Biomedical subjects

R B Jensen

Publications and source records attributed to R B Jensen.

At least 19 recordsLinked to original sources

PubMed2006

The impact of maternal smoking on fetal and infant growth.

BACKGROUND: Low birth weight is associated with accelerated postnatal growth and adverse adult health outcomes. Maternal smoking is a major risk factor for low birth weight. This study aims to assess: Pre- and postnatal growth associated with maternal smoking compared to other risk factors for low birth weight. The effect of reduction of maternal smoking on growth. SUBJECTS: A cohort (n=269) followed with ultrasound measurements in the third trimester and postnatal anthropometric measurements until 6 months of age. Mothers were interviewed about their smoking habits at 18 and 28 weeks of pregnancy. RESULTS: Maternal smoking was associated with a greater reduction in birth length SDS than other causes of equally reduced birth weight (mean difference: -0.25 SDS, P=0.013). The adjustment of gestational age, based on bi-parietal diameter at an early dating scan, indicated that mothers who reduced smoking carried smaller fetuses than mothers who continued to smoke heavily (mean difference=2.6 days, P=0.012). Birth weights in these two groups were similar (P=0.87). However at 3 months of age, reduced smoking was associated with lower weight (mean difference=-0.38 SDS, P=0.045). CONCLUSIONS: Maternal smoking was associated with a reduction of linear growth, which was more marked than that of other risk factors, and which seemed to occur before the 3rd trimester. The results indicated a beneficial effect of reduction of smoking upon third trimester growth, and that the decision to reduce smoking in mid-pregnancy may be influenced by early fetal size.

Female↗

PubMed2006

Low birth weight and male reproductive function.

Scientific interest in morbidity in children born small for gestational age (SGA) has increased considerably over the last few decades. The elevated risk of cardiovascular and metabolic diseases in adulthood in individuals born SGA has been well documented, whereas data on gonadal development are limited. Prospective studies, case-control investigations and registry surveys show that impaired intrauterine growth increases the risks of congenital hypospadias, cryptorchidism and testicular cancer approximately two- to threefold. Although few studies focus on the effect of intrauterine growth on male pubertal development, testicular hormone production or sperm quality, available evidence points towards a subtle impairment of both Sertoli cell and Leydig cell function. Animal studies support the hypothesis that impaired perinatal growth restriction, depending on the timing, can affect postnatal testis size and function into adulthood. Current human data, however, are often based on highly selected hospital populations and lack precise distinctions between low birth weight, SGA, timing of growth restriction and a differentiation of catch-up growth patterns. Despite the methodological inadequacies of individual study results, the combined evidence from all data leaves little doubt that fetal growth restriction is associated with increased risk of male reproductive health problems, including hypospadias, cryptorchidism and testicular cancer.

Birth Weight↗

PubMed2001

FYVE zinc-finger proteins in the plant model Arabidopsis thaliana: identification of PtdIns3P-binding residues by comparison of classic and variant FYVE domains.

Classic FYVE zinc-finger domains recognize the phosphoinositide signal PtdIns3P and share the basic (R/K)(1)(R/K)HHCR(6) (single-letter amino acid codes) consensus sequence. This domain is present in predicted PtdIns3P 5-kinases and lipases from Arabidopsis thaliana. Other Arabidopsis proteins, named PRAF, consist of a pleckstrin homology (PH) domain, a regulator of chromosome condensation (RCC1) guanine nucleotide exchange factor repeat domain, and a variant FYVE domain containing an Asn residue and a Tyr residue at positions corresponding to the PtdIns3P-interacting His(4) and Arg(6) of the basic motif. Dot-blot and liposome-binding assays were used in vitro to examine the phospholipid-binding ability of isolated PRAF domains. Whereas the PH domain preferentially bound PtdIns(4,5)P(2), the variant FYVE domain showed a weaker charge-dependent binding of phosphoinositides. In contrast, specificity for PtdIns3P was obtained by mutagenic conversion of the variant into a classic FYVE domain (Asn(4),Tyr(6)-->His(4),Arg(6)). Separate substitutions of the variant residues were not sufficient to impose preferential binding of PtdIns3P, suggesting a co-operative effect of these residues in binding. A biochemical function for PRAF was indicated by its ability to catalyse guanine nucleotide exchange on some of the small GTPases of the Rab family, permitting a discussion of the biological roles of plant FYVE proteins and their regulation by phosphoinositides.

Amino Acid Sequence↗

PubMed2001

[Acute deep venous thrombosis and PET scanning with 2-fluoro-2-deoxy-D-glucose, FDG].

UNLABELLED: A 30-year-old woman with a history of malignant non-Hodgkin lymphoma with a bulky tumour on the right thigh, primarily treated with high-dose chemotherapy and involving field radiation, developed a deep venous thrombosis (DVT) in her right leg two weeks after the end of therapy. Positron emission tomography with fluorine-18 flourodeoxyglucose (FDG PET) was performed to assess the response of the lymphoma to therapy. The PET scan showed several sites of pathological, high tracer uptake corresponding to residual lymphoma, but also intense activity in the right calf correlating to the deep veins located peripheral to the site of DVT. FDG PET performed two months later showed no pathological FDG uptake in this area. CONCLUSION: Acute DVT may cause pathological uptake of FDG and should therefore be considered a possible pitfall in the interpretation of FDG PET.

Acute Disease↗

PubMed2001

A moving DNA replication factory in Caulobacter crescentus.

The in vivo intracellular location of components of the Caulobacter replication apparatus was visualized during the cell cycle. Replisome assembly occurs at the chromosomal origin located at the stalked cell pole, coincident with the initiation of DNA replication. The replisome gradually moves to midcell as DNA replication proceeds and disassembles upon completion of DNA replication. Although the newly replicated origin regions of the chromosome are rapidly moved to opposite cell poles by an active process, the replisome appears to be an untethered replication factory that is passively displaced towards the center of the cell by the newly replicated DNA. These results are consistent with a model in which unreplicated DNA is pulled into the replication factory and newly replicated DNA is bidirectionally extruded from the complex, perhaps contributing to chromosome segregation.

Bacterial Proteins↗

PubMed2000

Proteins on the move: dynamic protein localization in prokaryotes.

Despite their small size and lack of obvious intracellular structures, bacteria have a complex and dynamic intracellular organization. Recent work has shown that many proteins, and even regions of the chromosome, are localized to specific subcellular regions that can change over time, sometimes extraordinarily fast. Protein function can depend on cellular position, so the analysis of the intracellular location of a protein can be crucial for understanding its activity. Because regulatory proteins are among those that reside at specific cellular sites, it is now necessary to consider three-dimensional organization when describing the genetic networks that control bacterial cells.

Bacteria↗

PubMed2000

Plasmid and chromosome segregation in prokaryotes.

Recent major advances in the understanding of prokaryotic DNA segregation have been achieved by using fluorescence microscopy to visualize the localization of cellular components. Plasmids and bacterial chromosomes are partitioned in a highly dynamic fashion, suggesting the presence of a mitotic-like apparatus in prokaryotes. The identification of chromosomal homologues of the well-characterized plasmid partitioning genes indicates that there could be a general mechanism of bacterial DNA partitioning.

Bacteria↗

PubMed2000

Promiscuous and specific phospholipid binding by domains in ZAC, a membrane-associated Arabidopsis protein with an ARF GAP zinc finger and a C2 domain.

Arabidopsis proteins were predicted which share an 80 residue zinc finger domain known from ADP-ribosylation factor GTPase-activating proteins (ARF GAPs). One of these is a 37 kDa protein, designated ZAC, which has a novel domain structure in which the N-terminal ARF GAP domain and a C-terminal C2 domain are separated by a region without homology to other known proteins. Zac promoter/beta-glucuronidase reporter assays revealed highest expression levels in flowering tissue, rosettes and roots. ZAC protein was immuno-detected mainly in association with membranes and fractionated with Golgi and plasma membrane marker proteins. ZAC membrane association was confirmed in assays by a fusion between ZAC and the green fluorescence protein and prompted an analysis of the in vitro phospholipid-binding ability of ZAC. Phospholipid dot-blot and liposome-binding assays indicated that fusion proteins containing the ZAC-C2 domain bind anionic phospholipids non-specifically, with some variance in Ca2+ and salt dependence. Similar assays demonstrated specific affinity of the ZAC N-terminal region (residues 1-174) for phosphatidylinositol 3-monophosphate (PI-3-P). Binding was dependent in part on an intact zinc finger motif, but proteins containing only the zinc finger domain (residues 1-105) did not bind PI-3-P. Recombinant ZAC possessed GTPase-activating activity on Arabidopsis ARF proteins. These data identify a novel PI-3-P-binding protein region and thereby provide evidence that this phosphoinositide is recognized as a signal in plants. A role for ZAC in the regulation of ARF-mediated vesicular transport in plants is discussed.

ADP-Ribosylation Factors↗

PubMed2000

The Brucella abortus CcrM DNA methyltransferase is essential for viability, and its overexpression attenuates intracellular replication in murine macrophages.

The CcrM DNA methyltransferase of the alpha-proteobacteria catalyzes the methylation of the adenine in the sequence GAnTC. Like Dam in the enterobacteria, CcrM plays a regulatory role in Caulobacter crescentus and Rhizobium meliloti. CcrM is essential for viability in both of these organisms, and we show here that it is also essential in Brucella abortus. Further, increased copy number of the ccrM gene results in striking changes in B. abortus morphology, DNA replication, and growth in murine macrophages. We generated strains that carry ccrM either on a low-copy-number plasmid (strain GR131) or on a moderate-copy-number plasmid (strain GR132). Strain GR131 has wild-type morphology and chromosome number, as assessed by flow cytometry. In contrast, strain GR132 has abnormal branched morphology, suggesting aberrant cell division, and increased chromosome number. Although these strains exhibit different morphologies and DNA content, the replication of both strains in macrophages is attenuated. These data imply that the reduction in survival in host cells is not due solely to a cell division defect but is due to additional functions of CcrM. Because CcrM is essential in B. abortus and increased ccrM copy number attenuates survival in host cells, we propose that CcrM is an appropriate target for new antibiotics.

Animals↗

PubMed2000

Complementation of the radiosensitive M059J cell line.

M059J is a radiosensitive cell line established from a human glioblastoma tumor that fails to express the catalytic subunit of DNA-dependent protein kinase (DNA-PKcs, now known as PRKDC). Another cell line, M059K, established from the same tumor is radioresistant. Neither M059J nor M059K cells have been fully characterized, beyond the lack of expression of PRKDC and low expression of ATM in M059J cells. To determine whether its radiosensitive phenotype is due to a defect in the gene that encodes PRKDC, we show here that M059J cells can be complemented with the PRKDC gene by introducing a fragment of human chromosome 8 containing a copy of the human PRKDC gene. Two hybrid cell lines that retain an extra copy of PRKDC display active kinase activity and are radioresistant, demonstrating that the primary defect in M059J cells is in PRKDC. In addition, these cell lines derived from M059J cells provide us with a closer genetic match to M059J than M059K cells in studies to elucidate the function of DNA-PK.

Animals↗

PubMed1999

[Informed consent in connection with autopsy and sending out discharge notes. A questionnaire study].

The purpose of this study was to illustrate the attitude towards informed consent in connection with performing an autopsy and sending out discharge notes amongst a group of patients, doctors and nurses. A questionnaire was given to four different groups consisting of 75 patients, 20 nursing staff, 20 hospital doctors and 20 family doctors. The attitudes amongst the two groups of doctors were generally close to the attitudes amongst patients. The majority of doctors and patients in contrary to the nursing staff found it unnecessary to obtain informed consent before sending out discharge notes. More than half of all of the groups thought that patients should take part in the decision of performing autopsy, but still the family should be asked as well.

Attitude of Health Personnel↗

PubMed1999

The Caulobacter crescentus smc gene is required for cell cycle progression and chromosome segregation.

The highly conserved SMC (Structural Maintenance of Chromosomes) proteins function in chromosome condensation, segregation, and other aspects of chromosome dynamics in both eukaryotes and prokaryotes. A null mutation in the Caulobacter crescentus smc gene is conditionally lethal and causes a cell cycle arrest at the predivisional cell stage. Chromosome segregation in wild-type and smc null mutant cells was examined by monitoring the intracellular localization of the replication origin and terminus by using fluorescence in situ hybridization. In wild-type cells, the origin is located at the flagellated pole of swarmer cells and, immediately after the initiation of DNA replication in stalked cells, one of the origins moves to the opposite pole, giving a bipolar localization of the origins. The terminus moves from the end of the swarmer cell opposite the origin to midcell. A subpopulation of the smc null mutant cells had mislocalized origins or termini, showing that the smc null mutation gives DNA segregation defects. Nucleoid morphology was also abnormal. Thus, we propose that the Caulobacter chromosomal origins have specific cellular addresses and that the SMC protein plays important roles in maintaining chromosome structure and in partitioning. The specific cell cycle arrest in the smc null mutant indicates the presence of a cell cycle checkpoint that senses perturbations in chromosome organization or segregation.

Bacterial Proteins↗

PubMed1999

Mechanism of DNA segregation in prokaryotes: ParM partitioning protein of plasmid R1 co-localizes with its replicon during the cell cycle.

The parA locus of plasmid R1 encodes a prokaryotic centromere-like system that mediates genetic stabilization of plasmids by an unknown mechanism. The locus codes for two proteins, ParM and ParR, and a centromere-like DNA region (parC) to which the ParR protein binds. We showed recently that ParR mediates specific pairing of parC-containing DNA molecules in vitro. To obtain further insight into the mechanism of plasmid stabilization, we examined the intracellular localization of the components of the parA system. We found that ParM forms discrete foci that localize to specific cellular regions in a simple, yet dynamic pattern. In newborn cells, ParM foci were present close to both cell poles. Concomitant with cell growth, new foci formed at mid-cell. A point mutation that abolished the ATPase activity of ParM simultaneously prevented cellular localization and plasmid partitioning. A parA-containing plasmid localized to similar sites, i.e. close to the poles and at mid-cell, thus indicating that the plasmid co-localizes with ParM. Double labelling of single cells showed that plasmid DNA and ParM indeed co-localize. Thus, our data indicate that parA is a true partitioning system that mediates pairing of plasmids at mid-cell and subsequently moves them to the cell poles before cell division.

Adenosine Triphosphatases↗

PubMed1999

Chromosome segregation during the prokaryotic cell division cycle.

Recent work has dramatically changed our view of chromosome segregation in bacteria. Rather than being a passive process, it involves rapid movement of parts of the circular chromosome. Several genes involved in chromosome segregation have been identified, and the analysis of their functions and intracellular localization are beginning to shed light on the mechanisms that ensure efficient chromosome segregation.

Bacillus subtilis↗

PubMed1998

Widespread occurrence of a highly conserved RING-H2 zinc finger motif in the model plant Arabidopsis thaliana.

Several novel Arabidopsis thaliana proteins containing a RING-H2 zinc finger motif were predicted after database searches. Alignment of 29 RING-H2 finger sequences shows that the motif is strikingly conserved in otherwise unrelated proteins. Only short, non-conserved polar/charged sequences distinguish these domains. The RING-H2 domain is most often present in multi-domain structures, a number of which are likely to contain a membrane-spanning region or an additional zinc finger. However, there are several small (126-200 residues) proteins consisting of an N-terminal domain, rich in aliphatic residues, and a C-terminal RING-H2 domain. Reverse-transcription PCR suggests that the RING-H2 genes are widely expressed at low levels.

Amino Acid Sequence↗

PubMed1998

Mechanism of DNA segregation in prokaryotes: replicon pairing by parC of plasmid R1.

Prokaryotic chromosomes and plasmids encode partitioning systems that are required for DNA segregation at cell division. The systems are thought to be functionally analogous to eukaryotic centromeres and to play a general role in DNA segregation. The parA system of plasmid R1 encodes two proteins ParM and ParR, and a cis-acting centromere-like site denoted parC. The ParR protein binds to parC in vivo and in vitro. The ParM protein is an ATPase that interacts with ParR specifically bound to parC. Using electron microscopy, we show here that parC mediates efficient pairing of plasmid molecules. The pairing requires binding of ParR to parC and is stimulated by the ParM ATPase. The ParM mediated stimulation of plasmid pairing is dependent on ATP hydrolysis by ParM. Using a ligation kinetics assay, we find that ParR stimulates ligation of parC-containing DNA fragments. The rate-of-ligation was increased by wild type ParM protein but not by mutant ParM protein deficient in the ATPase activity. Thus, two independent assays show that parC mediates pairing of plasmid molecules in vitro. These results are consistent with the proposal that replicon pairing is part of the mechanism of DNA segregation in prokaryotes.

Bacterial Proteins↗

PubMed1997

Partitioning of plasmid R1. The ParM protein exhibits ATPase activity and interacts with the centromere-like ParR-parC complex.

The parA system of plasmid R1 consists of two genes, parM and parR, and a cis-acting centromere-like site parC. The ParM protein exhibits similarity with a superfamily of ATPases that includes actin, hsp70 and hexokinase. ParM was purified to near-homogeneity and assayed for in vitro ATPase activity. The wild-type ParM protein was found to posses ATPase activity. Mutant ParM derivatives that exhibited decreased in vitro ATPase activity were non-functional in vivo, indicating that the ATP turnover by ParM is essential for correct plasmid partitioning. The mutant ParM proteins exhibited trans-dominance, suggesting that ParM participates as a structural component of the partitioning apparatus. The ATPase activity of ParM was activated slightly by the presence of ParR and activated to a much greater extent when ParR was bound to the centromere-like parC region. An analysis using the yeast two-hybrid system indicated that ParM and ParR interact, and demonstrated that ParR interacts with itself. Thus our results suggest a direct interaction of ParM and ParR at the natural partition site parC, and that the ATPase activity of ParM is specifically stimulated by this interaction.

Adenosine Triphosphatases↗

PubMed1996

The centromere-like parC locus of plasmid R1.

The parA partitioning system of plasmid R1 consists of three components: the cis-acting centromere-like parC locus, and two proteins, ParM and ParR. The parC locus contains two sets of five direct repeats (iterons) to which the ParR protein binds. The parA promoter is located in the core region between the two sets of iterons. Mini-R1 replicons carrying parC are stabilized by the simultaneous presence of ParM and ParR. The parC locus present on a co-resident plasmid leads to instability of the mini-R1 replicon (incompatibility). Here we present a genetic analysis of the stability and incompatibility phenotypes associated with parC. We show that all 10 iterons are required for maximum stabilization and incompatibility. Replacement of the core promoter region between the repeats by a foreign promoter region did not reduce stabilization. Thus, the only structural components in parC seem to be the two sets of iterons. The parA promoter, P parA, is repressed by ParR. We show that all 10 iterons are required for full repression of the promoter. The activity of the promoter was influenced by sequences located outside the core region. An A-rich region located upstream of the -35 element of PparA was found to increase promoter activity. The region encoding the parA mRNA leader region also strongly influenced the expression level of PparA- lacZ fusions. We show that this high expression (hex) element is a transcriptional antiterminator that prevents Rho-dependent termination.

Bacterial Proteins↗