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Biomedical subjects

D G Müller

Publications and source records attributed to D G Müller.

At least 19 recordsLinked to original sources
PubMed2002

Phycodnaviridae--large DNA algal viruses.

Members and prospective members of the family Phycodnaviridae are large icosahedral, dsDNA (180 to 560 kb) viruses that infect eukaryotic algae. The genomes of two phycodnaviruses have been sequenced: the 331 kb genome of Paramecium bursaria chlorella virus (PBCV-1) and more recently, the 336 kb genome of the Ectocarpus siliculosus virus (EsV-1). EsV-1 has approximately 231 protein-encoding genes whereas, the slightly smaller PBCV-1 genome has 11 tRNA genes and approximately 375 protein-encoding genes. Surprisingly, the two viruses only have 33 genes in common, of which 17 have no counterparts in the databases. The low number of homologous genes between the two viruses can probably be attributed to their different life styles. PBCV-1 is a lytic virus that infects a unicellular, endosymbiotic freshwater green alga whereas, EsV-1 is a lysogenic virus that infects a free-living filamentous marine brown alga. Furthermore, accumulating evidence indicates that the phycodnaviruses and their genes are ancient, thus allowing significant differences to have evolved. This review briefly describes some of the biological properties of the phycodnaviruses, focusing on PBCV-1 and EsV-1, and then compares their genomes.

Chlorella↗
PubMed2001

The complete DNA sequence of the Ectocarpus siliculosus Virus EsV-1 genome.

The Ectocarpus siliculosus Virus-1, EsV-1, is the type-species of a genus of Phycodnaviridae, the phaeoviruses, infecting marine filamentous brown algae. The EsV-1 genome of 335,593 bp contains tandem and dispersed repetitive elements in addition to a large number of open reading frames of which 231 are currently counted as genes. Many genes can be assigned to functional groups involved in DNA synthesis, DNA integration, transposition, and polysaccharide metabolism. Furthermore, EsV-1 contains components of a surprisingly complex signal transduction system with six different hybrid histidine protein kinases and four putative serine/threonine protein kinases. Several other genes encode polypeptides with protein-protein interaction domains. However, 50% of the predicted genes have no counterparts in data banks. Only 28 of the 231 identified genes have significant sequence similarities to genes of the Chlorella virus PBCV-1, another phycodnavirus. To our knowledge, the EsV-1 genome is the largest viral DNA sequenced to date.

Amino Acid Sequence↗
PubMed2001

A comparative study of an in situ adapted diffusion cell and an in vitro Franz diffusion cell method for transdermal absorption of doxylamine.

In order to determine whether a drug shows the potential for percutaneous absorption, both in situ and in vitro studies are used. In vitro studies are good indicators of transdermal drug delivery, but the possibility exists that anatomical changes in excised skin can influence drug delivery. The aim of this study was to compare the in vitro Franz diffusion cell method with an in situ adapted diffusion cell method. A saturated aqueous solution of doxylamine succinate was used as model drug and the receptor phase was an isotonic Sörensen buffered solution. The in vitro permeation studies were conducted using vertical Franz diffusion cells with nude mice skin. For in situ studies, a diffusion cell was implanted under the dorsal skin of a nude mouse, simulating the in vitro method. Both in situ and in vitro experiments were conducted over a period of 12 h during which samples were collected every 90 min. The mean steady-state flux from Franz diffusion cells was 0.164+/-0.045 microg/cm2/h and flux determined by the in situ method was 0.113+/-0.034 microg/cm2/h. A statistical significant difference existed between the permeation results of the in vitro and in situ experimental methods. A subjective, semi-quantitative assessment of histological changes to excised nude mouse skin was done using light microscopy. This showed that excised skin undergoes sub-lethal injury (necrosis) during in vitro experiments, which may lead to increased permeability of the drug. It was noticed that in vitro and in situ permeation results showed very close correlation until approximately 4.5 h after commencement of experiments, after which, the permeation through excised skin increased. It was assumed that cell necrosis occurred to such an extent after approximately 4.5 h, that the barrier function of the stratum corneum decreased and permeation of the drug increased.

Administration, Cutaneous↗
PubMed2001

Intranasal toxicity of selected absorption enhancers.

The intranasal toxicity of selected absorption enhancers (LPC, DM beta CD, N-trimethyl chitosan chloride (TMC) and chitosan hydrochloride) were determined in vivo by investigating the acute microscopic toxic potential on the morphology of rat nasal epithelium with transmission electron microscopy (TEM) and in vitro by measurement of the ciliary beat frequency (CBF), of human ciliated nasal epithelium. TEM evaluations showed that LPC (1% w/v) caused severe epithelial damage and pyknosis. No damage to the rat nasal epithelium was caused by the other absorption enhancers. CBF measurements showed that LPC resulted in total loss of ciliated cells while DM beta CD, TMC and chitosan hydrochloride did not cause any major changes in CBF.

Administration, Intranasal↗
PubMed2000

The brown algal virus EsV-1 particle contains a putative hybrid histidine kinase.

The Ectocarpus siliculosus virus, EsV-1, occurs worldwide in all populations of the filamentous marine brown alga E. siliculosus. We have screened an expression library of EsV-1 restriction fragments and identified a DNA clone with the potential to code for a 52-kDa histidine protein kinase. The derived amino acid sequence includes all homology boxes diagnostic for histidine protein kinases and, in addition, amino acid motifs that are commonly found in response regulators of bacterial two-component signal transduction proteins. Thus, the novel viral protein can be classified as a hybrid histidine protein kinase of a type that has previously been detected in fungi, slime molds, and plants. By using purified antibodies, we found that the protein with its potential kinase activity is located on the outer shell of viral particles. This is the first report on a two-component regulator-like protein in viruses and could provide the basis for speculations with regard to the evolution of EsV-1 and related viruses.

Amino Acid Sequence↗
PubMed2000

Characterization and immunolocalization of major structural proteins in the brown algal virus EsV-1.

The Ectocarpus siliculosus virus (EsV-1) is endemic in all populations of the cosmopolitan filamentous brown alga Ectocarpus siliculosus. EsV-1 has a large circular double-stranded DNA genome of about 320 kilobase pairs, and a complex virion structure with a central nucleoprotein core surrounded by several proteinaceous layers. To investigate the protein composition of the virion, we screened an expression library of EsV-1 with antibodies raised against purified detergent-disrupted viral particles. We isolated several clones encoding novel structural proteins and investigated two of them in detail. These clones encode viral proteins vp55 and vp74. Electron microscopy reveals that vp55 is most likely a component of the surface of the viral core, whereas vp74 may be part of an inner core structure. To initiate a genetic analysis, we sequenced regions of the EsV-1 genome encoding vp55 and vp74 and found several adjacent open reading frames with the potential to code for several interesting viral proteins including a putative calcium-binding protein, a collagen-like protein, and a RING finger protein.

Amino Acid Sequence↗
PubMed2000

The influence of the physicochemical characteristics and pharmacokinetic properties of selected NSAID's on their transdermal absorption.

The purpose of this study was to determine the plasma concentrations of selected NSAIDs after topical gel administration and to determine the influence of the physicochemical characteristics of these drugs on transdermal absorption. Plasma concentrations of the drugs were determined using high performance liquid chromatography. The logP values obtained from literature for piroxicam, ketoprofen, naproxen, ibuprofen and indomethacin, (1.8, 0.97, 3.22, 3.6 and 3.8, respectively) correlated with the area under the plasma-time curve (AUC) values. The AUC values determined were 527.00 (piroxicam) 269. 45 (ketoprofen) 258.65 (naproxen) 243.22 (indomethacin) and 88.09 (ibuprofen) microg/ml per h. It was concluded that the most reliable parameter for transdermal absorption was the lipophilic character of a drug (logP value). The molecular mass, solubility constraint and percentage unionized moiety can only be used in combination with other properties in the prediction of possible transdermal drug delivery.

Administration, Cutaneous↗
PubMed2000

Maullinia ectocarpii gen. et sp. nov. (Plasmodiophorea), an intracellular parasite in Ectocarpus siliculosus (Ectocarpales, Phaeophyceae) and other filamentous brown algae.

An obligate intracellular parasite infecting Ectocarpus spp. and other filamentous marine brown algae is described. The pathogen forms an unwalled multinucleate syncytium (plasmodium) within the host cell cytoplasm and causes hypertrophy. Cruciform nuclear divisions occur during early development. Mature plasmodia become transformed into single sporangia, filling the host cell completely, and then cleave into several hundred spores. The spores are motile with two unequal, whiplash-type flagella inserted subapically and also show amoeboid movement. Upon settlement, cysts with chitinous walls are formed. Infection of host cells is accomplished by means of an adhesorium and a stachel apparatus penetrating the host cell wall, and injection of the cyst content into the host cell cytoplasm. The parasite is characterized by features specific for the plasmodiophorids and is described as a new genus and species, Maullinia ectocarpii.

Animals↗
PubMed1996

Comparison of two DNA viruses infecting the marine brown algae Ectocarpus siliculosus and E. fasciculatus.

The marine brown algal genus Ectocarpus contains two species, E. siliculosus and E. fasciculatus. Field populations of both species include plants with infection symptoms caused by DNA viruses. We have established clonal cultures from infected and normal host plants and investigated the properties of the endogenous viruses. Both host species contain virus particles with a hexagonal cross-section and a diameter of ca. 150 nm. The genomes of both virus types consist of double-stranded DNA, approximately 320 kb in size. Restriction digestion with Sfil revealed differences between the two virus genomes. However, PCR experiments suggest that at least one gene, which encodes a major capsid protein, is quite similar in both virus species. In cross-infection experiments the E. siliculosus virus did not initiate an infection cycle in E. fasciculatus. In contrast, the E. fasciculatus virus infected E. siliculosus zoospores. The resulting plants showed aberrant symptoms and produced virus particles which were not infectious. We conclude that the two Ectocarpus species are hosts for different, but closely related viruses.

Capsid↗
PubMed1995

Coat protein of the Ectocarpus siliculosus virus.

Ectocarpus siliculosus virus, EsV, multiplies in sporangia and gametangia of the marine brown alga Ectocarpus siliculosus. We describe an improved method for the isolation of morphologically intact and infectious virus from diseased plants. We show that treatment of virus particles with high concentrations of CsCl results in a substantial loss of structural proteins. One of the proteins which resists CsCl treatment is glycoprotein-1, the largest of the three viral glycoproteins. We have isolated an EsV genomic fragment with an open reading frame encoding glycoprotein-1. The predicted amino acid sequence is rich in hydrophilic amino acids, but contains hydrophobic regions close to the amino and carboxy termini. A discrepancy between the molecular weight predicted from the coding region and the molecular weight determined by gel electrophoresis suggests that proteolytic processing is required for the maturation of the protein.

Amino Acid Sequence↗
PubMed1993

Genome structure of a virus infecting the marine brown alga Ectocarpus siliculosus.

We describe a procedure for the isolation of virus particles from the marine brown alga Ectocarpus siliculosus. Virus particles are composed of at least 13 different polypeptides, including two glycoproteins, and double-stranded DNA. A typical virus DNA preparation contains three fractions, namely linear DNA and circular DNA, each composed of about 320 kilobase pairs, as well as DNA fragments, 10 to 60 kilobase pairs in size. The large linear and the circular DNA contain single-stranded regions (average length: 2.9 kilobase). We propose that the native Ectocarpus virus genome is a circular DNA molecule whose double strand is interrupted by single-stranded regions. During the preparation procedure, the DNA circles tend to break at the single-stranded sites producing large linear as well as fragmented DNA.

DNA, Viral↗
PubMed1988

Qualitative and quantitative determination of pheromone secretion in female gametes of Ectocarpus siliculosus (Phaeophyceae).

Pheromone secretion in living female gametes of Ectocarpus siliculosus was examined by closed-loop extraction and gas chromatography. The pheromone (ectocarpene) recovery efficiency was calibrated with synthetic ectocarpene and was found to depend strongly on the volume of the closed-loop system. Maximum extraction efficiency of ectocarpene (17.4%) was obtained with a small-volume system. In addition to the main compound ectocarpene, the pheromone bouquet of E. siliculosus contained minor amounts of hormosirene, multifidene and dictyotene, which until now are known only as sperm-attractants in other brown algae. The pheromone bouquet was identical in 4 clones of different geographic origins. Settled female gametes of Ectocarpus siliculosus continued to secrete pheromone and to attract male gametes for up to 7 h after their release with an ectocarpene secretion rate of 1 x 10(5) molecules s-1 cell-1.

Chromatography, Gas↗
PubMed1984

Differentiation of algal chemoreceptors. A comparative receptor study with two seaweed pairs: Cutleria multifida/Syringoderma phinneyi and Desmarestia aculeata/Ectocarpus siliculosus (Phacophyceae).

Gamete encounter in the reproduction of brown algae is supported by lures produced by the female cells. These signals are low-molecular-mass, volatile, olefinic hydrocarbons. Specific receptors on the motile male gametes recognize the pheromones at threshold concentrations as low as 6.5 pmol/l. The pheromones are possibly bound by dispersion and dipolar interactions. Tight fitting has to compensate for these weak contact forces. This causes strong chiral discrimination (relative affinities to enantiomeric lures 1:100). Structurally related messengers with identical substitution patterns and overall space filling are mutually distinguished in several species by means of altered topologies in their receptor mould. Responses to systematically varied synthetic bis-alkenyl-cyclopentene pheromones showed that the sensors of Syringoderma and Cutleria androgametes consist of a mosaic of attachment sites individually adapted to specific structural elements in the messenger molecule. They may be permutated to afford optimal binding. An alternative strategy: distinct reading of electron density combined with variation of sensitivity, brings about 'fidelity' in signal transmission by the alkylated cycloheptadiene pheromones in two species of Desmarestia and Ectocarpus. Inhibition of chemotaxis by ectocarpene is observed in Ectocarpus males in the presence of desmarestene, the lure of Desmarestia, and related parapheromones. This indicates complex interactions between different species of algae sharing a common habitat, in their defense of living space.

Animals↗
PubMed1983

Comparative receptor study in gamete chemotaxis of the seaweeds Ectocarpus siliculosus and Cutleria multifida. An approach to interspecific communication of algal gametes.

Gamete fusion in phaeophytes is initiated by olefinic hydrocarbons as messenger substances. They are secreted by the female gametes and act on male gametes or gametangia. The sensitivity thresholds of the androgametes of Ectocarpus siliculosus and Cutleria multifida, two brown algae of different evolutionary stages, for ectocarpene, which is produced by either species, were found to be 0.89 nmol/l and 8.9 nmol/l sea water, respectively. The molecular recognition mechanism is shown to be identical for these two species and probably also for most other phaeophytes. The pheromones involved are structurally related and sometimes resemble each other in their overall pi-electron distribution (e.g. ectocarpene and multifidene). Knowing the specific messenger, the typical response behaviour of each receptor involved, the pheromone productivity of the considered species as well as other biological parameters (phytogeographic distribution, the natural benthic habitat and times of fertilization), a method is presented to uncover possible interspecific cross-reactions of such algal communication systems as a 'chemical warfare' device in their fight for living space.

Animals↗
PubMed1982

Binding-mechanism and sensitivity in gamete chemotaxis of the phaeophyte Cutleria multifida.

Female gametes of the marine brown alga Cutleria multifida discharge multifidene into the water to attract the swimming males. The physicochemical principle of interaction between semiochemical and membrane receptor site is seen in mutual but complementary induced dipoles. Halogenated derivatives of multifidene with intact overall structure and stereochemistry but altered electronic properties were synthesized and assayed as lures. A direct correlation was observed between increasing polarizability and biological activity, thus proving the proposed mechanism. The low threshold concentration of this communication system (4 X 10(9) molecules/ml), together with a detailed knowledge of the gamete's architecture, swimming velocity and stimulus response time, indicates that very few, may be even single, molecules are able to trigger the sensomotoric chain. The rigidity of the natural signal molecule was recognized as an important element in inducing conformational fitting in the ligand/receptor complex.

Binding Sites↗
PubMed1979

Isolation of a spermatozoid-releasing and -attracting substance from female gametophytes of Laminaria digitata.

SEVERAL dioecious marine brown algae have been valuable in studying chemical communication during sexual reproduction. For example, female gametes of Ectocarpus siliculosus, Cutleria multifida and Fucus serratus secrete olefinic hydrocarbons into the seawater to attract male gametes(1-3). A more complex system is found in the order Laminariales, which includes the large kelps. Mature female gametophytes in members of this group secrete highly volatile material with spermatozoid-attracting activity, which also induces explosive discharge of antheridia(4). We report here a study of this volatile material. It is now possible to attribute spermatozoid-releasing and -attracting activity to one specific compound.

Journal Article↗