Bipolar Pattern Research Articles

Spaceflight Enhances Cell Aggregation and Random Budding in Candida albicans

This study presents the first global transcriptional profiling and phenotypic characterization of the major human opportunistic fungal pathogen, Candida albicans, grown in spaceflight conditions. Microarray analysis revealed that C. albicans subjected to short-term spaceflight culture differentially regulated 452 genes compared to synchronous ground controls, which represented 8.3% of the analyzed ORFs. Spaceflight-cultured C. albicans–induced genes involved in cell aggregation (similar to flocculation), which was validated by microscopic and flow cytometry analysis. We also observed enhanced random budding of spaceflight-cultured cells as opposed to bipolar budding patterns for ground samples, in accordance with the gene expression data. Furthermore, genes involved in antifungal agent and stress resistance were differentially regulated in spaceflight, including induction of ABC transporters and members of the major facilitator family, downregulation of ergosterol-encoding genes, and upregulation of genes involved in oxidative stress resistance. Finally, downregulation of genes involved in actin cytoskeleton was observed. Interestingly, the transcriptional regulator Cap1 and over 30% of the Cap1 regulon was differentially expressed in spaceflight-cultured C. albicans. A potential role for Cap1 in the spaceflight response of C. albicans is suggested, as this regulator is involved in random budding, cell aggregation, and oxidative stress resistance; all related to observed spaceflight-associated changes of C. albicans. While culture of C. albicans in microgravity potentiates a global change in gene expression that could induce a virulence-related phenotype, no increased virulence in a murine intraperitoneal (i.p.) infection model was observed under the conditions of this study. Collectively, our data represent an important basis for the assessment of the risk that commensal flora could play during human spaceflight missions. Furthermore, since the low fluid-shear environment of microgravity is relevant to physical forces encountered by pathogens during the infection process, insights gained from this study could identify novel infectious disease mechanisms, with downstream benefits for the general public.

Bryophilous ascomycetes everywhere: Distribution maps of selected species on liverworts, mosses and Polytrichaceae*

Döbbeler, P. & Hertel, H. 2013. Bryophilous ascomycetes everywhere: Distribution maps of selected species on liverworts, mosses and Polytrichaceae. — Herzogia 26: 361–404.The biogeographical distributions of 21 selected species of ascomata-forming fungi that grow obligately on bryophyte gametophytes have been compiled and are presented as 27 dot maps. The maps are based on more than 1370 records, combing all hitherto published records (more than 970) with nearly 400 additional ones, cited here for the first time. Examples are given for European, holarctic, neotropical, tropical Afro-American, pantropical, Australasian, australsubantarctic, bipolar, nearly cosmopolitan, and endemic distribution patterns. Ten maps are devoted to nine fungal species found on foliose hepatics (Bryocentria brongniartii, Calonectria frullaniae, Dactylospora heimerlii, Epibryon deceptor, E. filiforme, E. pedinophylli, Octosporella jungermanniarum, Stenocybe nitida, Ticonectria perianthii), two maps refer to a species found on pleurocarpous mosses (Acrospermum adeanum), and 15 maps show the distributions of eleven taxa found on Polytrichaceae (Bryochiton perpusillus, Biyonectria phyllogena, Bryorella cryptocarpa, Dawsophila callichroma, D. polycarpa, Epibryon elegantissimum, E. pogonati-urnigeri, Hymenoscyphus erythropus, Lizonia sexangularis, Potridiscus polymoiphus, Potriphila navicularis). Host species are represented by liverworts (18 species), Polytrichaceae (29 species), and a few pleurocarpous mosses. Several new fungus-host relationships are revealed. Particular emphasis is placed on the multitude of systematically and biologically diverse groups to which these parasites belong. Sixteen genera from seven classes of Ascomycota are represented. Biological diversity is reflected in the varying degrees of host specificity, biotrophic or necrotrophic parasitism, and the colonization of distinct microniches (e.g. perianths of epiphyllous liverworts, interlamellar leaf spaces or male antheridial cups in Polytrichaceae). Some parasites are so common that screening potential host collections is a rewarding method of discovery. Other taxa are so rare that their observation was accidental and fortuitous, even in well-studied host groups. Bryochiton perpusillus and Epibryon pogonati-urnigeri, both occurring on a variety of Polytrichaceae, are the most well-documented species, with 234 and 236 records respectively. As it is typical of most obligate parasites such as the lichenicolous fungi, bryophilous ascomycetes tend to occur within the wider distribution ranges of their hosts. There are only a few examples of species whose distributions seem to be restricted to only a part of the area occupied by their hosts. Calonectria frullaniae, Potridiscus polymorphus, and Ticonectria perianthii are three such exceptions. The maps verify the hitherto largely ignored fact that many ascomycetes are widespread, and are regularly associated with bryophytes.

Latitudinal patterns in the diversity of two subgenera of the genus Daphnia O.F. Müller (Crustacea: Cladocera: Daphniidae).

Daphnia O.F. Müller (Crustacea: Cladocera: Daphniidae) is an important model in biology. It was concluded earlier that subgenus Daphnia s.str. occurs mainly in the northern hemisphere, subgenus Daphnia (Ctenodaphnia) in the southern hemisphere, which could suggest that: (1) the subgeneric differentiation is correlated with the Laurasia-Gondwanaland subdivision and (2) D. (Ctenodaphnia) is a taxon of Gondwanian origin. Some authors even discussed mechanisms of maintaince of the "ancient subgeneric north-south split", regarding such a pattern as paradoxical. But both molecular clock calculations and fossils of both subgenera from the Jurassic/Cretaceous boundary of Mongolia compromise such ideas and suggest an earlier, Pangaean, differentiation of the subgenera. We discuss the distribution of Daphnia worldwide based on recent literature. Our analysis covers literature data on all described and on undescribed taxa revealed by genetical methods. Distributional data were associated with five main zones: southern cold (I), southern temperate (II), tropical (III), northern temperate (IV), and northern cold (V) zone. We found no "subgeneric north-south split": the distribution of Daphnia s.str. is dissymmetric between the hemispheres (antipolar), while that of Ctenodaphnia is sub-symmetric (bipolar). We suggest that both patterns are not of Mesozoic, but of Cenozoic origin. Mesozoic differentiation of the subgenera does not contradict a recent origin of the extant species, as found in e.g. Notostraca. A superficially attractive hypothesis about a Gondwanian origin of a taxon (Daphnia (Ctenodaphnia)) therefore did not pass the test of the fossil records. In addition, we agree with the opinion that an antipolar is only a variant of a bipolar pattern, as a result of an extinction in the southern hemisphere, and that these patterns are mid-late Cenozoic instead of Mesozoic.

Role of endocytosis in localization and maintenance of the spatial markers for bud-site selection in yeast.

The yeast Saccharomyces cerevisiae normally selects bud sites (and hence axes of cell polarization) in one of two distinct patterns, the axial pattern of haploid cells and the bipolar pattern of diploid cells. These patterns depend on distinct sets of cortical-marker proteins that transmit positional information through a common signaling pathway based on a Ras-type GTPase. It has been reported previously that various proteins of the endocytic pathway may be involved in determining the bipolar pattern but not the axial pattern. To explore this question systematically, we constructed and analyzed congenic haploid and diploid deletion mutants for 14 genes encoding proteins that are involved in endocytosis. The mutants displayed a wide range of severities in their overall endocytosis defects, as judged by their growth rates and abilities to take up the lipophilic dye FM 4–64. Consistent with the previous reports, none of the mutants displayed a significant defect in axial budding, but they displayed defects in bipolar budding that were roughly correlated with the severities of their overall endocytosis defects. Both the details of the mutant budding patterns and direct examination of GFP-tagged marker proteins suggested that both initial formation and maintenance of the normally persistent bipolar marks depend on endocytosis, as well as polarized exocytosis, in actively growing cells. Interestingly, maintenance of the bipolar marks in non-growing cells did not appear to require normal levels of endocytosis. In some cases, there was a striking lack of correlation between the overall severities of the general-endocytosis defect and the bud-site selection defect, suggesting that various endocytosis proteins may differ in their importance for the uptake of various plasma-membrane targets.

Spatiotemporal control of PopZ localization through cell cycle–coupled multimerization

Bacterial cell poles constitute defined subcellular domains where numerous proteins localize, often at specific times, to affect various physiological processes. How pole recognition occurs and what governs the timing of protein localization are often unknown. In this paper, we investigate the mechanisms governing the localization of PopZ, a chromosome-anchoring protein whose unipolar to bipolar localization pattern is critical for cell cycle progression in Caulobacter crescentus. We provide evidence that polar localization of PopZ relied on its self-assembly into a higher-order structure (matrix) and that the unipolar to bipolar transition was coupled to the asymmetric distribution of ParA during the translocation of the origin-proximal ParB-parS partition complex. Collectively, our data suggest a model in which a local increase of ParA concentration promotes the assembly of a PopZ matrix precisely when and where this matrix is needed. Such coupling of protein assembly with a cell cycle-associated molecular asymmetry may represent a principle of cellular organization for controlling protein localization in both time and space.

Non-Equilibrium Polar Localization of Proteins in Bacterial Cells

Many proteins are observed to localize to the poles within bacterial cells. Some bacteria show unipolar localization, yet under different conditions bipolar patterns can emerge. One mechanism for spontaneous polar localization has been shown to involve the combination of protein aggregation and nucleoid occlusion. Whether the different observed patterns represent global energy minima for the cellular system remains to be determined. In this paper we show that for a model consisting only of protein aggregation along with an excluded volume effect due to the DNA polymer, that unipolar patterns are the global energy ground state regardless of protein concentration and DNA density. We extend the model to allow for proteins to be added to the cellular volume at a constant rate and show that bipolar (or multi-foci) patterns emerge as the result of the system being kinetically trapped in a local energy minimum. Lastly we also consider the situation of a growing cell that starts with a pre-existing aggregate at one of the poles and determine conditions under which either unipolar or bipolar patterns can exist at the point when it is ready to divide. This work sheds new interpretations on recently published experimental data and suggests experiments to test whether such a mechanism can drive patterning in bacteria.

The “MIS 11 paradox” and ocean circulation: Role of millennial scale events

The role of millennial scale climate variability in supplementing the astronomical forcing of glacial–interglacial transitions remains a major unresolved question. Here we compare the occurrence and character of “terminal” ice rafting events in both the North and South Atlantic during the last deglaciation (Termination I, TI) and during the transition between Marine Isotope Stages (MIS) 12 and 11 (or Termination V, TV). We show that TV experienced a massive terminal ice rafting event in the North Atlantic that was more intense and longer lasting than Heinrich event 1 (H1) of the last deglaciation. This massive ice rafting event was linked to cold stadial conditions and reduced deep water formation in the North Atlantic, in parallel with warming at high southern latitudes, similar to the bipolar seesaw pattern exhibited during H1 over the last deglaciation. We propose that the particular intensity and duration of the TV ice rafting event resulted from the especially large volume of Northern Hemisphere ice sheets during MIS12. In turn, the unusually long duration and large amplitude of TV likely resulted from the exceptionally prolonged collapse of the AMOC during the TV Heinrich stadial, and from a subsequent transient AMOC “overshoot” with respect to later MIS11 interglacial circulation. Furthermore, we suggest that the intense Heinrich stadial of TV contributed to the deglaciation primarily via meridional heat transport anomalies that would have enhanced the incipient warming arising from relatively weak insolation forcing, and only secondarily via CO2 release.

Pleistocene expansion of the bipolar lichen Cetraria aculeata into the Southern hemisphere

Many boreal and polar lichens occupy bipolar distributional ranges that frequently extend into high mountains at lower latitudes. Although such disjunctions are more common among lichens than in other groups of organisms, the geographic origin of bipolar lichen taxa, and the way and time frame in which they colonized their ranges have not been studied in detail. We used the predominantly vegetative, widespread lichen Cetraria aculeata as a model species. We surveyed the origin and history of its bipolar pattern using population genetics, phylogenetic and genealogical reconstruction methods. Cetraria aculeata originated in the Northern Hemisphere and dispersed southwards during the Pleistocene. The genetic signal suggests a Pleistocene dispersive burst in which a population size expansion concurred with the acquisition of a South-American range that culminated in the colonization of the Antarctic.

Nanoxerography utilizing bipolar charge patterns

We report a nanoxerography utilizing alternating bipolar surface charge patterns. Unlike a conventional nanoxerography using unipolar charge patterns, the present concept generates convex shaped equipotential planes with large curvature that can act as nanoscopic electrostatic lenses. Through these lenses, positively charged aerosol nanoparticles are focused into the center region of the negative surface charge pattern leading to the significant reduction of particle deposition width. We also demonstrate that the focusing capability can be controlled by changing ion flow rates. Numerical simulations of the trajectory and deposition of charged particles were done to support experimental results.

An Unsupervised Approach for Person Name Bipolarization Using Principal Component Analysis

A topic is usually associated with a specific time, place, and person(s). Generally, topics that involve bipolar or competing viewpoints are attention getting and are thus reported in a large number of documents. Identifying the association between important persons mentioned in numerous topic documents would help readers comprehend topics more easily. In this paper, we propose an unsupervised approach for identifying bipolar person names in a set of topic documents. Specifically, we employ principal component analysis (PCA) to discover bipolar word usage patterns of person names in the documents, and show that the signs of the entries in the principal eigenvector of PCA partition the person names into bipolar groups spontaneously. To reduce the effect of data sparseness, we introduce two techniques, called the weighted correlation coefficient and off-topic block elimination. We also present a timeline system that shows the intensity and activeness development of the identified bipolar person groups. Empirical evaluations demonstrate the efficacy of the proposed approach in identifying bipolar person names in topic documents, while the generated timelines provide comprehensive storylines of topics.

Apparent defect in yeast bud-site selection due to a specific failure to splice the pre-mRNA of a regulator of cell-type-specific transcription.

The yeast Saccharomyces cerevisiae normally selects bud sites (and hence axes of cell polarization) in one of two distinct patterns, the axial pattern of haploid cells and the bipolar pattern of diploid cells. Although many of the proteins involved in bud-site selection are known, it is likely that others remain to be identified. Confirming a previous report (Ni and Snyder, 2001, Mol. Biol. Cell 12, 2147–2170), we found that diploids homozygous for deletions of IST3/SNU17 or BUD13 do not show normal bipolar budding. However, these abnormalities do not reflect defects in the apparatus of bipolar budding. Instead, the absence of Ist3 or Bud13 results in a specific defect in the splicing of the MAT a 1 pre-mRNA, which encodes a repressor that normally blocks expression of haploid-specific genes in diploid cells. When Mata1 protein is lacking, Axl1, a haploid-specific protein critical for the choice between axial and bipolar budding, is expressed ectopically in diploid cells and disrupts bipolar budding. The involvement of Ist3 and Bud13 in pre-mRNA splicing is by now well known, but the degree of specificity shown here for MAT a 1 pre-mRNA, which has no obvious basis in the pre-mRNA structure, is rather surprising in view of current models for the functions of these proteins. Moreover, we found that deletion of PML1, whose product is thought to function together with Ist3 and Bud13 in a three-protein retention-and-splicing (RES) complex, had no detectable effect on the splicing in vivo of either MAT a 1 or four other pre-mRNAs.

A Response Regulator Interfaces between the Frz Chemosensory System and the MglA/MglB GTPase/GAP Module to Regulate Polarity in Myxococcus xanthus

How cells establish and dynamically change polarity are general questions in cell biology. Cells of the rod-shaped bacterium Myxococcus xanthus move on surfaces with defined leading and lagging cell poles. Occasionally, cells undergo reversals, which correspond to an inversion of the leading-lagging pole polarity axis. Reversals are induced by the Frz chemosensory system and depend on relocalization of motility proteins between the poles. The Ras-like GTPase MglA localizes to and defines the leading cell pole in the GTP-bound form. MglB, the cognate MglA GTPase activating protein, localizes to and defines the lagging pole. During reversals, MglA-GTP and MglB switch poles and, therefore, dynamically localized motility proteins switch poles. We identified the RomR response regulator, which localizes in a bipolar asymmetric pattern with a large cluster at the lagging pole, as important for motility and reversals. We show that RomR interacts directly with MglA and MglB in vitro. Furthermore, RomR, MglA, and MglB affect the localization of each other in all pair-wise directions, suggesting that RomR stimulates motility by promoting correct localization of MglA and MglB in MglA/RomR and MglB/RomR complexes at opposite poles. Moreover, localization analyses suggest that the two RomR complexes mutually exclude each other from their respective poles. We further show that RomR interfaces with FrzZ, the output response regulator of the Frz chemosensory system, to regulate reversals. Thus, RomR serves at the functional interface to connect a classic bacterial signalling module (Frz) to a classic eukaryotic polarity module (MglA/MglB). This modular design is paralleled by the phylogenetic distribution of the proteins, suggesting an evolutionary scheme in which RomR was incorporated into the MglA/MglB module to regulate cell polarity followed by the addition of the Frz system to dynamically regulate cell polarity.

Experimental research on hysteresis effects in GMR sensors for analog measurement applications

A Wheatstone bridge GMR sensor can be used for analog magnetic field measurements. This paper deals with hysteresis effects in GMR sensor, which is the major source of measurement error. Experiments are conducted by measuring hysteresis curves between applied magnetic field and sensor output voltage with different typical initial magnetization states. GMR sensor has two operation modes: bipolar and unipolar. Bipolar operation means internal magnetization pattern of GMR sensor changes direction during operation range. This mode is inappropriate for direct measurement, as experimental results indicate that the shape of measured curves with the same range of applied magnetic field may be severely distorted due to different initial magnetization states. Unipolar operation is an intermediate process of bipolar operation with invariant magnetization direction. Its input–output relationship is almost linear that is especially suitable for measurement. The principal measurement error within unipolar operation is DC offset voltage, which is induced by remanence. It can be fixed by saturating GMR sensor before operation.

Self-Organized Protein Localization and DNA Segregation Inside Bacterial Cells

Asymmetric cell division in C.Crescentus relies on differentially localizing certain proteins to the poles where they bind to the scaffolding protein PopZ that displays a bipolar pattern. On the other hand, expressing PopZ in E. coli favours unipolar patterning. Additionally, the aggregation of misfolded proteins as well as plasmids in bacteria also display unipolar and biopolar patterns, similar to that of PopZ. These different systems have led to the hypothesis that chromosome free regions + biomolecular aggregation can be sufficient to drive localization in bacterial cells. We have performed Monte-Carlo simulations to show that the entropic force provided by the self-avoiding chromosome confined in the cylindrical geometry of the cell and the energy gained from aggregation results in phase separation between proteins and the polymer. We fully explore the phase space showing how patterning depends on protein concentration, chromosome density, cell shape and aggregation strength. The exploration results in a rich phase diagram of patterns which the observed systems can be fit into. Additionally, the dynamics of pattern formation depends somewhat on the rate at which proteins are added to the system. When proteins are added very slowly to the cell, the unipolar phase dominates, whereas at faster rates the bipolar phase dominates and at yet faster still rate, aggregation at nonpolar locations occurs. Such a rate dependency may explain differences in the observed patterns reported for PopZ induced expression in E. coli cells. Lastly, we show how such a localization process may aid the segregation of other cellular components such as the replication origin which anchors to a pole. We find that adding extra interactions does not destabilize the polar patterning, nor is it sufficient to drive the localization of the origin and indeed other localization and stabilization mechanisms are required.

Multi-day rainfall trends over the Iberian Peninsula

In order to analyze the effects of the duration of precipitation events, trends in extreme rainfall over the Iberian Peninsula (IP) for multi-day extreme precipitation events (1 to 7 days) were evaluated from records of 52 observatories regularly distributed over Iberia with no missing data for the common period 1958–2004. Two approaches were used: first, the nonparametric Mann–Kendall test together with the Sen method, and second, a parametric test based on the statistical theory of extreme values, involving time-dependent parameters to account for possible temporal changes in the frequency distribution. It was found that, in winter, there were significant negative trends for a great part of the Iberian Peninsula, but significant positive trends for the southeast over areas that shrank as the number of days considered for the precipitation event increased. Spring also showed negative trends for a great part of the IP but with a major area of positive trend over the northeast that remained unchanged when considering the maxima of from 1 to 7 days of rainfall. Autumn showed a bipolar spatial pattern, with the west being positive and the east negative.

689 Bipolar electrogram signatures of therapeutic interest during human ventricular fibrillation

689 Bipolar electrogram signatures of therapeutic interest during human ventricular fibrillation

The road not taken: new destinations for yeast mRNAs on the move

The road not taken: new destinations for yeast mRNAs on the move

The German grand coalition of 2005–09 and party system change: Catalyst or continuity?

Two times in the last fifty years grand coalitions have altered traditionally bi-polar patterns of German electoral competition, changing the electoral context by making it difficult for voters to endorse anti-incumbent alternatives. How have voters reacted under these circumstances, and were their responses different because of the weakening of partisan attachments in the forty years between the two grand coalitions? This study explores these questions by examining voter behavior in German state elections under the federal grand coalitions of 1966–69 and 2005–09, comparing voters’ responses with long-term trends in German party system development. The second grand coalition saw a continuation of trends in declining turnout and increasing electoral volatility, but in contrast to the first grand coalition there was no surge in support for far-right parties. Such a change may be the result of differences between the party systems in the two period, with voters in unified Germany having many more options for expressing discontent.

Canine Distemper Virus Matrix Protein Influences Particle Infectivity, Particle Composition, and Envelope Distribution in Polarized Epithelial Cells and Modulates Virulence

In paramyxoviruses, the matrix (M) protein mediates the interaction between the envelope and internal proteins during particle assembly and egress. In measles virus (MeV), M mutations, such as those found in subacute sclerosing panencephalitis (SSPE) strains, and differences in vaccine and wild-type M proteins can affect the strength of interaction with the envelope glycoproteins, assembly efficiency, and spread. However, the contribution of the M protein to the replication and pathogenesis of the closely related canine distemper virus (CDV) has not been characterized. To this end this, we generated a recombinant wild-type CDV carrying a vaccine strain M protein. The recombinant virus retained the parental growth phenotype in VerodogSLAMtag cells, but displayed an increased particle-to-infectivity ratio very similar to that of the vaccine strain, likely due to inefficient H protein incorporation. Even though infectious virus was released only from the apical surface, consistent with the release polarity of the wild-type CDV strain, envelope protein distribution in polarized epithelial cells reproduced the bipolar pattern seen in vaccine strain-infected cells. Most notably, the chimeric virus was completely attenuated in ferrets and caused only a mild and transient leukopenia, indicating that the differences in particle infectivity and envelope protein sorting mediated by the vaccine M protein contribute importantly to vaccine strain attenuation.

Electrostatic effects influence the formation of two-dimensional crystals of bacteriorhodopsin reconstituted into dimyristoylphosphatidylcholine membranes

We examined how electrostatic shielding affects the formation of two-dimensional (2D) crystals of bacteriorhodopsin (bR) in reconstituted dimyristoylphosphatidylcholine (DMPC) membranes by varying the sodium chloride (NaCl) concentration. The 2D crystalline array of bR formed in the gel phase of DMPC membranes was characterized by a symmetric bipolar pattern in visible circular dichroic spectra collected around 560 nm. The amplitude of the bipolar pattern was systematically enhanced by increasing the NaCl concentration. A strong correlation between the amplitude of the bipolar pattern and the Debye constant of small ions indicated that a weakening of electrostatic repulsion by the shielding effect of small ions enhances the order of 2D bR crystals in the gel phase of DMPC membranes. Considering the 3D distribution of charged residues, we propose a model of interaction balance in reconstituted bR membranes in which effective attraction between bR molecules occurs as a result of the phase separation of the DMPC membrane in the gel phase overcoming electrostatic repulsion between bR molecules.