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R Christen

Publications and source records attributed to R Christen.

At least 19 recordsLinked to original sources
PubMed1992

Comparative variation of morphological and molecular evolution through geologic time: 28S ribosomal RNA versus morphology in echinoids.

The comparatively good fossil record of post-Palaeozoic echinoids allows rates of morphological change to be estimated over the past 260 million years and compared with rates of molecular evolution. Parsimony analysis of morphological data, based predominantly on skeletal characteristics, and parsimony, distance and maximum likelihood analyses of molecular data, from the first 380 bases from the 5' end of the 28S rRNA molecule, for 10 species of echinoid produce congruent phylogenies. The molecular sequence chosen is demonstrably far from saturation and sister groups have divergence times ranging from about 15 to 260 Ma. Parsimony analysis allows the great majority of molecular and morphological apomorphies to be placed in one of 18 independent geological time intervals, providing a direct measure of rates of evolution for periods in the geological past. Because most molecular fixed point mutations in our sequences cannot be polarized unambiguously by outgroup comparison (making the outgroup states effectively random), distance and parsimony analyses both tend spuriously to root the echinoid tree on the longest internal branch. A topology identical to that derived from morphological data is, however, obtained using Maximum Likelihood and also parsimony analysis where outgroup rooting is restricted to more conserved regions. This is taken as the correct topology for assessing rates of evolution. Overall, both morphological and molecular changes show a moderately strong correlation with time elapsed, but a weaker correlation with one another. Statistically significant differences in evolutionary rate are found between some, but not all, pair-wise comparisons of sister lineages for both molecular and morphological data. The molecular clock rate for echinaceans is three times faster than that for cidaroids and irregular echinoids. Spearman's rank correlation test, which requires only relative magnitude of changes to be known, suggests that morphological change has a slightly better correlation with time than does molecular change, averaged over all ten species. However, when just echinaceans are considered an extremely good correlation is found between the number of molecular changes and time elapsed, whereas morphological change remains poorly correlated. Thus, molecular rates approximate to a clocklike model within restricted echinoid clades, but vary significantly between clades. Averaging results over all echinoids produces a correlation that is no better than the correlation between morphological change and time elapsed.

Animals↗
PubMed1992

Modulation of cisplatin resistance in human malignant melanoma cells.

Previous studies have shown that the combination of dacarbazine, carmustine, cisplatin (DDP), and tamoxifen (TAM) produced a 53% overall response rate in patients with disseminated melanoma. Deletion of TAM from the regimen resulted in a fall in the response rate to 10%, and reincorporation of TAM returned the response rate to 52%, suggesting an important role for TAM. Using the human melanoma cell line T-289, we examined the nature of the interaction between TAM and each member of this combination in clonogenic assays in soft agar. The combination of TAM with DDP was highly synergistic as demonstrated by median effect analysis, whereas TAM was antagonistic with carmustine and an activated form of dacarbazine. The mean combination index at 50% kill was 0.26 +/- 0.02 (mean +/- SD) for TAM and DDP. This marked synergism was observed at concentrations of TAM that are clinically achievable. TAM had no effect on the uptake of the DDP analogue [3H]dichloro(ethylenediamine)platinum(II). There was no effect on the formation or repair of DDP intrastrand DNA adducts. Similarly, there was no effect demonstrated on the intracellular concentrations of glutathione or metallothioneins. We conclude that the interaction between TAM and DDP is truly synergistic in this cell line and is accomplished through none of the four mechanisms commonly associated with DDP resistance.

Carboplatin↗
PubMed1992

Contributions to a revision of the genus Trichosporon.

The genus Trichosporon was revised using characters of morphology, ultrastructure, physiology, ubiquinone systems, mol% G + C of DNA, DNA/DNA reassociations and 26S ribosomal RNA partial sequences. A total of 101 strains was used, including all available type and authentic cultures of previously described taxa. Nineteen taxa could be distinguished, 15 of which having Q-9 coenzyme systems and 4 having Q-10. Sixteen previously described names were reduced to synonymy. One new species was described. The genus is characterized by the presence of arthroconidia. Few species possess further diagnostic morphological characters, such as the presence of appressoria, macroconidia or meristematic conidiation. The septa of two species were found to be non-perforate, while those of the remaining species contained dolipores at variable degrees of differentiation, with or without vesicular or tubular parenthesomes. All species were able to assimilate a large number of carbon compounds; visible CO2 production was absent. The genus was found to be fairly homogeneous on the basis of a phylogenetic analysis of partial 26S rRNA sequences, with the exception of T. pullulans which proved to be unrelated. Most taxa were found to occupy well-defined ecological niches. Within the group of taxa isolated from humans, a distinction could be made between those involved in systemic mycoses and those which mainly caused pubic or non-pubic white piedras, respectively. One species was consistently associated with animals, while others came mainly from soil or water. One species was mesophilic and another psychrophilic.

Animals↗
PubMed1992

An analysis of partial 28S ribosomal RNA sequences suggests early radiations of sponges.

Sequences from the 5' end terminal part of 28S ribosomal RNA were obtained and compared for 22 animals belonging to all diploblastic phyla and for a large number of representatives of triploblastic Metazoa and protists. Phylogenetic analyses undertaken using different methods showed deep radiations of phyla such as Ctenophora, Cnidaria and Placozoa but also for groups of Porifera of low taxonomic rank. Short internodes between these radiations suggested an early rapid diversification of diploblasts. A long internal branch preceding the diversification of all triploblasts analyzed could be explained either by a long period with a single ancestor or by the extinction of the earliest triploblastic radiations. Finally some unexpected relationships were revealed among Porifera.

Animals↗
PubMed1992

Marinobacter hydrocarbonoclasticus gen. nov., sp. nov., a new, extremely halotolerant, hydrocarbon-degrading marine bacterium.

On the basis of phenotypical characteristics and analysis of 16S rRNA sequence, a new species belonging to a new genus is described, and the name Marinobacter hydrocarbonoclasticus is proposed. This organism, isolated from Mediterranean seawater near a petroleum refinery, is a gram-negative, aerobic, rod-shaped bacterium. It grows at NaCl concentrations of 0.08 to 3.5 M and uses various hydrocarbons as the sole source of carbon and energy. Its DNA has a guanine-plus-cytosine content of 52.7 mol%. The 16S rRNA analysis shows a clear affiliation between M. hydrocarbonoclasticus and the gamma group of the phylum Proteobacteria. A close phylogenetic relationship appears among the species Marinomonas vaga, Oceanospirillum linum, Halomonas elongata, and Pseudomonas aeruginosa. Because of the impossibility of finding a single most closely related species, we suggest that this bacterium be assigned to a new genus, at least temporarily. The possibility of a revision of this status when new data appear is, however, not excluded. The type strain is M. hydrocarbonoclasticus SP.17 (= ATCC 49840).

Bacteriolysis↗
PubMed1991

An analysis of the origin of metazoans, using comparisons of partial sequences of the 28S RNA, reveals an early emergence of triploblasts.

In order to study the origin of metazoans, we have compared sequences from the 5' end of the large subunit ribosomal RNA of a number of protists, fungi, plants and metazoans, including all diploblastic phyla (sequences of 10 new species have been determined, including that of the placozoan, Trichoplax adhaerens). These sequences were analyzed using distance matrix, maximum parsimony and maximum likelihood methods, and the validity of the results was ascertained with bootstrapping and species removal or addition. Triploblasts and diploblasts formed two clearly separated monophyletic units; this divergence, which apparently preceded the diversification of diploblastic animals (i.e. the successive sponge, ctenophore, cnidarian radiations), showed a much more ancient origin of triploblasts with respect to diploblasts than classically assumed. These results do not exclude the possibility that triploblasts and diploblasts arose independently from different protists.

Animals↗
PubMed1990

Ionic regulation of the plasma membrane potential of rainbow trout (Salmo gairdneri) spermatozoa: role in the initiation of sperm motility.

The ionic dependence of the trout sperm plasma membrane potential was analysed by measuring the accumulation of the lipophilic ions 3H-tetraphenylphosphonium (TPP) and 14C-thiocyanate (SCN) following dilution in artificial media isotonic to the seminal fluid. Our data showed that the trout sperm plasma membrane has a mixed conductance: the plasma membrane potential is sensitive upon the transmembrane gradients of K+, Na+, and H+. This potential is negative (less than -40 mV) in a 125 mM choline chloride media (ChM) at pH 8.5. Replacement of choline by sodium has a small depolarizing effect. The membrane potential is about -15 mV in a 125 mM potassium chloride and falls near zero mV only if valinomycin is added. In ChM changing the external pH (pHe) greatly affects the membrane potential: its value rises from less than -40 mV at pHe 9.0 to -17 mV at pHe 5.0. This pH effect is observed also in presence of sodium or potassium. A decrease in the transmembrane proton gradient produced by increasing internal pH without changing pHe induces also a depolarisation of the plasma membrane. In the different media in which trout sperm remain immotile after dilution (media with [K+] greater than 20-40 mM or a pH less than 7.5) the plasma membrane is more depolarized than in media allowing motility, suggesting a relationship between the state of membrane polarization and the intracellular effectors of the axonemal movement.

Animals↗
PubMed1989

Phosphagen kinase evolution. Expression in echinoderms.

Arginine kinase and creatine kinase that catalyze the transfer of a phosphate group between ATP and arginine and creatine, respectively, play an important role in cellular energetics. In contrast to most animals which exhibit a single phosphagen kinase activity (creatine kinase in chordates and arginine kinase in protostomians), echinoderms exhibit both arginine kinase and creatine kinase activities, sometimes in the same tissue. In contrast to chordates in which creatine kinases are dimers (consisting of two subunits of 40 kDa) and protostomians in which arginine kinases are usually monomers (40 kDa), echinoids contain specific phosphagen kinases: a dimeric arginine kinase (consisting of two subunits of 42 kDa) in eggs and a monomeric creatine kinase (145 kDa) in sperm. We have examined echinoderms from the five existing classes (echinoids, asteroids, ophiuroids, holothurians and crinoids) for the expression of these specific phosphagen kinases in different tissues. Gel filtration was used to determine the molecular masses of the native enzymes. Antibodies specific for arginine kinase or for creatine kinase were used to characterize the subunit composition of arginine kinase and creatine kinase after SDS/PAGE and transfer. In all echinoderms analyzed, arginine kinase always occurred as an enzyme of about 81 kDa consisting of two subunits of 42 kDa and creatine kinase as a monomeric enzyme of 140-155 kDa. The occurrence in echinoderms of both phosphagen kinases with distinct specificities and specific molecular structures is discussed from both a developmental and evolutionary point of view.

Animals↗
PubMed1989

Progressive dilated cardiomyopathy in a patient with longstanding and complete prednisone-induced hematological remission of idiopathic hypereosinophilic syndrome.

A female patient is described in whom the diagnosis of idiopathic hypereosinophilic syndrome (HES) with heart disease and peripheral neuropathy was made at the age of 32 years. Although prednisone induced a prompt and longstanding complete hematological remission, progressive and eventually intractable heart failure developed, and the patient died 6 years later. Endomyocardial biopsy at diagnosis showed infiltration with intact and disintegrated eosinophils and Charcot-Leyden crystals. Echocardiographic follow-up (including Doppler-Echocardiography) revealed mitral regurgitation with thickening and impaired motility of the posterior mitral leaflet, as well as progressive dilated cardiomyopathy. At autopsy, a diffuse interstitial fibrosis with patchy prominence in an eccentric hypertrophic and highly dilated heart was found. There were no significant endocardial thickening and no mural thrombi. In contrast to the findings of the initial endomyocardial biopsy, autopsy revealed no eosinophilic infiltrate. In this case, eosinophil-induced heart disease manifested as dilated cardiomyopathy, without endocardial fibrosis as originally described by Löffler. We speculate, that eosinophils have been deposited predominantly in the myocard at an early stage of disease, and - activated locally - secreted their granule proteins producing an initial damage to capillary endothelial cells and myocytes. After prednisone-induced clearance of eosinophils from blood and tissues, progressive, self-perpetuating interstitial fibrosis of the myocard and loss of myocytes eventually resulted in end-stage dilated cardiomyopathy.

Adult↗
PubMed1989

Cyclosporin-A therapy of pure red cell aplasia in a patient with B-cell chronic lymphocytic leukemia.

A 65-year-old woman with B-cell chronic lymphocytic leukemia (CLL) and pure red cell aplasia (PRCA) is described. After initial chemotherapy with three different regimens over 3 months (prednisone, chlorambucil/vincristine, cyclophosphamide, bleomycin/cyclophosphamide, etoposide, prednisone), normalization of the blood lymphocyte count was observed, but lymphocyte infiltration of the bone marrow persisted and erythropoiesis remained virtually absent. Monotherapy with cyclosporin-A (CyA) was begun. After 35 days, a marked increase in the reticulocyte count was observed, and with continuing therapy, there was a rapid increase in the hemoglobin level. Follow-up after 13 months of uninterrupted treatment with CyA revealed remission of both CLL and PRCA. CyA should be investigated further as a therapeutic modality for PRCA in patients with CLL, and such trials might provide further clues to the pathogenesis of this peculiar association.

Aged↗
PubMed1988

Purification and characterization of arginine kinase from sea-urchin eggs.

In most invertebrates, creatine kinase is replaced by arginine kinase, which catalyzes reversibly the transfer of a phosphate group between adenosine triphosphate and arginine. In sea-urchin larvae, arginine kinase only is expressed whereas in adult sea-urchins both arginine kinase and creatine kinase can be found in the same tissue. In order to study their developmental regulation and properties, we have purified arginine kinase to homogeneity from the eggs of the sea-urchin Paracentrotus lividus. The purification involves ethanol and ammonium sulfate precipitations, followed by an anion-exchange chromatography, an affinity chromatography and a gel filtration. A 500-fold increase in specific activity leads to a specific activity of 360 IU/mg protein at 25 degrees C. Arginine kinase (pI = 5.7) is rapidly and irreversibly inactivated at 45 degrees C. Amino acid composition and Km values (2.08 mM for phospho-L-arginine and 1.25 mM for ADP) are also given. Determination of molecular mass by gel filtration and separation by SDS/polyacrylamide gel electrophoresis indicate that the enzyme is an 81-kDa dimer of two subunits of 42 kDa.

Amino Acids↗
PubMed1987

Trout sperm motility. The transient movement of trout sperm is related to changes in the concentration of ATP following the activation of the flagellar movement.

For freshwater fish the motile period of sperm is extremely brief, even after a dilution in isotonic media. This result is in contrast to most other animals (ranging from invertebrates to mammals), in which sperm are generally motile for at least several hours. We have analyzed the reasons for the brevity of this movement by studying the relationships between the metabolism of trout sperm and the activation of their motility upon dilution. Sperm motility was not initiated when the dilution medium contained an elevated concentration of potassium (20-40 mM), but dilution in an isotonic solution of sodium chloride triggered an immediate activation of motility, and sperm swam vigorously. Motility of sperm decreased rapidly and 15 s after dilution sperm were moving slowly in small circles. Sperm became abruptly immotile at 20-30 s and flagella straightened. When millimolar concentrations of Ca2+ were also present in the dilution medium, movement did not stop abruptly, flagella kept beating and stopped only after 1-2 min. When sperm remained immotile they retained a high concentration of ATP. The activation of motility induced a rapid decrease of ATP. In the absence of calcium, and after the cessation of motility, ATP increased slowly back to its original concentration. In the presence of millimolar concentrations of calcium the concentration of ATP decreased to a very low level and remained low thereafter. The progressive decrease of the flagellar beat frequency, that had been observed during the period of trout sperm movement, might be related to the rapid exhaustion of intraflagellar ATP. Motility could be reinduced in sperm that had recovered high concentrations of ATP, demonstrating the functional integrity of the motile apparatus even after flagellar arrest. In conclusion we suggest that the maximum duration of trout sperm motility, at most 2 min (as a consequence of a depletion of ATP during the movement), is due to a low mitochondrial oxidative phosphorylation capacity.

Adenosine Triphosphate↗
PubMed1986

Ionic regulation of sea urchin sperm motility, metabolism and fertilizing capacity.

In order to pursue the significance of the ionic regulation of sea urchin sperm behaviour, alterations in the cation composition of sea water were tested for their effects on sperm fertilizing capacity. Nearly all changes which resulted in lowered sperm intracellular pH, including lowered sea-water pH, inclusion of the divalent ion chelator EGTA, addition of dithiothreitol, or removal of sea-water Na+, enhanced sperm viability for periods of up to a week. These conditions caused decreased cell motility and elevated ATP concentrations, and prevented the acrosome reaction. Conversely, changes which increased the intracellular pH, decreased sperm ATP concentrations, or induced the acrosome reaction, reduced sperm viability. A single medium, high sea-water K+ concentrations (greater than 100 mM), provided an exception to these general trends. At elevated K+ concentrations sperm were quiescent but became completely infertile. These data show that sperm fertilizing capacity is generally extended by maintenance of the sperm in an inactive state, and the results suggest that decreased cellular energy levels contribute to decreased fertility.

Adenosine Triphosphate↗
PubMed1985

Regulation of internal pH of sea urchin sperm. A role for the Na/K pump.

In the absence of sodium, sea urchin sperm have an acidic internal pH. The addition of sodium, lithium, or ammonium, but not of potassium ions, induces an internal alkalization. If potassium is added in the presence of sodium, a further alkalization is obtained; in contrast, potassium addition in presence of Li+ or NH+4 does not change the internal pH. The K+-induced pHi change is inhibited by ouabain and when sperm are depleted of their ATP. A large part of the potassium influx is stimulated by Na+, but not Li+, and inhibited by ouabain and cellular ATP depletion. We conclude that activity of Na/K-ATPase pumps located in the plasma membrane of sea urchin sperm could play a role in regulating the internal pH of sea urchin sperm by recycling sodium ions that enter the cell through Na/H countermovements.

Ammonia↗
PubMed1983

Metabolism of sea urchin sperm. Interrelationships between intracellular pH, ATPase activity, and mitochondrial respiration.

Mitochondria of sperm of the sea urchin Strongylo-centrotus purpuratus are tightly coupled before induction of the acrosomal reaction. When the sperm are diluted at low external pH (pH 5.5) or in high potassium (200 mM) or in the absence of sodium, their internal pH is acidic (6.2-7.0) as measured by amine accumulation. Under these conditions the internal ATPase activity (primarily the dynein ATPase) is inhibited, sperm are immotile, and mitochondria are in respiratory state 4 (ATP concentration is maximal). When the internal pH is alkalinized, the internal ATPase activity is increased, as estimated either in vivo by measuring the decrease in ATP concentration after addition of oligomycin to prevent ATP synthesis, or in vitro using Triton X-100 permeabilized cells. This increase in ATPase activity correlates with an increase of up to 50-fold in respiratory rates and a mitochondrial transition to state 3. Carbonyl cyanide p-trifluoromethoxyphenylhydrazone-uncoupled respiration is also sensitive to the internal pH for it is inhibited at acidic internal pH. However, since nonmotile, nonrespiring sperm that are obtained when the internal pH is acidic have high concentrations of ATP, we conclude that in vivo the internal pH controls the rate of dynein ATPase and that this ATPase activity is limiting for the respiration of tightly coupled mitochondria. The redox state of the respiratory chain may also be under the direct influence of the internal pH.

Adenosine Triphosphatases↗