Study protocol to investigate biomolecular muscle profile as predictors of long-term urinary incontinence in women with gestational diabetes mellitus

BACKGROUND

Pelvic floor muscles (PFM) and rectus abdominis muscles (RAM) of pregnant diabetic rats exhibit atrophy, co-localization of fast and slow fibers and an increased collagen type I/III ratio. However, the role of similar PFM or RAM hyperglycemic-related myopathy in women with gestational diabetes mellitus (GDM) remains poorly investigated. This study aims to assess the frequency of pelvic floor muscle disorders and pregnancy-specific urinary incontinence (PS-UI) 12 months after the Cesarean (C) section in women with GDM. Specifically, differences in PFM/RAM hyperglycemic myopathy will be evaluated.

METHODS

The Diamater is an ongoing cohort study of four groups of 59 pregnant women each from the Perinatal Diabetes Research Centre (PDRC), Botucatu Medical School (FMB)-UNESP (São Paulo State University), Brazil. Diagnosis of GDM and PS-UI will be made at 24-26 weeks, with a follow-up at 34-38 weeks of gestation. Inclusion in the study will occur at the time of C-section, and patients will be followed at 24-48 h, 6 weeks and 6 and 12 months postpartum. Study groups will be classified as (1) GDM plus PS-UI; (2) GDM without PS-UI; (3) Non-GDM plus PS-UI; and (4) Non-GDM without PS-UI. We will analyze relationships between GDM, PS-UI and hyperglycemic myopathy at 12 months after C-section. The mediator variables to be evaluated include digital palpation, vaginal squeeze pressure, 3D pelvic floor ultrasound, and 3D RAM ultrasound. RAM samples obtained during C-section will be analyzed for ex-vivo contractility, morphological, molecular and OMICS profiles to further characterize the hyperglycemic myopathy. Additional variables to be evaluated include maternal age, socioeconomic status, educational level, ethnicity, body mass index, weight gain during pregnancy, quality of glycemic control and insulin therapy.

DISCUSSION

To our knowledge, this will be the first study to provide data on the prevalence of PS-UI and RAM and PFM physical and biomolecular muscle profiles after C-section in mothers with GDM. The longitudinal design allows for the assessment of cause-effect relationships between GDM, PS-UI, and PFMs and RAMs myopathy. The findings may reveal previously undetermined consequences of GDM.

Neurological injury and death in all-terrain vehicle crashes in West Virginia: a 10-year retrospective review

OBJECTIVE

The purpose of this study was to profile all-terrain vehicle crash victims with neurological injuries who were treated at a Level I trauma center.

METHODS

We retrospectively reviewed trauma registry data for 238 patients who were admitted to the Jon Michael Moore Trauma Center at the West Virginia University School of Medicine after all-terrain vehicle crashes, between January 1991 and December 2000. Age, helmet status, alcohol and drug use, head injuries, length of stay, disposition, and hospital costs were studied. Death rates, head injuries, age, helmet use, and safety legislation in all 50 states were compared.

RESULTS

Eighty percent of victims were male, with an average age of 27.3 years. Only 22% of all patients were wearing helmets. Alcohol and/or drugs were involved in almost one-half of all incidents. Fifty-five of 238 patients sustained spinal axis injuries; only 5 were wearing helmets. One-third of victims (75 of 238 victims) were in the pediatric population, and only 21% were wearing helmets. Only 15% of victims less than 16 years of age were wearing helmets. There were a total of eight deaths; only one patient was wearing a helmet.

CONCLUSION

In the United States, all-terrain vehicles caused an estimated 240 deaths/yr between 1990 and 1994, which increased to 357 deaths/yr between 1995 and 2000. Brain and spine injuries occurred in 80% of fatal crashes. West Virginia has a fatality rate approximately eight times the national rate. Helmets reduce the risk of head injury by 64%, but only 21 states have helmet laws. Juvenile passengers on adult-driven vehicles are infrequently helmeted (<20%) and frequently injured (>65%). We conclude that safety legislation would save lives.

The cellular responses to DNA damage

The ability to survive spontaneous and induced DNA damage, and to minimize the number of heritable mutations that this causes, is essential to the maintenance of genome integrity for all organisms. Early studies on model eukaryotes focused on genes acting in defined DNA repair pathways. More recent work with the budding and fission yeasts and mammalian cells has started to integrate the DNA damage response with cell physiology and the cell cycle.

The evolution of diverse biological responses to DNA damage: insights from yeast and p53

The cellular response to ionizing radiation provides a conceptual framework for understanding how a yeast checkpoint system, designed to make binary decisions between arrest and cycling, evolved in a way as to allow reversible arrest, senescence or apoptosis in mammals. We propose that the diversity of responses to ionizing radiation in mammalian cells is possible because of the addition of a new regulatory control module involving the tumour-suppressor gene p53. We review the complex mechanisms controlling p53 activity and discuss how the p53 regulatory module enables cells to grow, arrest or die by integrating DNA damage checkpoint signals with the response to normal mitogenic signalling and the aberrant signalling engendered by oncogene activation.

Mrc1 transduces signals of DNA replication stress to activate Rad53

Cells experiencing DNA replication stress activate a response pathway that delays entry into mitosis and promotes DNA repair and completion of DNA replication. The protein kinases ScRad53 and SpCds1 (in baker's and fission yeast, respectively) are central to this pathway. We describe a conserved protein Mrc1, mediator of the replication checkpoint, required for activation of ScRad53 and SpCds1 during replication stress. mrc1 mutants are sensitive to hydroxyurea and have a checkpoint defect similar to rad53 and cds1 mutants. Mrc1 may be the replicative counterpart of Rad9 and Crb2, which are required for activating ScRad53 and Chk1 in response to DNA damage.

New insights into development from mitosis of a unicellular yeast

Studies in the fission yeast Schizosaccharomyces pombe have uncovered a new spindle checkpoint.

The G2-phase DNA-damage checkpoint

DNA damage causes cell-cycle delay before S phase, during replication and before mitosis. This involves a number of highly conserved proteins that sense DNA damage and signal the cell-cycle machinery. Kinases that were initially discovered in yeast model systems have recently been shown to regulate the regulators of cyclin-dependent kinases and to control the stability of p53. This shows the importance of checkpoint proteins for maintaining genome stability. Here, we discuss recent data from yeast and metazoans that suggest a remarkable conservation of the organization of the G2 DNA-damage checkpoint pathway.

Targeted disruption of the cell-cycle checkpoint gene ATR leads to early embryonic lethality in mice

Checkpoints of DNA integrity are conserved throughout evolution, as are the kinases ATM (Ataxia Telangiectasia mutated) and ATR (Ataxia- and Rad-related), which are related to phosphatidylinositol (PI) 3-kinase [1] [2] [3]. The ATM gene is not essential, but mutations lead to ataxia telangiectasia (AT), a pleiotropic disorder characterised by radiation sensitivity and cellular checkpoint defects in response to ionising radiation [4] [5] [6]. The ATR gene has not been associated with human syndromes and, structurally, is more closely related to the canonical yeast checkpoint genes rad3(Sp) and MEC1(Sc) [7] [8]. ATR has been implicated in the response to ultraviolet (UV) radiation and blocks to DNA synthesis [8] [9] [10] [11], and may phosphorylate p53 [12] [13], suggesting that ATM and ATR may have similar and, perhaps, complementary roles in cell-cycle control after DNA damage. Here, we report that targeted inactivation of ATR in mice by disruption of the kinase domain leads to early embryonic lethality before embryonic day 8.5 (E8.5). Heterozygous mice were fertile and had no aberrant phenotype, despite a lower ATR mRNA level. No increase was observed in the sensitivity of ATR(+/-) embryonic stem (ES) cells to a variety of DNA-damaging agents. Attempts to target the remaining wild-type ATR allele in heterozygous ATR(+/-) ES cells failed, supporting the idea that loss of both alleles of the ATR gene, even at the ES-cell level, is lethal. Thus, in contrast to the closely related checkpoint gene ATM, ATR has an essential function in early mammalian development.

Mik1 levels accumulate in S phase and may mediate an intrinsic link between S phase and mitosis

Two paradigms exist for maintaining order during cell-cycle progression: intrinsic controls, where passage through one part of the cell cycle directly affects the ability to execute another, and checkpoint controls, where external pathways impose order in response to aberrant structures. By studying the mitotic inhibitor Mik1, we have identified evidence for an intrinsic link between unperturbed S phase and mitosis. We propose a model in which S/M linkage can be generated by the production and stabilization of Mik1 protein during S phase. The production of Mik1 during unperturbed S phase is independent of the Rad3- and Cds1-dependent checkpoint controls. In response to perturbed S phase, Rad3-Cds1 checkpoint controls are required to maintain high levels of Mik1, probably indirectly by extending the S phase period, where Mik1 is stable. In addition, we find that Mik1 protein can be moderately induced in response to irradiation of G(2) cells in a Chk1-dependent manner.

Characterization of Schizosaccharomyces pombe Hus1: a PCNA-related protein that associates with Rad1 and Rad9

Hus1 is one of six checkpoint Rad proteins required for all Schizosaccharomyces pombe DNA integrity checkpoints. MYC-tagged Hus1 reveals four discrete forms. The main form, Hus1-B, participates in a protein complex with Rad9 and Rad1, consistent with reports that Rad1-Hus1 immunoprecipitation is dependent on the rad9(+) locus. A small proportion of Hus1-B is intrinsically phosphorylated in undamaged cells and more becomes phosphorylated after irradiation. Hus1-B phosphorylation is not increased in cells blocked in early S phase with hydroxyurea unless exposure is prolonged. The Rad1-Rad9-Hus1-B complex is readily detectable, but upon cofractionation of soluble extracts, the majority of each protein is not present in this complex. Indirect immunofluorescence demonstrates that Hus1 is nuclear and that this localization depends on Rad17. We show that Rad17 defines a distinct protein complex in soluble extracts that is separate from Rad1, Rad9, and Hus1. However, two-hybrid interaction, in vitro association and in vivo overexpression experiments suggest a transient interaction between Rad1 and Rad17.

The COP9/signalosome complex is conserved in fission yeast and has a role in S phase

The COP9/signalosome complex is conserved from plant to mammalian cells. In Arabidopsis, it regulates the nuclear abundance of COP1, a transcriptional repressor of photomorphogenic development [1] [2]. All COP (constitutive photomorphogenesis) mutants inappropriately express genes that are normally repressed in the dark. Eight subunits (Sgn1-Sgn8) of the homologous mammalian complex have been purified [3] [4]. Several of these have been previously identified through genetic or protein interaction screens. No coherent model for COP9/signalosome function has yet emerged, but a relationship with cell-cycle progression by transcriptional regulation, protein localisation or protein stability is possible. Interestingly, the COP9/signalosome subunits possess domain homology to subunits of the proteasome regulatory lid complex [5] [6]. Database searches indicate that only Sgn5/JAB1 is present in Saccharomyces cerevisiae, precluding genetic analysis of the complex in cell-cycle regulation. Here we identify a subunit of the signalosome in the fission yeast Schizosaccharomyces pombe through an analysis of the DNA-integrity checkpoint. We provide evidence for the conservation of the COP9/signalosome complex in fission yeast and demonstrate that it functions during S-phase progression.

A Rad3-Rad26 complex responds to DNA damage independently of other checkpoint proteins

The conserved PIK-related kinase Rad3 is required for all DNA-integrity-checkpoint responses in fission yeast. Here we report a stable association between Rad3 and Rad26 in soluble protein extracts. Rad26 shows Rad3-dependent phosphorylation after DNA damage. Unlike phosphorylation of Hus1, Crb2/Rhp9, Cds1 and Chk1, phosphorylation of Rad26 does not require other known checkpoint proteins. Rad26 phosphorylation is the first biochemical marker of Rad3 function, indicating that Rad3-related checkpoint kinases may have a direct role in DNA-damage recognition.

Requirement of sequences outside the conserved kinase domain of fission yeast Rad3p for checkpoint control

The fission yeast Rad3p checkpoint protein is a member of the phosphatidylinositol 3-kinase-related family of protein kinases, which includes human ATMp. Mutation of the ATM gene is responsible for the disease ataxia-telangiectasia. The kinase domain of Rad3p has previously been shown to be essential for function. Here, we show that although this domain is necessary, it is not sufficient, because the isolated kinase domain does not have kinase activity in vitro and cannot complement a rad3 deletion strain. Using dominant negative alleles of rad3, we have identified two sites N-terminal to the conserved kinase domain that are essential for Rad3p function. One of these sites is the putative leucine zipper, which is conserved in other phosphatidylinositol 3-kinase-related family members. The other is a novel motif, which may also mediate Rad3p protein-protein interactions.

Rad18 is required for DNA repair and checkpoint responses in fission yeast

To survive damage to the genome, cells must respond by activating both DNA repair and checkpoint responses. Using genetic screens in the fission yeast Schizosaccharomyces pombe, we recently isolated new genes required for DNA damage checkpoint control. We show here that one of these strains defines a new allele of the previously described rad18 gene, rad18-74. rad18 is an essential gene, even in the absence of extrinsic DNA damage. It encodes a conserved protein related to the structural maintenance of chromosomes proteins. Point mutations in rad18 lead to defective DNA repair pathways responding to both UV-induced lesions and, as we show here, double-stranded breaks. Furthermore, rad18p is required to maintain cell cycle arrest in the presence of DNA damage, and failure of this leads to highly aberrant mitoses. A gene encoding a BRCT-containing protein, brc1, was isolated as an allele-specific high-copy suppressor of rad18-74. brc1 is required for mitotic fidelity and for cellular viability in strains with rad18 mutations but is not essential for DNA damage responses. Mutations in rad18 and brc1 are synthetically lethal with a topoisomerase II mutant (top2-191), indicating that these proteins play a role in chromatin organization. These studies show a role for chromatin organization in the maintenance or activation of responses to DNA damage.

DNA structure checkpoint pathways in Schizosaccharomyces pombe

The response to DNA damage includes a delay to progression through the cell cycle to aid DNA repair. Incorrectly replicated chromosomes (replication checkpoint) or DNA damage (DNA damage checkpoint) delay the onset of mitosis. These checkpoint pathways detect DNA perturbations and generate a signal. The signal is amplified and transmitted to the cell cycle machinery. Since the checkpoint pathways are essential for genome stability, the related proteins which are found in all eukaryotes (from yeast to mammals) are expected to have similar functions to the yeast progenitors. This review article focuses on the function of checkpoint proteins in the model system Schizosaccharomyces pombe. Checkpoint controls in Saccharomyces cerevisiae and mammalian cells are mentioned briefly to underscore common or diverse features.

Analysis of Rad3 and Chk1 protein kinases defines different checkpoint responses

Eukaryotic cells respond to DNA damage and S phase replication blocks by arresting cell-cycle progression through the DNA structure checkpoint pathways. In Schizosaccharomyces pombe, the Chk1 kinase is essential for mitotic arrest and is phosphorylated after DNA damage. During S phase, the Cds1 kinase is activated in response to DNA damage and DNA replication blocks. The response of both Chk1 and Cds1 requires the six 'checkpoint Rad' proteins (Rad1, Rad3, Rad9, Rad17, Rad26 and Hus1). We demonstrate that DNA damage-dependent phosphorylation of Chk1 is also cell-cycle specific, occurring primarily in late S phase and G2, but not during M/G1 or early S phase. We have also isolated and characterized a temperature-sensitive allele of rad3. Rad3 functions differently depending on which checkpoint pathway is activated. Following DNA damage, rad3 is required to initiate but not maintain the Chk1 response. When DNA replication is inhibited, rad3 is required for both initiation and maintenance of the Cds1 response. We have identified a strong genetic interaction between rad3 and cds1, and biochemical evidence shows a physical interaction is possible between Rad3 and Cds1, and between Rad3 and Chk1 in vitro. Together, our results highlight the cell-cycle specificity of the DNA structure-dependent checkpoint response and identify distinct roles for Rad3 in the different checkpoint responses.

KEYWORDS

ATM/ATR/cell-cycle checkpoints/Chk1/Rad3

Cloning of caf1+, caf2+ and caf4+ from Schizosaccharomyces pombe: their involvement in multidrug resistance, UV and pH sensitivity

We previously identified four nuclear genes (caf1+ to caf4+) in Schizosaccharomyces pombe, mutations in which can confer caffeine resistance. Here we report the cloning and sequencing of caf1+, caf2+ and caf4+. All three genes are allelic to genes (hba1+, crm1+ and trr1+, respectively) involved in multidrug resistance mechanisms or in stress response systems. In agreement with this the caffeine-resistant mutants caf1(hba1)-21, caf2(crm1)-3 and caf4(trr1)-83 are also resistant to brefeldin. Disruption of caf1(hba1)+ and caf4(trr1)+ makes cells sensitive to high pH. The overlapping ranges of pleiotropic effects and the genetic interaction detected between caf1(hba1)+ and caf2(crm1)+ suggest that the three genes function in interlinked systems.

1st MRC Human Genetics Symposium: maintenance of genomic stability

This meeting served to juxtapose the fundamental studies on the distinct pathways which maintain genomic stability with work that addresses the phenotypic consequences of loss of genomic stability in humans. This created an exciting environment where we were prompted to think about the links between fundamental and applied research. It was also a forum where new ideas could be formed that will hopefully fuel interesting research in human disease. As we place the genome projects into perspective, the ideas arising from meetings such as the 1st MRC Human Genetics Symposium might be expected to guide studies that will reveal the molecular defects which underlie some of the more impenetrable phenotypes of human diseases.

Vectors for the expression of tagged proteins in Schizosaccharomyces pombe

A series of vectors is described which enables the episomal expression of proteins fused to different tag sequences in Schizosaccharomyces pombe. Proteins can be expressed with their amino termini fused to GFP/EGFP, three copies of the HA or Pk epitopes or a combined tag which contains two copies of the myc epitope and six histidine residues (MH). Fusion of the carboxyl terminus of a protein to a tag is possible with GFP/EGFP or Pk. Expression of the fusion proteins is controlled by the medium strength mutant version of the regulatable nmt1 promoter.

Splitting the ATM: distinct repair and checkpoint defects in ataxia-telangiectasia

Ataxia-telangiectasia (A-T) is an autosomal recessive human disorder that, because of its multisystem nature, is of interest to scientists and clinicians from many disciplines. A-T patients have defects in the neurological and immune systems, telangiectasia in the eyes and face, and are, in addition, cancer-prone and radiation-sensitive. A-T cell lines have a range of diverse phenotypes including sensitivity to ionizing radiation and defects in cell-cycle checkpoint control. The ATM protein is a member of the PI 3-kinase-like superfamily, and it has been widely accepted that A-T cells represent mammalian cell-cycle checkpoint mutants and that the radiation sensitivity is a consequence of this defect. However, several lines of evidence suggest that A-T cells have distinct repair and checkpoint defects. A-T cells therefore appear to harbour dual checkpoint/repair defects. Here, we review the evidence supporting this contention and consider its implications for an analysis of the A-T phenotype.

Protein kinase mutants of human ATR increase sensitivity to UV and ionizing radiation and abrogate cell cycle checkpoint control

In fission yeast, the rad3 gene product plays a critical role in sensing DNA structure defects and activating damage response pathways. A structural homologue of rad3 in humans (ATR) has been identified based on sequence similarity in the protein kinase domain. General information regarding ATR expression, protein kinase activity, and cellular localization is known, but its function in human cells remains undetermined. In the current study, the ATR protein was examined by gel filtration of protein extracts and was found to exist predominantly as part of a large protein complex. A kinase-inactivated form of the ATR gene was prepared by site-directed mutagenesis and was used in transfection experiments to probe the function of this complex. Introduction of this kinase-dead ATR into a normal fibroblast cell line, an ATM-deficient fibroblast line derived from a patient with ataxia-telangiectasia, or a p53 mutant cell line all resulted in significant losses in cell viability. Clones expressing the kinase-dead ATR displayed increased sensitivity to x-rays and UV and a loss of checkpoint control. We conclude that ATR functions as a critical part of a protein complex that mediates responses to ionizing and UV radiation in human cells. These responses include effects on cell viability and cell cycle checkpoint control.

Effect of ranitidine on the pharmacokinetics of orally administered eprosartan, an angiotensin II antagonist, in healthy male volunteers

OBJECTIVE

To assess the effect of ranitidine on the pharmacokinetics of eprosartan in healthy male volunteers.

DESIGN

Single-center, randomized, open-label, two-period, period-balanced, crossover study.

PATIENTS

Seventeen healthy men aged 19 to 43 years.

INTERVENTION

In each period (separated by a > or = 7 d washout), subjects received a single 400-mg oral dose of eprosartan alone, or a single oral dose of eprosartan 400 mg and ranitidine 150 mg on day 4 after 3 days of ranitidine 150 mg twice daily. Serial pharmacokinetic samples were obtained for up to 24 hours following eprosartan dosing.

MAIN OUTCOME MEASURES

Plasma and urine eprosartan concentrations during each treatment session.

RESULTS

Eprosartan maximum concentration (Cmax), the AUC from time-zero to the last quantifiable concentration (AUC0-t), and renal clearance (Cl(r)) values were approximately 7%, 11%, and 4% lower, respectively, when administered with ranitidine compared with eprosartan alone. The 95% CIs for the ratio of eprosartan plus ranitidine compared with eprosartan alone were 0.81 to 1.07, 0.77 to 1.03, and 0.64 to 1.43, for Cmax, AUC0-t, and Cl(r), respectively, indicating no statistically significant difference between regimens.

CONCLUSIONS

Repeated doses of ranitidine did not have a marked effect on the single-dose pharmacokinetics of eprosartan.

S-phase-specific activation of Cds1 kinase defines a subpathway of the checkpoint response in Schizosaccharomyces pombe

Checkpoints that respond to DNA structure changes were originally defined by the inability of yeast mutants to prevent mitosis following DNA damage or S-phase arrest. Genetic analysis has subsequently identified subpathways of the DNA structure checkpoints, including the reversible arrest of DNA synthesis. Here, we show that the Cds1 kinase is required to slow S phase in the presence of DNA-damaging agents. Cds1 is phosphorylated and activated by S-phase arrest and activated by DNA damage during S phase, but not during G1 or G2. Activation of Cds1 during S phase is dependent on all six checkpoint Rad proteins, and Cds1 interacts both genetically and physically with Rad26. Unlike its Saccharomyces cerevisiae counterpart Rad53, Cds1 is not required for the mitotic arrest checkpoints and, thus, defines an S-phase specific subpathway of the checkpoint response. We propose a model for the DNA structure checkpoints that offers a new perspective on the function of the DNA structure checkpoint proteins. This model suggests that an intrinsic mechanism linking S phase and mitosis may function independently of the known checkpoint proteins.

Role of Schizosaccharomyces pombe RecQ homolog, recombination, and checkpoint genes in UV damage tolerance

The cellular responses to DNA damage are complex and include direct DNA repair pathways that remove the damage and indirect damage responses which allow cells to survive DNA damage that has not been, or cannot be, removed. We have identified the gene mutated in the rad12.502 strain as a Schizosaccharomyces pombe recQ homolog. The same gene (designated rqh1) is also mutated in the hus2.22 mutant. We show that Rqhl is involved in a DNA damage survival mechanism which prevents cell death when UV-induced DNA damage cannot be removed. This pathway also requires the correct functioning of the recombination machinery and the six checkpoint rad gene products plus the Cdsl kinase. Our data suggest that Rqh1 operates during S phase as part of a mechanism which prevents DNA damage causing cell lethality. This process may involve the bypass of DNA damage sites by the replication fork. Finally, in contrast with the reported literature, we do not find that rqh1 (rad12) mutant cells are defective in UV dimer endonuclease activity.

Atm-dependent interactions of a mammalian chk1 homolog with meiotic chromosomes

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.

DNA structure-dependent checkpoints in model systems

DNA structure dependent checkpoints require a number of proteins which function to arrest the cell cycle in response to DNA damage (such as UV induced lesions) or blocks to DNA replication. Analogous to a signal transduction pathway, checkpoints communicate information between a DNA lesion and the cell cycle machinery. This brief review will focus on yeast model systems which have been instrumental in identifying the various components (initiating signal, detection, signal transduction and cell cycle effector) of the checkpoint pathways. The biological significance of these pathways in mammalian cells is illustrated in patients with ataxia telangiectasia (AT), a multi-system cancer-prone disorder in which DNA damage checkpoints affecting both DNA replication and mitosis are lost. ATM, the gene mutated in this disorder is structurally related to the yeast rad3/MEC1 checkpoint genes. This demonstrates the high degree of evolutionary conservation of checkpoints amongst eukaryotic organisms.

Characterisation of the Schizosaccharomyces pombe rad4/cut5 mutant phenotypes: dissection of DNA replication and G2 checkpoint control function

Mutation of the essential Schizosaccharomyces pombe rad4/cut5 gene causes sensitivity to UV and ionising radiation at the permissive temperature whilst at the restrictive temperature cells fail to undergo DNA replication but still attempt mitosis owing to a defective S-phase checkpoint response. Many mutations in genes encoding DNA replication proteins also abolish checkpoint responses, possibly because the replication machinery is a pre-requisite for the generation of the signal. We demonstrate here that rad4/cut5 cells fail to arrest cell division when treated with the replication inhibitor hydroxyurea at the semi-permissive temperature 32 degrees C, but retain essentially normal replicative capacity. This demonstrates that the replication and checkpoint function of the rad4/cut5 gene product can be separated and that the Rad4 protein differs from other replication proteins in being directly involved in generating the S-phase checkpoint signal. Furthermore, we have investigated the checkpoint response or rad4/cut5-deficient cells to gamma-irradiation and UV-mimetic drugs. We find that, at the restrictive temperature, the rad4-/cut5- cells fail to delay mitosis in response to gamma-irradiation whilst retaining a normal checkpoint response to the UV-mimetic drug 4-nitroquinoline-1-oxide. The lack of the gamma-irradiation checkpoint is reminiscent of the deficiency associated with mutation of the human ATM locus, the causative deficiency of the heritable disorder ataxia telangiectasia. The implications of our results for the organisation of distinct checkpoint-response pathways in both fission yeast and mammalian cells are discussed. Moreover the data are consistent with a model in which the generation of the S-Phase checkpoint signal is DNA polymerase epsilon dependent.

Caffeine-resistance in S. pombe: mutations in three novel caf genes increase caffeine tolerance and affect radiation sensitivity, fertility, and cell cycle

Caffeine is a well known base analogue and is cytotoxic to both animal and yeast cells. There are two possible mechanisms by which yeast cells tolerate caffeine concentrations higher than normal, by mutation or by physiological adaptation. We have isolated novel caffeine-resistant mutants of S. pombe which define three distinct genes caf2, caf3 and caf4. These mutants achieved a level of caffeine resistance which is presumed to represent the upper limit attainable by mutation. The caf2-caf4 mutations, as well as the previously identified caf1 mutation, confer UV-sensitivity, caffeine-resistant UV repair, impaired fertility and sporulation, as well as a lengthened cell cycle. They are partially dominant for caffeine resistance and recessive for UV sensitivity. Some auxotrophic caf3-89 double mutants show drastically decreased caffeine resistance. The caf4 mutant is more resistant to gamma-radiation than wild-type cells and shows pH-sensitive growth. As each caf mutation can, individually, confer maximum caffeine resistance to the cells, all four genes are expected to operate in the same pathway. This pathway might also be responsible for the physiological adaptation since adaptation is lost in caf1-caf4 mutants.

rqh1+, a fission yeast gene related to the Bloom's and Werner's syndrome genes, is required for reversible S phase arrest

In eukaryotic cells, S phase can be reversibly arrested by drugs that inhibit DNA synthesis or DNA damage. Here we show that recovery from such treatments is under genetic control and is defective in fission yeast rqh1 mutants. rqh1+, previously known as hus2+, encodes a putative DNA helicase related to the Escherichia coli RecQ helicase, with particular homology to the gene products of the human BLM and WRN genes and the Saccharomyces cerevisiae SGS1 gene. BLM and WRN are mutated in patients with Bloom's syndrome and Werner's syndrome respectively. Both syndromes are associated with genomic instability and cancer susceptibility. We show that, like BLM and SGS1, rqh1+ is required to prevent recombination and that in fission yeast suppression of inappropriate recombination is essential for reversible S phase arrest.

The Schizosaccharomyces pombe rad11+ gene encodes the large subunit of replication protein A

Replication protein A (RPA) is a heterotrimeric single-stranded DNA-binding protein present in all eukaryotes. In vitro studies have implicated RPA in simian virus 40 DNA synthesis and nucleotide excision repair, but little direct information is available about the in vivo roles of the protein. We report here the cloning of the largest subunit of RPA (rpa1+) from the fission yeast Schizosaccharomyces pombe. The rpa1+ gene is essential for viability and is expressed specifically at S phase of the cell cycle. Genetic analysis revealed that rpa1+ is the locus of the S. pombe radiation-sensitive mutation rad11. The rad11 allele exhibits pleiotropic effects consistent with an in vivo role for RPA in both DNA repair and DNA synthesis. The mutant is sensitive to both UV and ionizing radiation but is not defective in the DNA damage-dependent checkpoint, consistent with the hypothesis that RPA is part of the enzymatic machinery of DNA repair. When incubated in hydroxyurea, rad11 cells initially arrest with a 1C DNA content but then lose viability coincident with reentry into S phase, suggesting that DNA synthesis is aberrant under these conditions. A significant fraction of the mutant cells subsequently undergo inappropriate mitosis in the presence of hydroxyurea, indicating that RPA also plays a role in the checkpoint mechanism that monitors the completion of S phase. We propose that RPA is required to maintain the integrity of replication complexes when DNA replication is blocked. We further suggest that the rad11 mutation leads to the premature breakdown of such complexes, thereby preventing recovery from the hydroxyurea arrest and eliminating a signal recognized by the S-phase checkpoint mechanism.

Molecular analysis of hus1+, a fission yeast gene required for S-M and DNA damage checkpoints

The structure of hus1+, a Schizosaccharomyces pombe gene required for S-M and DNA damage checkpoints, has been determined. Expression of hus1+ requires splicing of five exons, including a microexon that is only 13 nucleotides long. hus1+ is predicted to encode a 33 kDa protein with no similarity to sequences in any database, including the entire S. cerevisiae genome. Yeast strains disrupted for the hus1+ gene are viable but checkpoint-defective. Polyclonal antibodies were raised against bacterially expressed Hus1 protein, and used to study Hus1 regulation. Hus1 protein levels are not affected by S-phase arrest, and are not altered by mutations in other checkpoint genes, suggesting that Hus1 is not regulated at the transcriptional or translational levels.

Control of cell cycle arrest by the Mec1sc/Rad3sp DNA structure checkpoint pathway

The Mec1(sc)/Rad3(sp) protein family is central to the checkpoint pathways of cells. Functions upstream and downstream of Mec1(sc)/Rad3(sp) show both similarities and differences when compared between organisms. Analogy with a related protein, DNAPKcs, suggests that different subunits may activate Mec1(sc)/Rad3(sp) in response to specific DNA or DNA-protein structures.

The Schizosaccharomyces pombe rad3 checkpoint gene

The rad3 gene of Schizosaccharomyces pombe is required for checkpoint pathways that respond to DNA damage and replication blocks. We report the complete rad3 gene sequence and show that rad3 is the homologue of Saccharomyces cerevisiae ESR1 (MEC1/SAD3) and Drosophila melanogaster mei-41 checkpoint genes. This establishes Rad3/Mec1 as the only conserved protein which is required for all the DNA structure checkpoints in both yeast model systems. Rad3 is an inessential member of the 'lipid kinase' subclass of kinases which includes the ATM protein defective in ataxia telangiectasia patients. Mutational analysis indicates that the kinase domain is required for Rad3 function, and immunoprecipitation of overexpressed Rad3 demonstrates an associated protein kinase activity. The previous observation that rad3 mutations can be rescued by a truncated clone lacking the kinase domain may be due to intragenic complementation. Consistent with this, biochemical data suggest that Rad3 exists in a complex containing multiple copies of Rad3. We have identified a novel human gene (ATR) whose product is closely related to Rad3/Esr1p/Mei-41. ATR can functionally complement esr1-1 radiation sensitivity in S. cerevisiae. Together, the structural conservation and functional complementation suggest strongly that the mechanisms underlying the DNA structure checkpoints are conserved throughout evolution.

The Atr and Atm protein kinases associate with different sites along meiotically pairing chromosomes

A number of cell-cycle checkpoint genes have been shown to play important roles in meiosis. We have characterized the human and mouse counterpart of the Schizosaccharomyces pombe Rad3 protein, named Atr (for ataxia-telangiectasia- and rad3-related), and the protein that is mutated in ataxia-telangiectasia, Atm. We demonstrate that ATR mRNA and protein are expressed in human and mouse testis. More detailed analysis of specific cells in seminiferous tubules shows localization of Atr to the nuclei of cells in the process of meiosis I. Using immunoprecipitation and immunoblot analysis, we show that Atr and Atm proteins are approximately 300 and 350 kD relative molecular mass, respectively, and further demonstrate that both proteins have associated protein kinase activity. Further, we demonstrate that Atr and Atm interact directly with meiotic chromosomes and show complementary localization patterns on synapsing chromosomes. Atr is found at sites along unpaired or asynapsed chromosomal axes, whereas Atm is found along synapsed chromosomal axes. This is the first demonstration of a nuclear association of Atr and Atm proteins with meiotic chromosomes and suggests a direct role for these proteins in recognizing and responding to DNA strand interruptions that occur during meiotic recombination.

Co-expression of steroid hormone receptors in opioid peptide-containing neurons correlates with patterns of gene expression during the estrous cycle

The anteroventral periventricular nucleus (AVPV) of the preoptic region represents an essential component of neural pathways regulating gonadotropin secretion, and contains sexually dimorphic populations of neurons that express dynorphin or enkephalin. In the present study we used in situ hybridization to measure prodynorphin (PDYN) and proenkephalin (PENK) mRNA in the AVPV of intact animals killed on each day of the cycle. Levels of PDYN mRNA were lowest in animals killed on the afternoon of proestrus and then increased by over 60% by the morning of the following day. Expression of PENK mRNA was generally stable during the cycle, but a small yet significant reduction was detected on proestrus relative to levels of PENK mRNA in animals killed on the day of diestrus. In addition, we used double in situ hybridization to demonstrate that the majority of PDYN mRNA-containing neurons express both estrogen (50%) and progesterone receptor (85%) mRNAs. Only one quarter of the PENK-containing neurons also co-express estrogen receptor mRNA, and fewer than 10% of the PENK mRNA neurons express PR mRNA. Thus, the differential expression of PDYN and PENK during the cycle generally correlates with distinct differences in the degree of colocalization of ER and PR mRNA in PDYN and PENK mRNA-containing neurons in the AVPV.

Ovarian steroid regulation of estrogen and progesterone receptor messenger ribonucleic acid in the anteroventral periventricular nucleus of the rat

The anteroventral periventricular nucleus of the preoptic region (AVPV) represents a key site for hormonal feedback on gonadotropin secretion. It plays a critical role in the neural control of luteinizing hormone secretion and contains high densities of neurons that express receptors for estrogen and progesterone. In this study in situ hybridization was used to examine the expression of mRNAs encoding the estrogen (ER) and progesterone (PR) receptors in the AVPV during the estrous cycle. ER gene expression fluctuated during the cycle with the lowest levels of ER mRNA observed in animals killed on the afternoon of proestrus, and the highest levels present in animals killed during metestrus. This apparent inverse relationship between circulating levels of estradiol (E2) and ER mRNA levels in AVPV neurons was supported by the observation that treatment of ovariectomized rats with E2 suppressed expression of ER mRNA in the AVPV. The influence of progesterone (P4) on ER expression was less pronounced, but a significant increase in ER mRNA in the AVPV was detected 3 h after treatment with P4. In contrast, PR mRNA levels were highest in the AVPV during diestrus and lowest on the morning of proestrus suggesting that PR expression in the AVPV is regulated in a complex manner that may reflect the combined regulatory effects of E2 and P4. E2 treatment caused a dramatic induction of PR mRNA in the AVPV, but P4 did not affect PR mRNA expression acutely, although PR mRNA appears to be attenuated in the AVPV 27 h after P4 treatment. These findings suggest that ovarian steroid hormones regulate ER and PR gene expression in the AVPV during the estrous cycle, which may represent molecular events that contribute to cyclic changes in the responsiveness of AVPV neurons to steroid hormones.

Isolation of the Schizosaccharomyces pombe RAD54 homologue, rhp54+, a gene involved in the repair of radiation damage and replication fidelity

The RAD54 gene of Saccharomyces cerevisiae encodes a putative helicase, which is involved in the recombinational repair of DNA damage. The RAD54 homologue of the fission yeast Schizosaccharomyces pombe, rhp54+, was isolated by using the RAD54 gene as a heterologous probe. The gene is predicted to encode a protein of 852 amino acids. The overall homology between the mutual proteins of the two species is 67% with 51% identical amino acids and 16% similar amino acids. A rhp54 deletion mutant is very sensitive to both ionizing radiation and UV. Fluorescence microscopy of the rhp54 mutant cells revealed that a large portion of the cells are elongated and occasionally contain aberrant nuclei. In addition, FACS analysis showed an increased DNA content in comparison with wild-type cells. Through a minichromosome-loss assay it was shown that the rhp54 deletion mutant has a very high level of chromosome loss. Furthermore, the rhp54 mutation in either a rad17 or a cdc2.3w mutant background (where the S-phase/mitosis checkpoint is absent) shows a significant reduction in viability. It is hypothesized that the rhp54+ gene is involved in the recombinational repair of UV and X-ray damage and plays a role in the processing of replication-specific lesions.

The rad18 gene of Schizosaccharomyces pombe defines a new subgroup of the SMC superfamily involved in DNA repair

The rad18 mutant of Schizosaccharomyces pombe is very sensitive to killing by both UV and gamma radiation. We have cloned and sequenced the rad18 gene and isolated and sequenced its homolog from Saccharomyces cerevisiae, designated RHC18. The predicted Rad18 protein has all the structural properties characteristic of the SMC family of proteins, suggesting a motor function--the first implicated in DNA repair. Gene deletion shows that both rad18 and RHC18 are essential for proliferation. Genetic and biochemical analyses suggest that the product of the rad18 gene acts in a DNA repair pathway for removal of UV-induced DNA damage that is distinct from classical nucleotide excision repair. This second repair pathway involves the products of the rhp51 gene (the homolog of the RAD51 gene of S. cerevisiae) and the rad2 gene.

Fission yeast rad17: a homologue of budding yeast RAD24 that shares regions of sequence similarity with DNA polymerase accessory proteins

Following DNA damage or a block to DNA synthesis, checkpoint pathways act to arrest mitosis and prevent the attempted segregation of damaged or unreplicated DNA. The rad17 locus of Schizosaccharomyces pombe is one of seven known radiation-sensitive (rad) loci which are absolutely required to prevent mitosis following DNA damage in fission yeast. Six of these (rad1, rad3, rad9, rad17, rad26 and hus1) are also required for the checkpoint which prevents mitosis from occurring before DNA replication is complete. We report here that the predicted rad17 gene product is a basic hydrophilic protein of 606 amino acids which contains five domains with sequence homology to replication factor C (RF-C)/activator 1 subunits. Western analysis and fusion with Green Fluorescent Protein indicate that the abundance and electrophoretic mobility of Rad17 is not significantly modified following a block to DNA synthesis or following DNA damage, and that Rad17 is localized in the nucleus. Rad17 function is not essential for growth, but is required for the function of the DNA structure-dependent checkpoints. Site-directed mutagenesis has been used to demonstrate the biological significance of the RF-C/activator 1-related domains. These studies have also defined an element of the radiation sensitivity caused by loss of Rad17 function which is not associated with the radiation-induced G2 arrest defect seen in the rad17.d null mutant cells.

The chk1 pathway is required to prevent mitosis following cell-cycle arrest at 'start'

BACKGROUND

The G2-M-phase transition is controlled by cell-cycle checkpoint pathways which inhibit mitosis if previous events are incomplete or if the DNA is damaged. Genetic analyses in yeast have defined two related, but distinct, pathways which prevent mitosis--one which acts when S phase is inhibited, and one which acts when the DNA is damaged. In the fission yeast Schizosaccharomyces pombe, many of the gene products involved have been identified. Six 'radiation checkpoint' (rad) gene products are required for both the S-M and DNA-damage checkpoints, whereas Chk1, a putative protein kinase, is required only for the DNA-damage checkpoint and not for the S-M checkpoint following the inhibition of DNA synthesis.

RESULTS

We have genetically defined a third mitotic control checkpoint pathway in fission yeast which prevents mitosis when passage through 'start' (the commitment point in G1) is compromized. In cycling cells arrested at start, mitosis is prevented by a Chk1-dependent pathway. In the absence of Chk1, G1 cells attempt an abortive mitosis with a 1C DNA content without entering S phase. Similar results are seen in the absence of Rad17, a typical example of a rad gene product.

CONCLUSIONS

Genetic dissection of checkpoints in logarithmically growing fission yeast has identified a pathway that couples mitosis to correct passage through start. This pathway is related to the DNA-structure check-points which ensure that mitosis is dependent on the completion of replication and the integrity of the DNA. We propose that all three mitotic control checkpoints monitor distinct DNA or protein structures at different stages in the cell cycle.

U.v.-hypermutability of xeroderma pigmentosum cells demonstrated with a DNA-based mutation system

We have developed a DNA-based system, to detect mutations at restriction sites without any selection in culture. DNA is exhaustively digested with a restriction enzyme. Primers flanking a chosen site for this enzyme are used in the polymerase chain reaction (PCR). Only DNA molecules mutated at the chosen site are resistant to digestion and can serve as templates for the PCR. We have initially used this system to demonstrate the generation of mutations by ethyl methanesulphonate (EMS) at a TaqI site in the aprt gene of Chinese hamster cells, and by u.v.-C irradiation at a TaqI site in the hprt gene of human fibroblasts. In repair-deficient xeroderma pigmentosum (XP) cells the u.v.-induced mutant frequency was greatly enhanced. We have been able to detect and analyse mutations in XP cells at TaqI sites in three different genes, hprt, p53 and c-Ha-ras1. Both u.v.-C and u.v.-B irradiation have been used as mutagenic agents with both lymphoblastoid and fibroblast cells from XP patients from complementation group G. The mutant DNA molecules have been sequenced. Following u.v.-C-irradiation, the majority of mutations analysed were GC-->AT transitions, but several double and tandem mutations were also found.