551
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Nelsen CJ, Hansen LK, Rickheim DG, Chen C, Stanley MW, Krek W, Albrecht JH. Induction of hepatocyte proliferation and liver hyperplasia by the targeted expression of cyclin E and skp2. Oncogene 2001; 20:1825-31. [PMID: 11313930 DOI: 10.1038/sj.onc.1204248] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2000] [Revised: 01/05/2001] [Accepted: 01/09/2001] [Indexed: 12/28/2022]
Abstract
Cells in culture become competent to replicate in the absence of growth factor after progressing beyond the late G1 restriction point, suggesting that a set of genes expressed during G1 phase is sufficient to trigger completion of the cell cycle. However, this has not been demonstrated in an in vivo system. In this study, we examined whether transfection of genes associated with the G1/S transition could trigger hepatocyte replication. Co-transfection of cyclin E and skp2 synergistically promoted cell cycle progression in cultured primary hepatocytes in the absence of mitogen or in the presence of growth inhibitors. Furthermore, transfection of hepatocytes in vivo with cyclin E and skp2 promoted abundant hepatocyte replication and hyperplasia of the liver. These studies confirm that transfection with a small number of genes can trigger proliferation of quiescent hepatocytes in vivo, and suggest that therapies to enhance liver regeneration by targeting cell cycle control genes may be feasible.
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Affiliation(s)
- C J Nelsen
- Department of Medicine, Hennepin County Medical Center, Minneapolis, Minnesota, MN 55415, USA
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552
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Grandori C, Cowley SM, James LP, Eisenman RN. The Myc/Max/Mad network and the transcriptional control of cell behavior. Annu Rev Cell Dev Biol 2001; 16:653-99. [PMID: 11031250 DOI: 10.1146/annurev.cellbio.16.1.653] [Citation(s) in RCA: 986] [Impact Index Per Article: 42.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
The Myc/Max/Mad network comprises a group of transcription factors whose distinct interactions result in gene-specific transcriptional activation or repression. A great deal of research indicates that the functions of the network play roles in cell proliferation, differentiation, and death. In this review we focus on the Myc and Mad protein families and attempt to relate their biological functions to their transcriptional activities and gene targets. Both Myc and Mad, as well as the more recently described Mnt and Mga proteins, form heterodimers with Max, permitting binding to specific DNA sequences. These DNA-bound heterodimers recruit coactivator or corepressor complexes that generate alterations in chromatin structure, which in turn modulate transcription. Initial identification of target genes suggests that the network regulates genes involved in the cell cycle, growth, life span, and morphology. Because Myc and Mad proteins are expressed in response to diverse signaling pathways, the network can be viewed as a functional module which acts to convert environmental signals into specific gene-regulatory programs.
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Affiliation(s)
- C Grandori
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109-1024, USA.
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553
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Baker NE, Yu SY. The EGF receptor defines domains of cell cycle progression and survival to regulate cell number in the developing Drosophila eye. Cell 2001; 104:699-708. [PMID: 11257224 DOI: 10.1016/s0092-8674(01)00266-5] [Citation(s) in RCA: 169] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The number of cells in developing organs must be controlled spatially by extracellular signals. Our results show how cell number can be regulated by cell interactions controlling proliferation and survival in local neighborhoods in the case of the Drosophila compound eye. Intercellular signals act during the second mitotic wave, a cell cycle that generates a pool of uncommitted cells used for most ommatidial fates. We find that G1/S progression to start the cell cycle requires EGF receptor inactivity. EGF receptor activation is then required for progression from G2 to M phase of the same cells, and also prevents apoptosis. EGF receptor activation depends on short-range signals from five-cell preclusters of photoreceptor neurons not participating in the second mitotic wave. Through proliferation and survival control, such signals couple the total number of uncommitted cells being generated to the neural patterning of the retina.
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Affiliation(s)
- N E Baker
- Department of Molecular Genetics, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA.
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554
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Tang AH, Neufeld TP, Rubin GM, Müller HA. Transcriptional regulation of cytoskeletal functions and segmentation by a novel maternal pair-rule gene, lilliputian. Development 2001; 128:801-13. [PMID: 11171404 DOI: 10.1242/dev.128.5.801] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Transcriptional control during early Drosophila development is governed by maternal and zygotic factors. We have identified a novel maternal transcriptional regulator gene, lilliputian (lilli), which contains an HMG1 (AT-hook) motif and a domain with similarity to the human fragile X mental retardation FMR2 protein and the AF4 proto-oncoprotein. Embryos lacking maternal lilli expression show specific defects in the establishment of a functional cytoskeleton during cellularization, and exhibit a pair-rule segmentation phenotype. These mutant phenotypes correlate with markedly reduced expression of the early zygotic genes serendipity alpha, fushi tarazu and huckebein, which are essential for cellularization and embryonic patterning. In addition, loss of lilli in adult photoreceptor and bristle cells results in a significant decrease in cell size. Our results indicate that lilli represents a novel pair-rule gene that acts in cytoskeleton regulation, segmentation and morphogenesis.
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MESH Headings
- Actins/metabolism
- Amino Acid Sequence
- Animals
- Body Patterning
- Cell Size
- Cytoskeleton/genetics
- Cytoskeleton/metabolism
- DNA-Binding Proteins/genetics
- DNA-Binding Proteins/metabolism
- Drosophila Proteins
- Drosophila melanogaster/embryology
- Drosophila melanogaster/genetics
- Embryo, Nonmammalian/cytology
- Embryo, Nonmammalian/physiology
- Female
- Flow Cytometry
- Fushi Tarazu Transcription Factors
- Gene Expression Regulation, Developmental
- Genes, Insect
- Genes, Reporter/genetics
- Homeodomain Proteins/genetics
- Homeodomain Proteins/metabolism
- Humans
- In Situ Hybridization
- Male
- Membrane Proteins/genetics
- Membrane Proteins/metabolism
- Microscopy, Confocal
- Microscopy, Fluorescence
- Microscopy, Video
- Microtubules/metabolism
- Molecular Sequence Data
- Nuclear Proteins/chemistry
- Nuclear Proteins/genetics
- Nuclear Proteins/metabolism
- Photoreceptor Cells, Invertebrate/cytology
- Photoreceptor Cells, Invertebrate/embryology
- Photoreceptor Cells, Invertebrate/metabolism
- RNA, Messenger/metabolism
- Sequence Alignment
- Transcription Factors
- Wings, Animal/anatomy & histology
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Affiliation(s)
- A H Tang
- Howard Hughes Medical Institute, Department of Molecular and Cell Biology, University of California-Berkeley, Berkeley, California 94720-3200, USA.
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555
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Abstract
A great deal of work has focused on how oncogenes regulate the cell cycle during normal development and in cancer, yet their roles in regulating cell growth have been largely unexplored. Recent work in several model organisms has demonstrated that homologs of several oncogenes regulate cell growth and has suggested that some of the effects of oncogenes on the cell cycle may be a result of growth promotion. These studies have also suggested how growth and cell-cycle progression may be coupled.
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Affiliation(s)
- D A Prober
- Molecular and Cellular Biology Program, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue North, Seattle, Washington 98109, USA.
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556
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Saka Y, Smith JC. Spatial and temporal patterns of cell division during early Xenopus embryogenesis. Dev Biol 2001; 229:307-18. [PMID: 11150237 DOI: 10.1006/dbio.2000.0101] [Citation(s) in RCA: 138] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We describe the spatial and temporal patterns of cell division in the early Xenopus embryo, concentrating on the period between the midblastula transition and the early tailbud stage. Mitotic cells were identified using an antibody recognising phosphorylated histone H3. At least four observations are of interest. First, axial mesodermal cells, including prospective notochord, stop dividing after involution and may not divide thereafter. Second, cell division is more pronounced in the neural plate than in nonneural ectoderm, and the pattern of cell division becomes further refined as neurogenesis proceeds. Third, cells in the cement gland cease proliferation completely as they begin to accumulate pigment. Finally, the precursors of peripheral sensory organs such as the ear and olfactory placode undergo active cell proliferation when they arise from the sensorial layer of the ectoderm. These observations and others should provide a platform to study the relationship between the regulation of developmental processes and the cell cycle during Xenopus embryogenesis.
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Affiliation(s)
- Y Saka
- Division of Developmental Biology, National Institute for Medical Research, The Ridgeway, Mill Hill, London, NW7 1AA, United Kingdom.
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557
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Schuhmacher M, Kohlhuber F, Hölzel M, Kaiser C, Burtscher H, Jarsch M, Bornkamm GW, Laux G, Polack A, Weidle UH, Eick D. The transcriptional program of a human B cell line in response to Myc. Nucleic Acids Res 2001; 29:397-406. [PMID: 11139609 PMCID: PMC29676 DOI: 10.1093/nar/29.2.397] [Citation(s) in RCA: 253] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
The proto-oncogene c-myc (myc) encodes a transcription factor (Myc) that promotes growth, proliferation and apoptosis. Myc has been suggested to induce these effects by induction/repression of downstream genes. Here we report the identification of potential Myc target genes in a human B cell line that grows and proliferates depending on conditional myc expression. Oligonucleotide microarrays were applied to identify downstream genes of Myc at the level of cytoplasmic mRNA. In addition, we identified potential Myc target genes in nuclear run-on experiments by changes in their transcription rate. The identified genes belong to gene classes whose products are involved in amino acid/protein synthesis, lipid metabolism, protein turnover/folding, nucleotide/DNA synthesis, transport, nucleolus function/RNA binding, transcription and splicing, oxidative stress and signal transduction. The identified targets support our current view that myc acts as a master gene for growth control and increases transcription of a large variety of genes.
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Affiliation(s)
- M Schuhmacher
- GSF Research Centre, Institute of Clinical Molecular Biology, Marchioninistrasse 25, D-81377 Munich, Germany
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558
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Abstract
The cell-division cycle is an orchestrated sequence of events that results in the duplication of a cell. In metazoa, cell proliferation is regulated in response to differentiation signals and body-size parameters, which either induce cell duplication or arrest the cell cycle, to ensure that organs develop to the correct size. In addition, the cell cycle may be altered to meet specialized requirements. This can be seen in the rapid cleavage cycles of vertebrates and insects that lack gap phases, in the nested S phases of Drosophila, and in the endocycles of nematodes, insects, plants and mammals that lack mitosis. Here we present the various modes of cell-cycle regulation in metazoa and discuss their possible generation by a combination of universally conserved molecules and new regulatory circuits.
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Affiliation(s)
- S J Vidwans
- Department of Biochemistry and Biophysics, University of California at San Francisco, California 94143-0448, USA
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559
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Abstract
Size regulation is a never-ending problem. Many of us worry that parts of ourselves are too big whereas other parts are too small. How organisms--and their tissues--are programmed to be a specific size, how this size is maintained, and what might cause something to become the wrong size, are key problems in developmental biology. But what are the mechanisms that regulate the size of multicellular structures?
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Affiliation(s)
- R H Gomer
- Howard Hughes Medical Institute and Department of Biochemistry and Cell Biology MS-140, Rice University, 6,100 South Main Street, Houston, Texas 77005-1892, USA.
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560
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Sotillos S, Campuzano S. DRacGAP, a novel Drosophila gene, inhibits EGFR/Ras signalling in the developing imaginal wing disc. Development 2000; 127:5427-38. [PMID: 11076763 DOI: 10.1242/dev.127.24.5427] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
We have identified a novel Drosophila gene, DRacGAP, which behaves as a negative regulator of Ρ-family GTPases DRac1 and DCdc42. Reduced function of DRacGAP or increased expression of DRac1 in the wing imaginal disc cause similar effects on vein and sensory organ development and cell proliferation. These effects result from enhanced activity of the EGFR/Ras signalling pathway. We find that in the wing disc, DRac1 enhances EGFR/Ras-dependent activation of MAP Kinase in the prospective veins. Interestingly, DRacGAP expression is negatively regulated by the EGFR/Ras pathway in these regions. During vein formation, local DRacGAP repression would ensure maximal activity of Rac and, in turn, of Ras pathways in vein territories. Additionally, maximal expression of DRacGAP at the vein/intervein boundaries would help to refine the width of the veins. Hence, control of DRacGAP expression by the EGFR/Ras pathway is a previously undescribed feedback mechanism modulating the intensity and/or duration of its signalling during Drosophila development.
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Affiliation(s)
- S Sotillos
- Centro de Biología Molecular Severo Ochoa, CSIC and UAM Cantoblanco, Spain
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561
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Suda M, Yamada S, Toda T, Miyakawa T, Hirata D. Regulation of Wee1 kinase in response to protein synthesis inhibition. FEBS Lett 2000; 486:305-9. [PMID: 11119724 DOI: 10.1016/s0014-5793(00)02299-7] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
To investigate the mechanism coupling growth (protein synthesis) with cell division, we examined the relationship between the tyrosine kinase Wee1 that inhibits Cdc2-Cdc13 mitosis-inducing kinase by phosphorylating it, and protein synthesis inhibition in fission yeast. The wee1-50 mutant showed supersensitivity to protein synthesis inhibitor, cycloheximide. Wee1 was essential for the G(2) delay upon a partial inhibition of protein synthesis. Indeed, the protein synthesis inhibition caused an increase in the Wee1 protein by the Sty1/Spc1 MAPK-dependent transcriptional and the Sty1/Spc1 MAPK-independent post-transcriptional regulations. Further, the results indicated that the post-transcriptional regulation is important for the G(2) delay.
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Affiliation(s)
- M Suda
- Department of Molecular Biotechnology, Graduate School of Advanced Sciences of Matter, Hiroshima University, Japan
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562
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Kondorosi E, Roudier F, Gendreau E. Plant cell-size control: growing by ploidy? CURRENT OPINION IN PLANT BIOLOGY 2000; 3:488-92. [PMID: 11074380 DOI: 10.1016/s1369-5266(00)00118-7] [Citation(s) in RCA: 185] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
The size of plant cells is determined by genetic, structural and physical factors as well as by internal and external signals. Our knowledge of the molecular mechanisms of these controls is still rudimentary. Recent studies indicate that ploidy level exerts an important control on cell size. By increasing ploidy, endoreduplication may allow cells to reach extraordinary sizes. This process is widespread in plants and may provide a means to manipulate the cell volume.
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Affiliation(s)
- E Kondorosi
- Institut des Sciences Végétales, Centre Nationale de la Recherche Scientifique (CNRS), Gif-sur-Yvette, France.
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563
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Zhang H, Stallock JP, Ng JC, Reinhard C, Neufeld TP. Regulation of cellular growth by the Drosophila target of rapamycin dTOR. Genes Dev 2000; 14:2712-24. [PMID: 11069888 PMCID: PMC317034 DOI: 10.1101/gad.835000] [Citation(s) in RCA: 484] [Impact Index Per Article: 20.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The TOR protein kinases (TOR1 and TOR2 in yeast; mTOR/FRAP/RAFT1 in mammals) promote cellular proliferation in response to nutrients and growth factors, but their role in development is poorly understood. Here, we show that the Drosophila TOR homolog dTOR is required cell autonomously for normal growth and proliferation during larval development, and for increases in cellular growth caused by activation of the phosphoinositide 3-kinase (PI3K) signaling pathway. As in mammalian cells, the kinase activity of dTOR is required for growth factor-dependent phosphorylation of p70 S6 kinase (p70(S6K)) in vitro, and we demonstrate that overexpression of p70(S6K) in vivo can rescue dTOR mutant animals to viability. Loss of dTOR also results in cellular phenotypes characteristic of amino acid deprivation, including reduced nucleolar size, lipid vesicle aggregation in the larval fat body, and a cell type-specific pattern of cell cycle arrest that can be bypassed by overexpression of the S-phase regulator cyclin E. Our results suggest that dTOR regulates growth during animal development by coupling growth factor signaling to nutrient availability.
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Affiliation(s)
- H Zhang
- Chiron Corporation, Emeryville, California 94608, USA
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564
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Beier R, Bürgin A, Kiermaier A, Fero M, Karsunky H, Saffrich R, Möröy T, Ansorge W, Roberts J, Eilers M. Induction of cyclin E-cdk2 kinase activity, E2F-dependent transcription and cell growth by Myc are genetically separable events. EMBO J 2000; 19:5813-23. [PMID: 11060032 PMCID: PMC305784 DOI: 10.1093/emboj/19.21.5813] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2000] [Revised: 09/08/2000] [Accepted: 09/08/2000] [Indexed: 12/23/2022] Open
Abstract
The c-myc gene has been implicated in three distinct genetic programs regulating cell proliferation: control of cyclin E-cdk2 kinase activity, E2F-dependent transcription and cell growth. We have now used p27(-/-) fibroblasts to dissect these downstream signalling pathways. In these cells, activation of Myc stimulates transcription of E2F target genes, S-phase entry and cell growth without affecting cyclin E-cdk2 kinase activity. Both cyclin D2 and E2F2, potential direct target genes of Myc, are induced in p27(-/-) MycER cells. Ectopic expression of E2F2, but not of cyclin D2, induces S-phase entry, but, in contrast to Myc, does not stimulate cell growth. Our results show that stimulation of cyclin E-cdk2 kinase, of E2F-dependent transcription and of cell growth by Myc can be genetically separated from each other.
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Affiliation(s)
- R Beier
- Institute of Molecular Biology and Tumour Research, Emil-Mannkopff-Strabetae 2, 35033 Marburg, Germany
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565
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Kim S, Li Q, Dang CV, Lee LA. Induction of ribosomal genes and hepatocyte hypertrophy by adenovirus-mediated expression of c-Myc in vivo. Proc Natl Acad Sci U S A 2000; 97:11198-202. [PMID: 11005843 PMCID: PMC17177 DOI: 10.1073/pnas.200372597] [Citation(s) in RCA: 146] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Overexpression of c-Myc in immortalized cells increases cell proliferation, inhibits cell differentiation, and promotes cell transformation. Recent evidence suggests that these effects, however, do not necessarily occur when c-Myc is overexpressed in primary mammalian cells. We sought to determine the immediate effects of transient overexpression of c-Myc in primary cells in vivo by using recombinant adenovirus to overexpress human MYC in mouse liver. Mice were intravenously injected with adenoviruses encoding MYC (Ad/Myc), E2F-1 (Ad/E2F-1), or beta-galactosidase (Ad/LacZ). Transgene expression was detectable 4 days after injection. Expression of ectopic c-Myc was immediately accompanied by enlarged and dysmorphic hepatocytes in the absence of significant cell proliferation or apoptosis. These findings were not present in the livers of mice injected with Ad/E2F-1 or Ad/LacZ. Prominent hepatocyte nuclei and nucleoli were associated with the up-regulation of large- and small-subunit ribosomal and nucleolar genes, suggesting that c-Myc may induce their expression to increase cell mass. Our studies support a role for c-Myc in the in vivo control of vertebrate cell size and metabolism independent of cell proliferation.
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Affiliation(s)
- S Kim
- Department of Medicine, and the Graduate Program of Molecular Medicine, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
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566
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de Nooij JC, Graber KH, Hariharan IK. Expression of the cyclin-dependent kinase inhibitor Dacapo is regulated by cyclin E. Mech Dev 2000; 97:73-83. [PMID: 11025208 DOI: 10.1016/s0925-4773(00)00435-4] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The Cip/Kip family of cyclin-dependent kinase inhibitors (CKIs) has been implicated in mediating cell cycle arrest prior to terminal differentiation. In many instances, increased expression of CKIs immediately precedes mitotic arrest. However, the mechanism that activates CKI expression in cells that are about to stop dividing has remained elusive. Here we have addressed this issue by investigating the expression pattern of dacapo, a Cip/Kip CKI in Drosophila. We show that the accumulation of dacapo RNA and protein requires Cyclin E and that increased expression of Cyclin E can induce dacapo expression. We also show that the oscillation of the Cyclin E and Dacapo proteins are tightly coupled during ovarian endocycles. Our results argue for a mechanism where Cyclin E/Cdk activity induces Dacapo expression but only within certain windows that are permissive for dacapo expression.
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Affiliation(s)
- J C de Nooij
- Massachusetts General Hospital Cancer Center, Building 149, Charlestown, MA 02129, USA
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567
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Abstract
Over the past 25 years, the genetic control of cell size has mainly been addressed in yeast, a single-celled organism. Recent insights from Drosophila have shed light on the signalling pathways responsible for adjusting and maintaining cell size in metazoans. Evidence is emerging for a signalling cascade conserved in evolution that links external nutrient sources to cell size.
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Affiliation(s)
- H Stocker
- Zoologisches Institut, Universität Zürich, Winterthurerstrasse 190, CH-8057, Zürich, Switzerland
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568
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Montagne J. Genetic and molecular mechanisms of cell size control. MOLECULAR CELL BIOLOGY RESEARCH COMMUNICATIONS : MCBRC 2000; 4:195-202. [PMID: 11409911 DOI: 10.1006/mcbr.2001.0284] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Since the discovery of the cell as the minimal indivisible living entity, scientists have tried to understand how all the various physiological aspects were assumed within this single functional unit. One fascinating question concerns the role of cell size and cell number in determining the overall size of an organism. During the past century, increasing knowledge in molecular genetics has allowed the characterization of a number of molecular events that influence the size of a cell. However, in spite of recent progress, precise molecular mechanisms governing cell size remain unclear. Although the existence of a master regulator is still possible, cell size may be primarily controlled by an interactive network linking gene expression with translational capacity and cell proliferation.
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Affiliation(s)
- J Montagne
- Friedrich Miescher-Institut, Maulbeerstrasse 66, Basel, CH-4058, Switzerland.
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569
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Abstract
Tradition holds that cyclin D is required for the initiation of cell division; recent studies in Drosophila, however, suggest that cyclin D has a separate function in governing growth.
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Affiliation(s)
- E Foley
- Department of Genetics, University of Cologne, Weyertal 121, D-50931, Cologne, Germany
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570
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Meyer CA, Jacobs HW, Datar SA, Du W, Edgar BA, Lehner CF. Drosophila Cdk4 is required for normal growth and is dispensable for cell cycle progression. EMBO J 2000; 19:4533-42. [PMID: 10970847 PMCID: PMC302073 DOI: 10.1093/emboj/19.17.4533] [Citation(s) in RCA: 167] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Complexes of D-type cyclins and cdk4 or 6 are thought to govern progression through the G(1) phase of the cell cycle. In Drosophila, single genes for Cyclin D and Cdk4 have been identified, simplifying genetic analysis. Here, we show that Drosophila Cdk4 interacts with Cyclin D and the Rb homolog RBF as expected, but is not absolutely essential. Flies homozygous for null mutations develop to the adult stage and are fertile, although only to a very limited degree. Overexpression of inactive mutant Cdk4, which is able to bind Cyclin D, does not enhance the Cdk4 mutant phenotype, confirming the absence of additional Cyclin D-dependent cdks. Our results indicate, therefore, that progression into and through the cell cycle can occur in the absence of Cdk4. However, the growth of cells and of the organism is reduced in Cdk4 mutants, indicating a role of D-type cyclin-dependent protein kinases in the modulation of growth rates.
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Affiliation(s)
- C A Meyer
- Department of Genetics, University of Bayreuth, 95440 Bayreuth, Germany
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571
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Rathmell JC, Vander Heiden MG, Harris MH, Frauwirth KA, Thompson CB. In the absence of extrinsic signals, nutrient utilization by lymphocytes is insufficient to maintain either cell size or viability. Mol Cell 2000; 6:683-92. [PMID: 11030347 DOI: 10.1016/s1097-2765(00)00066-6] [Citation(s) in RCA: 355] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Without receptor stimulation, cells from multicellular organisms die by apoptosis. Here we show that lymphocytes deprived of receptor stimulation undergo progressive atrophy before commitment to apoptosis. Following loss of receptor engagement, lymphocytes rapidly downregulated the glucose transporter, glut1. This was accompanied by reduction in mitochondrial potential and cellular ATP, suggesting that atrophy resulted from depletion of glucose-derived metabolic substrates. Expression of the antiapoptotic protein, Bcl-X(L), prevented death but not atrophy following either growth factor or glucose withdrawal. In Bcl-X(L) transgenic animals, size and metabolic activity of naive T cells were regulated through the TCR and correlated with TCR-dependent glut1 expression. These data suggest that ligands for cell-specific receptors promote cell survival by regulating nutrient uptake and utilization.
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Affiliation(s)
- J C Rathmell
- Department of Cancer Biology and Medicine and Abramson Family Cancer Research Institute, University of Pennsylvania, Philadelphia 19104, USA
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572
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Coelho CM, Leevers SJ. Do growth and cell division rates determine cell size in multicellular organisms? J Cell Sci 2000; 113 ( Pt 17):2927-34. [PMID: 10934032 DOI: 10.1242/jcs.113.17.2927] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Studies in yeast have provided some clues to how cell size might be determined in unicellular eukaryotes; yet little attention has been paid to this issue in multicellular organisms. Reproducible cell sizes might be achieved in the dividing cells of multicellular organisms by the coordination of growth with cell division. Recently, mutations in genes encoding homologues of components of the mammalian insulin/phosphoinositide 3-kinase signalling pathway have been shown to affect organ growth and cell size during Drosophila melanogaster imaginal disc development. The data suggest that signalling through this pathway alters cell size because it primarily affects the growth of these organs (i.e. their increase in mass) and does not have a proportional impact on cell division. These observations are in keeping with the hypothesis that growth and cell division are regulated independently, and that cell size is just a consequence of the rate at which tissues grow and the cells within them divide. However, signalling through this pathway can affect cell cycle phasing and at least influence cell division. These interactions may provide a means of coordinating growth and cell division, such that cells divide only when they are above a minimum size.
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Affiliation(s)
- C M Coelho
- Ludwig Institute for Cancer Research, London W1P 8BT, UK
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573
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Datar SA, Jacobs HW, de la Cruz AF, Lehner CF, Edgar BA. The Drosophila cyclin D-Cdk4 complex promotes cellular growth. EMBO J 2000; 19:4543-54. [PMID: 10970848 PMCID: PMC302080 DOI: 10.1093/emboj/19.17.4543] [Citation(s) in RCA: 218] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2000] [Revised: 07/19/2000] [Accepted: 07/19/2000] [Indexed: 11/14/2022] Open
Abstract
Mammalian cyclin D-Cdk4 complexes have been characterized as growth factor-responsive cell cycle regulators. Their levels rise upon growth factor stimulation, and they can phosphorylate and thus neutralize Retinoblastoma (Rb) family proteins to promote an E2F-dependent transcriptional program and S-phase entry. Here we characterize the in vivo function of Drosophila Cyclin D (CycD). We find that Drosophila CycD-Cdk4 does not act as a direct G(1)/S-phase regulator, but instead promotes cellular growth (accumulation of mass). The cellular response to CycD-Cdk4-driven growth varied according to cell type. In undifferentiated proliferating wing imaginal cells, CycD-Cdk4 caused accelerated cell division (hyperplasia) without affecting cell cycle phasing or cell size. In endoreplicating salivary gland cells, CycD-Cdk4 caused excessive DNA replication and cell enlargement (hypertrophy). In differentiating eyes, CycD-Cdk4 caused cell enlargement (hypertrophy) in post-mitotic cells. Interaction tests with a Drosophila Rb homolog, RBF, indicate that CycD-Cdk4 can counteract the cell cycle suppressive effects of RBF, but that its growth promoting activity is mediated at least in part via other targets.
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Affiliation(s)
- S A Datar
- Program in Molecular and Cellular Biology and Program in Developmental Biology, Fred Hutchinson Cancer Research Center, Seattle, WA 98109, USA
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574
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Scanga SE, Ruel L, Binari RC, Snow B, Stambolic V, Bouchard D, Peters M, Calvieri B, Mak TW, Woodgett JR, Manoukian AS. The conserved PI3'K/PTEN/Akt signaling pathway regulates both cell size and survival in Drosophila. Oncogene 2000; 19:3971-7. [PMID: 10962553 DOI: 10.1038/sj.onc.1203739] [Citation(s) in RCA: 145] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Akt (or PKB) is an oncogene involved in the regulation of cell survival. Akt is regulated by phosphatidylinositol 3-OH kinase (PI3'K) signaling and has shown to be hyperactivated through the loss of the PTEN tumor suppressor. In Drosophila, insulin signaling as studied using the Drosophila IRS-4 homolog (Chico) has been shown to be a crucial regulator of cell size. We have studied Drosophila Akt (Dakt1) and have shown that it is also involved in the regulation of cell size. Furthermore we have performed genetic epistasis tests to demonstrate that in Drosophila, PI3'K, PTEN and Akt comprise a signaling cassette that is utilized during multiple stages of development. In addition, we show that this signaling cassette is also involved in the regulation of cell survival during embryogenesis. This study therefore establishes the evolutionary conservation of this signaling pathway in Drosophila. Oncogene (2000) 19, 3971 - 3977.
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Affiliation(s)
- S E Scanga
- Department of Medical Biophysics, Division of Cell and Molecular Biology, Ontario Cancer Institute, University Health Network, Princess Margaret Hospital, University of Toronto, 610 University Avenue, Toronto, Ontario, Canada, M5G 2M9
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575
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Klingenberg CP, Zaklan SD. Morphological intergration between development compartments in the Drosophila wing. Evolution 2000; 54:1273-85. [PMID: 11005294 DOI: 10.1111/j.0014-3820.2000.tb00560.x] [Citation(s) in RCA: 181] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Developmental integration is the covariation among morphological structures due to connections between the developmental processes that built them. Here we use the methods of geometric morphometrics to study integration in the wing of Drosophila melanogaster. In particular, we focus on the hypothesis that the anterior and posterior wing compartments are separate developmental units that vary independently. We measured both variation among genetically diverse individuals and random differences between body sides of single individuals (fluctuating asymmetry, FA). For both of these sources of variation, the patterns of variation identified by principal component analyses all involved landmarks in both the anterior and posterior compartments simultaneously. Analyses focusing exclusively on the covariation between the anterior and posterior compartments, by the partial least-squares method, revealed pervasive integration of the two compartments, for both individual variation and FA. These analyses clearly indicate that the anterior and posterior compartments are not separate units of variation, but that the covariation between compartments is sufficient to account for nearly all the variation throughout the entire wing. We conclude that variation among individuals as well as the developmental perturbations responsible for FA generate shape variation primarily through developmental processes that are integrated across both compartments. In contrast, much less of the shape variation in our sample can be attributed to the localized processes that establish the identity of particular wing veins.
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Affiliation(s)
- C P Klingenberg
- Department of Zoology, Duke University, Durham, North Carolina 27708-0325, USA.
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576
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Myster DL, Bonnette PC, Duronio RJ. A role for the DP subunit of the E2F transcription factor in axis determination during Drosophila oogenesis. Development 2000; 127:3249-61. [PMID: 10887081 DOI: 10.1242/dev.127.15.3249] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The E2F family of transcription factors contributes to cell cycle control by regulating the transcription of DNA replication factors. Functional ‘E2F’ is a DNA-binding heterodimer composed of E2F and DP proteins. Drosophila contains two E2F genes (dE2F, dE2F2) and one DP gene (dDP). Mutation of either dE2F or dDP eliminates G(1)-S transcription of known replication factors during embryogenesis and compromises DNA replication. However, the analysis of these mutant phenotypes is complicated by the perdurance of maternally supplied gene function. To address this and to further analyze the role of E2F transcription factors in development we have phenotypically characterized mitotic clones of dDP mutant cells in the female germline. Our analysis indicates that dDP is required for several essential processes during oogenesis. In a fraction of the mutant egg chambers the germ cells execute one extra round of mitosis, suggesting that in this tissue dDP is uniquely utilized for cell cycle arrest rather than cell cycle progression. Mutation of dDP in the germline also prevents nurse cell cytoplasm transfer to the oocyte, resulting in a ‘dumpless’ phenotype that blocks oocyte development. This phenotype likely results from both disruption of the actin cytoskeleton and a failure of nurse cell apoptosis, each of which are required for normal cytoplasmic transfer. Lastly, we found that dDP is required for the establishment of the dorsal-ventral axis, as loss of dDP function prevents the localized expression of the EGFR ligand Gurken in the oocyte, which initiates dorsal-ventral polarity in the egg chamber. Thus we have uncovered new functions for E2F transcription factors during development, including an unexpected role in pattern formation.
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Affiliation(s)
- D L Myster
- Department of Biology, Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, NC 27599, USA
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577
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Oldham S, Böhni R, Stocker H, Brogiolo W, Hafen E. Genetic control of size in Drosophila. Philos Trans R Soc Lond B Biol Sci 2000; 355:945-52. [PMID: 11128988 PMCID: PMC1692799 DOI: 10.1098/rstb.2000.0630] [Citation(s) in RCA: 92] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
During the past ten years, significant progress has been made in understanding the basic mechanisms of the development of multicellular organisms. Genetic analysis of the development of Caenorhabditis elegans and Drosophila has unearthed a fruitful number of genes involved in establishing the basic body plan, patterning of limbs, specification of cell fate and regulation of programmed cell death. The genes involved in these developmental processes have been conserved throughout evolution and homologous genes are involved in the patterning of insect and human limbs. Despite these important discoveries, we have learned astonishingly little about one of the most obvious distinctions between animals: their difference in body size. The mass of the smallest mammal, the bumble-bee bat, is 2 g while that of the largest mammal, the blue whale, is 150 t or 150 million grams. Remarkably, even though they are in the same class, body size can vary up to 75-million-fold. Furthermore, this body growth can be finite in the case of most vertebrates or it can occur continuously throughout life, as for trees, molluscs and large crustaceans. Currently, we know comparatively little about the genetic control of body size. In this article we will review recent evidence from vertebrates and particularly from Drosophila that implicates insulin/insulin-like growth factor-I and other growth pathways in the control of cell, organ and body size.
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Affiliation(s)
- S Oldham
- Zoological Institute, University of Zurich, Switzerland
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578
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Abstract
Over many years evidence has accumulated that plants and animals can regulate growth with reference to overall size rather than cell number. Thus, organs and organisms grow until they reach their characteristic size and shape and then they stop - they can even compensate for experimental manipulations that change, over several fold, cell number or average cell size. If the cell size is altered, the organism responds with a change in cell number and vice versa. We look at the Drosophila wing in more detail: here, both extracellular and intracellular regulators have been identified that link cell growth, division and cell survival to final organ size. We discuss a hypothesis that the local steepness of a morphogen gradient is a measure of length in one axis, a measure that is used to determine whether there will be net growth or not.
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Affiliation(s)
- S J Day
- 28 St Oswalds Road, York, YO10 4PF, UK
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579
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Akiyama-Oda Y, Hotta Y, Tsukita S, Oda H. Distinct mechanisms triggering glial differentiation in Drosophila thoracic and abdominal neuroblasts 6-4. Dev Biol 2000; 222:429-39. [PMID: 10837130 DOI: 10.1006/dbio.2000.9727] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Neurons and glia are produced in stereotyped patterns after neuroblast cell division during development of the Drosophila central nervous system. The first cell division of thoracic neuroblast 6-4 (NB6-4T) is asymmetric, giving rise to a glial precursor cell and a neuronal precursor cell. In contrast, abdominal NB6-4 (NB6-4A) divides symmetrically to produce two glial cells. To understand the relationship between cell division and glia-neuron cell fate determination, we examined and compared the effects of known cell division mutations on the NB6-4T and NB6-4A lineages. Based on observation of expression of glial fate determination and early glial differentiation genes, the onset of glial differentiation occurred in NB6-4A but not in NB6-4T when both cell cycle progression and cytokinesis were genetically arrested. On the other hand, glial differentiation started in both lineages when cytokinesis was blocked with intact cell cycle progression. These results showed that NB6-4T, but not NB6-4A, requires cell cycle progression for acquisition of glial fate, suggesting that distinct mechanisms trigger glial differentiation in the different lineages.
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Affiliation(s)
- Y Akiyama-Oda
- Department of Cell Biology, Faculty of Medicine, Kyoto University, Yoshidakonoe-cho, Sakyo-ku, Kyoto, 606-8501, Japan
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580
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Abstract
The mechanisms by which plants modulate their growth rate in response to environmental and developmental conditions are unknown, but are presumed to involve specialized regions called meristems where cell division is concentrated. The possible role of cell division in influencing meristem activity and overall plant growth rate is controversial, with a prevailing view that cell division is secondary to higher order meristem controls. Here we show that a reduction in the length of the cell-cycle G1 phase and faster cell cycling occur when the rate of cell division in transgenic tobacco plants is increased by the plant D-type cyclin CycD2 (ref. 8). The plants have normal cell and meristem sizes, but elevated overall growth rates, an increased rate of leaf initiation and accelerated development in all stages from seedling to maturity. We conclude that cell division is a principal determinant of meristem activity and overall growth rate, and propose that modulation of plant growth rate is achieved through regulation of G1.
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Affiliation(s)
- C E Cockcroft
- Institute of Biotechnology, University of Cambridge, UK
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581
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Mata J, Curado S, Ephrussi A, Rørth P. Tribbles coordinates mitosis and morphogenesis in Drosophila by regulating string/CDC25 proteolysis. Cell 2000; 101:511-22. [PMID: 10850493 DOI: 10.1016/s0092-8674(00)80861-2] [Citation(s) in RCA: 297] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Morphogenesis and cell differentiation in multicellular organisms often require accurate control of cell divisions. We show that a novel cell cycle regulator, tribbles, is critical for this control during Drosophila development. During oogenesis, the level of tribbles affects the number of germ cell divisions as well as oocyte determination. The mesoderm anlage enters mitosis prematurely in tribbles mutant embryos, leading to gastrulation defects. We show that Tribbles acts by specifically inducing degradation of the CDC25 mitotic activators String and Twine via the proteosome pathway. By regulating CDC25, Tribbles serves to coordinate entry into mitosis with morphogenesis and cell fate determination.
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Affiliation(s)
- J Mata
- Developmental Biology Programme, European Molecular Biology Laboratory, Heidelberg, Germany
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582
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Gao X, Neufeld TP, Pan D. Drosophila PTEN regulates cell growth and proliferation through PI3K-dependent and -independent pathways. Dev Biol 2000; 221:404-18. [PMID: 10790335 DOI: 10.1006/dbio.2000.9680] [Citation(s) in RCA: 208] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The control of cell and organ growth is fundamental to the development of multicellular organisms. Here, we show that dPTEN, a Drosophila homolog of the mammalian PTEN tumor suppressor gene, plays an essential role in the control of cell size, cell number, and organ size. In mosaic animals, dPTEN(-) cells proliferate faster than their heterozygous siblings, show an autonomous increase in cell size, and form organs of increased size, whereas overexpression of dPTEN results in opposite phenotypes. The loss-of-function phenotypes of dPTEN are suppressed by mutations in the PI3K target Dakt1 and the translational initiation factor eif4A, suggesting that dPTEN acts through the PI3K signaling pathway to regulate translation. Although activation of PI3K and Akt has been reported to increase rates of cellular growth but not proliferation, loss of dPTEN stimulates both of these processes, suggesting that PTEN regulates overall growth through PI3K/Akt-dependent and -independent pathways. Furthermore, we show that dPTEN does not play a major role in cell survival during Drosophila development. Our results provide a potential explanation for the high frequency of PTEN mutation in human cancer.
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Affiliation(s)
- X Gao
- Department of Physiology, University of Texas Southwestern Medical Center at Dallas, 5323 Harry Hines Boulevard, Dallas, Texas, 75235-9040, USA
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583
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Shinagawa T, Dong HD, Xu M, Maekawa T, Ishii S. The sno gene, which encodes a component of the histone deacetylase complex, acts as a tumor suppressor in mice. EMBO J 2000; 19:2280-91. [PMID: 10811619 PMCID: PMC384369 DOI: 10.1093/emboj/19.10.2280] [Citation(s) in RCA: 86] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The Ski and Sno oncoproteins are components of a macromolecular complex containing the co-repressor N-CoR/SMRT, mSin3 and histone deacetylase. This complex has been implicated in the transcriptional repression exerted by a number of repressors including nuclear hormone receptors and Mad. Further more, Ski and Sno negatively regulate transforming growth factor-beta (TGF-beta) signaling by recruiting this complex to Smads. Here we show that loss of one copy of sno increases susceptibility to tumorigenesis in mice. Mice lacking sno died at an early stage of embryogenesis, and sno was required for blastocyst formation. Heterozygous (sno(+/-)) mice developed spontaneous lymphomas at a low frequency and showed an increased level of tumor formation relative to wild-type mice when challenged with a chemical carcinogen. sno(+/-) embryonic fibroblasts had an increased proliferative capacity and the introduction of activated Ki-ras into these cells resulted in neoplastic transformation. The B cells, T cells and embryonic fibroblasts of sno(+/-) mice had a decreased sensitivity to apoptosis or cell cycle arrest. These findings demonstrate that sno acts as a tumor suppressor at least in some types of cells.
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Affiliation(s)
- T Shinagawa
- Laboratory of Molecular Genetics, RIKEN Tsukuba Life Sciences Center, 3-1-1 Koyadai, Tsukuba, Ibaraki 305-0074, Japa
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584
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Abstract
Plant cell growth and development depend on continuous cell proliferation which is restricted to small regions of the plant called meristems. Infection by geminiviruses, small DNA viruses whose replicative cycle relies on host cell factors, is excluded from those proliferating areas. Since most of the replicative factors are present, almost exclusively, in proliferating cells, geminivirus infection is believed to induce a cellular state permissive for viral DNA replication, e.g. S-phase or, at least, some specific S-phase functions. The molecular basis for this effect seems to be the interference that certain geminivirus proteins exert on the retinoblastoma-related (RBR) pathway, which analogously to that of animal cells, regulates plant cell cycle activation and G(1)-S transition. In some cases, geminiviruses induce cell proliferation and abnormal growth. Mechanisms other than sequestering plant RBR probably contribute to the multiple effects of geminivirus proteins on cellular gene expression, cell growth control and cellular DNA replication. Current efforts to understand the coupling of geminivirus DNA replication to cell cycle and growth control as well as the directions in which future research is aiming are reviewed.
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Affiliation(s)
- C Gutierrez
- Centro de Biología Molecular 'Severo Ochoa', Consejo Superior de Investigaciones Cientificas (CSIC)-Universidad Autónoma de Madrid (UAM), Cantoblanco, 28049 Madrid, Spain.
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585
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Gilchrist AS, Azevedo RB, Partridge L, O'Higgins P. Adaptation and constraint in the evolution of Drosophila melanogaster wing shape. Evol Dev 2000; 2:114-24. [PMID: 11258389 DOI: 10.1046/j.1525-142x.2000.00041.x] [Citation(s) in RCA: 85] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
We have taken advantage of parallel instances of natural selection on body size in Drosophila melanogaster to investigate constraints and adaptation affecting wing shape. Using recently developed techniques for statistical shape analysis, we have examined variation in wing shape in similar body size clines on three continents. Gender-related shape differences were constant among all populations, suggesting that gender differences represent a developmental constraint on wing shape. In contrast, the underlying shape varied significantly between continents and shape change within each cline (i.e., between small and large body size populations) also varied between continents. Therefore, variation at these two levels presumably results from either drift or natural selection. Functional considerations suggest that shape variation between the continents is unlikely to be adaptive. However, cline-related shape change, which we show has a significant allometric component, may be adaptive. The overall range of wing shape variation, across a large range of wing size, is extremely small, and the possibility that wing shape is subject to stabilizing selection (or canalization) is discussed.
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Affiliation(s)
- A S Gilchrist
- Department of Biology, University College London, UK.
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586
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Gartner A, Milstein S, Ahmed S, Hodgkin J, Hengartner MO. A conserved checkpoint pathway mediates DNA damage--induced apoptosis and cell cycle arrest in C. elegans. Mol Cell 2000; 5:435-43. [PMID: 10882129 DOI: 10.1016/s1097-2765(00)80438-4] [Citation(s) in RCA: 402] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
To maintain genomic stability following DNA damage, multicellular organisms activate checkpoints that induce cell cycle arrest or apoptosis. Here we show that genotoxic stress blocks cell proliferation and induces apoptosis of germ cells in the nematode C. elegans. Accumulation of recombination intermediates similarly leads to the demise of affected cells. Checkpoint-induced apoptosis is mediated by the core apoptotic machinery (CED-9/CED-4/CED-3) but is genetically distinct from somatic cell death and physiological germ cell death. Mutations in three genes--mrt-2, which encodes the C. elegans homolog of the S. pombe rad1 checkpoint gene, rad-5, and him-7-block both DNA damage-induced apoptosis and cell proliferation arrest. Our results implicate rad1 homologs in DNA damage-induced apoptosis in animals.
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Affiliation(s)
- A Gartner
- Cold Spring Harbor Laboratory, New York 11724, USA
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587
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Abstract
The Ras GTPase links extracellular mitogens to intracellular mechanisms that control cell proliferation. To understand how Ras regulates proliferation in vivo, we activated or inactivated Ras in cell clones in the developing Drosophila wing. Cells lacking Ras were smaller, had reduced growth rates, accumulated in G1, and underwent apoptosis due to cell competition. Conversely, activation of Ras increased cell size and growth rates and promoted G1/S transitions. Ras upregulated the growth driver dMyc, and both Ras and dMyc increased levels of cyclin E posttranscriptionally. We propose that Ras primarily promotes growth and that growth is coupled to G1/S progression via cyclin E. Interestingly, upregulation of growth by Ras did not deregulate G2/M progression or a developmentally regulated cell cycle exit.
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Affiliation(s)
- D A Prober
- Molecular and Cellular Biology Program, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109, USA
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588
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Abstract
The genetic control of growth ensures that animals grow to reproducible sizes and that tumourous growth is rare. This year, the regulation of organ growth has been studied extensively in Drosophila imaginal discs, and a signalling pathway that regulates organ growth and size has been identified. Furthermore, the role of Drosophila homologues to human tumour suppressor genes and oncogenes in imaginal disc growth has been investigated.
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Affiliation(s)
- D Weinkove
- Department of Molecular Biology, The Netherlands Cancer Institute, Amsterdam, 1066 CX, The Netherlands.
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589
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Mizukami Y, Fischer RL. Plant organ size control: AINTEGUMENTA regulates growth and cell numbers during organogenesis. Proc Natl Acad Sci U S A 2000; 97:942-7. [PMID: 10639184 PMCID: PMC15435 DOI: 10.1073/pnas.97.2.942] [Citation(s) in RCA: 563] [Impact Index Per Article: 23.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/1999] [Indexed: 11/18/2022] Open
Abstract
The control of cell proliferation during organogenesis plays an important role in initiation, growth, and acquisition of the intrinsic size of organs in higher plants. To understand the developmental mechanism that controls intrinsic organ size by regulating the number and extent of cell division during organogenesis, we examined the function of the Arabidopsis regulatory gene AINTEGUMENATA (ANT). Previous observations revealed that ANT regulates cell division in integuments during ovule development and is necessary for floral organ growth. Here we show that ANT controls plant organ cell number and organ size throughout shoot development. Loss of ANT function reduces the size of all lateral shoot organs by decreasing cell number. Conversely, gain of ANT function, via ectopic expression of a 35S::ANT transgene, enlarges embryonic and all shoot organs without altering superficial morphology by increasing cell number in both Arabidopsis and tobacco plants. This hyperplasia results from an extended period of cell proliferation and organ growth. Furthermore, cells ectopically expressing ANT in fully differentiated organs exhibit neoplastic activity by producing calli and adventitious roots and shoots. Based on these results, we propose that ANT regulates cell proliferation and organ growth by maintaining the meristematic competence of cells during organogenesis.
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Affiliation(s)
- Y Mizukami
- Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720, USA
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590
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591
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Milán M, Cohen SM. Subdividing cell populations in the developing limbs of Drosophila: do wing veins and leg segments define units of growth control? Dev Biol 2000; 217:1-9. [PMID: 10625531 DOI: 10.1006/dbio.1999.9493] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Affiliation(s)
- M Milán
- European Molecular Biology Laboratory, Meyerhofstrasse 1, Heidelberg, 69117, Germany
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592
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Abstract
In recent years, Drosophila researchers have developed powerful genetic techniques that allow for the rapid identification and characterization of genes involved in tumor formation and development. The high level of gene and pathway conservation, the similarity of cellular processes and the emerging evidence of functional conservation of tumor suppressors between Drosophila and mammals, argue that studies of tumorigenesis in flies can directly contribute to the understanding of human cancer. In this review, we explore the historical and current roles of Drosophila in cancer research, as well as speculate on the future of Drosophila as a model to investigate cancer-related processes that are currently not well understood.
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Affiliation(s)
- C J Potter
- Howard Hughes Medical Institute, Department of Genetics, Yale University School of Medicine, Boyer Center for Molecular Medicine, NewHaven, CT 06536-0812,
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593
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Birdsall K, Zimmerman E, Teeter K, Gibson G. Genetic variation for the positioning of wing veins in Drosophila melanogaster. Evol Dev 2000; 2:16-24. [PMID: 11256413 DOI: 10.1046/j.1525-142x.2000.00034.x] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
To define the components of variation for wing shape in Drosophila in relation to what is known about the developmental control of wing patterning, we have characterized shape variation in the wings of 12 randomly chosen highly inbred lines. Despite large differences in wing size between males and females, and between flies reared at 18 degrees C or 25 degrees C, wing shape is remarkably unaffected by these variables and is highly line specific. The shape of each intervein region of the wing appears to be independently regulated at the genetic level, consistent with the role of secreted growth factors in establishing the locations of wing veins. Sex and temperature were found to have different effects on cell number in two intervein regions, with the result that wing shape is to a large extent independent of cell density. Dietary cholesterol was also shown to affect the breadth of the central intervein region, consistent with an effect on the strength of Hedgehog signaling during wing development. We conclude that wing shape is under tighter genetic control than wing size, and hypothesize that this control is achieved in large part by gene activity at the level of wing vein determination and differentiation.
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Affiliation(s)
- K Birdsall
- Department of Genetics, North Carolina State University, Raleigh 27695-7614, USA
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594
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Abstract
For many years, Myc function has been linked to the control of cell-cycle progression. Now, increasing evidence shows that Myc also controls cell growth, and that these two processes are regulated independently.
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Affiliation(s)
- M Elend
- Institut für Molekularbiologie und Tumorforschung, Marburg, D-35037, Germany
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595
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Goberdhan DC, Paricio N, Goodman EC, Mlodzik M, Wilson C. Drosophila tumor suppressor PTEN controls cell size and number by antagonizing the Chico/PI3-kinase signaling pathway. Genes Dev 1999; 13:3244-58. [PMID: 10617573 PMCID: PMC317204 DOI: 10.1101/gad.13.24.3244] [Citation(s) in RCA: 304] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/1999] [Accepted: 10/26/1999] [Indexed: 11/24/2022]
Abstract
The human tumor suppressor gene PTEN encodes a putative cytoskeleton-associated molecule with both protein phosphatase and phosphatidylinositol 3,4,5-trisphosphate (PIP3) 3-phosphatase activities. In cell culture, the lipid phosphatase activity of this protein is involved in regulating cell proliferation and survival, but the mechanism by which PTEN inhibits tumorigenesis in vivo is not fully established. Here we show that the highly evolutionarily conserved Drosophila PTEN homolog, DPTEN, suppresses hyperplastic growth in flies by reducing cell size and number. We demonstrate that DPTEN modulates tissue mass by acting antagonistically to the Drosophila Class I phosphatidylinositol 3-kinase, Dp110, and its upstream activator Chico, an insulin receptor substrate homolog. Surprisingly, although DPTEN does not generally affect cell fate determination, it does appear to regulate the subcellular organization of the actin cytoskeleton in multiple cell types. From these data, we propose that DPTEN has a complex role in regulating tissue and body size. It acts in opposition to Dp110 to control cell number and growth, while coordinately influencing events at the cell periphery via its effects on the actin cytoskeleton.
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Affiliation(s)
- D C Goberdhan
- Research School of Biosciences, Department of Biosciences, University of Kent, Canterbury, Kent CT2 7NJ, United Kingdom
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596
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597
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Zilian O, Frei E, Burke R, Brentrup D, Gutjahr T, Bryant PJ, Noll M. double-time is identical to discs overgrown, which is required for cell survival, proliferation and growth arrest in Drosophila imaginal discs. Development 1999; 126:5409-20. [PMID: 10556065 DOI: 10.1242/dev.126.23.5409] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
We have isolated the discs overgrown gene of Drosophila and shown that it encodes a homolog of the Casein kinase I(delta)/(epsilon) subfamily and is identical to the double-time gene. However, in contrast to the weak double-time alleles, which appear to affect only the circadian rhythm, discs overgrown alleles, including bona fide null alleles, show strong effects on cell survival and growth control in imaginal discs. Analysis of their phenotypes and molecular lesions suggests that the Discs overgrown protein is a crucial component in the mechanism that links cell survival during proliferation to growth arrest in imaginal discs. This work provides the first analysis in a multicellular organism of Casein kinase I(delta)/(epsilon) functions necessary for survival. Since the amino acid sequences and three-dimensional structures of Casein kinase I(delta)/(epsilon) enzymes are highly conserved, the results suggest that these proteins may also function in controlling cell growth and survival in other organisms.
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Affiliation(s)
- O Zilian
- Institute for Molecular Biology and Zoological Institute, University of Zürich, CH-8057 Zürich, Switzerland
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598
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Huang H, Potter CJ, Tao W, Li DM, Brogiolo W, Hafen E, Sun H, Xu T. PTEN affects cell size, cell proliferation and apoptosis during Drosophila eye development. Development 1999; 126:5365-72. [PMID: 10556061 DOI: 10.1242/dev.126.23.5365] [Citation(s) in RCA: 85] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
Mutations in the tumor suppressor gene PTEN (MMAC1/TEP1) are associated with a large number of human cancers and several autosomal-dominant disorders. Mice mutant for PTEN die at early embryonic stages and the mutant embryonic fibroblasts display decreased sensitivity to cell death. Overexpression of PTEN in different mammalian tissue culture cells affects various processes including cell proliferation, cell death and cell migration. We have characterized the Drosophila PTEN gene and present evidence that both inactivation and overexpression of PTEN affect cell size, while overexpression of PTEN also inhibits cell cycle progression at early mitosis and promotes cell death during eye development in a context-dependent manner. Furthermore, we have shown that PTEN acts in the insulin signaling pathway and all signals from the insulin receptor can be antagonized by either Drosophila or human PTEN, suggesting a potential means for alleviating symptoms associated with altered insulin signaling.
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Affiliation(s)
- H Huang
- Howard Hughes Medical Institute and Department of Genetics, Yale University School of Medicine, Boyer Center for Molecular Medicine, New Haven, CT 06536-0812, USA
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599
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Verdu J, Buratovich MA, Wilder EL, Birnbaum MJ. Cell-autonomous regulation of cell and organ growth in Drosophila by Akt/PKB. Nat Cell Biol 1999; 1:500-6. [PMID: 10587646 DOI: 10.1038/70293] [Citation(s) in RCA: 310] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Organismal size is determined by a tightly regulated mechanism that coordinates cell growth, cell proliferation and cell death. The Drosophila insulin receptor/Chico/Dp110 pathway regulates cell and organismal size. Here we show that genetic manipulation of the phosphoinositide-3-OH-kinase-dependent serine/threonine protein kinase Akt (protein kinase B) during development of the Drosophila imaginal disc affects cell and organ size in an autonomous manner. Ectopic expression of Akt does not affect cell-fate determination, apoptosis or proliferation rates in imaginal discs. Thus, Akt appears to stimulate intracellular pathways that specifically regulate cell and compartment size independently of cell proliferation in vivo.
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Affiliation(s)
- J Verdu
- Howard Hughes Medical Institute and the Department of Medicine, 415 Curie Boulevard, Clinical Research Building, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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600
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Schuhmacher M, Staege MS, Pajic A, Polack A, Weidle UH, Bornkamm GW, Eick D, Kohlhuber F. Control of cell growth by c-Myc in the absence of cell division. Curr Biol 1999; 9:1255-8. [PMID: 10556095 DOI: 10.1016/s0960-9822(99)80507-7] [Citation(s) in RCA: 225] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The c-Myc protein (Myc) is a transcription factor, and deregulated expression of the c-myc gene (myc) is frequently found in tumours. In Burkitt's lymphoma (BL), myc is transcriptionally activated by chromosomal translocation. We have used a B-cell line called P493-6 that carries a conditional myc allele to elucidate the role of Myc in the proliferation of BL cells. Regulation of proliferation involves the coordination of cell growth (accumulation of cell mass) and cell division [1] [2] [3]. Here, we show that division of P493-6 cells was strictly dependent on the expression of the conditional myc allele and the presence of foetal calf serum (FCS). More importantly, cell growth was regulated by Myc without FCS: Myc alone induced an increase in cell size and positively regulated protein synthesis. An increase in protein synthesis is thought to be one of the causes of cell mass increase. Furthermore, Myc stimulated metabolic activities, as indicated by the acidification of culture medium and the activation of mitochondrial enzymes. Our results confirm the model that Myc is involved in the regulation of cell growth [4] and provide, for the first time, direct evidence that Myc induces cell growth, that is, an increase in cell size, uncoupled from cell division.
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Affiliation(s)
- M Schuhmacher
- GSF Research Centre, Institute of Clinical Molecular Biology, Marchioninistrasse 25, D-81377, Munich, Germany
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