Biomedical subjects

K Nordström

Publications and source records attributed to K Nordström.

At least 19 recordsLinked to original sources

PubMed2001

Suppression of the deafness and thyroid dysfunction in Thrb-null mice by an independent mutation in the Thra thyroid hormone receptor alpha gene.

Deletion of thyroid hormone receptor beta (TR beta), a ligand-dependent transcription factor encoded by the Thrb gene, causes deafness and thyroid hyperactivity in Thrb-null (Thrb(tm1/tm1)) mice and in a recessive form of the human syndrome of resistance to thyroid hormone. Here, we have determined that a targeted mutation (Thra(tm2)) in the related Thra gene, encoding thyroid hormone receptor alpha suppresses these phenotypes in mice. Thra encodes a TR alpha 1 receptor which is non-essential for hearing and a TR alpha 2 splice variant of unknown function that neither binds thyroid hormone nor transactivates. The Thra(tm2) mutation deletes TR alpha 2 and concomitantly causes overexpression of TR alpha 1 as a consequence of the exon structure of the gene. Thra(tm2/tm2) mice have normal auditory thresholds indicating that TR alpha 2 is dispensable for hearing, and have only marginally reduced thyroid activity. However, a potent function for the Thra(tm2) allele is revealed upon its introduction into Thrb(tm1/tm1) mice, where it suppresses the auditory and thyroid phenotypes caused by loss of TR beta. These findings reveal a novel modifying function for a Thra allele and suggest that increased expression of TR alpha 1 may substitute for the absence of TR beta. The TR isotypes generated by the distinct Thrb and Thra genes represent a small family of receptors that have diverged to mediate different physiological roles; however, the ability of changes in Thra expression to compensate for loss of Thrb indicates that many functions of these genes remain closely related.

Animals↗

PubMed2001

Partitioning of the Escherichia coli chromosome: superhelicity and condensation.

Segregation in Escherichia coli, the process of separating the replicated chromosomes into daughter progeny cells, seems to start long before the duplication of the genome reaches completion. Soon after initiation in mid-cell region, the daughter oriCs rapidly move apart to fixed positions inside the cell (quarter length positions from each pole) and are anchored there by yet unknown mechanism(s). As replication proceeds, the rest of the chromosome is sequentially unwound and then refolded. At termination, the two sister chromosomes are unlinked by decatenation and separated by supercoiling and/or condensation. Muk and Seq proteins are involved in different stages of this replication-cum-partition process and thus can be categorized as important partition proteins along with topoisomerases. E. coli strains, lacking mukB or seqA functions, are defective in segregation and cell division. The nucleoids in these mutant strains exhibit altered condensation and superhelicity as can be demonstrated by sedimentation analysis and by fluorescence microscopy. As the supercoiling of an extrachromosomal element (a plasmid DNA) was also influenced by the mukB and seqA mutations we concluded that the MukB and SeqA proteins are possibly involved in maintaining the general supercoiling activity in the cell. The segregation of E. coli chromosome might therefore be predominantly driven by factors that operate by affecting the superhelicity and condensation of the nucleoid (MukB, SeqA, topoisomerases and additional unknown proteins). A picture thus emerges in which replication and partition are no longer compartmentalized into separable stages with clear gaps (S and M phases in eukaryotes) but are parallel processes that proceed concomitantly through a cell cycle continuum.

Bacterial Outer Membrane Proteins↗

PubMed2001

Replication arrests during a single round of replication of the Escherichia coli chromosome in the absence of DnaC activity.

We used a flow cytometric assay to determine the frequency of replication fork arrests during a round of chromosome replication in Escherichia coli. After synchronized initiation from oriC in a dnaC(Ts) strain, non-permissive conditions were imposed, such that active DnaC was not available during elongation. Under these conditions, about 18% of the cells failed to complete chromosome replication. The sites of replication arrests were random and occurred on either arm of the bidirectionally replicating chromosome, as stalled forks accumulated at the terminus from both directions. The forks at the terminal Ter sites disappeared in the absence of Tus protein, as the active forks could then pass through the terminus to reach the arrest site, and the unfinished rounds of replication would be completed without DnaC. In a dnaC2(Ts)rep double mutant, almost all cells failed to complete chromosome replication in the absence of DnaC activity. As inactivation of Rep helicase (the rep gene product) has been shown to cause frequent replication arrests inducing double-strand breaks (DSBs) in a replicating chromosome, DnaC activity appears to be essential for replication restart from DSBs during elongation.

Base Sequence↗

PubMed2001

RecA-mediated rescue of Escherichia coli strains with replication forks arrested at the terminus.

The recombinational rescue of chromosome replication was investigated in Escherichia coli strains with the unidirectional origin oriR1, from the plasmid R1, integrated within oriC in clockwise (intR1(CW)) or counterclockwise (intR1(CC)) orientations. Only the intR1(CC) strain, with replication forks arrested at the terminus, required RecA for survival. Unlike the strains with RecA-dependent replication known so far, the intR1(CC) strain did not require RecBCD, RecF, RecG, RecJ, RuvAB, or SOS activation for viability. The overall levels of degradation of replicating chromosomes caused by inactivation of RecA were similar in oriC and intR1(CC) strains. In the intR1(CC) strain, RecA was also needed to maintain the integrity of the chromosome when the unidirectional replication forks were blocked at the terminus. This was consistent with suppression of the RecA dependence of the intR1(CC) strain by inactivating Tus, the protein needed to block replication forks at Ter sites. Thus, RecA is essential during asymmetric chromosome replication for the stable maintenance of the forks arrested at the terminus and for their eventual passage across the termination barrier(s) independently of the SOS and some of the major recombination pathways.

Bacterial Proteins↗

PubMed2001

Ablation of TRalpha2 and a concomitant overexpression of alpha1 yields a mixed hypo- and hyperthyroid phenotype in mice.

Thyroid hormone governs a diverse repertoire of physiological functions through receptors encoded in the receptor genes alpha and beta, which each generate variant proteins. In mammals, the alpha gene generates, in addition to the normal receptor TRalpha1, a non-hormone-binding variant TRalpha2 whose exact function is unclear. Here, we present the phenotype associated with the targeted ablation of TRalpha2 expression. Selective ablation of TRalpha2 resulted in an inevitable, concomitant overexpression of TRalpha1. Both TRalpha2 +/- and -/- mice show a complex phenotype with low levels of free T3 and free T4, and have inappropriately normal levels of TSH. The thyroid glands exhibit mild morphological signs of dysfunction and respond poorly to TSH, suggesting that the genetic changes affect the ability of the gland to release thyroid hormones. However, the phenotype of the mutant mice also has features of hyperthyroidism, including decreased body weight, elevated heart rate, and a raised body temperature. Furthermore, TRalpha2-/- and TRalpha2+/- mice are obese and exhibit skeletal alterations, associated with a late-onset growth retardation. The results thus suggest that the overexpression of TRalpha1 and the concomitant decrease in TRalpha2 expression lead to a mixed hyper- and hypothyroid phenotype, dependent on the tissue studied. The phenotypes suggest that the balance of TRalpha1:TRalpha2 expressed from the TRalpha gene provides an additional level of tuning the control of growth and homeostasis in mammalian species.

Animals↗

PubMed2001

Fiber fractions from processing of barley in production and conservation of a biologic control agent.

Carriers are frequently used to overcome problems associated with microbial survival in soil after inoculation. Moreover, the use of carriers can prolong the shelf lives and lessen dusting of both biofungicides and biologic fertilizers. This study investigated the suitability of barley-based fiber fractions as growth media and immobilization matrices in the cultivation of a Streptomyces griseoviridis biologic control agent, as well as for the conservation of obtained biomass in dehydrated hydrogel capsules. The second main ingredient in all the examined carrier matrices was alginate. The aim was to find a hydrogel formulation suited for a production process in which all individual steps, including cultivation of the organism; downstream processing; and formulation, storage, and application of the product (i.e., biologic control agent), are carried out in the hydrogel matrix. Of the tested fractions, brewer's spent grain was the best choice, when considering the price vs the nutrient contents as well as the storage time and ease of processing of the crude and the finished products. It seems that cereal fibers can be replenished with cereal fractions less rich in fiber but having a higher content of utilizable nutrients and, hence, better suited for the production of biomass. A high content of water-insoluble fiber favorably influenced the appearance as well as the applicability of the products.

Alginates↗

PubMed2000

Plasmid R1 is present as clusters in the cells of Escherichia coli.

Fluorescence microscopy was used to determine the location(s) of the replication origin of plasmid R1 in exponentially growing cells of Escherichia coli. The number of oriR1 foci per cell was smaller than the number of R1 copies per cell and was found to be the same for a copA mutant of R1 and for the wild-type plasmid. The intensities of individual foci were stronger for the cop mutant than for the wild type. We interpreted these results to imply that the plasmid DNA molecules were localized in small groups/clusters, a result that seems contrary to the earlier observations that plasmid R1 replicates randomly and segregates as a single-copy unit. The implications for the quantitative behavior of plasmid R1 in stability, incompatibility tests, replication, and partition experiments are discussed.

Escherichia coli↗

PubMed2000

FtsZ ring formation without subsequent cell division after replication runout in Escherichia coli.

In this report, we have investigated cell division after inhibition of initiation of chromosome replication in Escherichia coli. In a culture grown to the stationary phase, cells containing more than one chromosome were able to divide some time after restart of growth, under conditions not allowing initiation of chromosome replication. This shows that there is no requirement for cell division to take place within a certain time after initiation of chromosome replication. Continued growth without initiation of replication resulted in filamented cells that generally did not have any constrictions. Interestingly, FtsZ rings were formed in a majority of these cells as they reached a certain cell length. These rings appeared and were maintained for some time at the cell quarter positions on both sides of the centrally localized nucleoid. These results confirm previous findings that cell division sites are formed independently of chromosome replication and indicate that FtsZ ring assembly is dependent on cell size rather than on the capacity of the cell to divide. Disruption of the mukB gene caused a significant increase in the region occupied by DNA after the replication runout, consistent with a role of MukB in chromosome condensation. The aberrant nucleoid structure was accompanied by a shift in FtsZ ring positioning, indicating an effect of the nucleoid on the positioning of the FtsZ ring. A narrow cell length interval was found, under and over which primarily central and non-central FtsZ rings, respectively, were observed. This finding correlates well with the previously observed oscillatory movement of MinC and MinD in short and long cells.

Bacterial Proteins↗

PubMed2000

Role of the mukB gene in chromosome and plasmid partition in Escherichia coli.

The intracellular locations of oriC and oriR1, the replication origins of the chromosome and plasmid R1, respectively, were visualized by fluorescence in situ hybridization (FISH) in exponentially growing populations of Escherichia coli. The locations of oriC and oriR1 (from a Par+ R1 plasmid) were unique and different in the wild-type host. In a mukB mutant, the positions were perturbed for both origins. The position of oriR1 from a plasmid with active partition (Par+) in the mukB host was as randomized as that of oriR1 from the Par- plasmid in a wild-type host. However, this mukB-induced randomization did not result in unstable inheritance of the Par+ plasmid, as measured by the conventional segregation assay. This might result from the preferential association of the Par+ plasmid with the bigger, decondensed nucleoid-containing daughters during cell division of MukB- cells, whereas the Par- plasmids were distributed at random and were lost by frequently ending up in anucleate cells.

Bacterial Proteins↗

PubMed2000

New genes with old modus operandi. The connection between supercoiling and partitioning of DNA in Escherichia coli.

The process of partitioning bacterial sister chromosomes into daughter cells seems to be distinct from chromatid segregation during eukaryotic mitosis. In Escherichia coli, partitioning starts soon after initiation of replication, when the two newly replicated oriCs move from the cell centre to quarter positions within the cell. As replication proceeds, domains of the compact, supercoiled chromosome are locally decondensed ahead of the replication fork. The nascent daughter chromosomes are recondensed and moved apart through the concerted activities of topoisomerases and the SeqA (sequestration) and MukB (chromosome condensation) proteins, all of which modulate nucleoid superhelicity. Thus, genes involved in chromosome topology, once set aside as 'red herrings' in the search for 'true' partition functions, are again recognized as being important for chromosome partitioning in E. coli.

Bacterial Outer Membrane Proteins↗

PubMed2000

Escherichia coli cell cycle control genes affect chromosome superhelicity.

We have used ethidium bromide titration for direct measurement of the changes in the negative supercoiling of Escherichia coli chromosome caused by mutations inactivating the cell cycle functions mukB and seqA. The amounts of the intercalative agent required to relax the supercoiled chromosome in mukB and seqA mutants were lower and higher, respectively, than for the wild-type parent, confirming that these cell cycle genes modulate the topology of the E. coli chromosome. Plasmid superhelicity measured in these mutant strains showed similar effects albeit of reduced magnitude. As the effects of mukB and seqA mutations were not restricted to the chromosome alone, MukB and SeqA proteins possibly interact with factors involved in the maintenance of intracellular DNA topology. To our knowledge, this is the first direct demonstration of the influence of mukB and seqA genes on the superhelicity of the E. coli chromosome.

Bacterial Outer Membrane Proteins↗

PubMed2000

Asthma symptoms in relation to measured building dampness in upper concrete floor construction, and 2-ethyl-1-hexanol in indoor air.

SETTING: Asthma symptoms in adults in relation to the indoor environment. OBJECTIVES: To study the relationships between current asthma symptoms (wheeze or attacks of breathlessness) and the indoor environment and dampness in hospitals. DESIGN: A study among personnel (n = 87) in four geriatric hospitals in winter. Indoor air pollutants, dampness in the concrete floor, and allergens in settled dust were measured. Multiple logistic regression analysis was applied, adjusting for age, sex, atopy, and dampness in the participants' own dwellings. RESULTS: Current asthma symptoms were reported by 17%, and 8% had doctor's diagnosed asthma. Asthma symptoms were more common (adjusted odds ratio = 8.6; 95% confidence interval 1.3-56.7) in two buildings with signs of dampness-related degradation of di(ethylhexyl)-phthalate (DEHP) in polyvinyl chloride (PVC) floor material, detected as presence of 2-ethyl-1-hexanol (2-32 microg/m3) in indoor air (CAS nr 104-76-7). Asthma symptoms were related to higher relative humidity in the upper concrete floor construction, and ammonia in the floor. The newest hospital, built by an anthroposophic society, had low levels of dampness and few asthma symptoms (4%). Cat (Fel d1) and dog allergens (Can f1) were found in dust from all buildings (geometric mean 340 ng/g and 2490 ng/g, respectively). House dust mite allergens (Derp1, Derf1, or Derm1) were found in 75% of all samples (geometric mean 130 ng/g). There was no relationship between allergen levels and asthma symptoms. CONCLUSIONS: Asthma symptoms may be related to increased humidity in concrete floor constructions and emission of 2-ethyl-1-hexanol, an indicator of dampness-related alkaline degradation of plasticiser DEHP. Moreover, geriatric hospitals can be contaminated by significant amounts of cat, dog and mite allergens.

Air Pollution, Indoor↗

PubMed1999

Nasal and ocular symptoms, tear film stability and biomarkers in nasal lavage, in relation to building-dampness and building design in hospitals.

OBJECTIVES: To study the relationships between dampness in concrete floors and building design on the one hand, and symptoms and medical signs of the eyes and nose in hospital workers, on the other. METHODS: Four hospitals for geriatrics were selected to represent buildings with different ages and design, irrespective of symptom prevalence. The first building was built in 1925. The second, built in 1985, was known to have dampness in the floor. Conventional building techniques were used in the third building, built in 1993, and the last building was built in 1994, and was specially designed to include high ceilings, and minimal use of fluorescent lighting and interior plastic materials. The interior surfaces were painted with water-based beeswax glazing. All staff (n=95) working day shifts were invited to take part in a medical examination of the eyes and nose including acoustic rhinometry and nasal lavage, and a medical questionnaire, and 93% participated. Measurements of temperature, relative air humidity, air flow, illumination, volatile organic compounds (VOCs), molds, and bacteria were carried out in all buildings, together with measurements of formaldehyde, respirable dust, carbon monoxide (CO), carbon dioxide (CO(2)), nitrogen dioxide (NO(2)) and ozone. Statistical analyses were performed by bivariate analysis, and linear, ordinal, and logistic multiple regressions, adjusting for age, gender, tobacco smoking, atopy, and the perceived psychosocial work environment. RESULTS: Dampness in the upper concrete floor surface (75-84%), ammonia under the floor [3 parts per million (ppm)], and 2-ethyl-1-hexanol in the air were detected in the two buildings built in 1985 and 1993. Increased occurrences of ocular and nasal symptoms, an increased concentration of lysozyme in nasal lavage, and decreased tear film stability were found in the subjects working in the damp buildings. Those in the specially designed building had fewer ocular and nasal symptoms, and increased tear film stability. All buildings had low levels of formaldehyde, molds, bacteria, ozone, and NO(2). The lowest total concentration of VOCs, and the highest concentration of specific VOCs of microbial origin, were found in the building with special design. CONCLUSION: The study provides new evidence of the role of dampness-related alkaline degradation of di-(2-ethylhexyl) phthalate (DEHP) in polyvinyl chloride (PVC) building material. Emissions related to degradation of DEHP due to dampness in the floor, indicated by increased 2-ethyl-1-hexanol in the air, seem to increase both the secretion of lysozyme from the nasal mucosa and the occurrence of ocular and nasal symptoms. The indoor environment of the specially designed building with high ceilings and no fluorescent lighting or interior plastics seemed to have a positive influence on the nasal and ocular mucous membranes.

Adult↗

PubMed1999

Mutual suppression of mukB and seqA phenotypes might arise from their opposing influences on the Escherichia coli nucleoid structure.

A strain of Escherichia coli in which both the seqA and mukB genes were inactivated displayed partial suppressions of their individual phenotypes. Temperature sensitivity, anucleate cell production and poor nucleoid folding seen in the mukB strain were suppressed by the seqA null mutation, whereas filamentation, asymmetric septation and compact folding of the nucleoids observed in the seqA strain were suppressed by inactivation of the mukB gene function. However, the asynchronous initiation of chromosome replication in the seqA strain was not reversed in the mukBseqA double mutant. Membrane-associated nucleoids were isolated from the wild-type, mukB, seqA and mukBseqA strains and their sedimentation rates were compared under identical conditions. Whereas the mukB mutation caused unfolding of the nucleoid, the seqA mutation led to a more compact packaging of the chromosome. The mukBseqA double mutant regained the wild-type nucleoid organization as revealed from its rate of sedimentation. Microscopic appearances of the nucleoids were consistent with the sedimentation profiles. The mukB mutant was oversensitive to novobiocin and this susceptibility was suppressed in the mukBseqA strain, suggesting possible roles of MukB and SeqA in maintaining chromosome topology. The mutual phenotypic suppression of mukB and seqA alleles thus suggests that these genes have opposing influences on the organization of the bacterial nucleoid.

Bacterial Outer Membrane Proteins↗

PubMed1999

On the equivalence of meta-analysis using literature and using individual patient data.

When data come from several independent studies for the purpose of estimating treatment control differences, meta-analysis can be carried out either on the best linear unbiased estimators computed from each study or on the pooled individual patient data modelled as a two-way model without interaction, where the two factors represent the different studies and the different treatments. Assuming that observations within and between studies are independent having a common variance, Olkin and Sampson (1998) have obtained the surprising result that the two meta-analytic procedures are equivalent, i.e., they both produce the same estimator. In this article, the same equivalence is established for the two-way fixed-effects model without interaction with the only assumption that the observations across studies be independent. A consequence of the equivalence result is that, regardless of the covariance structure, it is possible to get an explicit representation for the best linear unbiased estimator of any vector of treatment contrasts in a two-way fixed-effects model without interaction as long as the studies are independent. Another interesting consequence is that, for the purpose of best linear unbiased estimation, an unbalanced two-way fixed-effects model without interaction can be treated as several independent unbalanced one-way models, regardless of the covariance structure, when the studies are independent.

Analysis of Variance↗

PubMed1999

Analysis of protein synthesis rates after initiation of chromosome replication in Escherichia coli.

The aim of this study was to investigate whether the synthesis rates of some proteins change after the initiation of replication in Escherichia coli. An intR1 strain, in which chromosome replication is under the control of an R1 replicon integrated into an inactivated oriC, was used to synchronize chromosome replication, and the rates of protein synthesis were analyzed by two-dimensional polyacrylamide gel electrophoresis of pulse-labeled proteins. Computerized image analysis was used to search for proteins whose expression levels changed at least threefold after initiation of a single round of chromosome replication, which revealed 7 out of about 1,000 detected proteins. The various synthesis rates of three of these proteins turned out to be caused by unbalanced growth and the synthesis of one protein was suppressed in the intR1 strain. The rates of synthesis of the remaining three could be correlated only to the synchronous initiation of replication. These three proteins were analyzed by peptide mass mapping and appeared to be the products of the dps, gapA, and pyrI genes. Thus, the expression of the vast majority of proteins is not influenced by the state of chromosome replication, and a possible role of the replication-associated expression changes of the three identified proteins in the cell cycle is not clear.

Bacterial Proteins↗

PubMed1999

On the origin of branches in Escherichia coli.

Some Escherichia coli strains with impaired cell division form branched cells at high frequencies during certain growth conditions. Here, we show that neither FtsI nor FtsZ activity is required for the development of branches. Buds did not form at specific positions along the cell surface during high-branching conditions. Antibiotics affecting cell wall synthesis had a positive effect on branch formation in the case of ampicillin, cephalexin, and penicillin G, whereas mecillinam and D-cycloserine had no substantial effect. Altering the cell morphology by nutritional shifts showed that changes in morphology preceded branching, indicating that the cell's physiological state rather than specific medium components induced branching. Finally, there was no increased probability for bud formation in the daughters of a cell with a bud or branch, showing that bud formation is a random event. We suggest that branch formation is caused by abnormalities in cell wall elongation rather than by aberrant cell division events.

Anti-Bacterial Agents↗

PubMed1998

Quorum-sensing acts at initiation of chromosomal replication in Escherichia coli.

Chromosomal replication in Escherichia coli was studied by flow cytometry and was found to be inhibited by an extracellular factor present in conditioned media collected during late exponential and early stationary phase, i.e., via a quorum-sensing mechanism. Our results suggest that the inhibitory activity of the extracellular factor is exerted during initiation of DNA replication rather than during elongation. Furthermore, we present evidence that this interaction may occur directly at each of the replication forks. Unlike other quorum-sensing systems described so far for Gram-negative bacteria, this inhibitory activity does not require transcription or translation to be effective. Implications of quorum-sensing regulation of DNA replication are discussed.

Chromosomes, Bacterial↗