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1.
Nanotechnology ; 35(16)2024 Feb 21.
Article in English | MEDLINE | ID: mdl-38211321

ABSTRACT

We investigate the magnetic interlayer coupling and domain structure of ultra-thin ferromagnetic (FM) cobalt (Co) layers embedded between a graphene (G) layer and a platinum (Pt) layer on a silicon carbide (SiC) substrate (G/Co/Pt on SiC). Experimentally, a combination of x-ray photoemission electron microscopy with x-ray magnetic circular dichroism has been carried out at the Co L-edge. Furthermore, structural and chemical properties of the system have been investigated using low energy electron diffraction (LEED) and x-ray photoelectron spectroscopy (XPS).In situLEED patterns revealed the crystalline structure of each layer within the system. Moreover, XPS confirmed the presence of quasi-freestanding graphene, the absence of cobalt silicide, and the appearance of two silicon carbide surface components due to Pt intercalation. Thus, the Pt-layer effectively functions as a diffusion barrier. The magnetic structure of the system was unaffected by the substrate's step structure. Furthermore, numerous vortices and anti-vortices were found in all samples, distributed all over the surfaces, indicating Dzyaloshinskii-Moriya interaction. Only regions with a locally increased Co-layer thickness showed no vortices. Moreover, unlike in similar systems, the magnetization was predominantly in-plane, so no perpendicular magnetic anisotropy was found.

2.
Nanotechnology ; 30(2): 025702, 2019 Jan 11.
Article in English | MEDLINE | ID: mdl-30382025

ABSTRACT

We report on a study of the Co intercalation process underneath the [Formula: see text] R30° reconstructed 6H-SiC(0001) surface for Co film-thicknesses in a range of 0.4-12 nm using a combination of surface sensitive imaging, diffractive, and spectroscopic methods. In situ photoemission electron microscopy reveals a dependence of the intercalation temperature on the Co film-thickness. Using low energy electron diffraction and photoemission spectroscopy (XPS), we find that the SiC surface reconstruction is partially lifted and transformed. We show that the [Formula: see text] R30° reconstruction does not prevent silicide formation for Co film-thicknesses  ≥0.4 nm according to XPS and x-ray absorption spectra. Our results indicate that the silicide formation is self-limited to a thin interface region and is followed by Co intercalation between graphene and silicide. Furthermore, we analyze the magnetic properties using x-ray magnetic circular dichroism at the Co L-edge. In-plane magnetization is observed for all analyzed film-thicknesses. For ultra-thin Co films, self-assembled magnetic wires with a width of the order of 100 nm form at the step-edges.

3.
Environ Monit Assess ; 164(1-4): 337-48, 2010 May.
Article in English | MEDLINE | ID: mdl-19365607

ABSTRACT

The field site network (FSN) plays a central role in conducting joint research within all Assessing Large-scale Risks for biodiversity with tested Methods (ALARM) modules and provides a mechanism for integrating research on different topics in ALARM on the same site for measuring multiple impacts on biodiversity. The network covers most European climates and biogeographic regions, from Mediterranean through central European and boreal to subarctic. The project links databases with the European-wide field site network FSN, including geographic information system (GIS)-based information to characterise the test location for ALARM researchers for joint on-site research. Maps are provided in a standardised way and merged with other site-specific information. The application of GIS for these field sites and the information management promotes the use of the FSN for research and to disseminate the results. We conclude that ALARM FSN sites together with other research sites in Europe jointly could be used as a future backbone for research proposals.


Subject(s)
Biodiversity , Europe , Risk Assessment
4.
Urologe A ; 48(9): 1025-6, 1028, 1030-1, 2009 Sep.
Article in German | MEDLINE | ID: mdl-19705097

ABSTRACT

In order to improve the detection of flat urothelial neoplasia an improvement in optical methods might be helpful. We investigated the use of confocal laser scanning microscopy in a pilot study of specimens with bladder cancer. A total of 35 fresh ex vivo specimens of 20 human bladders of patients who underwent radical cystectomy were examined with a modified confocal laser scanning microscope (670 nm). The field size was 200x200 microm and tissue was investigated up to depths of 120 microm. Resulting data sets were reconstructed three-dimensionally by computer software. Results were compared with conventional histology. Microscopically diseased bladder mucosa showed cytological and histological criteria of malignancy which were readily identifiable by laser scanning microscopy. In all cases we were able to detect the presence of malignancy with the images generated by the confocal laser scanning technique. Atypical cellular structures and subepithelial hypervascularization were prominent features. Carcinoma in situ lesions could also be identified in many cases. Confocal laser scanning microscopy allows the analysis of cellular and epithelial architecture of the urothelium in a detail which is beyond the limitations of conventional endoscopy by white light cystoscopy. Therefore, the principle would probably be of benefit if the technical limitations can be overcome.


Subject(s)
Image Interpretation, Computer-Assisted/methods , Microscopy, Confocal/methods , Urinary Bladder Neoplasms/pathology , Urothelium/pathology , Humans , Reproducibility of Results , Sensitivity and Specificity
5.
Zentralbl Chir ; 133(6): 525-30, 2008 Dec.
Article in German | MEDLINE | ID: mdl-19090426

ABSTRACT

The 11th coordinated population forecast of the German Federal Statistical Office shows that the number of children in the age group 0-15 is going to decrease considerably up to 2050. Depending on the assumptions, the number of children will decrease to 50-80% of today's level. There are only small regional differences in this development, i. e., all regions will be equally affected by the population decline. However, large cities and surrounding areas will face smaller reductions than other community types. The timing of the decline differs somewhat between the regions. An exception is the age group 10-15 in East Germany. After a strong reduction of births in the years after the reunification, birth rates have been rising since 1998, which will lead to a relative increase of that age group in the coming years. However, also in this age group, the number of children is going to decrease to 85% of today's level up to 2050. In parallel to the reductions in the young population, there will be a reduction in the frequency of diagnoses, whereby in a simplified "status quo" model, the amount of diagnoses will decrease in proportion to the number of the 0-15-year-olds.


Subject(s)
Hospitals, Pediatric/trends , Morbidity/trends , Adolescent , Child , Child, Preschool , Cross-Sectional Studies , Female , Forecasting , Germany , Health Services Needs and Demand/trends , Hospitals, Pediatric/statistics & numerical data , Humans , Infant , Male , Population Dynamics , Utilization Review/trends
6.
Trends Biochem Sci ; 32(12): 555-60, 2007 Dec.
Article in English | MEDLINE | ID: mdl-17980602

ABSTRACT

The sirtuins are a group of proteins linked to aging, metabolism and stress tolerance in several organisms. Among the many genes that have been shown to affect aging in model organisms, sirtuin genes are unique in that their activity level is positively correlated with lifespan (i.e. they are anti-aging genes). Sirtuins are a druggable class of enzymes (i.e. amenable to intervention by small molecules) that could have beneficial effects on a variety of human diseases. In view of the many functions of Sirtuin 1 (SIRT1) in cells, this review focuses on its role in regulating important aspects of mitochondrial biology. Mitochondria have been linked to aging, and also to diseases of aging. Thus, sirtuins might provide a key link between mitochondrial dysfunction, aging and metabolic disease.


Subject(s)
Aging/pathology , Sirtuins/physiology , Animals , Humans , Mice , Sirtuin 1
7.
Cytogenet Genome Res ; 107(3-4): 256-62, 2004.
Article in English | MEDLINE | ID: mdl-15467370

ABSTRACT

ATM, the protein product of the gene mutated in the human autosomal recessive disorder ataxia telangiectasia, is involved in detection of double strand breaks (DSBs) and is a key component of the damage surveillance network of cell cycle proteins. In somatic cells ATM phosphorylates many other proteins including p53, an important regulator of cell cycle control. Mice deficient for Atm are male sterile with arrest and apoptosis occurring at testis epithelial stage IV, which in normal spermatocytes corresponds to mid-pachynema. Unlike the situation in somatic cells, we find no evidence that disruption of the Trp53 (p53) gene, or its down-stream target Cdkn1a (p21/Cip1) results in even a partial rescue of the Atm defect.


Subject(s)
Cell Cycle Proteins/genetics , DNA-Binding Proteins/genetics , Meiosis , Mutation/genetics , Protein Serine-Threonine Kinases/genetics , Spermatocytes/cytology , Spermatocytes/metabolism , Tumor Suppressor Protein p53/genetics , Tumor Suppressor Proteins/genetics , Animals , Apoptosis , Ataxia Telangiectasia Mutated Proteins , Cell Cycle Proteins/metabolism , Cyclin-Dependent Kinase Inhibitor p21 , DNA-Binding Proteins/deficiency , DNA-Binding Proteins/metabolism , Female , Male , Mice , Protein Serine-Threonine Kinases/deficiency , Protein Serine-Threonine Kinases/metabolism , Rad51 Recombinase , Tumor Suppressor Protein p53/deficiency , Tumor Suppressor Protein p53/metabolism , Tumor Suppressor Proteins/deficiency , Tumor Suppressor Proteins/metabolism
8.
Phys Rev Lett ; 93(12): 126101, 2004 Sep 17.
Article in English | MEDLINE | ID: mdl-15447281

ABSTRACT

The local environment of Si atoms at the interface between a thermally grown SiO2 film and Si(100) was studied by angle-scanned photoelectron diffraction. Experimental photoelectron diffraction patterns for each Si oxidation state were obtained from the results of least squares fitting on Si 2p core-level spectra. A comparison of the diffraction patterns with multiple-scattering calculations including an R-factor analysis was performed. An excellent agreement between experimental and simulated data was achieved within the proposed bridge-bonded interface model [Phys. Rev. Lett. 84, 4393 (2000)]].

9.
Phys Rev Lett ; 86(18): 4068-71, 2001 Apr 30.
Article in English | MEDLINE | ID: mdl-11328097

ABSTRACT

Local environments of Si suboxides at the interface between a thermally grown SiO2 film and Si(111) were studied by angle-scanned photoelectron diffraction. Si 2p core-level spectra containing chemically shifted components were recorded. The components were deconvoluted by least squares fitting and assigned to different Si oxidation states. The obtained diffraction patterns of the various suboxides exhibit different features. Comparison of these patterns with multiple scattering calculations including a multipole R-factor analysis shows that a simple chemical abrupt interface model describes well the environment of the suboxides and indicates ordered SiO2 close to the interface.

10.
Plasmid ; 44(2): 196-200, 2000 Sep.
Article in English | MEDLINE | ID: mdl-10964630

ABSTRACT

A novel type I restriction-modification specificity subunit, S. LlaW12I, has been identified on the naturally occurring 8.0-kb plasmid pAW122 in the lactic acid bacterium Lactococcus lactis subsp. cremoris W12. Presence of the HsdS protein together with a complete type I restriction-modification system conferred increased phage restriction to the host, indicating exchange of specificity subunits. Sequence analysis showed that the S.LlaW12I subunit is most probably of type IC. Presumably, the hsdS gene is organized together with the repB gene on one transcriptional unit.


Subject(s)
Bacterial Proteins/genetics , DNA Restriction-Modification Enzymes/genetics , Lactococcus lactis/genetics , Plasmids/genetics , Amino Acid Sequence , Bacterial Proteins/chemistry , Bacteriophages/genetics , Consensus Sequence , DNA Methylation , DNA Restriction-Modification Enzymes/chemistry , Lactococcus lactis/enzymology , Lactococcus lactis/virology , Molecular Sequence Data , Sequence Alignment , Sequence Homology, Amino Acid
12.
Mol Cell Biol ; 19(7): 5096-105, 1999 Jul.
Article in English | MEDLINE | ID: mdl-10373558

ABSTRACT

A-T (ataxia telangiectasia) individuals frequently display gonadal atrophy, and Atm-/- mice show spermatogenic failure due to arrest at prophase of meiosis I. Chromosomal movements take place during meiotic prophase, with telomeres congregating on the nuclear envelope to transiently form a cluster during the leptotene/zygotene transition (bouquet arrangement). Since the ATM protein has been implicated in telomere metabolism of somatic cells, we have set out to investigate the effects of Atm inactivation on meiotic telomere behavior. Fluorescent in situ hybridization and synaptonemal complex (SC) immunostaining of structurally preserved spermatocytes I revealed that telomere clustering occurs aberrantly in Atm-/- mice. Numerous spermatocytes of Atm-/- mice displayed locally accumulated telomeres with stretches of SC near the clustered chromosome ends. This contrasted with spermatogenesis of normal mice, where only a few leptotene/zygotene spermatocytes I with clustered telomeres were detected. Pachytene nuclei, which were much more abundant in normal mice, displayed telomeres scattered over the nuclear periphery. It appears that the timing and occurrence of chromosome polarization is altered in Atm-/- mice. When we examined telomere-nuclear matrix interactions in spermatocytes I, a significant difference was observed in the ratio of soluble versus matrix-associated telomeric DNA sequences between meiocytes of Atm-/- and control mice. We propose that the severe disruption of spermatogenesis during early prophase I in the absence of functional Atm may be partly due to altered interactions of telomeres with the nuclear matrix and distorted meiotic telomere clustering.


Subject(s)
Ataxia Telangiectasia , Chromosome Aberrations , Meiosis/genetics , Protein Serine-Threonine Kinases , Proteins/physiology , Telomere , Animals , Ataxia Telangiectasia Mutated Proteins , Cell Cycle Proteins , DNA-Binding Proteins/genetics , Gene Expression , Male , Mice , Mice, Knockout , Nuclear Matrix , Prophase , Proteins/genetics , Spermatogenesis , Spermatozoa/cytology , Spermatozoa/physiology , Testis/metabolism , Tumor Suppressor Proteins
13.
Cell ; 96(5): 689-700, 1999 Mar 05.
Article in English | MEDLINE | ID: mdl-10089884

ABSTRACT

The neuroendocrine protein 7B2 has been implicated in activation of prohormone convertase 2 (PC2), an important neuroendocrine precursor processing endoprotease. To test this hypothesis, we created a null mutation in 7B2 employing a novel transposon-facilitated technique and compared the phenotypes of 7B2 and PC2 nulls. 7B2 null mice have no demonstrable PC2 activity, are deficient in processing islet hormones, and display hypoglycemia, hyperproinsulinemia, and hypoglucagonemia. In contrast to the PC2 null phenotype, these mice show markedly elevated circulating ACTH and corticosterone levels, with adrenocortical expansion. They die before 9 weeks of severe Cushing's syndrome arising from pituitary intermediate lobe ACTH hypersecretion. We conclude that 7B2 is indeed required for activation of PC2 in vivo but has additional important functions in regulating pituitary hormone secretion.


Subject(s)
Adrenocorticotropic Hormone/metabolism , Corticosterone/metabolism , Cushing Syndrome/etiology , Nerve Tissue Proteins/physiology , Pituitary Gland, Anterior/metabolism , Pituitary Hormones/physiology , Pituitary-Adrenal System/physiopathology , Subtilisins/biosynthesis , Adipose Tissue/pathology , Adrenocorticotropic Hormone/biosynthesis , Adrenocorticotropic Hormone/blood , Animals , Antigens, Differentiation, B-Lymphocyte/metabolism , Blood Glucose/analysis , Corticosterone/blood , Cushing Syndrome/physiopathology , Glucagon/deficiency , Histocompatibility Antigens Class II/metabolism , Hypoglycemia/etiology , Insulin/blood , Lipid Metabolism , Mice , Mice, Knockout , Mutagenesis, Insertional , Nerve Tissue Proteins/genetics , Neuroendocrine Secretory Protein 7B2 , Peptides/metabolism , Pituitary Hormones/genetics , Point Mutation , Pro-Opiomelanocortin/metabolism , Proprotein Convertase 2 , Protein Processing, Post-Translational , Subtilisins/deficiency
14.
Cancer Res ; 58(24): 5637-9, 1998 Dec 15.
Article in English | MEDLINE | ID: mdl-9865712

ABSTRACT

An unusual clinical finding in ataxia-telangiectasia, a human disorder caused by mutations in atm, is exquisite sensitivity to gamma irradiation. By contrast, homozygous deletion of p53 is marked by radiation resistance in certain tissue compartments. Previous studies (A. J. Levine, Cell, 88: 323-331, 1997) have shown that, in vitro, p53-deficient bone marrow cells are resistant to gamma irradiation. Furthermore, the gastrointestinal radiosensitization engendered by the loss of atm has recently been shown (C. H. Westphal et al., Nat. Genet., 16: 397-401, 1997) to be independent of p53. Expanding on previous work, we have looked at in vivo bone marrow resistance in p53-deficient mice. Our results indicate that inbred FVB strain p53 null mice survive lethal irradiation doses because of bone marrow resistance. Moreover, the deletion of atm radiosensitizes even p53 null bone marrow and mouse embryonic fibroblast cells. The results presented here argue that the loss of atm radiosensitizes multiple tissues in a p53-independent manner. Hence, functional inhibition of atm in p53 null and p53 wild-type human tumors may be a useful adjunct to gamma irradiation-based antitumor therapy.


Subject(s)
Gene Deletion , Genes, p53 , Protein Serine-Threonine Kinases , Proteins/genetics , Radiation Tolerance , Animals , Ataxia Telangiectasia Mutated Proteins , Bone Marrow/radiation effects , Cell Cycle Proteins , DNA-Binding Proteins , Fibroblasts/radiation effects , Heterozygote , In Vitro Techniques , Mice , Mice, Inbred Strains , Time Factors , Tumor Suppressor Proteins
15.
Nat Genet ; 16(4): 397-401, 1997 Aug.
Article in English | MEDLINE | ID: mdl-9241281

ABSTRACT

Mutations in atm and p53 cause the human cancer-associated diseases ataxia-telangiectasia and Li-Fraumeni syndrome, respectively. The two genes are believed to interact in a number of pathways, including regulation of DNA damage-induced cell-cycle checkpoints, apoptosis and radiation sensitivity, and cellular proliferation. Atm-null mice, as well as those null for p53, develop mainly T-cell lymphomas, supporting the view that these genes have similar roles in thymocyte development. To study the interactions of these two genes on an organismal level, we bred mice heterozygous for null alleles of both atm and p53 to produce all genotypic combinations. Mice doubly null for atm and p53 exhibited a dramatic acceleration of tumour formation relative to singly null mice, indicating that both genes collaborate in a significant manner to prevent tumorigenesis. With respect to their roles in apoptosis, loss of atm rendered thymocytes only partly resistant to irradiation-induced apoptosis, whereas additional loss of p53 engendered complete resistance. This implies that the irradiation-induced atm and p53 apoptotic pathways are not completely congruent. Finally-and in contrast to prior predictions-atm and p53 do not appear to interact in acute radiation toxicity, suggesting a separate atm effector pathway for this DNA damage response and having implications for the prognosis and treatment of human tumours.


Subject(s)
Apoptosis/genetics , Neoplasms, Experimental/genetics , Protein Serine-Threonine Kinases , Proteins/genetics , Radiation Tolerance/genetics , Tumor Suppressor Protein p53/genetics , Acute Disease , Animals , Ataxia Telangiectasia Mutated Proteins , Cell Cycle Proteins , Cells, Cultured , DNA-Binding Proteins , Dexamethasone/pharmacology , Female , Gene Deletion , Gene Expression Regulation , Humans , Male , Mice , Radiation Injuries , Thymus Gland/cytology , Thymus Gland/drug effects , Thymus Gland/radiation effects , Tumor Suppressor Proteins
16.
Curr Biol ; 7(7): 530-3, 1997 Jul 01.
Article in English | MEDLINE | ID: mdl-9210379

ABSTRACT

The conventional technique for targeted mutation of mouse genes entails placing a genomic DNA fragment containing the gene of interest into a vector for fine mapping, followed by cloning of two genomic arms around a selectable neomycin-resistance cassette in a vector containing thymidine kinase [1]; this generally requires 1-2 months of work for each construct. The single 'knock-out' construct is then transfected into mouse embryonic stem (ES) cells, which are subsequently subjected to positive selection (using G418 to select for neomycin-resistance) and negative selection (using FIAU to exclude cells lacking thymidine kinase), allowing the selection of cells which have undergone homologous recombination with the knockout vector. This approach leads to inactivation of the gene of interest [2]. Recently, an in vitro reaction was developed, on the basis of the yeast Ty transposon, as a useful technique in shotgun sequencing [3]. An artificial transposable element, integrase enzyme and the target plasmid are incubated together to engender transposition. The DNA is then purified, and subsequently electroporated into bacteria. The transposon and the target plasmid bear distinct antibiotic resistance markers (trimethoprim and ampicillin, respectively), allowing double selection for transposition events. In the present study, we have modified this system to allow the rapid, simultaneous generation of a palette of potential gene targeting constructs. Our approach led from genomic clone to completed construct ready for transfection in a matter of days. The results presented here indicate that this technique should also be applicable to the generation of gene fusion constructs [4-8], simplifying this technically demanding method.


Subject(s)
DNA Transposable Elements , Gene Targeting/methods , Nerve Tissue Proteins/genetics , Pituitary Hormones/genetics , Animals , Genetic Vectors , Mice , Mice, Knockout , Neuroendocrine Secretory Protein 7B2 , Transfection
17.
Cancer Res ; 57(9): 1664-7, 1997 May 01.
Article in English | MEDLINE | ID: mdl-9135004

ABSTRACT

Ataxia-telangiectasia and Li-Fraumeni syndrome, pleiotropic disorders caused by mutations in the genes atm and p53, share a marked increase in cancer rates. A number of studies have argued for an interaction between these two genes (for comprehensive reviews, see M. S. Meyn, Cancer Res., 55: 5991-6001, 1995, and M. F. Lavin and Y. Shiloh, Annu. Rev., Immunol., 15: 177-202, 1996). Specifically, atm is placed upstream of p53 in mediating G1-S cell cycle checkpoint control, and both atm and p53 are believed to influence cellular proliferation. To analyze the genetic interactions of atm and p53, mouse embryonic fibroblasts (MEFs) homozygously deficient for both atm and p53 were used to assess cell cycle and growth control. These double-null fibroblasts proliferate rapidly and fail to exhibit the premature growth arrest seen with atm-null MEFs. MEFs null for both atm and p53 do not express any p21(cipl/wafl), showing that p53 is required for p21(cipl/wafl) expression in an atm-null background. By contrast, homozygous loss of either atm, p53, or both results in similar abnormalities of the irradiation-induced G1-S cell cycle checkpoint. Our results suggest two separate pathways of interaction between atm and p53, one linear, involving G1-S cell cycle control, and another more complex, involving aspects of growth regulation.


Subject(s)
Cell Cycle , Cell Division , Protein Serine-Threonine Kinases , Proteins/genetics , Tumor Suppressor Protein p53/physiology , Animals , Ataxia Telangiectasia/physiopathology , Ataxia Telangiectasia Mutated Proteins , Cell Cycle/radiation effects , Cell Cycle Proteins , Cell Division/radiation effects , Cells, Cultured , Cyclin-Dependent Kinase Inhibitor p21 , Cyclins/metabolism , DNA-Binding Proteins , Fibroblasts , Gamma Rays , Mice , Mice, Knockout , Tumor Suppressor Proteins
18.
J Healthc Qual ; 19(2): 5-9, 1997.
Article in English | MEDLINE | ID: mdl-10166013

ABSTRACT

Families of patients in critical care experience extreme anxiety and frustration while awaiting their loved ones' recovery or stabilization. To study the hypothesis that meeting families' informational needs can reduce their anxiety and help them cope with the initial crisis, a small task force at a Midwest acute care facility, using a CQI approach, studied possible solutions. Initial findings showed low satisfaction for families of critically ill patients with the present system of imparting information to them. After initiation of a storyboard to present information by the critical care team, families reported increased satisfaction and greater knowledge recall.


Subject(s)
Coronary Care Units/standards , Family/psychology , Pamphlets , Professional-Family Relations , Anxiety , Consumer Behavior , Health Education , Humans , Mental Recall , Midwestern United States , Nursing Staff, Hospital , Organizational Innovation , Pilot Projects
19.
Curr Biol ; 7(12): R789-92, 1997 Dec 01.
Article in English | MEDLINE | ID: mdl-9382823

ABSTRACT

The discovery of multiple signaling cascades downstream of Atm may lead to a clearer understanding of the diverse defects seen in ataxia-telangiectasia. These pathways - which include evolutionarily conserved Chk1 and Atr, and non-conserved p21, p53 and AbI - guard genomic integrity after DNA damage.


Subject(s)
Cell Cycle , Protein Serine-Threonine Kinases , Proteins/metabolism , Signal Transduction , Animals , Ataxia Telangiectasia Mutated Proteins , Cell Cycle Proteins , Checkpoint Kinase 1 , Cyclin-Dependent Kinase Inhibitor p21 , Cyclins/genetics , Cyclins/metabolism , DNA-Binding Proteins , Gamma Rays , Humans , Phosphorylation , Protein Kinases/metabolism , Proteins/genetics , Proto-Oncogene Proteins c-abl/metabolism , Schizosaccharomyces , Schizosaccharomyces pombe Proteins , Tumor Suppressor Protein p53/genetics , Tumor Suppressor Protein p53/metabolism , Tumor Suppressor Proteins
20.
Curr Biol ; 7(12): 977-86, 1997 Dec 01.
Article in English | MEDLINE | ID: mdl-9382850

ABSTRACT

BACKGROUND: Checkpoint pathways prevent cell-cycle progression in the event of DNA lesions. Checkpoints are well defined in mitosis, where lesions can be the result of extrinsic damage, and they are critical in meiosis, where DNA breaks are a programmed step in meiotic recombination. In mitotic yeast cells, the Chk1 protein couples DNA repair to the cell-cycle machinery. The Atm and Atr proteins are mitotic cell-cycle proteins that also associate with chromatin during meiotic prophase I. The genetic and regulatory interaction between Atm and mammalian Chk1 appears to be important for integrating DNA-damage repair with cell-cycle arrest. RESULTS: We have identified structural homologs of yeast Chk1 in human and mouse. Chk1(Hu/Mo) has protein kinase activity and is expressed in the testis. Chk1 accumulates in late zygotene and pachytene spermatocytes and is present along synapsed meiotic chromosomes. Chk1 localizes along the unsynapsed axes of X and Y chromosomes in pachytene spermatocytes. The association of Chk1 with meiotic chromosomes and levels of Chk1 protein depend upon a functional Atm gene product, but Chk1 is not dependent upon p53 for meiosis I functions. Mapping of CHK1 to human chromosomes indicates that the gene is located at 11q22-23, a region marked by frequent deletions and loss of heterozygosity in human tumors. CONCLUSIONS: The Atm-dependent presence of Chk1 in mouse cells and along meiotic chromosomes, and the late pachynema co-localization of Atr and Chk1 on the unsynapsed axes of the paired X and Y chromosomes, suggest that Chk1 acts as an integrator for Atm and Atr signals and may be involved in monitoring the processing of meiotic recombination. Furthermore, mapping of the CHK1 gene to a region of frequent loss of heterozygosity in human tumors at 11q22-23 indicates that the CHK1 gene is a candidate tumor suppressor gene.


Subject(s)
Meiosis/physiology , Protein Kinases/physiology , Protein Serine-Threonine Kinases , Proteins/physiology , Recombination, Genetic/physiology , Amino Acid Sequence , Animals , Ataxia Telangiectasia Mutated Proteins , Base Sequence , Cell Cycle Proteins , Checkpoint Kinase 1 , Chromosomes/metabolism , DNA, Complementary , DNA-Binding Proteins , Gene Expression Regulation, Developmental , Humans , Male , Mammals , Meiosis/genetics , Mice , Mice, Knockout , Molecular Sequence Data , Protein Kinases/genetics , Proteins/genetics , Recombinant Fusion Proteins/genetics , Recombinant Fusion Proteins/metabolism , Testis/metabolism , Tumor Suppressor Proteins
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