Versatile action of Escherichia coli ClpXP as protease or molecular chaperone for bacteriophage Mu transposition

The molecular chaperone ClpX of Escherichia coli plays two distinct functions for bacteriophage Mu DNA replication by transposition. As specificity component of a chaperone-linked protease, it recognizes the Mu immunity repressor for degradation by the peptidase component ClpP, thus derepressing Mu transposition functions. After strand exchange has been promoted by MuA transposase, ClpX alone can alter the conformation of the transpososome (the complex of MuA with Mu ends), and the remodeled MuA promotes transition to replisome assembly. Although ClpXP can degrade MuA, the presence of both ClpP and ClpX in the reconstituted transposition system did not destroy MuA essential for initiation of DNA replication by specific host replication enzymes. Levels of ClpXP needed to overcome inhibition by the repressor did not prevent MuA from promoting strand transfer, and ClpP stimulated alteration of the transpososome by ClpX. Apparently intact MuA was still present in the resulting transpososome, promoting initiation of Mu DNA replication by specific replication enzymes. The results indicate that ClpXP can discriminate repressor and MuA in the transpososome as substrates of the protease or the molecular chaperone alone, degrading repressor while remodeling MuA for its next critical function.

Ion channel mutations in mouse models of inherited neurological disease

Analysis of the molecular defects in mouse mutants can identify candidate genes for human neurological disorders. During the past 2 years, mutations in sodium channels, calcium channels and potassium channels have been identified by positional cloning of the spontaneous mouse mutants motor endplate disease, tottering, lethargic and weaver. The phenotypes of four allelic mutations identified in the sodium channel gene Scn8a range from ataxia and muscle weakness through severe dystonia and progressive paralysis, indicating that human mutations in this gene could be associated with a variety of clinical syndromes. Mutations of the calcium channel subunits beta 4 in the lethargic mouse and alpha 1A in the tottering mouse have specific effects on cerebellar function. Targeted mutation of ligand-gated ion channels has also been used to generate new models of neurological disease. We will review these recent achievements and their implications for human neurological disease. The mouse studies indicate that mutations in ion channel genes are likely to be responsible for a broad spectrum of clinical phenotypes in human neurological disorders.

The phiX174-type primosome promotes replisome assembly at the site of recombination in bacteriophage Mu transposition

Initiation of Escherichia coli DNA synthesis primed by homologous recombination is believed to require the phiX174-type primosome, a mobile priming apparatus assembled without the initiator protein DnaA. We show that this primosome plays an essential role in bacteriophage Mu DNA replication by transposition. Upon promoting transfer of Mu ends to target DNA, the Mu transpososome undergoes transition to a pre-replisome that permits initiation of DNA synthesis only in the presence of primosome assembly proteins PriA, DnaT, DnaB and DnaC. These assembly proteins promote the engagement of primase and DNA polymerase III holoenzyme, initiating semi-discontinuous replication preferentially at the Mu left end. The results indicate that these proteins play a crucial role in promoting replisome assembly on a recombination intermediate.

Communication of ClpXP protease hypersensitivity to bacteriophage Mu repressor isoforms

The immunity repressor (Rep) of bacteriophage Mu establishes and maintains lysogeny by shutting down transposition functions needed for phage DNA replication. Although Rep is stable in vivo, an altered immunity repressor (Vir) encoded by virulent, trans-dominant Mu mutants is rapidly degraded by Escherichia coli ClpXP protease. Rep and Vir are degraded at approximately the same maximal velocity (Vmax) by ClpXP, but the Km for Rep (3.6 microM) is over 20-fold higher than the Km for Vir (0.15 microM). Rep is also highly resistant to degradation in the presence of DNA whereas Vir is not. Vir increases the rate of Rep degradation by reducing its Km and imparts to Rep ClpXP sensitivity in the presence of DNA. Vir can drive at an accelerated rate the complete degradation of Rep molecules that outnumber Vir by eightfold or more. So long as Vir is present at a concentration of 0.1 microM or higher, Rep is degraded with a Km that is indistinguishable from that of Vir. These characteristics of repressor may be an important means of transducing physiological signals that induce Mu transposition in response to growth conditions or environmental stress, ClpXP hypersensitivity being disseminated among Rep molecules for the induction of Mu transposition.

Absence of p53 in a mouse mammary tumor model promotes tumor cell proliferation without affecting apoptosis

Loss or mutation of p53 may have multiple biological and genetic effects that result in accelerated tumor progression. Loss of p53 in some tumors has been correlated with a marked decrease in tumor cell apoptosis. p53 loss may also accelerate tumor growth through an increase in cell proliferation rates. To examine the effects of p53 loss on tumor progression in a controlled experimental context, we previously crossed p53-deficient mice to mammary tumor-susceptible Wnt-1 transgenic (TG) mice. The resulting female Wnt-1 TG offspring of this cross all developed mammary tumors, regardless of p53 status (p53+/+, p53+/-, or p53-/-). However, female p53-/- Wnt-1 TG mice developed tumors much sooner than their p53+/+ counterparts. In this report, we demonstrate that the average growth rates of tumors missing (p53-/-) or losing p53 (p53+/- with loss of heterozygosity) are accelerated compared to tumors with both wild-type p53 alleles (p53+/+). This accelerated growth rate appears to be due primarily to increases in rates of tumor cell proliferation. Tumor cell apoptotic levels were modest and were not measurably different in the presence or absence of wild-type p53. These results differ substantially from other mouse tumor models in which p53 loss was closely correlated with accelerated growth rates through attenuated apoptosis. Thus, the mechanisms by which p53 loss influences tumor progression may differ, depending on the tissue type and/or the oncogenic pathways involved.

Direct measurement of flow from the posterior lymph hearts of hydrated and dehydrated toads (Bufo marinus)

Flow from the posterior lymph hearts of Bufo marinus was measured using Doppler flow probes. These probes were placed on the posterior vertebral vein and recorded flow as lymph was ejected from the heart. In resting, hydrated toads, mean lymph flow from one of the paired posterior lymph hearts was 25.9 +/- 4.9 ml kg-1 h-1, stroke volume was 8.9 +/- 1.4 microL kg-1 and lymph heart rate was 47.5 +/- 3.7 beats min-1. We estimate that, together, the paired posterior lymph hearts are capable of generating flows that are approximately one-sixtieth of the resting cardiac output. Mean peak systolic pressure developed by the posterior lymph hearts was 1.62 +/- 0.08 kPa. Simultaneous measurements of lymph heart pressure development and flow revealed that the outflow pore of the heart opened at a pressure of 0.71 +/- 0.04 kPa, approximately 113 +/- 5 ms into systole. When toads were moderately disturbed, stroke volume increased by as much as fourfold with little change in lymph heart rate (< 5 beats min-1). When toads were dehydrated, lymph flow decreased by 70% at 12h and by 80% and 24h. Since there was only a modest non-significant decrease in lymph heart rate (30%), this reduction in flow was attributed to decreases in stroke volume (approximately 80%). Lymph heart flow and stroke volume returned to control values 30 min after adding water back into the experimental chamber. Stroke volume was clearly more important in regulating lymph flow than lymph heart rate under these conditions in Bufo marinus.

Mutation of the Ca2+ channel beta subunit gene Cchb4 is associated with ataxia and seizures in the lethargic (lh) mouse

Ca2+ channel beta subunits regulate voltage-dependent calcium currents through direct interaction with alpha 1 subunits. The beta- and alpha 1-binding motifs are conserved, and all beta subunits can stimulate current amplitude, voltage dependence, and kinetics when coexpressed with various alpha 1 subunits. We used a positional candidate approach to determine that the ataxia and seizures in the lethargic (lh) mouse arise from mutation of the beta-subunit gene Cchb4 on mouse chromosome 2. A four-nucleotide insertion into a splice donor site results in exon skipping, translational frameshift, and protein truncation with loss of the alpha 1-binding site. The lethargic phenotype is the first example of a mammalian neurological disease caused by an inherited defect in a non-pore-forming subunit of a voltage-gated ion channel.

Toward standardization of health information

NCVHS has made recommendations to the DHHS to standardize 42 core health data elements, a number of which relate to medical conditions and services. The committee has asked the DHHS Data Council to actively promote, both within the department and externally, standardization of data elements and definitions where substantial consensus already exists. For those elements that have been recognized as significant core data elements, but for which there is not consensus on approach or definition, the NCVHS is recommending that the Data Council support the formation of a public-private working group to conduct further study and evaluation. This group, or a separate group, could also be the focus for evaluating additions to the list of core data elements and for setting up methods for testing and promulgating the final products. The coming 12-18 months will be exceedingly important for health data standardization efforts in the US as the DHHS responds to both the NCVHS recommendations and the legislation recently enacted by Congress.

Cardiopulmonary arrest in general wards: a retrospective study of referral patterns to an intensive care facility and their influence on outcome

OBJECTIVE

To analyse the effect on outcome of referral to specialist facilities after cardiopulmonary arrest in a general ward.

METHODS

A retrospective analysis of resuscitation records of 743 patients in whom cardiopulmonary resuscitation was performed in a general ward between 1988 and 1992. After successful initial cardiopulmonary resuscitation, patients were identified as transferred to coronary care unit (CCU) or intensive care unit (ITU), or as staying in a general ward.

MAIN OUTCOME MEASURE

Survival to discharge home.

RESULTS

There were 322 initial survivors, of whom 148 (20% of the overall total) survived to be discharged from hospital; 63% of those transferred to CCU and 48% of those transferred to ITU survived to discharge, compared with 28% of those who stayed on the ward (P < 0.001). Of those aged less than 65 years, 75% survived to discharge after transfer to CCU and 54% after transfer to ITU, compared with 44% of those who stayed on the ward (P = 0.023); the respective figures for those over 65 years were: CCU 25%, ITU 34%, ward 25% (P = 0.014). Only half of those aged more than 65 years were transferred to a specialist facility, compared with 90% of those aged less than 65.

CONCLUSIONS

Transfer to a specialist care facility after resuscitation from cardiopulmonary arrest has an influence on outcome. Age as an independent factor is not an appropriate criterion to use in deciding on transfer. The decision to arrange transfer must always be taken by the most experienced person available, and in line with peer reviewed guidelines.

Appropriateness of acute medical admissions and length of stay

OBJECTIVE

To use the Appropriateness Evaluation Protocol (AEP) to assess the extent of inappropriate utilisation of hospital beds by acute medical patients. To determine whether clinicians viewed the AEP decisions as valid.

DESIGN

Retrospective review of the medical records of a 10% random sample of 8,210 patients admitted as medical emergencies. An objective independent review instrument (AEP) was used to assess the medical necessity for hospitalisation at admission and on each subsequent day. To test the validity of the screening instrument, a subsample of the reviewed records was further assessed by a panel of physicians.

SETTING

A district general hospital in the West Midlands region of England.

SUBJECTS

Eight hundred and twenty-one adult patients admitted to general medicine during one calendar year.

MAIN OUTCOME MEASURES

Proportions of admissions and days of care for which inpatient medical care was judged appropriate. Reasons for inappropriate utilisation and potential bed-days that could be saved by the development and use of alternative services were also considered. Validity of the AEP was tested by assessing agreement between the majority decision of an expert panel and the criterion-based AEP decision.

RESULTS

AEP identified 51/821 (6%) admissions and 2,195/4,885 (45%) days of care as inappropriate. Over half the patients had a hospital stay in which at least half the days were judged inappropriate. The commonest reason for inappropriate days was remaining in hospital after the medical purpose for admission had been accomplished. This accounted for 38% of inappropriate days reviewed. In validity testing there was a high level of agreement between the physicians and the AEP, with kappa values greater than 0.80 for admissions and days of care.

CONCLUSIONS

The AEP is a valid and useful instrument for assessing the utilisation of acute medical beds in a NHS hospital. In this study acute medical admissions were largely appropriate at the time of admission but a substantial proportion of subsequent days of care was considered inappropriate by AEP criteria. Most inappropriate utilisation was due to organisational issues within the hospital. As a result of this study, several service and policy developments were identified that should improve the efficiency of bed utilisation at the hospital.

Trophectoderm projections: a potential means for locomotion, attachment and implantation of bovine, equine and human blastocysts

The behaviour of bovine, equine and human blastocysts was studied in vitro by time-lapse videomicrography and computer imaging. This study revealed that cytoplasmic extensions of the trophectoderm ['trophectoderm projections' (TEP)] were expressed by embryos of all three species, prior to or during zona escape. Bovine and human blastocysts escaped their zonae with a combination of blastocoele expansion, collapse and re-expansion coupled with the penetration of the zona pellucida by TEP. In equine embryos, after several cycles of blastocoele expansion and collapse, trophectoderm ruptured the zona with the concomitant appearance of TEP. This study provides documentation that TEP are expressed by a diverse range of mammalian species, bringing the total number of species in which this phenomenon is found to six, since TEP are also known to be expressed by guinea-pig, hamster and rhesus monkey blastocysts, representing rodents, ungulates and primates. In all species studied, the dynamic nature (extension, retraction, and angular movement) of the TEP was similar, moving in an undulating manner with rapid cycles of extension and retraction. Because TEP appear to be a general feature of mammalian blastocysts, they are implicated in one or more key events in early development, namely zona escape, attachment and/or implantation.

The successful use of hyperstimulated washed therapeutic donor insemination after standard therapeutic donor insemination has failed

OBJECTIVE

To investigate whether an aggressive therapeutic donor insemination regimen (stimulated folliculogenesis and ovulation plus intrauterine insemination) can produce a better fecundability rate than a more traditional insemination regimen (non-stimulated folliculogenesis plus LH-timed intracervical insemination) in women who have failed to become pregnant during an initial series of six traditional insemination cycles.

DESIGN

A retrospective comparison of fecundability rates was undertaken between women undergoing the traditional insemination protocol and those who voluntarily switched to ovarian hyperstimulation coupled with intrauterine insemination.

PARTICIPANTS

Eight-two women who failed to become pregnant during an initial series of six intracervical insemination cycles.

RESULTS

Fecundability was 5.6% in cycles of continued urinary LH-timed intracervical insemination and 19.4% when the more aggressive regimen was applied. The difference in fecundability between protocols was significant (P < .005).

CONCLUSION

After an initial series of donor inseminations has failed, a more aggressive insemination regimen involving ovarian hyperstimulation followed by washed intrauterine insemination provides a higher fecundability rate than continued intracervical insemination.

Latex allergen levels of injectable collagen stored in syringes with rubber plungers

OBJECTIVES

To assess the latex allergen content of glutaraldehyde cross-linked injectable bovine collagen stored in rubber plunger syringes.

METHODS

Extracts of syringe plungers and collagen solutions before and after storage in syringes with natural rubber latex plungers were tested for latex protein allergens. Thirty-nine patients known to be allergic to latex underwent skin prick testing with extracts of the latex plungers, collagen solutions before and after storage in syringes, standard latex skin test reagents, four extracts from commercially available gloves, and positive (histamine) and negative (diluent) control solutions. Thirty-one control patients not known to be latex allergic were similarly tested.

RESULTS

No latex proteins were detected using in vitro immunochemical techniques. Only 1 of 39 (2.5%) latex allergic patients reacted to the syringe extract and the collagen stored in the syringe. No reactions were recorded to collagen that no contact with latex.

CONCLUSIONS

The level of latex antigens in injectable collagen is very low. The low prevalence of skin test reactivity in these highly latex allergic individuals suggests that type 1 hypersensitivity reactions as a result of latex contamination would be unlikely.

Twin transfusion syndrome: reassessment of ultrasound diagnosis

OBJECTIVE

To assess the antenatal ultrasonic diagnosis of the twin transfusion syndrome, an enigmatic disorder that results in an imbalance in the blood flow between monochorionic twins.

STUDY DESIGN

Retrospective review of 16 cases of twin transfusion syndrome confirmed by placental pathology and neonatal data.

RESULTS

A disparity in antenatal fetal weights, size difference between the two amniotic sacs and a single placenta were present in 81% (13/16) of confirmed cases. The finding of two separate umbilical cords with a disparity in the size or number of vessels was rare. Evidence of hydrops in either fetus or findings of congestive cardiac failure in the recipient twin were uncommon.

CONCLUSION

Our data strongly suggest that the twin transfusion syndrome can be diagnosed in a significant number (81%) of cases. The syndrome is variable, and it is rare to observe all the diagnostic criteria in one case.

Treatment and survival of lymphoid malignancy in the north-west of England: a population-based study

Classification of lymphoid malignancy has changed markedly in recent years and advances have been made in therapy. This study investigated the variations in treatment and survival of 1622 patients in a population-based registry. A total of 1009 cases of malignant lymphoma (ML) were classified according to the Kiel classification. Pathology review resulted in major diagnostic changes for 24% of cases. Of the ML cases, 39% had not had full staging procedures. Younger patients were more likely to have been treated with multiagent chemotherapy regimens, as were patients with B symptoms. Median survival for ML patients was 12 months for high-grade patients and more than 60 months for low-grade patients. Significant factors affecting the survival of ML patients were performance status, whether treatment had followed a recognised protocol, whether treatment had been carried out at a specialist oncology centre (SOC), grade of disease, stage, gender and age. The same factors had a significant effect on survival of the leukaemia patients, except for treatment at an SOC, which had a significant favourable effect on survival of acute lymphoblastic leukaemia (ALL) patients only. Median survival for patients with chronic lymphocytic leukaemia was 43 months and 7 months for ALL patients.