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Biomedical subjects

C Bowler

Publications and source records attributed to C Bowler.

At least 19 recordsLinked to original sources
PubMed2001

Molecular insights into the novel aspects of diatom biology.

Diatoms are unicellular photosynthetic eukaryotes that are thought to contribute as much as 25% of global primary productivity. In spite of their ecological importance in the worlds oceans, very little information is available at the molecular level about the novel aspects of their biology. Recent advances, such as the development of gene transfer protocols, are now allowing the genetic dissection of diatom biology. Notable examples are advances in understanding the genetic basis for the silica-based bioinorganic pattern formation of their cell walls and for elucidating key aspects of diatom ecophysiology. The potentiation of current research will allow an evaluation of the use of diatoms to construct submicrometre-scale silicon structures for the nanotechnology industry and will reveal the molecular secrets underlying their ecological success.

Animals↗
PubMed2000

Perception of environmental signals by a marine diatom.

Diatoms are a key component of marine ecosystems and are extremely important for the biogeochemical cycling of silica and as contributors to global fixed carbon. However, the answers to fundamental questions such as what diatoms can sense in their environment, how they respond to external signals, and what factors control their life strategies are largely unknown. We generated transgenic diatom cells containing the calcium-sensitive photoprotein aequorin to determine whether changes in calcium homeostasis are used to respond to relevant environmental stimuli. Our results reveal sensing systems for detecting and responding to fluid motion (shear stress), osmotic stress, and iron, a key nutrient that controls diatom abundance in the ocean.

Adaptation, Physiological↗
PubMed2000

The role of calcium and activated oxygens as signals for controlling cross-tolerance.

Plants are confronted on a regular basis with a range of environmental stresses. These include abiotic insults caused by, for example, extreme temperatures, altered water status or nutrients, and biotic stresses generated by a plethora of plant pathogens. Many studies have shown that the cellular responses to these environmental challenges are rather similar, which might be why plants resistant to one stress are sometimes cross-tolerant to others. To understand this phenomenon and to be able to take full advantage of it in agriculture, we must determine whether the individual biochemical pathways that make up the responses to each external stimulus are activated by unique, overlapping or redundant signalling systems. We discuss the potential role of signalling molecules, such as calcium and activated oxygen species, in underlying cross-tolerance.

Adaptation, Physiological↗
PubMed1999

Transformation of Nonselectable Reporter Genes in Marine Diatoms.

: We report the genetic transformation of two marine diatoms by microparticle bombardment. The pennate diatom Phaeodactylum tricornutum was transformed with the bacterial gene Sh ble from Streptoalloteichus hindustanus, which confers resistance to the antibiotics phleomycin and zeocin. Transformants contained between 1 and 10 copies of the exogenous DNA integrated into the genome by illegitimate recombination at apparently random locations. Transformation efficiencies were around 10(-6), and individual cell lines could be maintained at -80 degrees C following cryopreservation. Also, P. tricornutum could be transformed simultaneously with two different plasmids, one containing the Sh ble gene and another containing the firefly luciferase gene (LUC) under control of a promoter derived from a fucoxanthin, chlorophyll a/c-binding protein gene (FCP). In these cotransformants, LUC activity was light inducible. The transient transformation of the centric diatom Thalassiosira weissflogii with the bacterial beta-glucuronidase (GUS) gene has also been achieved using similar transformation technology. The availability of gene transfer protocols for marine diatoms, together with a range of functional reporter genes and regulated expression systems, will permit molecular dissection of their biology and allow an assessment of the biotechnological potential of these organisms.

Journal Article↗
PubMed1999

Semi-quantitative RT-PCR analysis of photoregulated gene expression in marine diatoms.

The low cell densities of diatoms and other phytoplankton in culture has precluded the use of classical RNA analysis techniques for routine studies of gene expression in large numbers of samples. This has seriously hampered studies of the basic biology of such organisms. To circumvent this problem, we have developed a high-throughput semi-quantitative RT-PCR-based protocol and used it to monitor expression of a gene encoding a fucoxanthin, chlorophyll a/c-binding protein (FCP) in the centric planktonic diatom Thalassiosira weissflogii. Analysis of FCP gene expression in dark-adapted diatom cultures revealed that mRNA levels increase 5- to 6-fold in response to white light irradiation and peak around 6 to 8 h. To determine the photoreceptors involved in this response action spectra of FCP gene expression were determined using the Okazaki large spectrograph. Responses consistent with the presence of cryptochrome-, rhodopsin- and phytochrome-type receptors could be detected. The apparent presence of phytochrome-mediated responses is of particular interest given the low fluences of red and far-red light wavelengths in the marine environment.

Actins↗
PubMed1999

Phenotype of the tomato high pigment-2 mutant is caused by a mutation in the tomato homolog of DEETIOLATED1.

Tomato high pigment (hp) mutants are characterized by their exaggerated photoresponsiveness. Light-grown hp mutants display elevated levels of anthocyanins, are shorter and darker than wild-type plants, and have dark green immature fruits due to the overproduction of chlorophyll pigments. It has been proposed that HP genes encode negative regulators of phytochrome signal transduction. We have cloned the HP-2 gene and found that it encodes the tomato homolog of the nuclear protein DEETIOLATED1 (DET1) from Arabidopsis. Mutations in DET1 are known to result in constitutive deetiolation in darkness. In contrast to det1 mutants, tomato hp-2 mutants do not display any visible phenotypes in the dark but only very weak phenotypes, such as partial chloroplast development. Furthermore, whereas det1 mutations are epistatic to mutations in phytochrome genes, analysis of similar double mutants in tomato showed that manifestation of the phenotype of the hp-2 mutant is strictly dependent upon the presence of active phytochrome. Because only one DET1 gene is likely to be present in each of the two species, our data suggest that the phytochrome signaling pathways in which the corresponding proteins function are regulated differently in Arabidopsis and tomato.

Amino Acid Sequence↗
PubMed1998

Molecular cloning and characterization of a cDNA encoding asparagine synthetase from soybean (Glycine max L.) cell cultures.

A cDNA encoding glutamine-dependent asparagine synthetase was isolated from dark-adapted Glycine max cell culture. The deduced amino acid sequence showed 76-89% identity with other plant sequences. The gene for asparagine synthetase is expressed predominantly in shoots as compared to roots of etiolated plants and the level of expression decreases following light treatment, suggesting that the gene expression is down-regulated by light.

Amino Acid Sequence↗
PubMed1997

Tuning in to the signals controlling photoregulated gene expression in plants.

Plants have developed flexible mechanisms to respond appropriately to environmental signals. These stimuli are transduced by largely unknown signalling pathways that are likely to be modulated by endogenous developmental signals to produce an integrated response that coordinately regulates gene expression. Light is a critical environmental signal that controls many aspects of plant development via a series of photoreceptors that are able to respond to different light wavelengths. Light is also the principal energy source for photosynthesis. The photosynthetic products are carbohydrates which are translocated in the form of sucrose from the photosynthetic (source) to non-photosynthetic (sink) organs. Consequently, the control of photoregulated genes must integrate developmental inputs with signals derived from the photoreceptors, from the photosynthetic apparatus and from metabolites such as sucrose.

Carbohydrates↗
PubMed1997

Phytochrome-regulated repression of gene expression requires calcium and cGMP.

The plant photoreceptor phytochrome A utilizes three signal transduction pathways, dependent upon calcium and/or cGMP, to activate genes in the light. In this report, we have studied the phytochrome A regulation of a gene that is down-regulated by light, asparagine synthetase (AS1). We show that AS1 is expressed in the dark and repressed in the light. Repression of AS1 in the light is likely controlled by the same calcium/cGMP-dependent pathway that is used to activate other light responses. The use of the same signal transduction pathway for both activating and repressing different responses provides an interesting mechanism for phytochrome action. Using complementary loss- and gain-of-function experiments we have identified a 17 bp cis-element within the AS1 promoter that is both necessary and sufficient for this regulation. This sequence is likely to be the target for a highly conserved phytochrome-generated repressor whose activity is regulated by both calcium and cGMP.

Aspartate-Ammonia Ligase↗
PubMed1997

Molecular cloning and characterization of a cDNA encoding early light-inducible protein from soybean (Glycine max L.).

A cDNA for early light-inducible protein (ELIP) was isolated from Glycine max L. and the nucleotides were sequenced. The cDNA encodes a 192-residue polypeptide of 20.3 kDa. The deduced amino acid sequence included a transit peptide in the amino-terminus and three hydrophobic regions long enough to span the thylakoid membranes, and had a high similarity to those of ELIPs and related polypeptides from other plants.

Amino Acid Sequence↗
PubMed1995

Cloning, subcellular localization and expression of CHL1, a subunit of magnesium-chelatase in soybean.

Mg-insertion is the first committed step in chlorophyll synthesis and is catalyzed by Mg-chelatase. In photosynthetic bacteria, bchI gene product was suggested to be a subunit of Mg-chelatase. We isolated a bchI homolog from a soybean cDNA library and designated it as chlI. CHLI consisted of 421 amino acid residues and the sequence exhibited a high similarity to other BchI homologs. CHLI contained an ATP-binding motif found in other BchI homologs. CHLI was localized in the soluble fraction in soybean chloroplasts, suggesting that it was a stromal subunit of Mg-chelatase. chlI mRNA in cell culture (SB-P) of soybean was reversibly induced by light.

Adenosine Triphosphate↗
PubMed1994

Phytochrome signal transduction pathways are regulated by reciprocal control mechanisms.

Three signal transduction pathways, dependent on cGMP and/or calcium, are utilized by phytochrome to control the expression of genes required for chloroplast development and anthocyanin biosynthesis in plant cells. For example, chs is controlled by a cGMP-dependent pathway, cab is controlled by a calcium-dependent pathway, and fnr is regulated by a pathway that requires both cGMP and calcium. Using a soybean photomixotrophic cell culture and microinjection into the cells of a phytochrome-deficient tomato mutant, we have studied the regulatory mechanisms acting within and between these three signaling pathways. We provide evidence that changes in cGMP levels mediate the observed induction and desensitization of chs gene expression in response to light and demonstrate that high cGMP concentrations cause negative regulation of both the calcium- and the calcium/cGMP-dependent pathways. Conversely, high activity of the calcium-dependent pathway can negatively regulate the cGMP-dependent pathway. We have termed these opposing regulatory mechanisms reciprocal control. In all cases, the molecules that are involved appear to be downstream components of the signal transduction pathways, rather than calcium and cGMP themselves. Furthermore, we have found that the calcium/cGMP-dependent pathway has a lower requirement for cGMP than does the cGMP-dependent pathway. The role of these phenomena in the regulation of plant photoresponses is discussed.

Calcium↗
PubMed1994

Cyclic GMP and calcium mediate phytochrome phototransduction.

We have previously used single-cell assays in a phytochrome-deficient tomato mutant to demonstrate that phytochrome signaling involves heterotrimeric G proteins, calcium, and calmodulin. While G protein activation could stimulate full chloroplast development and anthocyanin pigment biosynthesis, calcium and calmodulin could not induce anthocyanins and were only able to stimulate the development of immature chloroplasts lacking cytochrome b6f and photosystem I core components. We now report that cyclic GMP is able to trigger the production of anthocyanins, and that a combination of cyclic GMP with calcium can induce the development of fully mature chloroplasts containing all the photosynthetic machinery. Furthermore, using reporter genes for these different pathways (cab-gus, chs-gus, and fnr-gus) we demonstrate that cGMP and calcium act primarily by modulating gene expression.

Anthocyanins↗
PubMed1994

Detection of psychiatric disorders in elderly medical inpatients.

In a psychiatric census of a 196-bed acute inpatient Medicine for the Elderly unit, 76.1% of patients resident during 1 week were screened and interviewed in a two-stage diagnostic procedure. Of 153 patients studied, 11.1% were delirious, 26.8% were demented, and 9.2% were depressed. Overall, 56.9% of the cases were identified by ward nurses, and 55.5% by the ward doctors; taken together, ward staff identified 75.0% of the cases (kappa = 0.46), indicating that detection of psychiatric disorder in this population might be improved if doctors and nurses pooled their observations on this aspect of patient assessment.

Aged↗