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Biomedical subjects

L Dolan

Publications and source records attributed to L Dolan.

At least 19 recordsLinked to original sources
PubMed1999

Signalling in cell type specification.

Positional information is an important determinant in the establishment of cellular identity in plants. It is established during pattern formation and is maintained in growing organs. Cells maintain the ability to respond to changes in positional information during development indicating that the mechanism for perceiving such information must remain intact until relatively late in development. Once positional cues are perceived they set in motion a number of cascades resulting in the differentiation of particular cell types in defined locations. The circuitry underpinning these later events is being teased out using genetics. Evidence is emerging for the existence of an array of both positive and negative genetic regulators from studies in a number of diverse plant model systems

Arabidopsis↗
PubMed1999

The movement of coiled bodies visualized in living plant cells by the green fluorescent protein.

Coiled bodies are nuclear organelles that contain components of at least three RNA-processing pathways: pre-mRNA splicing, histone mRNA 3'- maturation, and pre-rRNA processing. Their function remains unknown. However, it has been speculated that coiled bodies may be sites of splicing factor assembly and/or recycling, play a role in histone mRNA 3'-processing, or act as nuclear transport or sorting structures. To study the dynamics of coiled bodies in living cells, we have stably expressed a U2B"-green fluorescent protein fusion in tobacco BY-2 cells and in Arabidopsis plants. Time-lapse confocal microscopy has shown that coiled bodies are mobile organelles in plant cells. We have observed movements of coiled bodies in the nucleolus, in the nucleoplasm, and from the periphery of the nucleus into the nucleolus, which suggests a transport function for coiled bodies. Furthermore, we have observed coalescence of coiled bodies, which suggests a mechanism for the decrease in coiled body number during the cell cycle. Deletion analysis of the U2B" gene construct has shown that the first RNP-80 motif is sufficient for localization to the coiled body.

Arabidopsis↗
PubMed1999

Stulberg classification system for evaluation of Legg-Calvé-Perthes disease: intra-rater and inter-rater reliability.

BACKGROUND: Researchers and clinicians commonly use the classification system of Stulberg et al. as a basis for treatment decisions during the active phase of Legg-Calvé-Perthes disease because of its putative utility as a predictor of long-term outcome. It is generally assumed that this system has an acceptable degree of reliability. This assumption, however, is not convincingly supported by the literature. METHODS: The purpose of the present study was to assess the inter-rater and intra-rater reliability of the classification system of Stulberg et al. with use of a pre-test, post-test design. During the pre-test phase, nine raters independently used the system to evaluate the radiographs of skeletally mature patients who had been managed for Legg-Calvé-Perthes disease. The intervention between the pre-test and post-test phases consisted of a consensus-building session during which all raters jointly arrived at standardized definitions of the various joint structures that are assessed with use of the classification system. The effect of these definitions on reliability then was assessed by reevaluating the radiographs during the post-test phase. RESULTS: The pre-test intra-rater reliability coefficients ranged from 0.709 to 0.915, and the post-test coefficients ranged from 0.568 to 0.874. The pre-test inter-rater reliability coefficients ranged from 0.603 to 0.732, and the post-test coefficients ranged from 0.648 to 0.744. Contributing to the variance was a lack of agreement concerning the assessment of joint structures and the way in which the raters translated these evaluations into a classification according to the system of Stulberg et al. CONCLUSIONS: Although intra-rater reliability was marginally acceptable, the degree of variability between the classifications assigned by different raters even after the intervention - calls into question the reliability of the system of Stulberg et al.; consequently, the validity of any treatment decisions, outcome evaluations, or epidemiological studies based on this system is also in question.

Acetabulum↗
PubMed1998

Coiled body numbers in the Arabidopsis root epidermis are regulated by cell type, developmental stage and cell cycle parameters.

We have used whole mount immunofluorescence labelling with the antibody 4G3, raised against the human snRNP-specific protein U2B", and whole mount in situ hybridization with an anti-sense probe to a conserved region of U2 snRNA, in combination with confocal microscopy, to examine the organization of spliceosomal components throughout the development of the Arabidopsis thaliana root epidermis. We show that the number of coiled bodies, nuclear organelles in which splicing snRNPs and snRNAs concentrate, is developmentally regulated in the Arabidopsis root epidermis. Firstly, there is a progression from a small number of coiled bodies in the quiescent centre and initial cells, to a larger number in the cell division zone, returning to a lower number in the cell elongation and differentiation zone. Secondly, trichoblasts (root-hair forming epidermal cells) have on average 1.5 times more and often smaller coiled bodies than atrichoblasts (hairless epidermal cells). Moreover, we have shown that these differences in coiled body numbers are related to differences in cell cycle stage, cell type and developmental stage, but are not due to differences in nucleolar or general metabolic activity per se. We discuss possible explanations, including a model in which coiled bodies coalesce during interphase, for the developmental dynamics of coiled bodies.

Arabidopsis↗
PubMed1998

Inhibition of PhIP mutagenicity by caffeine, lycopene, daidzein, and genistein.

The heterocyclic amine 2-amino-1-methyl-6-phenylimidazo[4,5-beta]pyridine NPhIP) is a major dietary component in individuals eating cooked meats or fish. This heterocyclic amine requires biochemical activation, mainly through cytochrome P4501A2, and can be detoxified chiefly by 4'hydroxylation through other cytochromes, and be in turn converted through phase 2 enzymes to readily excreted conjugates. The active form of PhIP is mutagenic in Salmonella typhimurium TA98 and is a useful substrate to study the possible chemoprotective action of phytochemicals. We found that black and green tea depressed the mutagenicity of PhIP in dose-related fashion, and decaffeinated tea was less powerful an inhibitor. This led to the study of caffeine, that displayed effective dose-related inhibition of the mutagenicity of PhIP. Other antioxidants such as lycopene, the active antioxidant from tomatoes, and daidzein and genistein from soy products, also had a dose-related inhibition of the mutagenicity of PhIP. We conclude that PhIP is a good substrate found in several human foods to determine the protective effect of phytochemicals from vegetables, and beverages.

Antioxidants↗
PubMed1998

The ROOT HAIRLESS 1 gene encodes a nuclear protein required for root hair initiation in Arabidopsis.

The epidermis of Arabidopsis wild-type primary roots, in which some cells grow hairs and others remain hairless in a position-dependent manner, has become an established model system to study cell differentiation. Here we present a molecular analysis of the RHL1 (ROOT HAIRLESS 1) gene that, if mutated, prevents the formation of hairs on primary roots and causes a seedling lethal phenotype. We have cloned the RHL1 gene by use of a T-DNA-tagged mutant and found that it encodes a protein that appears to be plant specific. The predicted RHL1 gene product is a small hydrophilic protein (38.9 kD) containing putative nuclear localization signals and shows no significant homology to any known amino acid sequence. We demonstrate that a 78-amino-acid sequence at its amino terminus is capable of directing an RHL1-GFP fusion protein to the nucleus. The RHL1 transcript is present throughout the wild-type plant and in suspension culture cells, but in very low amounts, suggesting a regulatory function for the RHL1 protein. Structural evidence suggests a role for the RHL1 gene product in the nucleolus. We have examined the genetic relationship between RHL1 and GL2, an inhibitor of root hair initiation in non-hair cells. Our molecular and genetic data with double mutants, together with the expression analysis of a GL2 promoter-GUS reporter gene construct, indicate that the RHL1 gene acts independently of GL2.

Amino Acid Sequence↗
PubMed1998

The influence of selected herd factors and a badger-intervention tuberculosis-control programme on the risk of a herd-level trade restriction to a bovine population in Ireland.

The risk of a trade restriction to cattle herds between 1990-1994, as a result of failing the tuberculin skin test or disclosure of visible lesions in the abattoir, was compared in two areas in East Offaly, Ireland. Cattle herds from the Project area where badgers were systematically removed over a 7-year period (1989-1995) were compared to herds from a Control area where no wildlife-intervention programme had taken place. A Cox proportional hazard model indicated, for example, that the risk of a herd-level trade restriction to herds with 30 animals in the Control area was 1.4 times the risk to similar-sized herds in the Project area. The study provides evidence that a badger-control programme is effective in reducing the risk of a trade restriction to cattle herds as the badger represents an important reservoir of Mycobacterium bovis infection for cattle.

Animals↗
PubMed1998

Positional information in root epidermis is defined during embryogenesis and acts in domains with strict boundaries.

BACKGROUND: Cell position rather than cell lineage governs most aspects of development in plants. However, the nature and the origin of positional information remains elusive. Animal epidermal patterning relies in many cases on positional information provided by cell-cell communication. The epidermal layer of the Arabidopsis root is made of alternating files of two cell types and thus presents a simple pattern to study positional mechanisms. RESULTS: Clonal analysis of the root epidermis in combination with molecular and morphological markers has shown that cell fate is determined by position relative to the underlying cell layer, the cortex. The epidermal pattern appears to be organised during embryogenesis. Fate is not fixed in the developing root, though, as cells that move into a position previously occupied by neighbour cells ablated using laser microsurgery change fate. In contrast, cell fate is not altered when communication with living neighbour cells is impaired. Precise mapping of the influence of the position of extracellular cues on cell fate has shown that domains of positional information are organised with well-defined boundaries. CONCLUSIONS: Cell-fate specification in the root epidermis relies on positional information that is organised in stable domains with sharp boundaries. The epidermal pattern is defined during embryogenesis and positional information remains active in the root until the initiation of cell morphogenesis. The origin of some positional cues might be extracellular.

Arabidopsis↗
PubMed1998

Control of cell division in the root epidermis of Arabidopsis thaliana.

The formation of the root epidermis in Arabidopsis thaliana provides a simple model to study mechanisms underlying patterning in plants. In this paper we have analyzed the relationships between cell fate specification and the pattern of cell division that occur in the root epidermis. Using clonal analysis, the two cell types of the developing root epidermis, trichoblasts and atrichoblasts, were distinguished by different rates of cell division, highest in trichoblasts. This character appears to be dependent on TTG which controls epidermal cell fate specification. The ability of epidermal cells to undergo longitudinal divisions which are involved in the control of the radial symmetry was shown to be controlled in a cell-specific manner by TTG. The control of the rate and the orientation of cell division in the root meristem epidermal layer thus appear to be under the control of cell fate specification mechanisms.

Arabidopsis↗
PubMed1998

Stomata patterning on the hypocotyl of Arabidopsis thaliana is controlled by genes involved in the control of root epidermis patterning.

Stomata complexes are epidermal specialized structures typical of the upper aerial part of plants (shoot). In the model plant Arabidopsis thaliana, we show that in the hypocotyl (the) junction between the shoot and the root), stomata are organized according to a clear pattern reminiscent of the root epidermis pattern. Although stomata complexes are typical of the shoot epidermis, their pattern on the hypocotyl is under the control of genes involved in root epidermis patterning. Moreover, we have isolated a GFP marker line for the hypocotyl epidermal cells which do not differentiate stomata complexes. In this line the root and the hypocotyl epidermal patterns are similar. Our data support the existence of interactions between developmental mechanisms involved in the control of the apical/basal polarity and the radial symmetry of the plant body.

Arabidopsis↗
PubMed1998

Root pattern: shooting in the dark?

Root pattern formation takes place in the embryo and is propagated through subsequent growth and development of the seedling root meristem. Pattern is maintained by positional cues and in some cases by local cell interactions. Such interactions are involved in the balance between cell division and differentiation in cells neighbouring the quiescent centre. This balancing act also occurs in the shoot in which the genetic circuitry underpinning this phenomenon has been characterised. The common genetic mechanism of patterned cell differentiation in the epidermis between the root and shoot extends these parallels further. Given that these shared mechanisms exist, it is tempting to speculate that they reflect the fact that roots may be derived, shoot structures. Alternatively such mechanisms may reflect an evolutionary convergence of genetic mechanism.

Body Patterning↗
PubMed1998

Comparative mouse skin tumorigenicity and induction of Ha-ras mutations by bay region diol epoxides of 5-methylchrysene and 5,6-dimethylchrysene.

We compared the tumor-initiating activities toward mouse skin of two structurally related polycyclic aromatic hydrocarbon diol epoxides: racemic anti-1,2,3,4-tetrahydro-5,6-dimethylchrysene-1,2-diol-3,4-epoxide (5,6-diMeCDE) and racemic anti-1,2,3,4-tetrahydro-5-methylchrysene-1,2-diol-3,4-epoxide (5-MeCDE). Tumors induced by these diol epoxides were analysed for mutations in the Ha-ras gene. 5,6-diMeCDE is derived from the non-planar parent compound 5,6-dimethylchrysene, and reacts to approximately equal extents with dA and dG in DNA, whereas 5-MeCDE is derived from a nearly planar parent compound, 5-methylchrysene, and reacts mainly with dG in DNA. 5,6-diMeCDE, at initiating doses of 33, 100 or 400 nmol per mouse, induced 1.2, 2.2 and 6.2 skin tumors per mouse, respectively. It was significantly less tumorigenic than 5-MeCDE which induced 3.1, 7.5 and 9.1 skin tumors per mouse at the same doses. Tumors induced by 5,6-diMeCDE had a large number of CAA-->CTA mutations in codon 61 of the Ha-ras gene: 50, 55 and 75% of the tumors analysed had this mutation at the 33, 100 and 400 nmol doses. No mutations were found in codons 12 and 13 in the tumors induced by 5,6-diMeCDE. In contrast, CAA-->CTA mutations in codon 61 were rarely seen in tumors induced by 5-MeCDE. At the highest dose of 5-MeCDE, 20% of the tumors analysed had mutations at G of codons 12 and 13. The results of this comparative study support the hypothesis that mutations in the Ha-ras gene in mouse skin tumors induced by PAH diol epoxides occur as a result of their direct reaction with the gene. However, pathways other than the commonly observed Ha-ras codon 61 mutations are clearly important in mouse skin tumorigenesis by these diol epoxides.

Animals↗
PubMed1998

Cell fate in plants. Lessons from the Arabidopsis root.

Classical studies in plant development have indicated that the fate of plant cells is fixed late, after cell division has ceased. Earlier commitment events are therefore considered reversible. To gain a mechanisatic understanding of the processes involved in specification and fixation of cell fate in plants, we are using the Arabidopsis root epidermis as a model system. The Arabidopsis root epidermis is composed of two cell types whose pattern of differentiation is directed by positional cues during development. Examination of mutations has identified genes involved in the establishment of cell fate specification in this tissue. TRANSPARENT TESTA GLABRA (TTG) and GLABRA2 (GL2) are positive regulators of non-hair fate and are active during the early differentiation of the epidermis in the meristem. GL2 encodes a homeobox protein which is expressed in non-hair cells in the meristem and is positively regulated by TTG. Mutations in genes involved in the regulation of ethylene biosynthesis and signal transduction indicate that ethylene is a positive regulator of hair cell fate. Treatment of ttg and gl2 plants with modulators of ethylene biosynthesis indicate that ethylene acts down stream of TTG and GL2 during the fate specification process. The relationship between meristem organisation and the mechanism underpinning the establishment of cell fate in other systems is also discussed.

Arabidopsis↗
PubMed1997

The COW1 locus of arabidopsis acts after RHD2, and in parallel with RHD3 and TIP1, to determine the shape, rate of elongation, and number of root hairs produced from each site of hair formation.

Two recessive mutant alleles at CAN OF WORMS1 (COW1), a new locus involved in root hair morphogenesis, have been identified in Arabidopsis thaliana L. Heynh. Root hairs on Cow1- mutants are short and wide and occasionally formed as pairs at a single site of hair formation. The COW1 locus maps to chromosome 4. Root hairs on Cow1- plants form in the usual positions, suggesting that the phenotype is not the result of abnormal positional signals. Root hairs on Cow1- roots begin hair formation normally, forming a small bulge, or root hair initiation site, of normal size and shape and in the usual position on the hair-forming cell. However, when Cow1- root hairs start to elongate by tip growth, abnormalities in the shape and elongation rate of the hairs become apparent. Genetic evidence from double-mutant analysis of cow1-1 and other loci involved in root hair development supports our conclusion that COW1 is required during root hair elongation.

Alleles↗
PubMed1997

Structural and genetic analysis of epidermal cell differentiation in Arabidopsis primary roots.

In a screen designed to identify genes in the specification of epidermal cell fate in Arabidopsis primary roots we have isolated 8 new mutants that fall into 6 complementation groups corresponding to the 'root hairless' genes RHL1, RHL2 and RHL3 and the 'ectopic root hair' genes ERH1, ERH2 and ERH3. The erh2 mutant is allelic to pom1, a conditional root expansion mutant, and reveals a possible link between epidermal root hair initiation and radial cell expansion. Apart from erh1 the mutants also show defects in shoot development, indicating a complex role for the affected genes. Mutant phenotypes in the patterning and shape of leaf trichomes in rhl1, rhl2, rhl3 and erh3 were particularly obvious. The root hairless mutants are only partly responsive to increased ethylene concentrations, while the ectopic root hair mutants are fully responsive to reduced concentrations of ethylene, a permissive regulator of root hair initiation. This result and the analysis of double mutants suggest a complex pathway leading to root hair initiation that requires the RHL and ERH genes for correct differentiation.

Arabidopsis↗
PubMed1996

Tea polyphenols as inhibitors of mutagenicity of major classes of carcinogens.

Previous research suggested that the mutagenicity of some genotoxic carcinogens, mainly heterocyclic amines, was decreased by green or black tea extracts, or tea polyphenol fractions. Thus, it seemed important to test a variety of genotoxic carcinogens with distinct chemical structures and means of biochemical activation as regards modification of mutagenicity in appropriate strains of Salmonella typhimurium by 3 concentrations of polyphenols 60, 100, or B, standard commercial polyphenol preparations from green or black tea. Polyphenols sharply decreased the mutagenicity of a number of aryl- and heterocyclic amines, of aflatoxin B1, benzo[a]pyrene, 1,2-dibromoethane, and more selectively, of 2-nitropropane, all involving an induced rat liver S9 fraction. Good inhibition was found with 2 nitrosamines that required a hamster S9 fraction for biochemical activation. No effect was found with 1-nitropyrene, and with the direct-acting (no S9) 2-chloro-4-methyl-thiobutanoic acid. Thus, with some exceptions, polyphenols considerably decreased the mutagenicity of diverse types of carcinogens.

Amines↗
PubMed1996

Phosphorylation-dependent targeting of c-Jun ubiquitination by Jun N-kinase.

Ubiquitination of key cellular regulatory proteins marks them for efficient degradation via the proteasome pathway. The delta domain of c-jun is essential for its ubiquitination and also for the activating phosphorylation of neighboring serines by the stress activated jun-N-terminal kinases (JNK). Using an in vitro model system we demonstrate that JNK is among the hydrophobic binding proteins that target c-jun for efficient ubiquitination. Immunodepletion of JNK markedly inhibits c-jun ubiquitination. Conversely, c-jun ubiquitination is increased by adding purified JNK2 or extracts prepared from cells transfected with JNK2. Although c-jun ubiquitination is enhanced by JNK, the phosphorylation of c-jun on Ser73 by JNK protects c-jun from ubiquitination and prolongs its half-life. The dual activity of JNK in targeting c-jun for ubiquitination or in protecting c-jun from entering this pathway via phosphorylation points to the role of JNK in the control of c-jun stability in cells exposed to environmental stress or inflammatory cytokines.

Animals↗