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C Dean

Publications and source records attributed to C Dean.

At least 91 records · Page 5Linked to original sources
PubMed1997

Increased Ac excision (iae): Arabidopsis thaliana mutations affecting Ac transposition.

The maize transposable element Ac is highly active in the heterologous hosts tobacco and tomato, but shows very much reduced levels of activity in Arabidopsis. A mutagenesis experiment was undertaken with the aim of identifying Arabidopsis host factors responsible for the observed low levels of Ac activity. Seed from a line carrying a single copy of the Ac element inserted into the streptomycin phosphotransferase (SPT) reporter fusion, and which displayed typically low levels of Ac activity, were mutagenized using gamma rays. Nineteen mutants displaying high levels of somatic Ac activity, as judged by their highly variegated phenotypes, were isolated after screening the M2 generation on streptomycin-containing medium. The mutations fall into two complementation groups, iae1 and iae2, are unlinked to the SPT::Ac locus and segregate in a Mendelian fashion. The iae1 mutation is recessive and the iae2 mutation is semi-dominant. The iae1 and iae2 mutants show 550- and 70-fold increases, respectively, in the average number of Ac excision sectors per cotyledon. The IAE1 locus maps to chromosome 2, whereas the SPT::Ac reporter maps to chromosome 3. A molecular study of Ac activity in the iae1 mutant confirmed the very high levels of Ac excision predicted using the phenotypic assay, but revealed only low levels of Ac re-insertion. Analyses of germinal transposition in the iae1 mutant demonstrated an average germinal excision frequency of 3% and a frequency of independent Ac re-insertions following germinal excision of 22%. The iae mutants represents a possible means of improving the efficiency of Ac/Ds transposon tagging systems in Arabidopsis, and will enable the dissection of host involvement in Ac transposition and the mechanisms employed for controlling transposable element activity.

Arabidopsis↗
PubMed1997

Response of Schwann cells to mitogens in vitro is determined by pre-exposure to serum, time in vitro, and developmental age.

We compared the mitogenic response of Schwann cells freshly isolated from adult, neonatal, and embryonic nerves, and compared these cells with cells that had been cultured in serum for 5 days. DNA synthesis in response to growth factors was measured using bromodeoxyuridine and immunocytochemistry. Freshly isolated adult Schwann cells were unresponsive to growth factors with or without forskolin to elevate intracellular cAMP levels. After 5 days of culture in serum, or alternatively in defined medium containing fibroblast growth factor 2 plus forskolin, or neu-differentiation factor beta2, adult cells were responsive to mitogens, whereas cells cultured in defined medium alone remained unresponsive. Serum also increased expression of type 1 fibroblast growth factor receptor. Freshly isolated embryonic and neonatal Schwann cells in contrast responded to growth factors even in the absence of forskolin. This responsiveness changed with time in culture. Neonatal cells cultured for 5 days in defined medium in the presence or absence of serum no longer responded to FGF alone, but required forskolin for a mitogenic response. Thus, the response of freshly isolated cells to mitogens is developmentally regulated; extrinsic signals are required to render adult cells responsive to mitogens; and with time in culture, neonatal cells develop a requirement for cAMP elevation for mitogenic response.

Animals↗
PubMed1996

A novel repetitive sequence associated with the centromeric regions of Arabidopsis thaliana chromosomes.

The middle repetitive fraction of the Arabidopsis genome has been relatively poorly characterized. We describe here a novel repetitive sequence cloned in the plasmid mi167, and present in approximately 90 copies in the genome of Arabidopsis thaliana ecotype Columbia. Hybridization analysis to physically mapped YAC clones representing Arabidopsis chromosome 4 revealed four mi167-hybridizing loci, all clustered near the centromere. No other loci were detected on YAC clones covering chromosome 4. In situ hybridisation experiments to Arabidopsis chromosome spreads showed that mi167-hybridizing sequences are clustered at the centromeric heterochromatin of all five chromosomes; on two chromosomes the hybridization appeared to be localised on one arm. Additional mi167-hybridizing loci were detected, one of which was adjacent to a non-centromeric, heterochromatic region. This work supports the idea that the majority of middle repetitive DNA in the Arabidopsis genome is clustered. It also adds to our understanding of the organization of the centromere of Arabidopsis chromosome 4.

Arabidopsis↗
PubMed1996

Identification and distribution of seven classes of middle-repetitive DNA in the Arabidopsis thaliana genome.

In order to analyse further the genomic distribution of repetitive sequences in the Arabidopsis genome, we have identified and characterized seven novel repetitive sequences. Analysis of genomic representation, genomic location and DNA sequence divided the seven repeated sequences into two classes. The first was represented by three cosmid subclones (182A, 74A, 191A) carrying sequences that hybridised to up to 20 genomic fragments and showed sequence homology to the genes, Arabidopsis CCR2, Arabidopsis MYB and to various ATP-binding transport proteins. These multigene families mapped to various positions within the genome, as judged by hybridization to YAC clones constituting the Arabidopsis physical map. The second class was represented by four cosmid subclones (106B, 164A, 163A, 278A) that hybridised to between 20 and 300 genomic fragments. One of these, 106B, is a diverged, partial copy of the LTR of the Arabidopsis retrotransposon Athila. The other three sequences showed no homology to known genes or proteins. The distribution of these sequences on chromosome 4 was analysed and sequences hybridizing to 106B, 164A and 163A were found exclusively at the centromeric region of this chromosome. Their detailed arrangement at the centromeric region of chromosome 4, relative to other repeated sequence families and single copy sequences, was determined.

Arabidopsis↗
PubMed1996

A twin study examining the effect of parity on the prevalence of psychiatric disorder.

The study compares the prevalence of current and lifetime psychiatric illness in twin pairs where one twin is more parous than the other. The main finding was that parity did not affect the prevalence of psychiatric disorder. This adds confirmation to the study of Bebbington et al. (1991) that high prevalence rates in women with children is due to an effect of marriage rather than an effect of parity. There was a diagnostic difference between the twins with the less parous twin having significantly more cases of Research Diagnostic Criteria (RDC; Spitzer et al., 1978) major and minor depression and the more parous twin more cases of generalised anxiety disorder. The life events and difficulties in the previous 12 months were also established in the whole group and events and difficulties over the whole of the subjects life for the first 20 pairs. The total number of events in the previous 12 months was significantly higher in the more parous twin of the pair, these were child-related events and not associated with an increased likelihood of current psychiatric illness. There were no differences in the number of events and difficulties during the lifetime between the first 20 twin pairs.

Adult↗
PubMed1996

Monoclonal antibodies to the EGF receptor act as betacellulin antagonists.

Betacellulin (BTC), a recently discovered member of the EGF family that is produced by certain tumour cells, is thought to be involved in autocrine growth by activating the EGF receptor (EGFR). We have investigated whether monoclonal antibodies (mAbs) to the EGFR which act as EGF, TGF alpha and HB-EGF antagonists could also be effective as BTC antagonists by blocking its binding to the EGFR. We report that the binding of 125I-BTC to a range of tumour cells expressing the EGFR was inhibited by rat mAbs that bound to three distinct epitopes on the extracellular domain of the EGFR. We show that one of these mAbs (ICR62) also prevents activation of the EGFR by betacellulin as evidenced by reversal of the effects on the growth of human fibroblasts and the head and neck carcinoma cell line HN5 and by inhibition of receptor phosphorylation in HN5 cells. We conclude that mAbs such as ICR62 have potential for use as therapeutic agents by blocking betacellulin-induced growth of tumours which over-express the EGFR.

Animals↗
PubMed1996

Analysis of the occurrence and nature of repeated DNA in an 850 kb region of Arabidopsis thaliana chromosome 4.

The occurrence and nature of repeated DNA sequences has been analysed within an 850 kb YAC contig on Arabidopsis thaliana chromosome 4. Hybridization analysis with seven RFLP markers, six cosmid contigs, 29 YAC end probes and eight YAC clones showed that a least 585 kb of the 850 kb contained only low-copy sequences. One YAC end probe, EG15C8LE, hybridized to multiple genomic fragments and contained a sequence with predicted protein homology to cytochrome P450 monooxygenases. Another one, EG11B7RE, was found to be non-contiguous with the other YAC clones and contained a dispersed repetitive sequence associated with centromeric regions.

Arabidopsis↗
PubMed1996

Phase I trial and tumour localisation of the anti-EGFR monoclonal antibody ICR62 in head and neck or lung cancer.

The purpose of this study was to determine the effect of the first rat monoclonal antibody (MAb ICR62) to the epidermal growth factor receptor (EGFR) in a phase I clinical trial in patients with unresectable squamous cell carcinomas. This antibody effectively blocks the binding of EGF, transforming growth factor (TGF)-alpha and HB-EGF to the EGFR, inhibits the growth in vitro of tumour cell lines which overexpress the EGFR and eradicates such tumours when grown as xenografts in athymic mice. Eleven patients with squamous cell carcinoma of the head and neck and nine patients with squamous cell carcinoma of the lung, whose tumours expressed EGFR, were recruited. Groups of three patients were treated with 2.5 mg, 10 mg, 20 mg or 40 mg of ICR62 and a further eight patients received 100 mg. All patients were evaluated for toxicity using WHO criteria. Patients' sera were tested for the clearance of MAb ICR62 and the development of human anti-rat antibodies (HARA). No serious (WHO Grade III-IV) toxicity was observed in patients treated with up to 100 mg of antibody ICR62. Antibody ICR62 could be detected at 4 h and 24 h in the sera of patients treated with 40 mg or 100 mg of ICR62. Only 4/20 patients showed HARA responses (one at 20 mg, one at 40 mg and two at 100 mg doses) and of these only the former two were anti-idiotypic responses. In four patients receiving doses of ICR62 at 40 mg or greater, biopsies were obtained from metastatic lesions 24 h later and examined for the localisation of ICR62 using anti-rat antibody reagent. In these patients we showed the localisation of MAb ICR62 to the membranes of tumour cells; this appeared to be more prominent at the higher dose of 100 mg. On the basis of these data we conclude that MAb ICR62 can be administered safely to patients with squamous cell carcinomas and that it can localise efficiently to metastases even at relatively low doses.

Adult↗
PubMed1996

Arabidopsis mutants showing an altered response to vernalization.

Flowering in many plant species is accelerated by a long period of cold temperature, known as a vernalization period. This research investigates how this cold temperature signal is perceived by plant cells and the mechanism by which it influences the transition to flowering. Mutagenesis of the late-flowering, vernalization-responsive, Arabidopsis mutant, fca, has yielded five independent mutations (termed vrn mutations) conferring an altered vernalization response. Allelism tests showed that these mutations fall into at least three complementation groups defining three loci named VRN 1, 2 and 3. The vrn1 and vrn2 mutations did not affect the acclimation response as judged by expression of cold-induced transcripts and freezing tolerance assays. vrn1-1 affected the short-day vernalization response of Landsberg erecta and reduced the vernalization response of other late-flowering Arabidopsis mutants. The acceleration of flowering by GA3 was not affected by vrn1-1. The VRN 1 locus was mapped to chromosome 3.

Acclimatization↗
PubMed1996

Isolation and mapping of a new set of 129 RFLP markers in Arabidopsis thaliana using recombinant inbred lines.

A new collection of 129 Arabidopsis thaliana RFLP markers has been established based upon DNA fragments cloned in the pUC119 plasmid vector and insert end sequences of P1 clones. Dominant/null alleles affecting low-copy number sequences account for nine of the mapped polymorphisms, suggesting that deletions are not rare in A. thaliana. Recombinant inbred (RI) lines were used for mapping these marker loci. RI line-based mapping allows integration of this set of markers with markers previously reported as well as with any markers mapped in the future using this replenishable mapping resource. These markers are useful for map-based gene isolation and genome physical mapping in A. thaliana as well as studies of chromosome colinearity (synteny) with related species.

Arabidopsis↗
PubMed1996

Detailed description of four YAC contigs representing 17 Mb of chromosome 4 of Arabidopsis thaliana ecotype Columbia.

The detailed arrangement of 563 YAC clones comprising four contigs covering approximately 17 Mbp of chromosome 4 is presented. YAC clones were positioned relative to each other and to markers by taking into account marker and end fragment hybridization data and the sizes of all YAC clones. This analysis made it possible to estimate physical distances between the majority of chromosome 4 markers. It also identified a relatively large number of YAC clones containing chimaeric inserts. The YAC contig map of the Columbia ecotype presents an important resource for map-based cloning experiments, rapid mapping of DNA sequences and large-scale genomic sequencing programs.

Arabidopsis↗
PubMed1996

Use of Ac as an insertional mutagen in Arabidopsis.

A pilot-scale transposon mutagenesis experiment using a modified autonomous Activator (Ac) element, Ac delta Nael, was carried out in Arabidopsis thaliana. Four different transformants carrying Ac elements in different and defined genomic locations were used to generate 1000 plants carrying approximately 500 independent germinal transposition events. These plants were then selfed and the 1000 families screened in tissue culture and soil for phenotypic mutants. Fifty different families segregated mutations in their progeny. Preliminary Southern blot analysis of 29 families which segregated mutant progeny, showed that 28 had a transposed Ac. Six of the families were further tested for linkage between the transposed Ac and the mutant phenotype, and instability of the putatively tagged locus. Two of the mutants were shown to be tagged as they were tightly linked to a transposed Ac, and somatic and germinal reversion was associated with loss of Ac. One other mutant locus was shown to be closely linked to a transposed Ac, and therefore was likely to be tagged. The remaining three mutations were not tagged as they were not linked to a transposed Ac. In two of the tagged mutants Ac had transposed to closely linked sites, while in a third mutant the co-segregating Ac had transposed to a site which was not tightly linked to the donor T-DNA. Multiple insertions into the DIF1 locus were found, due to the preferential transposition of Ac to a linked site.

Arabidopsis↗
PubMed1996

Changes in newspaper coverage of cardiovascular health issues in conjunction with a community-based intervention.

Numerous community-based prevention projects, with significant media components, have been conducted over the past decade. Multiple evaluation strategies have been used to document the effectiveness of these interventions, including intermediate measures of community impact such as assessment of media coverage. As part of the evaluation of a community-based intervention (the Bootheel Heart Health Project), dissemination of information on cardiovascular disease (CVD) was measured through a media content analysis of newspapers. Data were analyzed from 23 newspapers in six rural counties in southeastern Missouri for the period October 1988 through August 1993. An increase was observed in CVD-related coverage in the pre-intervention period (mean articles per month = 31.5) compared with the post-intervention period (mean articles per month = 50.7) (F = 10.2; P = 0.003). In supporting data from a separate randomized risk factor survey of 1510 residents in the same area, respondents reported hearing of heart health coalitions primarily through local newspapers. The current study documents increasing print media coverage of cardiovascular health issues in a high-risk, rural area and shows that media content analysis can be a useful evaluation tool in community-based interventions.

Cardiovascular Diseases↗
PubMed1995

The genome of Arabidopsis thaliana.

Arabidopsis thaliana is a small flowering plant that is a member of the family cruciferae. It has many characteristics--diploid genetics, rapid growth cycle, relatively low repetitive DNA content, and small genome size--that recommend it as the model for a plant genome project. The current status of the genetic and physical maps, as well as efforts to sequence the genome, are presented. Examples are given of genes isolated by using map-based cloning. The importance of the Arabidopsis project for plant biology in general is discussed.

Arabidopsis↗
PubMed1995

Physical map and organization of Arabidopsis thaliana chromosome 4.

A physical map of Arabidopsis thaliana chromosome 4 was constructed in yeast artificial chromosome clones and used to analyze the organization of the chromosome. Mapping of the nucleolar organizing region and the centromere integrated the physical and cytogenetic maps. Detailed comparison of physical with genetic distances showed that the frequency of recombination varied substantially, with relative hot and cold spots occurring along the whole chromosome. Eight repeated DNA sequence families were found in a complex arrangement across the centromeric region and nowhere else on the chromosome.

Arabidopsis↗
PubMed1995

QTL analysis of flowering time in Arabidopsis thaliana.

Quantitative trait loci (QTL) analyses based on restriction fragment length polymorphism maps have been used to resolve the genetic control of flowering time in a cross between two Arabidopsis thaliana ecotypes H51 and Landsberg erecta, differing widely in flowering time. Five quantitative trait loci affecting flowering time were identified in this cross (RLN1-5), four of which are located in regions containing mutations or loci previously identified as conferring a late-flowering phenotype. One of these loci is coincident with the FRI locus identified as the major determinant for late flowering and vernalization responsiveness in the Arabidopsis ecotype Stockholm. RLN5, which maps to the lower half of chromosome five (between markers mi69 and m233), only affected flowering time significantly under short day conditions following a vernalization period. The late-flowering phenotype of H51 compared to Landsberg erecta was due to alleles conferring late flowering at only two of the five loci. At the three other loci, H51 possessed alleles conferring early flowering in comparison to those of Landsberg erecta. Combinations of alleles conferring early and late flowering from both parents accounted for the transgressive segregation of flowering time observed within the F2 population. Three QTL, RLN1, RLN2 and RLN3 displayed significant genotype-by-environment interactions for flowering time. A significant interaction between alleles at RLN3 and RLN4 was detected.

Alleles↗