bluuebunny/crossref_metadata_2025 huggingface dataset:
A totally synthetic vaccine of generic structure that targets Toll-like receptor 2 on dendritic cells and promotes antibody or cytotoxic T cell responses
Authors: Jackson David C. , Lau Yuk Fai , Le Thuy , Suhrbier Andreas , Deliyannis Georgia , Cheers Christina , Smith Corey , Zeng Weiguang , Brown Lorena E.
Published: October 2004

A simple generic peptide-based vaccine structure that targets Toll-like receptor 2-expressing dendritic cells and causes their activation is described. The vaccines are totally synthetic, serve as their own adjuvant, and are composed of (i) a single helper T cell epitope, (ii) a target epitope that is either recognized by CD8+T cells or B cells, and (iii) a Toll-like receptor 2-targeting lipid moiety,S-[2,3-bis(palmitoyloxy)propyl]cysteine, that is situated between the peptide epitopes to form a branched configuration. The different CD8+T cell epitopes examined were from (i) influenza virus, (ii) the intracellular bacteriumListeria monocytogenes, and (iii) ovalbumin as a model tumor antigen. Vaccines containing a B cell epitope from gastrin or luteinizing hormone-releasing hormone as a B cell epitope were also examined for their ability to elicit antibody against the parent hormones. Each of the vaccines was capable of inducing either CD8+T cell or antibody-mediated immune responses. The lipidated vaccines, but not the nonlipidated vaccines, were able to mediate protection against viral or bacterial infection and mediate prophylactic and therapeutic anticancer activity. The two hormone-based vaccines induced high antibody titers, which in the case of luteinizing hormone-releasing hormone resulted in abrogation of reproductive function. These results highlight the utility of simple, totally synthetic, epitope-based vaccines.
Pleiotropic effects of the 8.1 HLA haplotype in patients with autoimmune myasthenia gravis and thymus hyperplasia
Authors: Vandiedonck Claire , Beaurain Geneviève , Giraud Matthieu , Hue-Beauvais Catherine , Eymard Bruno , Tranchant Christine , Gajdos Philippe , Dausset Jean , Garchon Henri-Jean
Published: October 2004

The 8.1 haplotype of the HLA complex has been reproducibly associated with several autoimmune diseases and traits, notably with thymus hyperplasia in patients with acquired generalized myasthenia gravis, an autoantibody-mediated disease directed at the muscle acetylcholine receptor. However, the strong linkage disequilibrium across this haplotype has prevented the identification of the causative locus, termed MYAS1. Here, we localized MYAS1 to a 1.2-Mb genome segment by reconstructing haplotypes and assessing their transmission in 73 simplex families. This segment encompasses the class III and proximal class I regions, between the BAT3 and C3-2-11 markers, therefore unambiguously excluding the class II loci. In addition, a case-control study revealed a very strong association with a core haplotype in this same region following an additive model (
P
= 7 × 10
-11
, odds ratio 6.5 for one copy and 42 for two copies of the core haplotype). Finally, we showed that this region is associated with a marked increase in serum titers of anti-acetylcholine receptor autoantibodies (
P
= 8 × 10
-6
). Remarkably, this effect was suppressed by a second locus in cis on the 8.1 haplotype and located toward the class II region. Altogether, these data demonstrate the highly significant but complex effects of the 8.1 haplotype on the phenotype of myasthenia gravis patients and might shed light on its role in other autoimmune diseases.
Translationally controlled tumor protein is a target of tumor reversion
Authors: Tuynder Marcel , Fiucci Giusy , Prieur Sylvie , Lespagnol Alexandra , Géant Anne , Beaucourt Séverine , Duflaut Dominique , Besse Stéphanie , Susini Laurent , Cavarelli Jean , Moras Dino , Amson Robert , Telerman Adam
Published: October 2004

By analyzing the gene expression profile between tumor cells and revertant counterparts that have a suppressed malignant phenotype, we previously reported a significant down-regulation of translationally controlled tumor protein (TCTP) in the revertants. In the present study, we derived, by using the H1 parvovirus as a selective agent, revertants from three major solid cancers: colon, lung, and melanoma cell lines. These cells have a strongly suppressed malignant phenotype both
in vitro
and
in vivo
. The level of TCTP is decreased in most of the revertants. To verify whether inhibition of TCTP expression induces changes in the malignant phenotype, in the classical, well established model of “flat reversion,” v-src-transformed NIH3T3 cells were transfected with antisense TCTP. By inhibiting the expression of TCTP, the number of revertant cells was raised to 30%, instead of the reported rate for spontaneous flat revertants of 10
-6
. Because TCTP encodes for a histamine-releasing factor, we tested the hypothesis that inhibitors of the histaminic pathway could be effective against tumor cells. We show that some antihistaminic compounds (hydroxyzine and promethazine) and other pharmacological compounds with a related structure (including thioridazine and sertraline) kill tumor cells and significantly decrease the level of TCTP. All together, these data suggest that, with tumor reversion used as a working model, TCTP was identified as a target and drugs were selected that decrease its expression and kill tumor cells.
Imp3p and Imp4p mediate formation of essential U3–precursor rRNA (pre-rRNA) duplexes, possibly to recruit the small subunit processome to the pre-rRNA
Authors: Gérczei Tímea , Correll Carl C.
Published: October 2004

In eukaryotes, formation of short duplexes between the U3 small nucleolar RNA (snoRNA) and the precursor rRNA (pre-rRNA) at multiple sites is a prerequisite for three endonucleolytic cleavages that initiate small subunit biogenesis by releasing the 18S rRNA precursor from the pre-rRNA. The most likely role of these RNA duplexes is to guide the U3 snoRNA and its associated proteins, designated the small subunit processome, to the target cleavage sites on the pre-rRNA. Studies by others in
Saccharomyces cerevisiae
have identified the proteins Mpp10p, Imp3p, and Imp4p as candidates to mediate U3–pre-rRNA interactions. We report here that Imp3p and Imp4p appear to stabilize an otherwise unstable duplex between the U3 snoRNA hinge region and complementary bases in the external transcribed spacer of the pre-rRNA. In addition, Imp4p, but not Imp3p, seems to rearrange the U3 box A stem structure to expose the site that base-pairs with the 5′ end of the 18S rRNA, thereby mediating duplex formation at a second site. By mediating formation of both essential U3–pre-rRNA duplexes, Imp3p and Imp4p may help the small subunit processome to dock onto the pre-rRNA, an event indispensable for ribosome biogenesis and hence for cell growth.
A Novel Generalized Impedance Converter Using Single Second Generation Current Conveyor
Authors: Khan Iqbal A. , Zaidi Mehmood H.
Published: October 2004

A generalized impedance converter (GIC) using single CCII(−)
is presented. The circuit uses no matching constraints and provides a wide variety of ideal component simulators and multipliers. The GIC can also be made tunable by using
CCCII(−)
instead of CCII(−). The proposed GIC is verified using SPICE with excellent results.
On the Reliability of Accelerated Testing in AIGaAs/InGaAs/GaAsPHEMTs
Authors: Yarn K. F. , Chien W. C. , Wang C. S.
Published: October 2004

The study of different stress on device characteristics of AlGaAs/InGaAs/GaAs PHEMTs has been researched and developed in this report. Many catastrophic degradation mechanisms such as hot‐electron, gate‐drain breakdown, IDS, IG
, VP
and gate Schottky barrier effects are discussed in detail. In addition, the accelerated testing of the
temperature‐dependent effects on ID
,Gm
and Schottky barrier are examined.
Cardiomyocytes fuse with surrounding noncardiomyocytes and reenter the cell cycle
Authors: Matsuura Katsuhisa , Wada Hiroshi , Nagai Toshio , Iijima Yoshihiro , Minamino Tohru , Sano Masanori , Akazawa Hiroshi , Molkentin Jeffery D. , Kasanuki Hiroshi , Komuro Issei
Published: October 2004

The concept of the plasticity or transdifferentiation of adult stem cells has been challenged by the phenomenon of cell fusion. In this work, we examined whether neonatal cardiomyocytes fuse with various somatic cells including endothelial cells, cardiac fibroblasts, bone marrow cells, and endothelial progenitor cells spontaneously in vitro. When cardiomyocytes were cocultured with endothelial cells or cardiac fibroblasts, they fused and showed phenotypes of cardiomyocytes. Furthermore, cardiomyocytes reentered the G2-M phase in the cell cycle after fusing with proliferative noncardiomyocytes. Transplanted endothelial cells or skeletal muscle–derived cells fused with adult cardiomyocytes in vivo. In the cryoinjured heart, there were Ki67-positive cells that expressed both cardiac and endothelial lineage marker proteins. These results suggest that cardiomyocytes fuse with other cells and enter the cell cycle by maintaining their phenotypes.
Interaction of Brn3a and HIPK2 mediates transcriptional repression of sensory neuron survival
Authors: Wiggins Amanda K. , Wei Guangwei , Doxakis Epaminondas , Wong Connie , Tang Amy A. , Zang Keling , Luo Esther J. , Neve Rachael L. , Reichardt Louis F. , Huang Eric J.
Published: October 2004

The Pit1-Oct1-Unc86 domain (POU domain) transcription factor Brn3a controls sensory neuron survival by regulating the expression of Trk receptors and members of the Bcl-2 family. Loss of Brn3a leads to a dramatic increase in apoptosis and severe loss of neurons in sensory ganglia. Although recent evidence suggests that Brn3a-mediated transcription can be modified by additional cofactors, the exact mechanisms are not known. Here, we report that homeodomain interacting protein kinase 2 (HIPK2) is a pro-apoptotic transcriptional cofactor that suppresses Brn3a-mediated gene expression. HIPK2 interacts with Brn3a, promotes Brn3a binding to DNA, but suppresses Brn3a-dependent transcription of brn3a, trkA, and bcl-xL. Overexpression of HIPK2 induces apoptosis in cultured sensory neurons. Conversely, targeted deletion of HIPK2 leads to increased expression of Brn3a, TrkA, and Bcl-xL, reduced apoptosis and increases in neuron numbers in the trigeminal ganglion. Together, these data indicate that HIPK2, through regulation of Brn3a-dependent gene expression, is a critical component in the transcriptional machinery that controls sensory neuron survival.
NK Cells and Trophoblasts
Authors: Parham Peter
Published: October 2004

In placental mammals, viviparity—the production of living young within the mother's body—evolved under the auspices of the immune system. Elements of immunity were incorporated, giving pregnancy a mildly inflammatory character. Formation of the placenta, the organ that feeds the fetus, involves a cooperation between maternal natural killer (NK) cells and fetal trophoblast cells that remodels the blood supply. Recent research reveals that this process and human reproductive success are influenced by polymorphic HLA-C ligands and their killer cell immunoglobulin-like receptors (KIR).
Isoflurane Alters the Amount of Dopamine Transporter Expressed on the Plasma Membrane in Humans
Authors: Votaw John R. , Byas-Smith Michael G. , Voll Ronald , Halkar Raghu , Goodman Mark M.
Published: October 2004

Background

Isoflurane increases extracellular dopamine concentration and causes trafficking of the dopamine transporter (DAT) in transfected cells. Also, the binding potentials of highly specific positron-emitting DAT ligands are altered by isoflurane in rhesus monkeys. The purpose of this study was to determine the dose-response curve for isoflurane altering the binding potential of one of these ligands ([F-18]FECNT) in humans.

Methods

Twenty human volunteers underwent positron emission tomography using [F-18]FECNT. All subjects were scanned while awake and then again after assignment to one of four groups (n = 5 each): awake-control, propofol-control, or light or deep isoflurane anesthesia as defined by Bispectral Index monitoring. Bispectral Index values in the light anesthesia group were 40 +/- 7 (end-tidal isoflurane, 1.02 +/- 0.08) versus 27 +/- 10 (end-tidal isoflurane, 1.6 +/- 0.3) in the deep anesthesia group. The within-subject percent change in putamen binding potential between the awake and second scans was determined for each subject, averaged within groups, and compared across groups.

Results

The [F-18]FECNT binding potential exhibited a biphasic shape as a function of anesthetic dose. The binding potential for the second scan in the awake-control and propofol-control groups was significantly less than the initial scan; for the light anesthesia group, the binding potential was significantly increased during anesthesia, and no change was detected between the two scans in the deeper anesthesia group.

Conclusion

Isoflurane causes a dose-dependent change in the [F-18]FECNT binding potential for DAT consistent with isoflurane causing trafficking of the DAT between the plasma membrane and the cell interior. Concentrations of isoflurane below minimum alveolar concentration causes DAT to be trafficked to the plasma membrane from the cell interior, but no net trafficking occurs at higher concentrations. The data are most easily explained if isoflurane alters the amount of functionally expressed DAT through an indirect pathway. This phenomena should be more fully explored to help make the next generation of anesthetics more mechanistically specific and to reduce undesired side effects.
Genome-wide mRNA surveillance is coupled to mRNA export
Authors: Hieronymus Haley , Yu Michael C. , Silver Pamela A.
Published: October 2004

Nuclear export of mRNA is a central step in gene expression that shows extensive coupling to transcription and transcript processing. However, little is known about the fate of mRNA and its export under conditions that damage the DNA template and RNA itself. Here we report the discovery of four new factors required for mRNA export through a screen of all annotated nonessential Saccharomyces cerevisiae genes. Two of these factors, mRNA surveillance factor Rrp6 and DNA repair protein Lrp1, are nuclear exosome components that physically interact with one another. We find that Lrp1 mediates specific mRNA degradation upon DNA-damaging UV irradiation as well as general mRNA degradation. Lrp1 requires Rrp6 for genomic localization to genes encoding its mRNA targets, and Rrp6 genomic localization in turn correlates with transcription. Further, Rrp6 and Lrp1 are both required for repair of UV-induced DNA damage. These results demonstrate coupling of mRNA surveillance to mRNA export and suggest specificity of the RNA surveillance machinery for different transcript populations. Broadly, these findings link DNA and RNA surveillance to mRNA export.
Alveolar rhabdomyosarcomas in conditional Pax3:Fkhr mice: cooperativity of Ink4a/ARF and Trp53 loss of function
Authors: Keller Charles , Arenkiel Benjamin R. , Coffin Cheryl M. , El-Bardeesy Nabeel , DePinho Ronald A. , Capecchi Mario R.
Published: October 2004

Alveolar rhabdomyosarcoma is an aggressive childhood muscle cancer for which outcomes are poor when the disease is advanced. Although well-developed mouse models exist for embryonal and pleomorphic rhabdomyosarcomas, neither a spontaneous nor a transgenic mouse model of alveolar rhabdomyosarcoma has yet been reported. We report the first mouse model of alveolar rhabdomyosarcoma using a conditional Pax3:Fkhr knock-in allele whose activation in late embryogenesis and postnatally is targeted to terminally differentiating Myf6-expressing skeletal muscle. In these mice, alveolar rhabdomyosarcomas occur but at low frequency, and Fkhr haploinsufficiency does not appear to accelerate tumorigenesis. However, Pax3:Fkhr homozygosity with accompanying Ink4a/ARF or Trp53 pathway disruption, by means of conditional Trp53 or Ink4a/ARF loss of function, substantially increases the frequencies of tumor formation. These results of successful tumor generation postnatally from a target pool of differentiating myofibers are in sharp contrast to the birth defects and lack of tumors for mice with prenatal and postnatal satellite cell triggering of Pax3:Fkhr. Furthermore, these murine alveolar rhabdomyosarcomas have an immunohistochemical profile similar to human alveolar rhabdomyosarcoma, suggesting that this conditional mouse model will be relevant to study of the disease and will be useful for preclinical therapeutic testing.
The elementary economics of social dilemmas
Authors: Curtis Eaton B.
Published: October 2004

Abstract. A social dilemma is, in essence, a prisoners’ dilemma in a continuous strategy space. I discuss a number of social dilemmas that have caught my attention, offer an elementary, diagrammatic synthesis of them, and discuss some of the economic insights that the diagrams capture, including incentives for pre‐commitment. Finally, I model pre‐commitment via delegation and link results to the literature on the evolution of preferences.
Are migrants more skilled than non‐migrants? Repeat, return, and same‐employer migrants
Authors: Hunt Jennifer
Published: October 2004

Abstract. I examine the determinants of inter‐state migration of adults within western Germany, using the German Socio‐Economic Panel from 1984–2000. Migrants who do not change employers represent one‐fifth of all migrants and have higher education and pre‐move wages than non‐migrants. Skilled workers thus have a low‐cost migration avenue that has not been considered in the previous literature. Other migrants are heterogeneous and not unambiguously more skilled than non‐migrants. I confirm that long‐distance migrants are more skilled than short‐distance migrants, as predicted by theory, and I show that return migrants are a mix of successes and failures. Most repeat migration is return migration. JEL classification: J6
The disintegrating Canadian labour market? The extent of the market then and now
Authors: Coe Patrick J. , Herbert Emery J.C.
Published: October 2004

Abstract.  Analysis of real wages for three occupations in 13 Canadian cities for 1901–50 suggests Canada had a national labour market at least until 1950. However, analysis of real wages for 10 Canadian cities for 1971–2000 yields little evidence favouring integration of Canada's regional labour markets. The apparent lack of labour market integration reflects a weakness of an approach that assumes markets are in equilibrium. Unemployment rates after 1970 suggest that some regional markets may be characterized by excess labour supply. Analysis of relative provincial unemployment rates yields evidence consistent with local labour force adjustment to changing labour market conditions. JEL classification: E24, J61
A theory of gender differences in parental altruism
Authors: Eswaran Mukesh , Kotwal Ashok
Published: October 2004

Abstract.  We offer a theory of gender differences in parental altruism based on the asymmetry that female fertility is constrained but male fertility is relatively unconstrained. Modelling human preferences as having been shaped during the Pleistocene, we derive evolutionarily stable, co‐evolved male and female preferences for altruism towards one's children. We demonstrate that there would be gender differences in parental altruism that depend on the relative abundance or scarcity of resources and the importance and substitutability of parental inputs in promoting the survival of offspring. The results point to greater altruism in females, under plausible conditions. JEL Classification: D64, J16, P46
The performance and robustness of simple monetary policy rules in models of the Canadian economy
Authors: Côté Denise , Kuszczak John , Lam Jean‐Paul , Liu Ying , St‐Amant Pierre
Published: October 2004

Abstract.  In this paper, we evaluate seven simple monetary policy rules in a wide range of models of the Canadian economy. Our results indicate that none of the seven simple policy rules we examined is robust to model uncertainty, in that no single rule performs well in all models. In fact, our results show that the performance of some of the simple rules, particularly rules with interest rate smoothing and rules with a high coefficient on the inflation gap, can substantially deviate from that of the optimal rule and can even be unstable in some models. Furthermore, we find that “open‐economy” rules do not perform well in many models. We find that adding an exchange rate term to a simple policy rule often increases the value of the policy‐maker's loss function. Although it is not robust, we find that a simple nominal Taylor‐type rule that has a coefficient of 2 on the inflation gap and 0.5 on the output gap outperforms the other simple rules in a certain class of models. However, even in those models, the loss‐function value of this simple rule can be substantially higher than that of the optimal or base‐case rule. JEL classification: E52, E58
Canadian and U.S. financial markets: testing the international integration hypothesis under time‐varying conditional volatility
Authors: Normandin Michel
Published: October 2004

Abstract.  This paper evaluates the international integration hypothesis, that is, that risk‐adjusted anticipated returns are identical, even when financial instruments are traded in different countries. Under time‐varying conditional volatility, this hypothesis is tested by verifying the equality between domestic and foreign risk prices associated with a multi‐factor analytic specification. The maximum‐likelihood and Kalman‐filter estimates are used to assess the national risk prices and interpret the factors. Empirically, the integration of Canadian and U.S. financial markets depends on the risk prices of two factors, which are related to certain non‐monetary events and to the conduct of monetary policies. JEL classification: G15, C32
Lobbying, multisector trade, and sustainability of free‐trade agreements
Authors: Qiu Larry D.
Published: October 2004

Abstract. This paper is concerned with the sustainability of free‐trade agreements (FTA). FTA sustainability is influenced by governments’ valuations of political contributions, discount factors, the lobbying position of the specific‐interest groups in the intra‐industry trade sectors, and the sectoral coverage of the FTA. I find that (i) under certain conditions, the FTA under protectionist lobbying could be more sustainable than the FTA under no political pressure; (ii) the lobby‐supported FTA is more sustainable than the lobby‐opposed FTA and the FTA under no political pressure; and (iii) multisector trade enhances FTA sustainability. JEL Classification: F12, F13, F15.
Voluntary import expansions with non‐stationary demand
Authors: Yin Xiaopeng
Published: October 2004

Abstract.  In this paper the effect of voluntary imports expansions (VIEs) on welfare in a dynamic game is analysed. It is found that (1) there exists a Markov perfect Nash equilibrium (MPNE) and a unique stable steady state; (2) with habit formation in consumption, the welfare and output for each firm are higher than that without habit formation; and (3) VIEs can increase an importing country's welfare with raised consumption and lowered price. Therefore, VIEs can be voluntary to an importing country. JEL classification: F13, F12
Armington elasticities in intermediate inputs trade: a problem in using multilateral trade data
Authors: Saito Mika
Published: October 2004

Abstract. In this paper we find that the estimates of Armington elasticities (the elasticity of substitution between groups of products identified by country of origin) obtained from multilateral trade data can differ from those obtained from bilateral trade data. In particular, the former tends to be higher than the latter when trade consists largely of intermediate inputs. Given that the variety of intermediate inputs traded across borders is increasing rapidly and that the effect of this increase is not adequately captured in multilateral trade data, the evidence shows that the employment of multilateral trade data to estimate Armington elasticities needs caution. JEL classification: F14, C51
THE PAS/ACCUMULATION BODIES IN PROROCENTRUM LIMA AND PROROCENTRUM MACULOSUM (DINOPHYCEAE) ARE DINOFLAGELLATE LYSOSOMES1
Authors: Zhou Juan , Fritz Lawrence
Published: October 2004

Numerous spherical bodies containing electron‐dense material, fibrous material, and membranous material are present in the cytoplasm of two dinoflagellate species, Prorocentrum lima (Ehr.) Dodge and Prorocentrum maculosum Faust. Similar bodies have been observed in other dinoflagellates and have been termed accumulation bodies or PAS bodies. In both Prorocentrum species, these bodies autofluoresce under blue light excitation and increase in size with cell culture age. They possess acid phosphatase activity, react positively with the periodic acid/Schiff reagent, and stain with acridine orange. All these properties are characteristic of eukaryotic lysosomes; thus, we propose that dinoflagellate accumulation bodies and PAS bodies are identical organelles and are, in fact, dinoflagellate lysosomes.
SILICON DEPOSITION DURING THE CELL CYCLE OF THALASSIOSIRA WEISSFLOGII (BACILLARIOPHYCEAE) DETERMINED USING DUAL RHODAMINE 123 AND PROPIDIUM IODIDE STAINING1
Authors: Brzezinski Mark A. , Conley Daniel J.
Published: October 2004

The relatively non‐toxic dye, rhodamine 123 (R123), was incorporated into the frustule of Thalassiosira weissflogii Grun. clone ACTIN in direct proportion to biogenic silica (BSi). R123 was used together with the DNA stain propidium iodide to track and quantify Si deposition during the cell cycle of T. weissflogii using flow cytometry. Silicon deposition was not continuous through the cell cycle. Deposition of the valves occurred during M phase. The hypocingulum was largely deposited during G1 with some suggestion of minor girdle band deposition during G2. Silicon deposition did not occur during S phase. Assuming that a complete frustule consists of an epivalve, epicingulum, hypocingulum, and hypovalve, then 40% of cellular BSi was contained within the cingulum of T. weissflogii with 60% present in the valves. These percentages correspond to 0.38 pmol Si in the two cingula and 0.57 pmol Si in the valves. Temporal differences in the timing of silicic acid uptake and deposition during the cell cycle of T. weissflogii suggested that deposition of both the new valves and the cingulum is supported by an internal pool of dissolved Si acquired during G2.
TRACKING DISPERSAL ROUTES: PHYLOGEOGRAPHY OF THE ARCTIC‐ANTARCTIC DISJUNCT SEAWEED ACROSIPHONIA ARCTA (CHLOROPHYTA)1
Authors: van Oppen Madeleine J. H. , Diekmann Onno E. , Wiencke Christian , Stam Wytze T. , Olsen Jeanine L.
Published: October 2004

Phylogenetic relationships in the Arctic‐Antarctic disjunct seaweed species Acrosiphonia arcta (Dillwyn) J. G. Agardh (Acrosiphoniales, Chlorophyta) were examined using restriction fragment‐length polymorphism analysis of the fast‐evolving nuclear ribosomal intergenic spacer (IGS) region and random amplified polymorphic DNA (RAPD) markers. Twenty‐two isolates collected from 10 different locations in both hemispheres were compared. Five IGS length classes were identified among the 10 locations. Throughout the North Atlantic, IGS regions were found to be extremely homogeneous whereas RAPD patterns revealed subdivided populations that suggest founder effects. Acrosiphonia arcta populations found in the Arctic and North Atlantic oceans are hypothesized to be of Pacific origin. Extensive differences found between Arctic Greenland populations and those in the North Atlantic suggest that colonization of Arctic Greenland occurred as an independent event. Recolonization of the Antarctic peninsula from Southern Chile is favored, whereas the directionality of transequatorial passage along the western coast of the Americas could be in either direction.
MOLECULAR DELINEATION OF SPECIES AND SYNGENS IN VOLVOCACEAN GREEN ALGAE (CHLOROPHYTA)1
Authors: Coleman Annette W. , Suarez Arturo , Goff Lynda J.
Published: October 2004

Two species of the colonial green flagellate family Volvocaceae are worldwide in distribution yet exhibit contrasting species structure. Geographically disparate isolatesof Gonium pectoraleMueller can interbreed while isolates ofPandorina morumBory behave quite differently. More than 20 sexually isolated subpopulations occur within this species; these have been termed “syngens” (sensu Sonneborn). Because prezygotic barriers to mating cause intersyngen pairings to fail, breeding analyses cannot be used to estimate genetic relatedness among the syngens of P.morum.DNA comparisons provide an alternative method of assessing genetic relatedness. We compared the nucleotide sequence of the internal transcribed spacer (ITS) region of the nuclear ribosomal repeat among clones of P.morumand ofG. pectorale.Members of syngens ofP. morumwith distribution restricted to one small geographical area show great similarity. Likewise, members of any syngen of worldwide distribution show near uniformity, even those from different continents. However, the ITS sequence of each syngen differs from that of other syngens. In contrast,G. pectorale, which has an ITS region that is remarkably uniform throughout the world, appears to consist of a single syngen within North America and Europe by mating tests. The molecular data are in complete conformity with previous syngen assignment. Because the latter is based on mating affinity, with two complementary mating types per syngen, the evolution of new mating type pairs appears to be the basis of microevolution in these algae. We infer that eitherP. morumis a more ancient species thanG. pectoraleor thatP. morumhas a less stable genome. In either case, the biogeographic distribution of certain syngens may reflect climatological changes of the past.
CIRCADIAN GROWTH RHYTHM IN JUVENILE SPOROPHYTES OF LAMINARIALES (PHAEOPHYTA)1
Authors: Lüning Klaus
Published: October 2004

A circadian rhythm in growth was detected by computer‐aided image analysis in 3–4‐cm‐long, juvenile sporophytes of the kelp species Pterygophora California Rupr. and in seven Laminaria spp. In P. californica, the free‐running rhythm occurred in continuous white fluorescent light, had a period of 26 h at 10°or 15°C, and persisted for at least 2 weeks in white or blue light. The rhythm became insignificant in continuous green or red light after 3 cycles. Synchronization by white light‐dark regimes, e.g. by 16 h light per day, resulted in an entrained period of 24 h and in a shift of the circadian growth minimum into the middle of the light phase. A morning growth peak represented the decreasing portion of the circadian growth curve, and an evening peak the increasing portion. The circadian growth peak was not visible during the dark phase, because growth rate decreased immediately after the onset of darkness. At night, some growth still occurred at 16 or 12 h light per day, whereas growth stopped completely at 8 h light per day, as in continuous darkness. During 11 days of darkness, the thallus area became reduced by 3.5%, but growth rate recovered in subsequent light–dark cycles, and the circadian growth rhythm reappeared in subsequent continuous light.
A CYANOPHYTE CAPABLE OF FIXING NITROGEN UNDER HIGH LEVELS OF OXYGEN1
Authors: Prosperi Carlos H.
Published: October 2004

Nostoc cordubensis Prosperi (Cyanophyta, Nostocaceae) is characterized by its mucilaginous colonies. Much of this mucilage is produced by heterocysts. By controlling growth conditions, heterocysts with and without mucilage were obtained. Mucilaginous heterocysts retained nitrogen‐fixing capability at high oxygen concentrations, whereas heterocysts lacking mucilage were unable to fix nitrogen at oxygen concentrations higher than 20%. Comparison of results obtained using tetrazolium salts as indicators of highly reduced zones showed similar results.
PHOTOSYNTHETIC ACTIVITY OF TWO DEVELOPMENTAL STAGES OF A NOSTOC STRAIN (CYANOBACTERIA) ISOLATED FROM GEOSIPHON PYRIFORME (MYCOTA)1
Authors: Bilger Wolfgang , Büdel Burkhard , Mollenhauer Resi , Mollenhauer Dieter
Published: October 2004

Sessile colonies and motile hormogonia, the two main developmental stages in the life cycle of a Nostoc strain isolated from the endocytobiosis with Geosiphon pyriforme (Kützing) F. v. Wettstein, were investigated for their photosynthetic competence. Large‐scale fractionation of the two stages is presented. Photosynthetic parameters were assessed by measurement of chlorophyll fluorescence and oxygen evolution. Hormogonia were as photosynthetically competent as the colonial stage. In addition, hormogonia showed an enhanced capability for nonradiative dissipation of absorbed light energy, a feature that might be important for their function as propagula. Data for the quantum yield of photosystem II of the isolated Nostoc strain were compared to the values determined in situ in G. pyriforme and indicated the possibility of a higher photosynthetic capacity of the endosymbiotic as compared to the isolated cyanobacterium.
FUNCTIONAL ASPECTS OF SECONDARY CAROTENOIDS IN HAEMATOCOCCUS LACUSTRIS (VOLVOCALES). III. ACTION AS A “SUNSHADE”1
Authors: Hagen Christoph , Braune Wolfram , Björn Lars Olof
Published: October 2004

We investigated the protection from photoinhibition by different developmental stages of Haematococcus lacustris [Girod] Rostafinski using chlorophyll fluorescence measurements of single cells and suspensions. An overall correlation between higher cellular content of secondary carotenoids and the capacity to withstand excessive irradiation was observed in flagellated cells and aplanospores of H. lacustris. Low‐light‐reversible spreading of extra‐chloroplastic secondary carotenoids occurred in the periphery of the cell during strong irradiation. This process resulted in increased shading of the cup‐shaped chloroplast as demonstrated by a decrease in chlorophyll fluorescence. Extrachloroplastic accumulation of secondary carotenoids in H. lacustris can be interpreted as a specific adaptation to habitats that exhibit strong insolation.
FREEZING STRESS AND OSMOTIC DEHYDRATION IN FUCUS DISTICHUS (PHAEOPHYTA): EVIDENCE FOR PHYSIOLOGICAL SIMILARITY1
Authors: Pearson Gareth A. , Davison Ian R.
Published: October 2004

The effects of osmotic dehydration and freezing on photosynthesis were studied in the brown alga Fucus distichus L. The data indicated that F. distichus exhibits similar physiological responses to both osmotic dehydration and freezing stress and that these responses resemble those in the literature for the effect of desiccation in air. Both stresses inhibited light‐limited (Psubsat) and light‐saturated (Pmax) photosynthesis measured immediately after plants were reimmersed in seawater. The degree of initial inhibition and subsequent recovery of photosynthesis were proportional to the severity of the dehydration or freezing treatment. Psubsat and Pmax recovered completely from osmotic dehydration for 3 h in 200% and 3 hr at – 10°C, but recovery was only partial following 3 h in 300%o or 3 h at – 15°C. In most cases, recovery was complete within 2 h following dehydration, with little further recovery occurring between 2 and 24 h posttreatment. No time‐dependent recovery occurred following severe freezing. Observations using the vital stain fluorescein diacetate suggested that the lack of complete recovery might be due to severe damage or death of a proportion of cells in the thallus. There were no clear effects of either osmotic dehydration or freezing on dark respiration (Rd), although Rd was stimulated in all emersed treatments (frozen plants and 5° C controls) immediately following reimmersion. Measurement of chlorophyll fluorescence induction kinetics indicated that both osmotic dehydration and freezing reduced the ratio of variable to maximum florescence (Fv/Fm), indicating a decrease in the quantum efficiency of photosystem I. Based on these data, we suggest that there are common cellular and physiological components involved in the response of fucoid algae to a range of water stresses. This hypothesis was supported by experiments that showed that osmoacclimation in hyperosmotic seawater (51%o)for 2 weeks increased the ability of F. distichus to recover from freezing at – 15° C. During acclimation, mannitol content increased under hyperosmotic conditions and decreased under hypoosmotic conditions. Changes in plasma membrane integrity, determined by fresh weight: dry weight ratio, and amino acid release following freezing indicated an increasing gradient of freezing tolerance from low to high salinity. However, none of these physiological changes fully explained the marked increase in the freezing tolerance of photosynthesis observed in plants acclimated under hyperosmotic conditions.
STORAGE OF PHOSPHORUS IN NITROGEN‐FIXING ANABAENA FLOS‐AQUAE (CYANOPHYCEAE)1
Authors: Thompson Patsy‐Ann , Oh Hee‐Mock , Rhee G‐Yull
Published: October 2004

P accumulation and metabolic pathway in N2‐fixing Anabaena flos‐aquae (Lyngb.) Bréb were investigated in P‐sufficient (20 μMP) and P‐limited (2 μMP) turbidostats in combined N‐free medium. The cyanobacterium grew at its maximum rate (μmax, 1.13 d−1) at the high P concentration and at 65% of μmax under P limitation, with total cell P concentrations (QP) at steady states of 12.0 and 5.2 fmol·cell−1, respectively. At steady state, polyphosphates (PPi) accounted for only 3% of QP (0.4 fmol·cell−1) in P‐rich cells. Its concentration in P‐limited cells was 5.8% (0.3 fmol·cell−1). On the other hand, sugar P was very high at 22% of QP in P‐rich cells and was undetectable in P‐limited cells. Pulse chase experiments with 32P showed that P‐rich cells initially incorporated the labeled P into the acid‐soluble PPi fraction within the first few minutes and to a lesser extent into nucleotide P. Radioactivity in the PPi then declined rapidly with concomitant increases in sugar P and nucleotide P fractions. In contrast, in P‐limited cells, no radiolabel was detected in acid‐soluble PPi, and 32P was initially incorporated into nucleotide P, sugar P, and ortho P fractions. The latter two fractions then subsequently declined. Therefore, under N2‐fixing conditions the cyanobacteria appeared to store P as sugar P and also utilize P through different pathways under P‐rich and ‐limited conditions. When nitrate was supplied as the N source under P‐sufficient conditions, PPi accounted for about 15% of steady‐state QP, but no sugar P was detected. Therefore, the same organism stored P in different cell P fractions depending on its N sources.
THE EFFECT OF HYDROXYUREA AND FLUORODEOXYURIDINE ON CELL CYCLE EVENTS IN THE CHLOROCOCCAL ALGA SCENEDESMUS QUADRICAUDA (CHLOROPHYTA)1
Authors: Zachleder Vilém
Published: October 2004

The effect of hydroxyurea and 5‐fluorodeoxyuridine (FdUrd) on the course of growth (RNA and protein synthesis) and reproductive (DNA replication and nuclear and cellular division) processes was studied in synchronous cultures of the chlorococcal alga Scenedesmus quadricauda (Turp.) Bréb. The presence of hydroxyurea (5 mg·L−1)from the beginning of the cell cycle prevented growth and further development of the cells because of complete inhibition of RNA synthesis. In cells treated later in the cell cycle at the time when the cells were committed to division, hydroxyurea present in light affected the cells in the same way as a dark treatment without hydroxyurea; i. e. RNA synthesis was immediately inhibited followed after a short time period by cessation of protein synthesis. Reproductive processes including DNA replication to which the commitment was attained, however, were initiated and completed. DNA synthesis continued until the constant minimal ratio of RNA to DNA was reached.

FdUrd (25 mg·L−1) added before initiation of DNA replication in control cultures prevented DNA synthesis in treated cells. Addition of FdUrd at any time during the cell cycle prevented or immediately stopped DNA replication. However, by adding excess thymidine (100 mg·L−1), FdUrd inhibition of DNA replication could be prevented. FdUrd did not affect synthesis of RNA, protein, or starch for at least one cell cycle. After removal of FdUrd, DNA synthesis was reinitiated with about a 2‐h delay. The later in the cell cycle FdUrd was removed, the longer it took for DNA synthesis to resume. At exposures to FdUrd longer than two or three control cell cycles, cells in the population were gradually damaged and did not recover at all.
ULTRASTRUCTURE OF PRYMNESIUM NEMAMETHECUM SP. NOV. (PRYMNESIOPHYCEAE)1
Authors: Pienaar Richard N. , Birkhead Monica
Published: October 2004

Based on material collected from Cape Town, a new sand‐dwelling, marine species of Prymnesium is described. Using light and electron microscopy, Prymnesium nemamethecum sp. nov. has been found to resemble other species of the genus in size, organelle arrangement, and swimming behavior. It differs from other described species in that it has three types of scales, one of which is confined to the region of appendage insertion and forms a sheath of simple plate scales over the haptonema. In addition, the scales constituting the proximal body scale layer(s) are unusual because they are not simple plate scales but are specifically ornamented.
TIP CELL GROWTH AND THE FREQUENCY AND DISTRIBUTION OF CELLULOSE MICROFIBRIL‐SYNTHESIZING COMPLEXES IN THE PLASMA MEMBRANE OF APICAL SHOOT CELLS OF THE RED ALGA PORPHYRA YEZOENSIS1
Authors: Tsekos Ioannes , Reiss Hans‐Dieter
Published: October 2004

The supramolecular organization of the plasma membrane of apical cells in shoot filaments of the marine red alga Porphyra yezoensis Ueda (conchocelis stage) was studied in replicas of rapidly frozen and fractured cells. The protoplasmic fracture (PF) face of the plasma membrane exhibited both randomly distributed single particles (with a mean diameter of 9.2 ± 0.2 nm) and distinct linear cellulose microfibril‐synthesizing terminal complexes (TCs) consisting of two or three rows of linearly arranged particles (average diameter of TC particles 9.4 plusmn; 0.3 nm). The density of the single particles of the PF face of the plasma membrane was 3000 μm−2, whereas that of the exoplasmic fracture face was 325 μm−2. TCs were observed only on the PF face. The highest density of TCs was at the apex of the cell (mean density 23.0 plusmn; 7.4 TCs μm−2 within 5 μm from the tip) and decreased rapidly from the apex to the more basal regions of the cell, dropping to near zero at 20 μm. The number of particle subunits of TCs per μm2 of the plasma membrane also decreased from the tip to the basal regions following the same gradient as that of the TC density. The length of TCs increased gradually from the tip (mean length 46.0 plusmn; 1.4 nm in the area at 0–5 μm from the tip) to the cell base (mean length 60.0 plusmn; 7.0 μm in the area at 15–20 μm). In the very tip region (0–4 μm from the apex), randomly distributed TCs but no microfibril imprints were observed, while in the region 4–9 μm from the tip microfibril imprints and TCs, both randomly distributed, occurred. Many TCs involved in the synthesis of cellulose microfibrils were associated with the ends of microfibril imprints. Our results indicate that TCs are involved in the biosynthesis, assembly, and orientation of cellulose microfibrils and that the frequency and distribution of TCs reflect tip growth (polar growth) in the apical shoot cell of Porphyra yezoensis. Polar distribution of linear TCs as “cellulose synthase” complexes within the plasma membrane of a tip cell was recorded for the first time in plants.
TEMPORAL VARIATIONS IN THE TAXONOMIC COMPOSITION OF FLAGELLATED NANOPLANKTON IN A TEMPERATE FJORD1
Authors: Smith Patricia J. , Hobson Louis A.
Published: October 2004

We studied the taxonomic composition of flagellated nanoplankton in a temperate Canadian fjord, Saanich Inlet, for 1 year using electron microscopy. Most of the species that we identified were from the algal classes Prasinophyceae, Prymnesiophyceae, and Chrysophyceae and the protistan order Choanoflagellida. During summer months, we observed a diverse group of prymnesiophyte, prasinophyte, and chrysophyte species. In fall and winter, the number of species of prasinophyte and prymnesiophyte species in our samples decreased. At times, numerous chrysophyte species were present, and many of these were heterotrophic and typical of freshwater environments, presumably having been carried into the inlet by freshwater runoff. We suggest that during the winter months of 1991 a food web composed of dissolved and particulate organic debris, bacteria, algal cells, and choanoflagellates was an important feature of the plankton.

We identified 71 species from 41 genera, and most of these have been reported for either other parts of the world ocean or freshwater environments, indicating that they have widespread distributions. Some species differed in cell and scale morphologies from those documented in the literature, and these distinctions are described. Thirty‐two of these species were recorded for the first time from the coastal waters of the northeastern Pacific Ocean.
MICROSENSOR STUDIES OF OXYGEN AND LIGHT DISTRIBUTION IN THE GREEN MACROALGA CODIUM FRAGILE1
Authors: Lassen Carsten , Bebout Leslie E. , Paerl Hans W. , Jørgensen Bo B.
Published: October 2004

Scalar irradiance, oxygen concentration, and oxygenic photosynthesis were measured at 0.1 mm spatial resolution within the tissue of the siphonous green macroalga Codium fragile subsp. tomentosoides (van Goor) Silva by fiber‐optic scalar irradiance microsensors and oxygen microelectrodes. The scalar irradiance of visible light was strongly attenuated in the outer 0.2 mm of the tissue but was nearly constant for the subsequent 1.0 mm of photo‐synthetic tissue. Far‐red scalar irradiance at 750 nm increased below the tissue surface to a maximum of 200% of incident irradiance at 1.2 mm depth due to multiple scattering in the medullary tissue. The constant intensity of visible light below 0.2 mm was thus a result of the combined effects of absorption and backscattering from the medulla.

The oxygen exchange between the alga and the surrounding water was diffusion‐limited with a steep O2gradient inside and around the alga. In darkness, the tissue below 0.6 mm became anoxic, and endophytic extracellular space provided an environment where anoxygenic microbial processes may occur. When illuminated at 160 nmol photons·−2·−1, O2 concentrations exceeded ambient levels throughout the thallus, with a maximum of 250% of air saturation just below the surface. The amplitude of oxygen variation was buffered by gas bubbles formed in the medullary tissue.
PICOPHYTOPLANKTON BIOMASS IN RELATION TO LAKE TROPHIC STATE AND THE TN:TP RATIO OF LAKE WATER IN JAPAN1
Authors: Takamura Noriko , Nojiri Yukihiro
Published: October 2004

Picophytoplankton biomass and its contribution to total phytoplankton biomass were investigated in relation to the nutrient concentration and total N: total P ratio of the epilimnetic waters of 42 Japanese lakes during the warm season in 1991 (April–October). Picophytoplankton biomass (as chlorophyll a) in meso‐, eu‐, and hypertrophic lakes was significantly higher than those observed in oligotrophic lakes. However, picophytoplankton biomass increased significantly with increased total P concentrations in all systems excluding hypertrophic lakes. Picophytoplankton contribution to total chlorophyll a content was significantly higher in oligo‐ and mesotrophic lakes than in eu‐ and hypertrophic lakes and was inversely correlated with total P concentrations in lake water. Picophytoplankton contribution to the total phytoplankton biomass was positively (r = 0.54, n = 42, P = 0.0003) correlated with the total N: total P ratio of lake waters. Each lake trophic type, with the exception of hypertrophic lakes, showed this trend, although the correlation was not significant. We suggest that picophytoplankton contribution is influenced by the total N: total P ratio rather than lake trophic state; however, picophytoplankton were of little importance in hypertrophic lakes.