNA which differ at the 5' end. Transcripts are possibly initiated at a putative alternative promoter located further upstream in the genome, and undergoes alternative splicing.
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Affiliation(s)
- E Principaud
- Université de Genève, Département de Biologie Cellulaire, Switzerland
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18
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Laird-Offringa IA, Elfferich P, van der Eb AJ. Rapid c-myc mRNA degradation does not require (A + U)-rich sequences or complete translation of the mRNA. Nucleic Acids Res 1991; 19:2387-94. [PMID: 1645870 PMCID: PMC329447 DOI: 10.1093/nar/19.9.2387] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
The c-myc proto-oncogene encodes a highly unstable mRNA. Stabilized, truncated myc transcripts have been found in several human and murine tumors of hematopoietic origin. Recently, two tumors expressing 3' truncated c-myc mRNAs that were five times more stable than normal myc transcripts, were described. We have tried to determine the cause of the increased stability of the 3' truncated myc transcripts by studying the half-life of mutated c-myc mRNAs. The c-myc 3' untranslated region has been shown to contain sequences that confer mRNA instability. Possible candidates for such sequences are two (A + U)-rich regions in the 3' end of the c-myc RNA that resemble RNA destabilizing elements present in the c-fos and GMCSF mRNAs. We show that deletions in the (A + U)-rich regions do not stabilize c-myc messengers, and that hybrid mRNAs containing SV40 sequences at their 3' ends and terminating at an SV40 polyadenylation signal decay as quickly as normal c-myc transcripts. Our results indicate that neither the loss of (A + U)-rich sequences nor the mere addition of non-myc sequences to the 3' end of the mRNA lead to stabilization. We also show that rapid degradation of c-myc mRNA does not require complete translation of the coding sequences.
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Affiliation(s)
- I A Laird-Offringa
- Laboratory for Molecular Carcinogenesis, Sylvius Laboratories, University of Leiden, The Netherlands
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19
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Mugrauer G, Ekblom P. Contrasting expression patterns of three members of the myc family of protooncogenes in the developing and adult mouse kidney. J Biophys Biochem Cytol 1991; 112:13-25. [PMID: 1986001 PMCID: PMC2288803 DOI: 10.1083/jcb.112.1.13] [Citation(s) in RCA: 82] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
The myc family of protooncogenes encode similar but distinct nuclear proteins. Since N-myc, c-myc, and L-myc have been found to be expressed in the newborn kidney, we studied their expression during murine kidney development. By organ culture studies and in situ hybridization of tissue sections, we found that each of the three members of the myc gene family shows a remarkably distinct expression pattern during kidney development. It is known that mesenchymal stem cells of the embryonic kidney convert into epithelium if properly induced. We demonstrate the N-myc expression increases during the first 24 h of in vitro culture as an early response to induction. Moreover, the upregulation was transient and expression levels were already low during the first stages of overt epithelial cell polarization. In contrast, neither c-myc nor L-myc were upregulated by induction of epithelial differentiation. c-myc was expressed in the uninduced mesenchyme but subsequently became restricted to the newly formed epithelium and was not expressed in the surrounding loose mesenchyme. At onset of terminal differentiation c-myc expression was turned off also from the epithelial tubules. We conclude that N-myc is a marker for induction and early epithelial differentiation states. That the undifferentiated mesenchyme, unlike stromal cells of later developmental stages, express c-myc demonstrates that the undifferentiated mesenchymal stem cells are distinct from the stromal cells. The most astonishing finding, however, was the high level of L-myc mRNA in the ureter, ureter-derived renal pelvis, papilla, and collecting ducts. In the ureter, expression increased, rather than decreased, with advancing maturation and was highest in adult tissue. Our results suggest that each of the three members of the myc gene family are involved in quite disparate differentiation processes, even within one tissue.
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Affiliation(s)
- G Mugrauer
- Friedrich-Miescher-Laboratorium der Max-Planck-Gesellschaft, Tübingen,Federal Republic of Germany
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Géraudie J, Hourdry J, Vriz S, Singer M, Méchali M. Enhanced c-myc gene expression during forelimb regenerative outgrowth in the young Xenopus laevis. Proc Natl Acad Sci U S A 1990; 87:3797-801. [PMID: 1692624 PMCID: PMC53990 DOI: 10.1073/pnas.87.10.3797] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Analysis of the expression of the c-myc protooncogene has been carried out in the forelimb regenerate of the Xenopus laevis froglet. Northern blot hybridization analysis revealed the presence of a 2.5-kilobase c-myc transcript in the regenerate forelimb at a level at least 7-fold more than the one found in nonregenerating forelimbs or stumps of regenerating forelimbs. In situ hybridization analyses confirmed the relative abundance of c-myc RNA in the regenerate forelimb and provided evidence of spatial localization of high levels of c-myc RNA in specific cell layers. The deepest layers of the wound epithelium of epidermal origin showed a strong signal, whereas virtually no c-myc RNA was detected in the outermost layers. Labeling was also observed in mesenchymal cells of the blastema where it was relatively evenly distributed. This pattern of c-myc RNA in the regenerate might indicate that the expression of c-myc plays a role in the regulation of the continued proliferation of specific cells of the regenerate, whereas repression of this gene in the epidermis correlates with terminal differentiation of keratinocytes.
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Affiliation(s)
- J Géraudie
- Laboratoire d'Anatomie comparée, Université Paris VII, France
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Translocation of a store of maternal cytoplasmic c-myc protein into nuclei during early development. Mol Cell Biol 1990. [PMID: 2685563 DOI: 10.1128/mcb.9.12.5395] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The c-myc proto-oncogene is expressed as a maternal protein during oogenesis in Xenopus laevis, namely, in nondividing cells. A delayed translation of c-myc mRNA accumulated in early oocytes results in the accumulation of the protein during late oogenesis. The oocyte c-myc protein is unusually stable and is located in the cytoplasm, contrasting with its features in somatic cells. A mature oocyte contains a maternal c-myc protein stockpile of 4 x 10(5) to 6 x 10(5) times the level in a somatic growing cell. This level of c-myc protein is preserved only during the cleavage stage of the embryo. Fertilization triggers its rapid migration into the nuclei of the cleaving embryo and a change in the phosphorylation state of the protein. The c-myc protein content per nucleus decreases exponentially during the cleavage stage until a stoichiometric titration by the embryonic nuclei is reached during a 0.5-h period at the midblastula stage. Most of the maternal c-myc store is degraded by the gastrula stage. These observations implicate the participation of c-myc in the events linked to early embryonic development and the midblastula transition.
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Gusse M, Ghysdael J, Evan G, Soussi T, Méchali M. Translocation of a store of maternal cytoplasmic c-myc protein into nuclei during early development. Mol Cell Biol 1989; 9:5395-403. [PMID: 2685563 PMCID: PMC363707 DOI: 10.1128/mcb.9.12.5395-5403.1989] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
The c-myc proto-oncogene is expressed as a maternal protein during oogenesis in Xenopus laevis, namely, in nondividing cells. A delayed translation of c-myc mRNA accumulated in early oocytes results in the accumulation of the protein during late oogenesis. The oocyte c-myc protein is unusually stable and is located in the cytoplasm, contrasting with its features in somatic cells. A mature oocyte contains a maternal c-myc protein stockpile of 4 x 10(5) to 6 x 10(5) times the level in a somatic growing cell. This level of c-myc protein is preserved only during the cleavage stage of the embryo. Fertilization triggers its rapid migration into the nuclei of the cleaving embryo and a change in the phosphorylation state of the protein. The c-myc protein content per nucleus decreases exponentially during the cleavage stage until a stoichiometric titration by the embryonic nuclei is reached during a 0.5-h period at the midblastula stage. Most of the maternal c-myc store is degraded by the gastrula stage. These observations implicate the participation of c-myc in the events linked to early embryonic development and the midblastula transition.
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Affiliation(s)
- M Gusse
- Institut Jacques Monod, Centre National de la Recherche Scientifique, Paris, France
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Abstract
A single nuclear protein (Myc-associated protein) can be specifically cross-linked to avian Myc proteins by treatment of nuclei or cells with the reversible cross-linker dimethyl 3,3'-dithiobis-propionimidate. Myc-associated protein has a molecular weight of approximately 500,000, is not detectably phosphorylated and, in contrast to Myc, has a long apparent half-life of greater than 3 h.
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Abstract
A single nuclear protein (Myc-associated protein) can be specifically cross-linked to avian Myc proteins by treatment of nuclei or cells with the reversible cross-linker dimethyl 3,3'-dithiobis-propionimidate. Myc-associated protein has a molecular weight of approximately 500,000, is not detectably phosphorylated and, in contrast to Myc, has a long apparent half-life of greater than 3 h.
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Affiliation(s)
- D A Gillespie
- Fred Hutchinson Cancer Research Center, Seattle, Washington 98104
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Abstract
The proteins encoded by both viral and cellular forms of the c-myc oncogene have been previously demonstrated to have exceptionally short in vivo half-lives. In this paper we report a comparative study on the parameters affecting turnover of nuclear oncoproteins c-myc, c-myb, and the rapidly metabolized cytoplasmic enzyme ornithine decarboxylase. The degradation of all three proteins required metabolic energy, did not result in production of cleavage intermediates, and did not involve lysosomes or ubiquitin. A five- to eightfold increase in the half-life of c-myc proteins, and a twofold increase in the half-life of c-myb proteins was detected after heat-shock treatment at 46 degrees C. In contrast, heat shock had no effect on the turnover of ornithine decarboxylase. Heat shock also had the effect of increasing the rate of c-myc protein synthesis twofold, whereas c-myb protein synthesis was decreased nearly fourfold. The increased stability and synthesis of c-myc proteins led to an overall increase in the total level of c-myc proteins in response to heat-shock treatment. Furthermore, treatments which reduced c-myc and c-myb protein turnover, such as heat shock and exposure to inhibitors of metabolic energy production, resulted in reduced detergent solubility of both proteins. The recovery from heat shock, as measured by increased turnover and solubility, was energy dependent and considerably more rapid in thermotolerant cells.
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Lüscher B, Eisenman RN. c-myc and c-myb protein degradation: effect of metabolic inhibitors and heat shock. Mol Cell Biol 1988; 8:2504-12. [PMID: 3043180 PMCID: PMC363451 DOI: 10.1128/mcb.8.6.2504-2512.1988] [Citation(s) in RCA: 54] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
The proteins encoded by both viral and cellular forms of the c-myc oncogene have been previously demonstrated to have exceptionally short in vivo half-lives. In this paper we report a comparative study on the parameters affecting turnover of nuclear oncoproteins c-myc, c-myb, and the rapidly metabolized cytoplasmic enzyme ornithine decarboxylase. The degradation of all three proteins required metabolic energy, did not result in production of cleavage intermediates, and did not involve lysosomes or ubiquitin. A five- to eightfold increase in the half-life of c-myc proteins, and a twofold increase in the half-life of c-myb proteins was detected after heat-shock treatment at 46 degrees C. In contrast, heat shock had no effect on the turnover of ornithine decarboxylase. Heat shock also had the effect of increasing the rate of c-myc protein synthesis twofold, whereas c-myb protein synthesis was decreased nearly fourfold. The increased stability and synthesis of c-myc proteins led to an overall increase in the total level of c-myc proteins in response to heat-shock treatment. Furthermore, treatments which reduced c-myc and c-myb protein turnover, such as heat shock and exposure to inhibitors of metabolic energy production, resulted in reduced detergent solubility of both proteins. The recovery from heat shock, as measured by increased turnover and solubility, was energy dependent and considerably more rapid in thermotolerant cells.
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Affiliation(s)
- B Lüscher
- Viral Oncology, Fred Hutchinson Cancer Research Center, Seattle, Washington 98104
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Baltus E, Hanocq-Quertier J, Hanocq F, Brachet J. Injection of an antibody against a p21 c-Ha-ras protein inhibits cleavage in axolotl eggs. Proc Natl Acad Sci U S A 1988; 85:502-6. [PMID: 3277177 PMCID: PMC279578 DOI: 10.1073/pnas.85.2.502] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
The presence of a ras protein was demonstrated in cleaving axolotl eggs by selective immunoprecipitation with a polyclonal antibody against a peptide encoded by the c-Ha-ras oncogene, cellular homolog of the v-Ha-ras oncogene of Harvey rat sarcoma virus. Injection of this antibody into axolotl oocytes subjected to progesterone treatment does not prevent meiotic maturation. Injection of the same antibody into a blastomere of axolotl eggs at the 2- or 4-cell stage causes cleavage arrest in the descendants of the injected blastomere. Cytological observations of the injected eggs show, in the arrested blastomeres, enlarged nuclei always surrounded by an intact nuclear envelope and containing uncondensed chromatin. The possible role of ras protein in meiosis and mitosis is discussed.
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Affiliation(s)
- E Baltus
- Département de Biologie Moléculaire, Université Libre de Bruxelles, Rhode-St.-Genèse, Belgium
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