Search PubMed⌕ Search

Biomedical subjects

A Caplan

Publications and source records attributed to A Caplan.

At least 55 records · Page 3Linked to original sources
PubMed1991

Organ-dependent regulation of a plant promoter isolated from rice by 'promoter-trapping' in tobacco.

A vector containing a transcriptionally inactive neomycin phosphotransferase II gene was used to select promoter sequences from a pool of random genomic DNA fragments. This paper describes how one such sequence (P4.7) isolated from Oryza sativa acts as a hormonally regulated promoter in Nicotiana tabacum. Relative expression ratios in leaf, root, midrib, callus, and stem tissue of tobacco plants are 1:5:4:10:17. Histochemical assays show that P4.7 activates the uidA reporter gene throughout the phloem and cortex of tobacco stems. Transcription from the P4.7 fragment is inducible in leaf tissue by low levels of alpha-naphthalene acetic acid or 6-benzyl-aminopurine, even when cell proliferation is inhibited by colchicine or hydroxyurea. Conversely, 1% DMSO was found to inhibit activation of P4.7 without interfering with callus formation. The fragment contains TATA and CAAT sequences normally found at the 5' end of many plant genes, and an additional region homologous to sequences located in similar positions in a variety of similarly regulated promoters. Promoter deletion and fusion experiments have indicated the location of a stem enhancer element in P4.7. The promoter trap system we have described may potentially be used to characterize transcriptional factors common to monocot and dicot species.

Base Sequence↗
PubMed1990

Characterization of a rice gene showing organ-specific expression in response to salt stress and drought.

Protein changes induced by salinity stress were investigated in the roots of the salt-sensitive rice cultivar Taichung native 1. We found eight proteins to be induced and obtained partial sequences of one with a molecular mass of 15 kilodaltons and an isoelectric point of 5.5. Using an oligonucleotide probe based on this information, a cDNA clone, salT, was selected and found to contain an open reading frame coding for a protein of 145 amino acid residues. salT mRNA accumulates very rapidly in sheaths and roots from mature plants and seedlings upon treatment with Murashige and Skoog salts (1%), air drying, abscisic acid (20 microM), polyethylene glycol (5%), sodium chloride (1%), and potassium chloride (1%). Generally, no induction was seen in the leaf lamina even when the stress should affect all parts of the plant uniformly. The organ-specific response of salT is correlatable with the pattern of Na+ accumulation during salt stress.

Amino Acid Sequence↗
PubMed1989

An Auxin-Regulated Gene of Arabidopsis thaliana Encodes a DNA-Binding Protein.

We have isolated a single-copy gene from the plant Arabidopsis thaliana, called dbp, which encodes a lysine-rich, DNA-binding protein. The Dbp protein has a molecular weight and a composition resembling histone H1. When the dbp gene was expressed in bacteria, the protein product bound DNA nonspecifically. The dbp gene is expressed constitutively in all parts of the plant but is induced five times above this basal level in apical zones. In vitro hormone-depletion experiments showed that the expression in the shoot apex could be induced by exogenous auxin. In situ hybridizations in the root apex indicated that the expression of dbp is enhanced in the region of cell division.

Journal Article↗
PubMed1989

Evaluation of selectable markers for rice transformation.

A variety of expression systems and selection régimes have been developed to transform plants such as tobacco, petunia, and tomato. We investigated several of these to determine whether the promoters and selectable markers used in dicotyledonous plants are suitable for selecting transformed rice callus. We compared transient expression driven by constitutive and regulated promoters in rice (Oryza sativa) protoplasts and found that the 2' promoter of the octopine T-DNA is approximately 3 to 4 times more efficient than the CAMV 35S promoter, 10 times more efficient than the nos promoter and the 1' promoter, and more than 100 times better than two other regulated plant promoters. Similar results were obtained in tobacco (Nicotiana tabacum) protoplasts with the exception that the nos promoter was expressed nearly 10 times better in rice. Further studies demonstrated that rice callus growth is sensitive to low concentrations of methotrexate, phosphinothricin, and bleomycin, and to moderate concentrations of G418 and hygromycin, but is only partially inhibited by relatively high concentrations of kanamycin. Finally, we tested the ability of stably introduced resistance genes to protect callus against some of the selective agents. Genes that inactivated phosphinothricin or G418 permitted transformed calli to grow almost unimpeded on toxic concentrations of these selective agents. However, a gene conferring resistance to methotrexate could not be used to select for activily growing transformants. Southern analysis of the transformed cell lines demonstrated that 50% of the transformants contained a single plasmid copy and that nearly all integrated copies showed rearrangements. These results on the use of selectable markers in rice should facilitate efforts to obtain transformants of this important grain.

Journal Article↗
PubMed1989

Multi-course sequential learning as a model for content integration: ethics as a prototype.

Multi-course sequential learning (MCSL), a model for integrating content throughout the curriculum, is described using ethics education as a prototype. In this model, content is presented via a vertical course, with units embedded in existing courses across various levels of the nursing program, which is designed to provide coherent organization of content, visibility, and accountability, and to prevent gaps and unnecessary duplication. This article describes the process of developing an Ethics MCSL, which is being implemented and evaluated with support from a three-year grant from the Fund for the Improvement of Postsecondary Education (FIPSE).

Curriculum↗
PubMed1989

Wrestling with the larger picture: placing ethical behavior in clinical situations in context.

This article provides an account of the use of a model-building process as an educational strategy for the teaching of ethics. Designed to integrate students' growing knowledge and skill in nursing with their intellectual and professional development, this model-building process has its theoretical foundations in cognitive moral development theory, and in an integrative approach to nursing education called Multi-Course Sequential Learning (MCSL).

Clinical Competence↗
PubMed1987

Perturbation of chromatin structure in the region of the adult beta-globin gene in chicken erythrocyte chromatin.

An EcoRI chromatin fragment containing the adult beta-globin gene and flanking sequences, isolated from chicken erythrocyte nuclei, sediments at a reduced rate relative to bulk chromatin fragments of the same size. We show that the specific retardation cannot be reversed by adding extra linker histones to native chromatin. When the chromatin fragments are unfolded either by removing linker histones or lowering the ionic strength, the difference between globin and bulk chromatin fragments is no longer seen. The refolded chromatin obtained by restoring the linker histones to the depleted chromatin, however, exhibits the original sedimentation difference. This difference is therefore due to a special property of the histone octamers on the active gene that determines the extent of its folding into higher-order structure. That it is not due to the differential binding of linker histones in vitro is shown by measurements of the protein to DNA ratios using CsCl density-gradients. Both before and after selective removal of the linker histones, the globin gene fragment and bulk chromatin fragments exhibit only a marginal difference in buoyant density. In addition, we show that cleavage of the EcoRI fragment by digestion at the 5' and 3' nuclease hypersensitive sites flanking the globin gene liberates a fragment from between these sites that sediments normally. We conclude that the hypersensitive sites per se are responsible for the reduction in sedimentation rate. The non-nucleosomal DNA segments appear to be too long to be incorporated into the chromatin solenoid and thus create spacers between separate solenoidal elements in the chromatin, which can account for its hydrodynamic behaviour.

Animals↗
PubMed1986

Moral community and the responsibility of scientists.

There is a quaint term in English for describing the science of the care and production of domestic animals--animal husbandry. While not particularly useful as a description of the scientific methods by which such production is achieved, the term does capture what I believe is the moral ethos which ought to govern the scientific treatment of animals in the context of scientific experimentation. While great attention has been given to the claims of some philosophers and animal welfare advocates that animals have rights, less attention has been paid either to alternative foundations for conferring moral standing on animals, or, on the nature of the duties and responsibilities that would arise if it were true that animals could be said to have moral rights. I will argue that animals, or most animals, cannot reasonably be said to have moral rights. And even if one decides to stretch this term to include all animals, it cannot be done without conflating what I believe to be important differences in the moral standing of humans and animals. Rather than attempt to motivate humane treatment and reduction in animal use on the basis of animal rights I argue that scientists have an obligation, based upon their duty to care for the helpless and the powerless who can nonetheless be wronged, to act as stewards toward animals. Husbandry carries the connotation of care for a household and I believe this is the ethos that should pervade the animal laboratory or storage facility.

Animal Husbandry↗
PubMed1983

Genetic analysis of T-DNA transcripts in nopaline crown galls.

Plant crown gall tumor cells result from the insertion and expression of a defined DNA sequence, called T-DNA, which is derived from the Ti plasmid, harbored by Agrobacterium tumefaciens strains. To study the function of the genes of the T-DNA of the nopaline Ti plasmid, pTiC58, a collection of mutants was isolated so that T-DNA genes are inactivated either separately or in various combinations. It was found that no single T-DNA gene or T-region border is absolutely essential for stable tumor formation. We have identified the gene responsible for synthesis in transformed cells of the phosphorylated sugar, agrocinopine, and at least three additional genes controlling the morphology of plant tumors. Two of these latter genes work together to inhibit shoot formation and ensure efficient tumorous growth. Inactivation of these genes can be suppressed by the addition of auxins. The third gene inhibits root formation and appears to play a role in the cytokinin-independent growth of transformed cells. Mutants missing all three genes do not induce tumors, nor shoot or root formation, although the mutant T-DNA sequence is transferred to plant cells.

Arginine↗
PubMed1978

Chromatin structure through the cell cycle. Studies with regeneration rat liver.

Liver nuclei were prepared through the first cell cycle in partially hepatectomized young rats showing 30% parenchymal cell synchrony. To determine if nucleosome structure altered during this period, liver nuclei from sham-operated rats were compared with nuclei isolated at various times after partial hepatectomy. These nuclei were exposed to deoxyribonuclease I (EC 3.1.4.5), deoxyribonuclease II (EC 3.1.4.6) or micrococcal nuclease (EC 3.1.4.7) and the nucleosome-associated DNA length was ascertained. In no case was a difference in the DNA lengths associated with nucleosome structure observed. Differences were observed with regard to the histones and their relative association with nuclear material. When nuclei from normal rat livers were incubated in hypo-osmolar medium 9% of histone 1 and 4% of the other histones were released. These released histones, unlike those remaining bound to the nuclei, showed high [3H]adenosine and [3H]acetate uptakes in vivo. [32P]P1 uptake was also much greater into released than bound histones 1 and 3, but was not different for histone2A. At 3.5-4.5 h after partial hepatectomy, the release of histone 1 was trebled and that of histone 4 doubled. By 13.5 h, when phosphorylation of the bound forms of histones 2A and especially 1 was increased, no further changes in histone release in hypo-osmolar medium were found. The released histones from partially hepatectomized livers had indistinguishable [3H]adenosine uptakes from controls. The roles are discussed of phosphorylation and ADP-ribosylation in labilizing histone binding.

Adenosine Diphosphate↗