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Tanaka T, Ochi H, Takahashi S, Ueno N, Taira M. Genes coding for cyclin-dependent kinase inhibitors are fragile in Xenopus. Dev Biol 2017; 426:291-300. [PMID: 27393661 DOI: 10.1016/j.ydbio.2016.06.019] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2016] [Revised: 06/16/2016] [Accepted: 06/16/2016] [Indexed: 11/27/2022]
Abstract
Cell proliferation is strictly regulated by the dosage balance among cell-cycle regulators such as CDK/cyclin complexes and CDK-Inhibitors. Even in the allotetraploid genome of Xenopus laevis, the dosage balance must be maintained for animals to stay alive, and the duplicated homeologous genes seem to have gradually changed, through evolution, resulting in the best genes for them to thrive. In the Xenopus laevis genome, while homeologous gene pairs of CDKs are fundamentally maintained and a few cyclin genes are amplified, homeologous gene pairs of the important CDK-Inhibitors, CDKn1c and CDKn2a, are deleted from chromosomes L and S. Although losses of CDKn1c and CDKn2a can lead to diseases in humans, their loss in X. laevis does not affect the animals' health. Also, another gene coding CDKn1b is lost besides CDKn1c and CDKn2a in the genome of Xenopus tropicalis. These findings suggest a high resistance of Xenopus to diseases. We also found that CDKn2c.S expression is higher than that of CDKn2c.L, and a conserved noncoding sequence (CNS) of CDKn2c genomic loci on X. laevis chromosome S and X. tropicalis has an enhancement activity in regulating the different expression. These findings together indicate a surprising fragility of CDK inhibitor gene loci in the Xenopus genome in spite of their importance, and may suggest that factors other than CDK-inhibitors decelerate cell-cycling in Xenopus.
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Affiliation(s)
- Toshiaki Tanaka
- School of Life Science and Technology, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8501, Japan.
| | - Haruki Ochi
- Institute for Promotion of Medical Science Research, Yamagata University Faculty of Medicine, 2-2-2 Iida-Nishi, Yamagata, Yamagata 990-9585, Japan
| | - Shuji Takahashi
- Institute for Amphibian Biology, Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan
| | - Naoto Ueno
- National Institute for Basic Biology, National Institutes of Natural Sciences, 38 Nishigonaka, Myodaiji, Okazaki 444-8585, Aichi, Japan
| | - Masanori Taira
- Department of Biological Sciences, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
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2
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Regulation of DNA Replication in Early Embryonic Cleavages. Genes (Basel) 2017; 8:genes8010042. [PMID: 28106858 PMCID: PMC5295036 DOI: 10.3390/genes8010042] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2016] [Revised: 01/06/2017] [Accepted: 01/11/2017] [Indexed: 11/18/2022] Open
Abstract
Early embryonic cleavages are characterized by short and highly synchronous cell cycles made of alternating S- and M-phases with virtually absent gap phases. In this contracted cell cycle, the duration of DNA synthesis can be extraordinarily short. Depending on the organism, the whole genome of an embryo is replicated at a speed that is between 20 to 60 times faster than that of a somatic cell. Because transcription in the early embryo is repressed, DNA synthesis relies on a large stockpile of maternally supplied proteins stored in the egg representing most, if not all, cellular genes. In addition, in early embryonic cell cycles, both replication and DNA damage checkpoints are inefficient. In this article, we will review current knowledge on how DNA synthesis is regulated in early embryos and discuss possible consequences of replicating chromosomes with little or no quality control.
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Siefert JC, Clowdus EA, Sansam CL. Cell cycle control in the early embryonic development of aquatic animal species. Comp Biochem Physiol C Toxicol Pharmacol 2015; 178:8-15. [PMID: 26475527 PMCID: PMC4755307 DOI: 10.1016/j.cbpc.2015.10.003] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/17/2015] [Revised: 10/07/2015] [Accepted: 10/09/2015] [Indexed: 01/02/2023]
Abstract
The cell cycle is integrated with many aspects of embryonic development. Not only is proper control over the pace of cell proliferation important, but also the timing of cell cycle progression is coordinated with transcription, cell migration, and cell differentiation. Due to the ease with which the embryos of aquatic organisms can be observed and manipulated, they have been a popular choice for embryologists throughout history. In the cell cycle field, aquatic organisms have been extremely important because they have played a major role in the discovery and analysis of key regulators of the cell cycle. In particular, the frog Xenopus laevis has been instrumental for understanding how the basic embryonic cell cycle is regulated. More recently, the zebrafish has been used to understand how the cell cycle is remodeled during vertebrate development and how it is regulated during morphogenesis. This review describes how some of the unique strengths of aquatic species have been leveraged for cell cycle research and suggests how species such as Xenopus and zebrafish will continue to reveal the roles of the cell cycle in human biology and disease.
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Affiliation(s)
- Joseph C Siefert
- Oklahoma Medical Research Foundation, Cell Cycle and Cancer Biology Research Program, Oklahoma City, OK, USA; University of Oklahoma Health Sciences Center, Department of Cell Biology, Oklahoma City, OK, USA
| | - Emily A Clowdus
- Oklahoma Medical Research Foundation, Cell Cycle and Cancer Biology Research Program, Oklahoma City, OK, USA; University of Oklahoma Health Sciences Center, Department of Cell Biology, Oklahoma City, OK, USA
| | - Christopher L Sansam
- Oklahoma Medical Research Foundation, Cell Cycle and Cancer Biology Research Program, Oklahoma City, OK, USA; University of Oklahoma Health Sciences Center, Department of Cell Biology, Oklahoma City, OK, USA.
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4
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Janesick A, Wu SC, Blumberg B. Retinoic acid signaling and neuronal differentiation. Cell Mol Life Sci 2015; 72:1559-76. [PMID: 25558812 PMCID: PMC11113123 DOI: 10.1007/s00018-014-1815-9] [Citation(s) in RCA: 193] [Impact Index Per Article: 21.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2014] [Revised: 12/15/2014] [Accepted: 12/19/2014] [Indexed: 01/13/2023]
Abstract
The identification of neurological symptoms caused by vitamin A deficiency pointed to a critical, early developmental role of vitamin A and its metabolite, retinoic acid (RA). The ability of RA to induce post-mitotic, neural phenotypes in various stem cells, in vitro, served as early evidence that RA is involved in the switch between proliferation and differentiation. In vivo studies have expanded this "opposing signal" model, and the number of primary neurons an embryo develops is now known to depend critically on the levels and spatial distribution of RA. The proneural and neurogenic transcription factors that control the exit of neural progenitors from the cell cycle and allow primary neurons to develop are partly elucidated, but the downstream effectors of RA receptor (RAR) signaling (many of which are putative cell cycle regulators) remain largely unidentified. The molecular mechanisms underlying RA-induced primary neurogenesis in anamniote embryos are starting to be revealed; however, these data have been not been extended to amniote embryos. There is growing evidence that bona fide RARs are found in some mollusks and other invertebrates, but little is known about their necessity or functions in neurogenesis. One normal function of RA is to regulate the cell cycle to halt proliferation, and loss of RA signaling is associated with dedifferentiation and the development of cancer. Identifying the genes and pathways that mediate cell cycle exit downstream of RA will be critical for our understanding of how to target tumor differentiation. Overall, elucidating the molecular details of RAR-regulated neurogenesis will be decisive for developing and understanding neural proliferation-differentiation switches throughout development.
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Affiliation(s)
- Amanda Janesick
- Department of Developmental and Cell Biology, 2011 Biological Sciences 3, University of California, Irvine, 92697-2300 USA
| | - Stephanie Cherie Wu
- Department of Developmental and Cell Biology, 2011 Biological Sciences 3, University of California, Irvine, 92697-2300 USA
| | - Bruce Blumberg
- Department of Developmental and Cell Biology, 2011 Biological Sciences 3, University of California, Irvine, 92697-2300 USA
- Department of Pharmaceutical Sciences, University of California, Irvine, USA
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Sabherwal N, Thuret R, Lea R, Stanley P, Papalopulu N. aPKC phosphorylates p27Xic1, providing a mechanistic link between apicobasal polarity and cell-cycle control. Dev Cell 2015; 31:559-71. [PMID: 25490266 PMCID: PMC4262734 DOI: 10.1016/j.devcel.2014.10.023] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2013] [Revised: 09/05/2014] [Accepted: 10/29/2014] [Indexed: 11/30/2022]
Abstract
During the development of the nervous system, apicobasally polarized stem cells are characterized by a shorter cell cycle than nonpolar progenitors, leading to a lower differentiation potential of these cells. However, how polarization might be directly linked to the kinetics of the cell cycle is not understood. Here, we report that apicobasally polarized neuroepithelial cells in Xenopus laevis have a shorter cell cycle than nonpolar progenitors, consistent with mammalian systems. We show that the apically localized serine/threonine kinase aPKC directly phosphorylates an N-terminal site of the cell-cycle inhibitor p27Xic1 and reduces its ability to inhibit the cyclin-dependent kinase 2 (Cdk2), leading to shortening of G1 and S phases. Overexpression of activated aPKC blocks the neuronal differentiation-promoting activity of p27Xic1. These findings provide a direct mechanistic link between apicobasal polarity and the cell cycle, which may explain how proliferation is favored over differentiation in polarized neural stem cells. aPKC shortens G1 and S phases of cell cycle by phosphorylating p27Xic1 Phosphorylated p27Xic1 exhibits weaker binding to and inhibition of Cdk2 p27Xic1 promotes neuronal differentiation and elongates cell cycle via G1 phase Effects of p27Xic1 on neuronal differentiation are rescued by activated aPKC
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Affiliation(s)
- Nitin Sabherwal
- Faculty of Life Sciences, University of Manchester, Oxford Road, Manchester M13 9PT, UK.
| | - Raphael Thuret
- Faculty of Life Sciences, University of Manchester, Oxford Road, Manchester M13 9PT, UK
| | - Robert Lea
- Faculty of Life Sciences, University of Manchester, Oxford Road, Manchester M13 9PT, UK
| | - Peter Stanley
- Faculty of Life Sciences, University of Manchester, Oxford Road, Manchester M13 9PT, UK
| | - Nancy Papalopulu
- Faculty of Life Sciences, University of Manchester, Oxford Road, Manchester M13 9PT, UK.
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Zhou W, Marcus AI, Vertino PM. Dysregulation of mTOR activity through LKB1 inactivation. CHINESE JOURNAL OF CANCER 2013; 32:427-33. [PMID: 23668926 PMCID: PMC3845579 DOI: 10.5732/cjc.013.10086] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Mammalian target of rapamycin (mTOR) is aberrantly activated in many cancer types, and two rapamycin derivatives are currently approved by the Food and Drug Administration (FDA) of the United States for treating renal cell carcinoma. Mechanistically, mTOR is hyperactivated in human cancers either due to the genetic activation of its upstream activating signaling pathways or the genetic inactivation of its negative regulators. The tumor suppressor liver kinase B1 (LKB1), also known as serine/threonine kinase 11 (STK11), is involved in cell polarity, cell detachment and adhesion, tumor metastasis, and energetic stress response. A key role of LKB1 is to negatively regulate the activity of mTOR complex 1 (mTORC1). This review summarizes the molecular basis of this negative interaction and recent research progress in this area.
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Affiliation(s)
- Wei Zhou
- The Winship Cancer Institute, Department of Hematology and Oncology, Department of Pathology and Laboratory Medicine, Emory University School of Medicine, Atlanta, GA 30322, USA.
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7
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Zhu XN, Kim DH, Lin HR, Budhavarapu VN, Rosenbaum HB, Mueller PR, Yew PR. Proteolysis of Xenopus Cip-type CDK inhibitor, p16Xic2, is regulated by PCNA binding and CDK2 phosphorylation. Cell Div 2013; 8:5. [PMID: 23607668 PMCID: PMC3655096 DOI: 10.1186/1747-1028-8-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2013] [Accepted: 04/17/2013] [Indexed: 11/10/2022] Open
Abstract
Background Cell division is positively regulated by cyclin-dependent kinases (CDKs) partnered with cyclins and negatively regulated by CDK inhibitors. In the frog, Xenopus laevis, three types of CDK inhibitors have been described: p27Xic1 (Xic1) which shares sequence homology with both p21Cip1 and p27Kip1 from mammals, p16Xic2 (Xic2) which shares sequence homology with p21Cip1, and p17Xic3 (Xic3) which shares sequence homology with p27Kip1. While past studies have demonstrated that during DNA polymerase switching, Xic1 is targeted for protein turnover dependent upon DNA, Proliferating Cell Nuclear Antigen (PCNA), and the ubiquitin ligase CRL4Cdt2, little is known about the processes that regulate Xic2 or Xic3. Methods We used the Xenopus interphase egg extract as a model system to examine the regulation of Xic2 by proteolysis and phosphorylation. Results Our studies indicated that following primer synthesis during the initiation of DNA replication, Xic2 is targeted for DNA- and PCNA-dependent ubiquitin-mediated proteolysis and that Cdt2 can promote Xic2 turnover. Additionally, during interphase, Xic2 is phosphorylated by CDK2 at Ser-98 and Ser-131 in a DNA-independent manner, inhibiting Xic2 turnover. In the presence of double-stranded DNA ends, Xic2 is also phosphorylated at Ser-78 and Ser-81 by a caffeine-sensitive kinase, but this phosphorylation does not alter Xic2 turnover. Conversely, in the presence or absence of DNA, Xic3 was stable in the Xenopus interphase egg extract and did not exhibit a shift indicative of phosphorylation. Conclusions During interphase, Xic2 is targeted for DNA- and PCNA-dependent proteolysis that is negatively regulated by CDK2 phosphorylation. During a response to DNA damage, Xic2 may be alternatively regulated by phosphorylation by a caffeine-sensitive kinase. Our studies suggest that the three types of Xenopus CDK inhibitors, Xic1, Xic2, and Xic3 appear to be uniquely regulated which may reflect their specialized roles during cell division or early development in the frog.
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Affiliation(s)
- Xi-Ning Zhu
- Department of Molecular Medicine, Institute of Biotechnology, The University of Texas Health Science Center at San Antonio, San Antonio, TX 78229, USA.
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8
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Xue XY, Harris WA. Using myc genes to search for stem cells in the ciliary margin of the Xenopus retina. Dev Neurobiol 2012; 72:475-90. [PMID: 21465669 DOI: 10.1002/dneu.20887] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The ciliary marginal zone (CMZ) of fish and frog retinas contains cells that proliferate throughout postembryonic development as the retina grows with increasing body size, indicating the presence of stem cells in this region. However, neither the location nor the molecular identity of retinal stem cells has been identified. Here, we show in Xenopus that c-myc and n-myc are sequentially expressed both during development and in the post-embryonic retina. The c-myc+/n-myc- cells near the extreme periphery of the CMZ cycle more slowly and preferentially retain DNA label compared to their more central cmyc+/n-myc+ neighbors which cycle rapidly and preferentially dilute DNA label. During retinal development c-myc is functionally required earlier than n-myc, and n-myc expression depends on earlier c-myc expression. The expression of c-myc but not n-myc in the CMZ depends on growth factor signaling. Our results suggest that c-myc+/n-myc- cells in the far peripheral CMZ are candidates for a niche-dependent population of retinal stem cells that give rise to more centrally located and rapidly dividing n-myc+ progenitors of more limited proliferative potential. Analysis of homologues of these genes in the zebrafish CMZ suggests that the transition from c-myc to n-myc expression might be conserved in other lower vertebrates whose retinas growth throughout life.
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Affiliation(s)
- Xiao Yan Xue
- Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge, United Kingdom
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Gotoh T, Villa LM, Capelluto DGS, Finkielstein CV. Regulatory pathways coordinating cell cycle progression in early Xenopus development. Results Probl Cell Differ 2011; 53:171-99. [PMID: 21630146 DOI: 10.1007/978-3-642-19065-0_9] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
The African clawed frog, Xenopus laevis, is used extensively as a model organism for studying both cell development and cell cycle regulation. For over 20 years now, this model organism has contributed to answering fundamental questions concerning the mechanisms that underlie cell cycle transitions--the cellular components that synthesize, modify, repair, and degrade nucleic acids and proteins, the signaling pathways that allow cells to communicate, and the regulatory pathways that lead to selective expression of subsets of genes. In addition, the remarkable simplicity of the Xenopus early cell cycle allows for tractable manipulation and dissection of the basic components driving each transition. In this organism, early cell divisions are characterized by rapid cycles alternating phases of DNA synthesis and division. The post-blastula stages incorporate gap phases, lengthening progression, and allowing more time for DNA repair. Various cyclin/Cdk complexes are differentially expressed during the early cycles with orderly progression being driven by both the combined action of cyclin synthesis and degradation and the appropriate selection of specific substrates by their Cdk components. Like other multicellular organisms, chief developmental events in early Xenopus embryogenesis coincide with profound remodeling of the cell cycle, suggesting that cell proliferation and differentiation events are linked and coordinated through crosstalk mechanisms acting on signaling pathways involving the expression of cell cycle control genes.
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Affiliation(s)
- Tetsuya Gotoh
- Integrated Cellular Responses Laboratory, Department of Biological Sciences, Virginia Polytechnic Institute and State University, 1981 Kraft Drive, Blacksburg, VA 24061, USA
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Brandt Y, Mitchell T, Wu Y, Hartley RS. Developmental downregulation of Xenopus cyclin E is phosphorylation and nuclear import dependent and is mediated by ubiquitination. Dev Biol 2011; 355:65-76. [PMID: 21539834 DOI: 10.1016/j.ydbio.2011.04.014] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2010] [Revised: 03/16/2011] [Accepted: 04/14/2011] [Indexed: 11/29/2022]
Abstract
Cyclins are regulatory subunits that bind to and activate catalytic Cdks. Cyclin E associates with Cdk2 to mediate the G1/S transition of the cell cycle. Cyclin E is overexpressed in breast, lung, skin, gastrointestinal, cervical, and ovarian cancers. Its overexpression correlates with poor patient prognosis and is involved in the etiology of breast cancer. We have been studying how cyclin E is normally downregulated during development in order to determine if disruption of similar mechanisms could either contribute to its overexpression in cancer, or be exploited to decrease its expression. In Xenopus laevis embryos, cyclin E protein level is high and constant until its abrupt destabilization by an undefined mechanism after the 12th cell cycle, which corresponds to the midblastula transition (MBT) and remodeling of the embryonic to the adult cell cycle. Since degradation of mammalian cyclin E is regulated by the ubiquitin proteasome system and is phosphorylation dependent, we examined the role of phosphorylation in Xenopus cyclin E turnover. We show that similarly to human cyclin E, phosphorylation of serine 398 and threonine 394 plays a role in cyclin E turnover at the MBT. Immunofluorescence analysis shows that cyclin E relocalizes from the cytoplasm to the nucleus preceding its degradation. When nuclear import is inhibited, cyclin E stability is markedly increased after the MBT. To investigate whether degradation of Xenopus cyclin E is mediated by the proteasomal pathway, we used proteasome inhibitors and observed a progressive accumulation of cyclin E in the cytoplasm after the MBT. Ubiquitination of cyclin E precedes its proteasomal degradation at the MBT. These results show that cyclin E destruction at the MBT requires both phosphorylation and nuclear import, as well as proteasomal activity.
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The CRL4Cdt2 ubiquitin ligase mediates the proteolysis of cyclin-dependent kinase inhibitor Xic1 through a direct association with PCNA. Mol Cell Biol 2010; 30:4120-33. [PMID: 20606006 DOI: 10.1128/mcb.01135-09] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
During DNA polymerase switching, the Xenopus laevis Cip/Kip-type cyclin-dependent kinase inhibitor Xic1 associates with trimeric proliferating cell nuclear antigen (PCNA) and is recruited to chromatin, where it is ubiquitinated and degraded. In this study, we show that the predominant E3 for Xic1 in the egg is the Cul4-DDB1-XCdt2 (Xenopus Cdt2) (CRL4(Cdt2)) ubiquitin ligase. The addition of full-length XCdt2 to the Xenopus extract promotes Xic1 turnover, while the N-terminal domain of XCdt2 (residues 1 to 400) cannot promote Xic1 turnover, despite its ability to bind both Xic1 and DDB1. Further analysis demonstrated that XCdt2 binds directly to PCNA through its C-terminal domain (residues 401 to 710), indicating that this interaction is important for promoting Xic1 turnover. We also identify the cis-acting sequences required for Xic1 binding to Cdt2. Xic1 binds to Cdt2 through two domains (residues 161 to 170 and 179 to 190) directly flanking the Xic1 PCNA binding domain (PIP box) but does not require PIP box sequences (residues 171 to 178). Similarly, human p21 binds to human Cdt2 through residues 156 to 161, adjacent to the p21 PIP box. In addition, we identify five lysine residues (K180, K182, K183, K188, and K193) immediately downstream of the Xic1 PIP box and within the second Cdt2 binding domain as critical sites for Xic1 ubiquitination. Our studies suggest a model in which both the CRL4(Cdt2) E3- and PIP box-containing substrates, like Xic1, are recruited to chromatin through independent direct associations with PCNA.
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Naylor RW, Collins RJ, Philpott A, Jones EA. Normal levels of p27 are necessary for somite segmentation and determining pronephric organ size. Organogenesis 2010; 5:201-10. [PMID: 20539739 DOI: 10.4161/org.5.4.9973] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2009] [Revised: 07/31/2009] [Accepted: 09/02/2009] [Indexed: 11/19/2022] Open
Abstract
The Xenopus laevis cyclin dependent kinase inhibitor p27(Xic1) has been shown to be involved in exit from the cell cycle and differentiation of cells into a quiescent state in the nervous system, muscle tissue, heart and retina. We show that p27(Xic1) is expressed in the developing kidney in the nephrostomal regions. Using overexpression and morpholino oligonucleotide (MO) knock-down approaches we show normal levels of p27(Xic1) regulate pronephros organ size by regulating cell cycle exit. Knock-down of p27(Xic1) expression using a MO prevented myogenesis, as previously reported; an effect that subsequently inhibits pronephrogenesis. Furthermore, we show that normal levels of p27(Xic1) are required for somite segmentation also through its cell cycle control function. Finally, we provide evidence to suggest correct paraxial mesoderm segmentation is not necessary for pronephric induction in the intermediate mesoderm. These results indicate novel developmental roles for p27(Xic1), and reveal its differentiation function is not universally utilised in all developing tissues.
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Affiliation(s)
- Richard W Naylor
- Department of Biological Sciences; and Warwick University; Coventry, UK
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Self-regulation of Stat3 activity coordinates cell-cycle progression and neural crest specification. EMBO J 2009; 29:55-67. [PMID: 19851287 DOI: 10.1038/emboj.2009.313] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2009] [Accepted: 09/25/2009] [Indexed: 01/13/2023] Open
Abstract
A complex set of extracellular signals is required for neural crest (NC) specification. However, how these signals function to coordinate cell-cycle progression and differentiation remains poorly understood. Here, we report in Xenopus a role for the transcription factor signal transducers and activators of transcription-3 (Stat3) in this process downstream of FGF signalling. Depletion of Stat3 inhibits NC gene expression and cell proliferation, whereas overexpression expands the NC domain and promotes cell proliferation. Stat3 is phosphorylated and activated in ectodermal cells by FGFs through binding with FGFR4. Stat3 activation is also modulated by Hairy2 and Id3 proteins that, respectively, facilitate and disrupt Stat3-FGFR4 complex formation. Furthermore, distinct levels of Stat3 activity control Hairy2 and Id3 transcription, leading to Stat3 self-regulation. Finally, high Stat3 activity maintains cells in an undifferentiated state, whereas low activity promotes cell proliferation and NC differentiation. Together, our data suggest that Stat3, downstream of FGFs and under the positive and negative feedback regulation of Hairy2 and Id3, plays an essential role in the coordination of cell-cycle progression and differentiation during NC specification.
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Murato Y, Hashimoto C. Xhairy2functions inXenopuslens development by regulatingp27xic1expression. Dev Dyn 2009; 238:2179-92. [DOI: 10.1002/dvdy.21883] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
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Philpott A, Yew PR. The Xenopus cell cycle: an overview. Mol Biotechnol 2008; 39:9-19. [PMID: 18266114 DOI: 10.1007/s12033-008-9033-z] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2007] [Accepted: 12/28/2007] [Indexed: 01/03/2023]
Abstract
Oocytes, eggs and embryos from the frog Xenopus laevis have been an important model system for studying cell-cycle regulation for several decades. First, progression through meiosis in the oocyte has been extensively investigated. Oocyte maturation has been shown to involve complex networks of signal transduction pathways, culminating in the cyclic activation and inactivation of Maturation Promoting Factor (MPF), composed of cyclin B and cdc2. After fertilisation, the early embryo undergoes rapid simplified cell cycles which have been recapitulated in cell-free extracts of Xenopus eggs. Experimental manipulation of these extracts has given a wealth of biochemical information about the cell cycle, particularly concerning DNA replication and mitosis. Finally, cells of older embryos adopt a more somatic-type cell cycle and have been used to study the balance between cell cycle and differentiation during development.
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Affiliation(s)
- Anna Philpott
- Department of Oncology, Hutchison/MRC Research Centre, Addenbrooke's Hospital, University of Cambridge, Hills Road, Cambridge, CB2 0XZ, England.
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16
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Boix-Perales H, Horan I, Wise H, Lin HR, Chuang LC, Yew PR, Philpott A. The E3 ubiquitin ligase skp2 regulates neural differentiation independent from the cell cycle. Neural Dev 2007; 2:27. [PMID: 18081928 PMCID: PMC2244796 DOI: 10.1186/1749-8104-2-27] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2007] [Accepted: 12/14/2007] [Indexed: 11/24/2022] Open
Abstract
Background The SCFskp2 complex is an E3 ubiquitin ligase that is known to target a number of cell cycle regulators, including cyclin-dependent kinase inhibitors, for proteolysis. While its role in regulation of cell division has been well documented, additional functions in differentiation, including in the nervous system, have not been investigated. Results Using Xenopus as a model system, here we demonstrate that skp2 has an additional role in regulation of differentiation of primary neurons, the first neurons to differentiate in the neural plate. Xenopus skp2 shows a dynamic expression pattern in early embryonic neural tissue and depletion of skp2 results in generation of extra primary neurons. In contrast, over-expression of skp2 inhibits neurogenesis in a manner dependent on its ability to act as part of the SCFskp2 complex. Moreover, inhibition of neurogenesis by skp2 occurs upstream of the proneural gene encoding NeuroD and prior to cell cycle exit. We have previously demonstrated that the Xenopus cyclin dependent kinase inhibitor Xic1 is essential for primary neurogenesis at an early stage, and before these cells exit the cell cycle. We show that SCFskp2 degrades Xic1 in embryos and this contributes to the ability of skp2 to regulate neurogenesis. Conclusion We conclude that the SCFskp2 complex has functions in the control of neuronal differentiation additional to its role in cell cycle regulation. Thus, it is well placed to be a co-ordinating factor regulating both cell proliferation and cell differentiation directly.
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Affiliation(s)
- Hector Boix-Perales
- Department of Oncology, University of Cambridge, Hutchison/MRC Research Centre, Addenbrookes Hospital, Hills Road, Cambridge CB2 0XZ, UK.
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17
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Wroble BN, Finkielstein CV, Sible JC. Wee1 kinase alters cyclin E/Cdk2 and promotes apoptosis during the early embryonic development of Xenopus laevis. BMC DEVELOPMENTAL BIOLOGY 2007; 7:119. [PMID: 17961226 PMCID: PMC2176066 DOI: 10.1186/1471-213x-7-119] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/15/2007] [Accepted: 10/25/2007] [Indexed: 12/04/2022]
Abstract
Background The cell cycles of the Xenopus laevis embryo undergo extensive remodeling beginning at the midblastula transition (MBT) of early development. Cell divisions 2–12 consist of rapid cleavages without gap phases or cell cycle checkpoints. Some remodeling events depend upon a critical nucleo-cytoplasmic ratio, whereas others rely on a maternal timer controlled by cyclin E/Cdk2 activity. One key event that occurs at the MBT is the degradation of maternal Wee1, a negative regulator of cyclin-dependent kinase (Cdk) activity. Results In order to assess the effect of Wee1 on embryonic cell cycle remodeling, Wee1 mRNA was injected into one-cell stage embryos. Overexpression of Wee1 caused cell cycle delay and tyrosine phosphorylation of Cdks prior to the MBT. Furthermore, overexpression of Wee1 disrupted key developmental events that normally occur at the MBT such as the degradation of Cdc25A, cyclin E, and Wee1. Overexpression of Wee1 also resulted in post-MBT apoptosis, tyrosine phosphorylation of Cdks and persistence of cyclin E/Cdk2 activity. To determine whether Cdk2 was required specifically for the survival of the embryo, the cyclin E/Cdk2 inhibitor, Δ34-Xic1, was injected in embryos and also shown to induce apoptosis. Conclusion Taken together, these data suggest that Wee1 triggers apoptosis through the disruption of the cyclin E/Cdk2 timer. In contrast to Wee1 and Δ34-Xic1, altering Cdks by expression of Chk1 and Chk2 kinases blocks rather than promotes apoptosis and causes premature degradation of Cdc25A. Collectively, these data implicate Cdc25A as a key player in the developmentally regulated program of apoptosis in X. laevis embryos.
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Affiliation(s)
- Brian N Wroble
- Department of Biological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA, USA.
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18
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Nagatomo KI, Hashimoto C. Xenopus hairy2 functions in neural crest formation by maintaining cells in a mitotic and undifferentiated state. Dev Dyn 2007; 236:1475-83. [PMID: 17436284 DOI: 10.1002/dvdy.21152] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The neural crest is a population of mitotically active, multipotent progenitor cells that arise at the neural plate border. Neural crest progenitors must be maintained in a multipotent state until after neural tube closure. However, the molecular underpinnings of this process have yet to be fully elucidated. Here we show that the basic helix-loop-helix (bHLH) transcriptional repressor gene, Xenopus hairy2 (Xhairy2), is an essential early regulator of neural crest formation in Xenopus. During gastrulation, Xhairy2 is localized at the presumptive neural crest prior to the expression of such neural crest markers as Slug and FoxD3. Morpholino-mediated knockdown of Xhairy2 results in the repression of neural crest marker gene expression while inducing the ectopic expression of the cell cycle inhibitor p27(xic1) in the presumptive neural crest. We also found that ectopic p27(xic1) disturbs neural crest formation. Furthermore, the depletion of Xhairy2 leads to the apoptosis of mitotic cells. Our results suggest that Xhairy2 functions in neural crest specification by maintaining cells in the mitotic and undifferentiated state.
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Affiliation(s)
- Kan-Ichiro Nagatomo
- Department of Biology, Graduate School of Science, Osaka University, and JT Biohistory Research Hall, Osaka, Japan
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19
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Peng A, Lewellyn AL, Maller JL. Undamaged DNA transmits and enhances DNA damage checkpoint signals in early embryos. Mol Cell Biol 2007; 27:6852-62. [PMID: 17664286 PMCID: PMC2099229 DOI: 10.1128/mcb.00195-07] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
In Xenopus laevis embryos, the midblastula transition (MBT) at the 12th cell division marks initiation of critical developmental events, including zygotic transcription and the abrupt inclusion of gap phases into the cell cycle. Interestingly, although an ionizing radiation-induced checkpoint response is absent in pre-MBT embryos, introduction of a threshold amount of undamaged plasmid or sperm DNA allows a DNA damage checkpoint response to be activated. We show here that undamaged threshold DNA directly participates in checkpoint signaling, as judged by several dynamic changes, including H2AX phosphorylation, ATM phosphorylation and loading onto chromatin, and Chk1/Chk2 phosphorylation and release from nuclear DNA. These responses on physically separate threshold DNA require gamma-H2AX and are triggered by an ATM-dependent soluble signal initiated by damaged DNA. The signal persists in egg extracts even after damaged DNA is removed from the system, indicating that the absence of damaged DNA is not sufficient to end the checkpoint response. The results identify a novel mechanism by which undamaged DNA enhances checkpoint signaling and provide an example of how the transition to cell cycle checkpoint activation during development is accomplished by maternally programmed increases in the DNA-to-cytoplasm ratio.
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Affiliation(s)
- Aimin Peng
- Howard Hughes Medical Institute, Department of Pharmacology, University of Colorado School of Medicine, Aurora, CO 80045, USA
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20
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Zaghloul NA, Moody SA. Alterations of rx1 and pax6 expression levels at neural plate stages differentially affect the production of retinal cell types and maintenance of retinal stem cell qualities. Dev Biol 2007; 306:222-40. [PMID: 17434474 DOI: 10.1016/j.ydbio.2007.03.017] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2006] [Revised: 02/28/2007] [Accepted: 03/12/2007] [Indexed: 01/23/2023]
Abstract
rx1 and pax6 are necessary for the establishment of the vertebrate eye field and for the maintenance of the retinal stem cells that give rise to multiple retinal cell types. They also are differentially expressed in cellular layers in the retina when cell fates are being specified, and their expression levels differentially affect the production of amacrine cell subtypes. To determine whether rx1 and pax6 expression after the eye field is established simply maintains stem cell-like qualities or affects cell type differentiation, we used hormone-inducible constructs to increase or decrease levels/activity of each protein at two different neural plate stages. Our results indicate that rx1 regulates the size of the retinal stem cell pool because it broadly affected all cell types, whereas pax6 regulates more restricted retinal progenitor cells because it selectively affected different cell types in a time-dependent manner. Analysis of rx1 and pax6 effects on proliferation, and expression of stem cell or differentiation markers demonstrates that rx1 maintains cells in a stem cell state by promoting proliferation and delaying expression of neural identity and differentiation markers. Although pax6 also promotes proliferation, it differentially regulates neural identity and differentiation genes. Thus, these two genes work in parallel to regulate different, but overlapping aspects of retinal cell fate determination.
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Affiliation(s)
- Norann A Zaghloul
- Department of Anatomy and Cell Biology, George Washington University Medical Center, 2300 I (eye) Street, NW, Washington, DC 20854, USA
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21
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Kim SY, Ferrell JE. Substrate competition as a source of ultrasensitivity in the inactivation of Wee1. Cell 2007; 128:1133-45. [PMID: 17382882 DOI: 10.1016/j.cell.2007.01.039] [Citation(s) in RCA: 183] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2006] [Revised: 11/28/2006] [Accepted: 01/31/2007] [Indexed: 01/22/2023]
Abstract
The mitotic regulators Wee1 and Cdk1 can inactivate each other through inhibitory phosphorylations. This double-negative feedback loop is part of a bistable trigger that makes the transition into mitosis abrupt and decisive. To generate a bistable response, some component of a double-negative feedback loop must exhibit an ultrasensitive response to its upstream regulator. Here, we experimentally demonstrate that Wee1 exhibits a highly ultrasensitive response to Cdk1. Several mechanisms can, in principle, give rise to ultrasensitivity, including zero-order effects, multisite phosphorylation, and competition mechanisms. We found that the ultrasensitivity in the inactivation of Wee1 arises mainly through two competition mechanisms: competition between two sets of phosphorylation sites in Wee1 and between Wee1 and other high-affinity Cdk1 targets. Based on these findings, we were able to reconstitute a highly ultrasensitive Wee1 response with purified components. Competition provides a simple way of generating the equivalent of a highly cooperative allosteric response.
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Affiliation(s)
- Sun Young Kim
- Department of Chemical and Systems Biology, Stanford University School of Medicine, Center for Clinical Sciences Research, Stanford, CA 94305-5174, USA
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22
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De Clercq A, Inzé D. Cyclin-dependent kinase inhibitors in yeast, animals, and plants: a functional comparison. Crit Rev Biochem Mol Biol 2006; 41:293-313. [PMID: 16911957 DOI: 10.1080/10409230600856685] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The cell cycle is remarkably conserved in yeast, animals, and plants and is controlled by cyclin-dependent kinases (CDKs). CDK activity can be inhibited by binding of CDK inhibitory proteins, designated CKIs. Numerous studies show that CKIs are essential in orchestrating eukaryotic cell proliferation and differentiation. In yeast, animals, and plants, CKIs act as regulators of the G1 checkpoint in response to environmental and developmental cues and assist during mitotic cell cycles by inhibiting CDK activity required to arrest mitosis. Furthermore, CKIs play an important role in regulating cell cycle exit that precedes differentiation and in promoting differentiation in cooperation with transcription factors. Moreover, CKIs are essential to control CDK activity in endocycling cells. So, in yeast, animals, and plants, CKIs share many functional similarities, but their functions are adapted toward the specific needs of the eukaryote.
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Affiliation(s)
- Annelies De Clercq
- Department of Plant Systems Biology, Flanders Interuniversity Institute for Biotechnology (VIB), Ghent University, Ghent, Belgium
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23
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Vernon AE, Movassagh M, Horan I, Wise H, Ohnuma S, Philpott A. Notch targets the Cdk inhibitor Xic1 to regulate differentiation but not the cell cycle in neurons. EMBO Rep 2006; 7:643-8. [PMID: 16648822 PMCID: PMC1479590 DOI: 10.1038/sj.embor.7400691] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2005] [Revised: 02/16/2006] [Accepted: 03/27/2006] [Indexed: 11/08/2022] Open
Abstract
The proneural protein neurogenin (XNGNR1) drives differentiation of primary neurons in combination with the cyclin-dependent kinase (Cdk) inhibitor Xic1. Differentiation is inhibited by Notch signalling, resulting in a scattered neuronal distribution. Here we show that Notch signalling regulates the level of Xic1 transcription, yet this does not correlate with Notch's ability to perturb the cell cycle. Instead, Notch may regulate Xic1 levels to control its differentiation function directly, which is required in parallel with XNGNR1 to promote primary neurogenesis. Indeed, Notch-mediated repression of both XNGNR1 and Xic1 must be relieved for neuronal differentiation to occur. Interestingly, although Xic1 is required for XNGNR1-mediated neurogenesis, it is not required for XNGNR1-mediated upregulation of Delta, allowing establishment of the negative feedback loop involved in lateral inhibition. Therefore, Notch targets Cdk inhibitor expression to regulate differentiation of primary neurons, and its effects on the cell cycle may be of secondary importance.
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Affiliation(s)
- Ann E Vernon
- Department of Oncology, University of Cambridge, Hutchison/MRC Research Centre, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2XZ, UK
| | - Mehregan Movassagh
- Department of Oncology, University of Cambridge, Hutchison/MRC Research Centre, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2XZ, UK
| | - Ian Horan
- Department of Oncology, University of Cambridge, Hutchison/MRC Research Centre, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2XZ, UK
| | - Helen Wise
- Department of Oncology, University of Cambridge, Hutchison/MRC Research Centre, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2XZ, UK
| | - Shinichi Ohnuma
- Department of Oncology, University of Cambridge, Hutchison/MRC Research Centre, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2XZ, UK
| | - Anna Philpott
- Department of Oncology, University of Cambridge, Hutchison/MRC Research Centre, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2XZ, UK
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24
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Chuang LC, Zhu XN, Herrera CR, Tseng HM, Pfleger CM, Block K, Yew PR. The C-terminal domain of the Xenopus cyclin-dependent kinase inhibitor, p27Xic1, is both necessary and sufficient for phosphorylation-independent proteolysis. J Biol Chem 2005; 280:35290-8. [PMID: 16118210 DOI: 10.1074/jbc.m506430200] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Cell cycle progression is regulated by cyclin-dependent kinases (CDKs), cyclins, and CDK inhibitors. In the frog, Xenopus laevis, the CDK inhibitor p27(Xic1) (Xic1) inhibits DNA synthesis by negatively regulating CDK2-cyclin E. Using the frog egg extract as a model system for the study of Xic1, studies have demonstrated that Xic1 protein levels are regulated by nuclear ubiquitination and proteolysis. To characterize the molecular mechanism that regulates Xic1 turnover, we have identified the minimal sequences of Xic1 that are necessary and sufficient for its nuclear ubiquitination and degradation. Using deletion mutagenesis, our studies indicated that the C-terminal 50 amino acids of Xic1 are critical for its proteolysis beyond a role in nuclear transport. Replacement of the Xic1 C terminus with the SV40 nuclear localization sequence resulted in the nuclear localization of Xic1 but not its ubiquitination or degradation. Our deletion studies also indicated that the CDK2-cyclin binding domain of Xic1 is important for its efficient retention in the nucleus. Further deletion analyses identified at least 3 lysine residues within the Xic1 C terminus that are targeted for specific ubiquitination. Importantly, our studies demonstrated that the Xic1 C-terminal 50 amino acids can serve as a nuclear degradation signal when fused to a stable heterologous nuclear protein. Moreover, a 30-amino-acid region within the C terminus of Xic1 can serve as a nuclear ubiquitination signal. To address the role of phosphorylation on Xic1 turnover, all the potential phosphorylation sites within the C-terminal 50 amino acids of Xic1 were mutated to alanine to prevent possible phosphorylation. This resulted in a Xic1 protein that was nevertheless degraded in a manner similar to wild-type Xic1, suggesting that phosphorylation of Xic1 is not critical for its nuclear ubiquitination or proteolysis.
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Affiliation(s)
- Li-Chiou Chuang
- Department of Molecular Medicine, Institute of Biotechnology, University of Texas Health Science Center at San Antonio, San Antonio, Texas 78245, USA
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25
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Chuang LC, Yew PR. Proliferating cell nuclear antigen recruits cyclin-dependent kinase inhibitor Xic1 to DNA and couples its proteolysis to DNA polymerase switching. J Biol Chem 2005; 280:35299-309. [PMID: 16118211 DOI: 10.1074/jbc.m506429200] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The Xenopus cyclin-dependent kinase (CDK) inhibitor, p27(Xic1) (Xic1), binds to CDK2-cyclins and proliferating cell nuclear antigen (PCNA), inhibits DNA synthesis in Xenopus extracts, and is targeted for ubiquitin-mediated proteolysis. Previous studies suggest that Xic1 ubiquitination and degradation are coupled to the initiation of DNA replication, but the precise timing and molecular mechanism of Xic1 proteolysis has not been determined. Here we demonstrate that Xic1 proteolysis is temporally restricted to late replication initiation following the requirements for DNA polymerase alpha-primase, replication factor C, and PCNA. Our studies also indicate that Xic1 degradation is absolutely dependent upon the binding of Xic1 to PCNA in both Xenopus egg and gastrulation stage extracts. Additionally, extracts depleted of PCNA do not support Xic1 proteolysis. Importantly, while the addition of recombinant wild-type PCNA alone restores Xic1 degradation, the addition of a PCNA mutant defective for trimer formation does not restore Xic1 proteolysis in PCNA-depleted extracts, suggesting Xic1 proteolysis requires both PCNA binding to Xic1 and the ability of PCNA to be loaded onto primed DNA by replication factor C. Taken together, our studies suggest that Xic1 is targeted for ubiquitination and degradation during DNA polymerase switching through its interaction with PCNA at a site of initiation.
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Affiliation(s)
- Li-Chiou Chuang
- University of Texas Health Science Center at San Antonio, Department of Molecular Medicine, Institute of Biotechnology, San Antonio, Texas 78245-3207, USA
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26
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Hashiguchi A, Okabayashi K, Asashima M. Role of TSC-22 during early embryogenesis in Xenopus laevis. Dev Growth Differ 2005; 46:535-44. [PMID: 15610143 DOI: 10.1111/j.1440-169x.2004.00770.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Transforming growth factor-beta1-stimulated clone 22 (TSC-22) encodes a leucine zipper-containing protein that is highly conserved. During mouse embryogenesis, TSC-22 is expressed at the site of epithelial-mesenchymal interaction. Here, we isolated Xenopus laevis TSC-22 (XTSC-22) and analyzed its function in early development. XTSC-22 mRNA was first detected in the ectoderm of late blastulae. Translational knockdown using XTSC-22 antisense morpholino oligonucleotides (XTSC-22-MO) caused a severe delay in blastopore closure in gastrulating embryos. This was not due to mesoderm induction or convergent-extension, as confirmed by whole-mount in situ hybridization and animal cap assay. Cell lineage tracing revealed that migration of ectoderm cells toward blastopore was disrupted in XTSC-22-depleted embryos, and these embryos had a marked increase in the number of dividing cells. In contrast, cell division was suppressed in XTSC-22 mRNA-injected embryos. Co-injection of XTSC-22-MO and mRNA encoding p27Xic1, which inhibits cell cycle promotion by binding cyclin/Cdk complexes, reversed aberrant cell division. This was accompanied by rescue of the delay in blastopore closure and cell migration. These results indicate that XTSC-22 is required for cell movement during gastrulation though cell cycle regulation.
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Affiliation(s)
- Akiko Hashiguchi
- Department of Biological Sciences, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8654, Japan
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27
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Kee Y, Bronner-Fraser M. To proliferate or to die: role of Id3 in cell cycle progression and survival of neural crest progenitors. Genes Dev 2005; 19:744-55. [PMID: 15769946 PMCID: PMC1065727 DOI: 10.1101/gad.1257405] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
The neural crest is a unique population of mitotically active, multipotent progenitors that arise at the vertebrate neural plate border. Here, we show that the helix-loop-helix transcriptional regulator Id3 has a novel role in cell cycle progression and survival of neural crest progenitors in Xenopus. Id3 is localized at the neural plate border during gastrulation and neurulation, overlapping the domain of neural crest induction. Morpholino oligonucleotide-mediated depletion of Id3 results in the absence of neural crest precursors and a resultant loss of neural crest derivatives. This appears to be mediated by cell cycle inhibition followed by cell death of the neural crest progenitor pool, rather than a cell fate switch. Conversely, overexpression of Id3 increases cell proliferation and results in expansion of the neural crest domain. Our data suggest that Id3 functions by a novel mechanism, independent of cell fate determination, to mediate the decision of neural crest precursors to proliferate or die.
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Affiliation(s)
- Yun Kee
- Division of Biology, California Institute of Technology, Pasadena, California 91125, USA
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28
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Masai I, Yamaguchi M, Tonou-Fujimori N, Komori A, Okamoto H. The hedgehog-PKA pathway regulates two distinct steps of the differentiation of retinal ganglion cells: the cell-cycle exit of retinoblasts and their neuronal maturation. Development 2005; 132:1539-53. [PMID: 15728672 DOI: 10.1242/dev.01714] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
In the developing zebrafish retina, neurogenesis is initiated in cells adjacent to the optic stalk and progresses to the entire neural retina. It has been reported that hedgehog (Hh) signalling mediates the progression of the differentiation of retinal ganglion cells (RGCs) in zebrafish. However, the progression of neurogenesis seems to be only mildly delayed by genetic or chemical blockade of the Hh signalling pathway. Here, we show that cAMP-dependent protein kinase (PKA) effectively inhibits the progression of retinal neurogenesis in zebrafish. Almost all retinal cells continue to proliferate when PKA is activated, suggesting that PKA inhibits the cell-cycle exit of retinoblasts. A cyclin-dependent kinase (cdk) inhibitor p27 inhibits the PKA-induced proliferation, suggesting that PKA functions upstream of cyclins and cdk inhibitors. Activation of the Wnt signalling pathway induces the hyperproliferation of retinal cells in zebrafish. The blockade of Wnt signalling inhibits the PKA-induced proliferation, but the activation of Wnt signalling promotes proliferation even in the absence of PKA activity. These observations suggest that PKA inhibits exit from the Wnt-mediated cell cycle rather than stimulates Wnt-mediated cell-cycle progression. PKA is an inhibitor of Hh signalling, and Hh signalling molecule morphants show severe defects in cell-cycle exit of retinoblasts. Together, these data suggest that Hh acts as a short-range signal to induce the cell-cycle exit of retinoblasts. The pulse inhibition of Hh signalling revealed that Hh signalling regulates at least two distinct steps of RGC differentiation: the cell-cycle exit of retinoblasts and RGC maturation. This dual requirement of Hh signalling in RGC differentiation implies that the regulation of a neurogenic wave is more complex in the zebrafish retina than in the Drosophila eye.
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Affiliation(s)
- Ichiro Masai
- Masai Initiative Research Unit, RIKEN (The Institute of Physical and Chemical Research, Hirosawa, Saitama, Japan.
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29
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Abstract
Eukaryotic genomes are replicated from large numbers of replication origins distributed on multiple chromosomes. The activity of these origins must be coordinated so that the entire genome is efficiently and accurately replicated yet no region of the genome is ever replicated more than once. The past decade has seen significant advances in understanding how the initiation of DNA replication is regulated by key cell-cycle regulators, including the cyclin dependent kinases (CDKs) and the anaphase promoting complex/cyclosome (APC/C). The assembly of essential prereplicative complexes (pre-RCs) at origins only occurs when CDK activity is low and APC/C activity is high. Origin firing, however, can only occur when the APC/C is inactivated and CDKs become active. This two step mechanism ensures that no origin can fire more than once in a cell cycle. In all eukaryotes tested, CDKs can contribute to the inhibition of pre-RC assembly. This inhibition is characterised both by high degrees of redundancy and evolutionary plasticity. Geminin plays a crucial role in inhibiting licensing in metazoans and, like cyclins, is inactivated by the APC/C. Strategies involved in preventing re-replication in different organisms will be discussed.
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Affiliation(s)
- John F X Diffley
- Cancer Research UK London Research Institute, Clare Hall Laboratories, South Mimms, Hertfordshire EN6 3LD, UK.
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30
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Wroble BN, Sible JC. Chk2/Cds1 protein kinase blocks apoptosis during early development ofXenopus laevis. Dev Dyn 2005; 233:1359-65. [PMID: 15937936 DOI: 10.1002/dvdy.20449] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Early Xenopus laevis embryos possess cell cycles that do not arrest at checkpoints in response to damaged DNA. At the midblastula transition (MBT), embryos with damaged DNA undergo apoptosis. After the MBT, DNA damage triggers cell cycle arrest rather than apoptosis. The transition from checkpoint-unregulated to checkpoint-regulated cycles makes Xenopus embryos compelling for studying mechanisms regulating response to genomic damage. The DNA damage checkpoint is mediated by the Chk2/Cds1 kinase. Conflicting evidence implicates Chk2 as an inhibitor or promoter of apoptosis. To better understand the developmental function of Chk2, we expressed wild-type (wt) and dominant-negative (DN) Chk2 in Xenopus embryos. Wt-Chk2 created a pre-MBT checkpoint due to degradation of Cdc25A and phosphorylation of cyclin-dependent kinases. Embryos expressing DN-Chk2 developed normally until gastrulation and then underwent apoptosis. Conversely, low doses of wt-Chk2 blocked radiation-induced apoptosis. Therefore, Chk2 operates at a switch between cell cycle arrest or apoptosis in response to genomic assaults.
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Affiliation(s)
- Brian N Wroble
- Department of Biology, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061-0406, USA
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31
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Daniels M, Dhokia V, Richard-Parpaillon L, Ohnuma SI. Identification of Xenopus cyclin-dependent kinase inhibitors, p16Xic2 and p17Xic3. Gene 2004; 342:41-7. [PMID: 15527964 DOI: 10.1016/j.gene.2004.07.038] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2004] [Revised: 07/12/2004] [Accepted: 07/29/2004] [Indexed: 11/23/2022]
Abstract
The Cip/Kip family of mammalian cyclin-dependent kinase (cdk) inhibitors plays important roles in development, particularly in cell fate determination and differentiation, in addition to their function of blocking cell cycle progression. We have identified two novel members of the Kip/Cip cdk inhibitor family, p16Xic2 and p17Xic3, from Xenopus laevis. Sequence analysis revealed that p16Xic2 and p17Xic3 are orthologues of mammalian p21Cip1 and p27Kip1, respectively. Overexpression of these inhibitors results in cell cycle arrest by inhibition of cdk2 activity. Interestingly, the expression of these inhibitors is highly developmentally regulated. p16Xic2 is highly expressed in differentiating somite, tail bud, lens, and cement gland, while p17Xic3 is expressed in the central nervous system. In a retinal cell fate determination assay, both p16Xic2 and p17Xic3 have an activity that influences cell fate determination. These observations suggest that p16Xic2 and p17Xic3 might be involved in cell fate determination in a tissue-specific manner by coordinating proliferation and differentiation as observed with p27Xic1.
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MESH Headings
- Amino Acid Sequence
- Animals
- Carrier Proteins/genetics
- Cell Cycle/drug effects
- Cell Division/drug effects
- Cloning, Molecular
- Cyclin-Dependent Kinase Inhibitor Proteins
- Cyclin-Dependent Kinases/antagonists & inhibitors
- Cyclin-Dependent Kinases/metabolism
- DNA, Complementary/chemistry
- DNA, Complementary/genetics
- DNA, Complementary/isolation & purification
- Embryo, Nonmammalian/cytology
- Embryo, Nonmammalian/drug effects
- Embryo, Nonmammalian/metabolism
- Female
- Gene Expression Regulation, Developmental
- In Situ Hybridization
- Male
- Microinjections
- Molecular Sequence Data
- Phylogeny
- RNA, Messenger/administration & dosage
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- Sequence Alignment
- Sequence Analysis, DNA
- Sequence Homology, Amino Acid
- Time Factors
- Xenopus Proteins/genetics
- Xenopus laevis/embryology
- Xenopus laevis/genetics
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Affiliation(s)
- Maki Daniels
- Department of Oncology, The Hutchison/MRC Research Centre, University of Cambridge, Hills Road, Cambridge, CB2 2XZ, UK
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32
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Habermann B, Bebin AG, Herklotz S, Volkmer M, Eckelt K, Pehlke K, Epperlein HH, Schackert HK, Wiebe G, Tanaka EM. An Ambystoma mexicanum EST sequencing project: analysis of 17,352 expressed sequence tags from embryonic and regenerating blastema cDNA libraries. Genome Biol 2004; 5:R67. [PMID: 15345051 PMCID: PMC522874 DOI: 10.1186/gb-2004-5-9-r67] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2003] [Revised: 05/06/2004] [Accepted: 06/29/2004] [Indexed: 11/30/2022] Open
Abstract
An EST database has been generated for the axolotl Ambystoma mexicanum. Analysis of this data has uncovered an unusual phylogenetic distribution of the cyclin dependent kinase inhibitor 1 gene family in amphibians. Background The ambystomatid salamander, Ambystoma mexicanum (axolotl), is an important model organism in evolutionary and regeneration research but relatively little sequence information has so far been available. This is a major limitation for molecular studies on caudate development, regeneration and evolution. To address this lack of sequence information we have generated an expressed sequence tag (EST) database for A. mexicanum. Results Two cDNA libraries, one made from stage 18-22 embryos and the other from day-6 regenerating tail blastemas, generated 17,352 sequences. From the sequenced ESTs, 6,377 contigs were assembled that probably represent 25% of the expressed genes in this organism. Sequence comparison revealed significant homology to entries in the NCBI non-redundant database. Further examination of this gene set revealed the presence of genes involved in important cell and developmental processes, including cell proliferation, cell differentiation and cell-cell communication. On the basis of these data, we have performed phylogenetic analysis of key cell-cycle regulators. Interestingly, while cell-cycle proteins such as the cyclin B family display expected evolutionary relationships, the cyclin-dependent kinase inhibitor 1 gene family shows an unusual evolutionary behavior among the amphibians. Conclusions Our analysis reveals the importance of a comprehensive sequence set from a representative of the Caudata and illustrates that the EST sequence database is a rich source of molecular, developmental and regeneration studies. To aid in data mining, the ESTs have been organized into an easily searchable database that is freely available online.
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Affiliation(s)
- Bianca Habermann
- Scionics Computer Innovation GmbH, Pfotenhauerstrasse 110, Dresden 01307, Germany
| | - Anne-Gaelle Bebin
- Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, Dresden 01307, Germany
| | - Stephan Herklotz
- Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, Dresden 01307, Germany
| | - Michael Volkmer
- Scionics Computer Innovation GmbH, Pfotenhauerstrasse 110, Dresden 01307, Germany
| | - Kay Eckelt
- Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, Dresden 01307, Germany
| | - Kerstin Pehlke
- Institute of Anatomy, Medical Faculty of the Carl Gustav Carus Technical University, Dresden, Fetscherstrasse 74, Dresden 01307, Germany
| | - Hans Henning Epperlein
- Institute of Anatomy, Medical Faculty of the Carl Gustav Carus Technical University, Dresden, Fetscherstrasse 74, Dresden 01307, Germany
| | - Hans Konrad Schackert
- Department of Surgical Research, Medical Faculty of the Carl Gustav Carus Technical University, Dresden, Fetscherstrasse 74, Dresden 01307, Germany
| | - Glenis Wiebe
- Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, Dresden 01307, Germany
| | - Elly M Tanaka
- Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, Dresden 01307, Germany
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Richard-Parpaillon L, Cosgrove RA, Devine C, Vernon AE, Philpott A. G1/S phase cyclin-dependent kinase overexpression perturbs early development and delays tissue-specific differentiation in Xenopus. Development 2004; 131:2577-86. [PMID: 15115752 DOI: 10.1242/dev.01121] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Cell division and differentiation are largely incompatible but the molecular links between the two processes are poorly understood. Here, we overexpress G1/S phase cyclins and cyclin-dependent kinases in Xenopus embryos to determine their effect on early development and differentiation. Overexpression of cyclin E prior to the midblastula transition (MBT), with or without cdk2, results in a loss of nuclear DNA and subsequent apoptosis at early gastrula stages. By contrast, overexpressed cyclin A2 protein does not affect early development and, when stabilised by binding to cdk2, persists to tailbud stages. Overexpression of cyclin A2/cdk2 in post-MBT embryos results in increased proliferation specifically in the epidermis with concomitant disruption of skin architecture and delay in differentiation. Moreover, ectopic cyclin A2/cdk2 also inhibits differentiation of primary neurons but does not affect muscle. Thus, overexpression of a single G1/S phase cyclin/cdk pair disrupts the balance between division and differentiation in the early vertebrate embryo in a tissue-specific manner.
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Affiliation(s)
- Laurent Richard-Parpaillon
- Department of Oncology, Cambridge University, Hutchison/MRC Research Centre, Addenbrookes Hospital, Hills Road, Cambridge CB2 2XZ, UK.
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Andreazzoli M, Gestri G, Cremisi F, Casarosa S, Dawid IB, Barsacchi G. Xrx1 controls proliferation and neurogenesis in Xenopus anterior neural plate. Development 2003; 130:5143-54. [PMID: 12975341 DOI: 10.1242/dev.00665] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
In Xenopus neuroectoderm, posterior cells start differentiating at the end of gastrulation, while anterior cells display an extended proliferative period and undergo neurogenesis only at tailbud stage. Recent studies have identified several important components of the molecular pathways controlling posterior neurogenesis, but little is known about those controlling the timing and positioning of anterior neurogenesis. We investigate the role of Xrx1, a homeobox gene required for eye and anterior brain development, in the control of proliferation and neurogenesis of the anterior neural plate. Xrx1 is expressed in the entire proliferative region of the anterior neural plate delimited by cells expressing the neuronal determination gene X-ngnr-1, the neurogenic gene X-Delta-1, and the cell cycle inhibitor p27Xic1. Positive and negative signals position Xrx1 expression to this region. Xrx1 is activated by chordin and Hedgehog gene signaling, which induce anterior and proliferative fate, and is repressed by the differentiation-promoting activity of neurogenin and retinoic acid. Xrx1 is required for anterior neural plate proliferation and, when overexpressed, induces proliferation, inhibits X-ngnr-1, X-Delta-1 and N-tubulin and counteracts X-ngnr-1- and retinoic acid-mediated differentiation. We find that Xrx1 does not act by increasing lateral inhibition but by inducing the antineurogenic transcriptional repressors Xhairy2 and Zic2, and by repressing p27Xic1. The effects of Xrx1 on proliferation, neurogenesis and gene expression are restricted to the most rostral region of the embryo, implicating this gene as an anterior regulator of neurogenesis.
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Affiliation(s)
- Massimiliano Andreazzoli
- Dipartimento di Fisiologia e Biochimica, Università degli Studi di Pisa, Via Carducci 13, 56010 Ghezzano (Pisa), Italy.
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Ciliberto A, Petrus MJ, Tyson JJ, Sible JC. A kinetic model of the cyclin E/Cdk2 developmental timer in Xenopus laevis embryos. Biophys Chem 2003; 104:573-89. [PMID: 12914904 DOI: 10.1016/s0301-4622(03)00060-7] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Early cell cycles of Xenopus laevis embryos are characterized by rapid oscillations in the activity of two cyclin-dependent kinases. Cdk1 activity peaks at mitosis, driven by periodic degradation of cyclins A and B. In contrast, Cdk2 activity oscillates twice per cell cycle, despite a constant level of its partner, cyclin E. Cyclin E degrades at a fixed time after fertilization, normally corresponding to the midblastula transition. Based on published data and new experiments, we constructed a mathematical model in which: (1) oscillations in Cdk2 activity depend upon changes in phosphorylation, (2) Cdk2 participates in a negative feedback loop with the inhibitory kinase Wee1; (3) cyclin E is cooperatively removed from the oscillatory system; and (4) removed cyclin E is degraded by a pathway activated by cyclin E/Cdk2 itself. The model's predictions about embryos injected with Xic1, a stoichiometric inhibitor of cyclin E/Cdk2, were experimentally validated.
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Affiliation(s)
- Andrea Ciliberto
- Biology Department, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0406, USA.
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36
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Carruthers S, Mason J, Papalopulu N. Depletion of the cell-cycle inhibitor p27(Xic1) impairs neuronal differentiation and increases the number of ElrC(+) progenitor cells in Xenopus tropicalis. Mech Dev 2003; 120:607-16. [PMID: 12782277 DOI: 10.1016/s0925-4773(03)00010-8] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
The Xenopus p27(Xic1) gene encodes a cyclin dependent kinase (CDK) inhibitor of the Cip/Kip family. We have previously shown that p27(Xic1) is expressed in the cells of the neural plate as they become post-mitotic (Development 127 (2000) 1303). To investigate whether p27(Xic1) is necessary for cell cycle exit and/or neuronal differentiation, we used antisense morpholino oligos (MO) to knockdown the protein levels in vivo. For such knockdown studies, Xenopus tropicalis is a better model system than Xenopus laevis, since it has a diploid genome. Indeed, while X. laevis has two p27(Xic1) paralogs, p27(Xic1) and p28(Kix1), we have found only one ortholog in X. tropicalis, equidistant from the X. laevis genes. The X. tropicalis p27(Xic1) was expressed in a similar pattern to the X. laevis gene. Depletion of p27(Xic1) in X. tropicalis caused an increase in proliferation and a suppression of the neuronal differentiation marker, N-tubulin. At the same time, we found an increase in the expression of ElrC, a marker of cells as they undergo a transition from proliferation to differentiation. We conclude that p27(Xic1) is necessary for cells to exit the cell cycle and differentiate; in its absence, cells accumulate in a progenitor state. The expression of p27(Xic1) in the embryo is regionalised but the transcriptional regulation of p27(Xic1) is not well understood. We report the isolation of a p27(Xic1) genomic clone and we identify a 5' region capable of driving reporter gene expression specifically in the neural tube and the eye.
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Affiliation(s)
- Samantha Carruthers
- Wellcome Trust/Cancer Research UK Institute, Tennis Court Road, Cambridge CB2 1QR, UK
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37
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Vernon AE, Philpott A. A single cdk inhibitor, p27Xic1, functions beyond cell cycle regulation to promote muscle differentiation in Xenopus. Development 2003; 130:71-83. [PMID: 12441292 DOI: 10.1242/dev.00180] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The molecular basis of the antagonism between cellular proliferation and differentiation is poorly understood. We have investigated the role of the cyclin-dependent kinase inhibitor p27(Xic1) in the co-ordination of cell cycle exit and differentiation during early myogenesis in vivo using Xenopus embryos. In this report, we demonstrate that p27(Xic1) is highly expressed in the developing myotome, that ablation of p27(Xic1) protein prevents muscle differentiation and that p27(Xic1) synergizes with the transcription factor MyoD to promote muscle differentiation. Furthermore, the ability of p27(Xic1) to promote myogenesis resides in an N-terminal domain and is separable from its cell cycle regulation function. This data demonstrates that a single cyclin-dependent kinase inhibitor, p27(Xic1), controls in vivo muscle differentiation in Xenopus and that regulation of this process by p27(Xic1) requires activities beyond cell cycle inhibition.
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Affiliation(s)
- Ann E Vernon
- Department of Oncology, University of Cambridge, Cambridge Institute for Medical Research, Wellcome Trust/MRC Building, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2XY, UK
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38
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Vernon AE, Devine C, Philpott A. The cdk inhibitor p27Xic1 is required for differentiation of primary neurones in Xenopus. Development 2003; 130:85-92. [PMID: 12441293 DOI: 10.1242/dev.00193] [Citation(s) in RCA: 109] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
We have investigated the role of the cyclin-dependent kinase inhibitor, p27(Xic1), in the coordination of cell cycle exit and differentiation during early neurogenesis. We demonstrate that p27(Xic1) is highly expressed in cells destined to become primary neurones and is essential for an early stage of neurogenesis. Ablation of p27(Xic1) protein prevents differentiation of primary neurones, while overexpressing p27(Xic1) promotes their formation. p27(Xic1) may enhance neurogenesis by stabilising the bHLH protein, neurogenin. Moreover, the ability of p27(Xic1) to stabilise neurogenin and enhance neurogenesis localises to an N-terminal domain of the molecule and is separable from its ability to inhibit the cell cycle.
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Affiliation(s)
- Ann E Vernon
- Department of Oncology, University of Cambridge, Cambridge Institute for Medical Research, Wellcome Trust/MRC Building, Addenbrooke's Hospital, Cambridge CB2 2XY, UK
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39
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Finkielstein CV, Chen LG, Maller JL. A role for G1/S cyclin-dependent protein kinases in the apoptotic response to ionizing radiation. J Biol Chem 2002; 277:38476-85. [PMID: 12176996 DOI: 10.1074/jbc.m206184200] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In Xenopus development the mid-blastula transition (MBT) marks a dramatic change in response of the embryo to ionizing radiation. Whereas inhibition of cyclin D1-Cdk4 and cyclin A2-Cdk2 by p27(Xic1) has been linked to cell cycle arrest and prevention of apoptosis in embryos irradiated post-MBT, distinct roles for these complexes during apoptosis are evident in embryos irradiated pre-MBT. Cyclin A2 is cleaved by caspases to generate a truncated complex termed Delta N-cyclin A2-Cdk2, which is kinase active, not inhibited by p27(Xic1), and not sensitive to degradation by the ubiquitin-mediated proteasome pathway. Moreover, Delta N-cyclin A2-Cdk2 has an expanded substrate specificity and can phosphorylate histone H2B at Ser-32, which may facilitate DNA cleavage. Consistent with a role for cyclin A2 in apoptosis, the addition of Delta N-cyclin A2-Cdk2, but not full-length cyclin A2-Cdk2, to Xenopus egg extracts triggers apoptotic DNA fragmentation even when caspases are not activated. Similarly, cyclin D1 is targeted by caspases, and the generated product exhibits higher affinity for p27(Xic1), leading to reduced phosphorylation of the retinoblastoma protein (pRB) during apoptosis. These data suggest that caspase cleavage of both cyclin D1-Cdk4 and cyclin A2-Cdk2 promotes specific apoptotic events in embryos undergoing apoptosis in response to ionizing radiation.
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Affiliation(s)
- Carla V Finkielstein
- Howard Hughes Medical Institute and Department of Pharmacology, University of Colorado School of Medicine, Denver, Colorado 80262, USA
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40
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Affiliation(s)
- Edward H Hinchcliffe
- Department of Biological Sciences, and the Walther Cancer Research Institute, University of Notre Dame, Notre Dame, Indiana, IN 46556, USA
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41
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Ohnuma SI, Hopper S, Wang KC, Philpott A, Harris WA. Co-ordinating retinal histogenesis: early cell cycle exit enhances early cell fate determination in the Xenopus retina. Development 2002; 129:2435-46. [PMID: 11973275 DOI: 10.1242/dev.129.10.2435] [Citation(s) in RCA: 109] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The laminar arrays of distinct cell types in the vertebrate retina are built by a histogenic process in which cell fate is correlated with birth order. To explore this co-ordination mechanistically, we altered the relative timing of cell cycle exit in the developing Xenopus retina and asked whether this affected the activity of neural determinants. We found that Xath5, a bHLH proneural gene that promotes retinal ganglion cell (RGC) fate, (Kanekar, S., Perron, M., Dorsky, R., Harris, W. A., Jan, L. Y., Jan, Y. N. and Vetter, M. L. (1997) Neuron19, 981-994), does not cause these cells to be born prematurely. To drive cells out of the cell cycle early, therefore, we misexpressed the cyclin kinase inhibitor, p27Xic1. We found that early cell cycle exit potentiates the ability of Xath5 to promote RGC fate. Conversely, the cell cycle activator, cyclin E1, which inhibits cell cycle exit, biases Xath5-expressing cells toward later neuronal fates. We found that Notch activation in this system caused cells to exit the cell cycle prematuely, and when it is misexpressed with Xath5, it also potentiates the induction of RGCs. The potentiation is counteracted by co-expression of cyclin E1. These results suggest a model of histogenesis in which the activity of factors that promote early cell cycle exit enhances the activity of factors that promote early cellular fates.
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Affiliation(s)
- Shin-ichi Ohnuma
- Department of Anatomy, University of Cambridge, Downing Street, Cambridge CB2 3DY, UK
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42
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You Z, Harvey K, Kong L, Newport J. Xic1 degradation in Xenopus egg extracts is coupled to initiation of DNA replication. Genes Dev 2002; 16:1182-94. [PMID: 12023298 PMCID: PMC186278 DOI: 10.1101/gad.985302] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
CDK2 activity is regulated by phosphorylation/dephosphorylation, subcellular localization, cyclin levels, and cyclin dependent kinase inhibitors (CKIs). Using Xenopus egg extracts, we find that degradation of Xic1, a Xenopus p21(cip1)/p27(kip1) family member, is coupled to initiation of DNA replication. Xic1 turnover requires the formation of a prereplication complex (pre-RC). Additionally, downstream initiation factors including CDK2, Cdc7, and Cdc45, but not RPA or DNA polymerase alpha, are necessary for activating the degradation system. Xic1 degradation is attenuated following completion of DNA replication. Unlike degradation of p27(kip1) in mammalian cells, CDK2 activity is not directly involved in Xic1 degradation and interactions between Xic1 and CDK2/cyclin E are dispensable for Xic1 turnover. Interestingly, a C-terminal region (162-192) of Xic1 is essential and apparently sufficient for triggering Xic1 ubiquitination prior to degradation. These observations demonstrate that a direct link exists between DNA replication and CKI degradation.
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Affiliation(s)
- Zhongsheng You
- Division of Biology, University of California, San Diego, La Jolla, California 92093-0349, USA
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43
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Matsumoto Y, Maller JL. Calcium, calmodulin, and CaMKII requirement for initiation of centrosome duplication in Xenopus egg extracts. Science 2002; 295:499-502. [PMID: 11799245 DOI: 10.1126/science.1065693] [Citation(s) in RCA: 82] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Aberrant centrosome duplication is observed in many tumor cells and may contribute to genomic instability through the formation of multipolar mitotic spindles. Cyclin-dependent kinase 2 (Cdk2) is required for multiple rounds of centrosome duplication in Xenopus egg extracts but not for the initial round of replication. Egg extracts undergo periodic oscillations in the level of free calcium. We show here that chelation of calcium in egg extracts or specific inactivation of calcium/calmodulin-dependent protein kinase II (CaMKII) blocks even initial centrosome duplication, whereas inactivation of Cdk2 does not. Duplication can be restored to inhibited extracts by addition of CaMKII and calmodulin. These results indicate that calcium, calmodulin, and CaMKII are required for an essential step in initiation of centrosome duplication. Our data suggest that calcium oscillations in the cell cycle may be linked to centrosome duplication.
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Affiliation(s)
- Yutaka Matsumoto
- Howard Hughes Medical Institute and Department of Pharmacology, University of Colorado School of Medicine, Denver, CO 80262, USA
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44
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Rodier G, Montagnoli A, Di Marcotullio L, Coulombe P, Draetta GF, Pagano M, Meloche S. p27 cytoplasmic localization is regulated by phosphorylation on Ser10 and is not a prerequisite for its proteolysis. EMBO J 2001; 20:6672-82. [PMID: 11726503 PMCID: PMC125773 DOI: 10.1093/emboj/20.23.6672] [Citation(s) in RCA: 229] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
The activity of the cyclin-dependent kinase inhibitor p27 is controlled by its concentration and subcellular localization. However, the mechanisms that regulate its intracellular transport are poorly understood. Here we show that p27 is phosphorylated on Ser10 in vivo and that mutation of Ser10 to Ala inhibits p27 cytoplasmic relocalization in response to mitogenic stimulation. In contrast, a fraction of wild-type p27 and a p27(S10D)-phospho-mimetic mutant translocates to the cytoplasm in the presence of mitogens. G1 nuclear export of p27 and its Ser10 phosphorylation precede cyclin-dependent kinase 2 (Cdk2) activation and degradation of the bulk of p27. Interestingly, leptomycin B-mediated nuclear accumulation accelerates the turnover of endogenous p27; the p27(S10A) mutant, which is trapped in the nucleus, has a shorter half-life than wild-type p27 and the p27(S10D) mutant. In summary, p27 is efficiently degraded in the nucleus and phosphorylation of Ser10 is necessary for the nuclear to cytoplasmic redistribution of a fraction of p27 in response to mitogenic stimulation. This cytoplasmic localization may serve to decrease the abundance of p27 in the nucleus below a certain threshold required for activation of cyclin-Cdk2 complexes.
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Affiliation(s)
- Geneviève Rodier
- Institut de recherches cliniques de Montréal and Departments of Molecular Biology and Pharmacology, University of Montreal, Montreal, Quebec, Canada H2W 1R7, Department of Pathology and Kaplan Comprehensive Cancer Center, New York University School of Medicine, New York, NY 10016, USA and European Institute of Oncology, 20141 Milan, Italy Corresponding author e-mail:
| | - Alessia Montagnoli
- Institut de recherches cliniques de Montréal and Departments of Molecular Biology and Pharmacology, University of Montreal, Montreal, Quebec, Canada H2W 1R7, Department of Pathology and Kaplan Comprehensive Cancer Center, New York University School of Medicine, New York, NY 10016, USA and European Institute of Oncology, 20141 Milan, Italy Corresponding author e-mail:
| | - Lucia Di Marcotullio
- Institut de recherches cliniques de Montréal and Departments of Molecular Biology and Pharmacology, University of Montreal, Montreal, Quebec, Canada H2W 1R7, Department of Pathology and Kaplan Comprehensive Cancer Center, New York University School of Medicine, New York, NY 10016, USA and European Institute of Oncology, 20141 Milan, Italy Corresponding author e-mail:
| | - Philippe Coulombe
- Institut de recherches cliniques de Montréal and Departments of Molecular Biology and Pharmacology, University of Montreal, Montreal, Quebec, Canada H2W 1R7, Department of Pathology and Kaplan Comprehensive Cancer Center, New York University School of Medicine, New York, NY 10016, USA and European Institute of Oncology, 20141 Milan, Italy Corresponding author e-mail:
| | - Giulio F. Draetta
- Institut de recherches cliniques de Montréal and Departments of Molecular Biology and Pharmacology, University of Montreal, Montreal, Quebec, Canada H2W 1R7, Department of Pathology and Kaplan Comprehensive Cancer Center, New York University School of Medicine, New York, NY 10016, USA and European Institute of Oncology, 20141 Milan, Italy Corresponding author e-mail:
| | - Michele Pagano
- Institut de recherches cliniques de Montréal and Departments of Molecular Biology and Pharmacology, University of Montreal, Montreal, Quebec, Canada H2W 1R7, Department of Pathology and Kaplan Comprehensive Cancer Center, New York University School of Medicine, New York, NY 10016, USA and European Institute of Oncology, 20141 Milan, Italy Corresponding author e-mail:
| | - Sylvain Meloche
- Institut de recherches cliniques de Montréal and Departments of Molecular Biology and Pharmacology, University of Montreal, Montreal, Quebec, Canada H2W 1R7, Department of Pathology and Kaplan Comprehensive Cancer Center, New York University School of Medicine, New York, NY 10016, USA and European Institute of Oncology, 20141 Milan, Italy Corresponding author e-mail:
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Nguyên V, Candal Suárez EM, Sharif A, Joly JS, Bourrat F. Expression of Ol-KIP, a cyclin-dependent kinase inhibitor, in embryonic and adult medaka (Oryzias latipes) central nervous system. Dev Dyn 2001; 222:439-49. [PMID: 11747078 DOI: 10.1002/dvdy.1203] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
From an expression screen in a fish model, the medaka, we have isolated Ol-KIP (Oryzias latipes-kinase inhibitor protein), a new member of the KIP subfamily of cyclin-dependent kinase (Cdk) inhibitors. We have analysed its expression in the developing and adult brain by in situ hybridization and by double labeling with Ol-KIP mRNA and proliferating cell nuclear antigen (PCNA) antibodies. Ol-KIP presents a complex expression pattern in several areas of the embryonic central nervous system, most often in close vicinity to proliferative neuroepithelia. We studied in great detail its expression in the optic tectum: Ol-KIP is expressed in a ring-shaped domain lying exactly between the proliferative and the postmitotic zones of this structure and is, therefore, potentially involved in cell cycle exit. In the adult CNS, Ol-KIP expression persists in numerous nuclei, both close and distant from proliferative ventricular areas. So, Ol-KIP expression is in part compatible with a sustained "stop signal" role for proliferation, but its expression in postmitotic zones suggests that KIP proteins may have late neuronal function(s), in addition to inhibiting Cdks. This first detailed study of the expression profile of a KIP gene in a nonmammalian vertebrate, thus, opens perspectives for analysing the role of these regulators in brain development and function.
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Affiliation(s)
- V Nguyên
- Jeune Equipe INRA "Morphogenèse du Système Nerveux des Chordés," UPR 2197 DEPSN, CNRS, Institut Fessard, Gif-sur-Yvette Cedex, France
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46
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Abstract
The initiation of DNA replication is restrained by Cip/Kip proteins that inhibit Cdk2. Degradation of Xenopus Xic1, a Kip1 orthologue, is dependent on its recruitment to replication origins. This ensures that activation of Cdk2 and (subsequent initiation of replication) is co-ordinately regulated at, and localised to, replication origins.
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Affiliation(s)
- A Li
- CRC Chromsome Replication Research Group, Wellcome Trust Biocentre, University of Dundee, Dow Street, Dundee DD1 5EH, UK
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47
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Furstenthal L, Swanson C, Kaiser BK, Eldridge AG, Jackson PK. Triggering ubiquitination of a CDK inhibitor at origins of DNA replication. Nat Cell Biol 2001; 3:715-22. [PMID: 11483956 DOI: 10.1038/35087026] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
To ensure proper timing of the G1-S transition in the cell cycle, the cyclin E-Cdk2 complex, which is responsible for the initiation of DNA replication, is restrained by the p21(Cip1)/p27(Kip1)/p57(Kip2) family of CDK (cyclin-dependent kinase) inhibitors in humans and by the related p27(Xic1) protein in Xenopus. Activation of cyclin E-Cdk2 is linked to the ubiquitination of human p27(Kip1) or Xenopus p27(Xic1) by SCF (for Skp1-Cullin-F-box protein) ubiquitin ligases. For human p27(Kip1), ubiquitination requires direct phosphorylation by cyclin E-Cdk2. We show here that Xic1 ubiquitination does not require phosphorylation by cyclin E-Cdk2, but it does require nuclear accumulation of the Xic1-cyclin E-Cdk2 complex and recruitment of this complex to chromatin by the origin-recognition complex together with Cdc6 replication preinitiation factors; it also requires an activation step necessitating cyclin E-Cdk2-kinase and SCF ubiquitin-ligase activity, and additional factors associated with mini-chromosome maintenance proteins, including the inactivation of geminin. Components of the SCF ubiquitin-ligase complex, including Skp1 and Cul1, are also recruited to chromatin through cyclin E-Cdk2 and the preinitiation complex. Thus, activation of the cyclin E-Cdk2 kinase and ubiquitin-dependent destruction of its inhibitor are spatially constrained to the site of a properly assembled preinitiation complex.
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Affiliation(s)
- L Furstenthal
- Departments of Pathology and Microbiology & Immunology, Stanford University School of Medicine, 300 Pasteur Drive, MC 5324, Palo Alto, California 94305-5324, USA
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Affiliation(s)
- J W Harper
- Department of Biochemistry and Molecular Biology, Baylor College of Medicine, One Baylor Plaza, Houston, Texas 77030, USA.
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Hinchcliffe EH, Sluder G. "It Takes Two to Tango": understanding how centrosome duplication is regulated throughout the cell cycle. Genes Dev 2001; 15:1167-81. [PMID: 11358861 DOI: 10.1101/gad.894001] [Citation(s) in RCA: 212] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Affiliation(s)
- E H Hinchcliffe
- Department of Cell Biology, University of Massachusetts Medical School, Worcester, Massachusetts 01605, USA
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Mattock H, Jares P, Zheleva DI, Lane DP, Warbrick E, Blow JJ. Use of peptides from p21 (Waf1/Cip1) to investigate PCNA function in Xenopus egg extracts. Exp Cell Res 2001; 265:242-51. [PMID: 11302689 DOI: 10.1006/excr.2001.5181] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Cell-free systems derived from unfertilized Xenopus eggs have been particularly informative in the study of the regulation and biochemistry of DNA replication. We have developed a Xenopus-based system to analyze proliferating cell nuclear antigen (PCNA)-specific effects on the functional properties of egg extracts. To do this, we have coupled peptides derived from p21 (Waf1/Cip1) to beads and used these to deplete PCNA from Xenopus egg extracts. The effect on various aspects of DNA replication can be analyzed after the readdition of PCNA and other purified proteins. Using this system, we have shown that replication of single-stranded M13 DNA is entirely dependent upon PCNA. By adding exogenous T7 DNA polymerase to PCNA-depleted extracts, we have uncoupled processive DNA replication from PCNA activity and so created an experimental system to analyze the dependence of postreplicative processes on PCNA function. We have shown that successful chromatin assembly is specifically dependent on PCNA. However, systems for analyzing the far more complex mechanisms required for the replication of nuclear double-stranded DNA have proved so far to be refractory to specific PCNA depletion.
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Affiliation(s)
- H Mattock
- Department of Surgery and Molecular Oncology, University of Dundee, Ninewells Hospital and Medical School, Dundee DD1 9SY, United Kingdom
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