@article{3757, abstract = {A central problem in biology is determining how genes interact as parts of functional networks. Creation and analysis of synthetic networks, composed of well-characterized genetic elements, provide a framework for theoretical modeling. Here, with the use of a combinatorial method, a library of networks with varying connectivity was generated in Escherichia coli. These networks were composed of genes encoding the transcriptional regulators Lacl, TetR, and lambda Cl, as well as the corresponding promoters. They displayed phenotypic behaviors resembling binary logical circuits, with two chemical “inputs” and a fluorescent protein “output.” Within this simple system, diverse computational functions arose through changes in network connectivity. Combinatorial synthesis provides an alternative approach for studying biological networks, as well as an efficient method for producing diverse phenotypes in vivo.}, author = {Guet, Calin C and Elowitz, Michael and Hsing, Weihong and Leibler, Stanislas}, issn = {0036-8075}, journal = {Science}, number = {5572}, pages = {1466 -- 1470}, publisher = {American Association for the Advancement of Science}, title = {{Combinatorial synthesis of genetic networks}}, doi = {10.1126/science.1067407}, volume = {296}, year = {2002}, } @article{3799, abstract = {GABAergic interneurones are diverse in their morphological and functional properties. Perisomatic inhibitory cells show fast spiking during sustained current injection, whereas dendritic inhibitory cells fire action potentials with lower frequency. We examined functional and molecular properties of K(+) channels in interneurones with horizontal dendrites in stratum oriens-alveus (OA) of the hippocampal CA1 region, which mainly comprise somatostatin-positive dendritic inhibitory cells. Voltage-gated K(+) currents in nucleated patches isolated from OA interneurones consisted of three major components: a fast delayed rectifier K(+) current component that was highly sensitive to external 4-aminopyridine (4-AP) and tetraethylammonium (TEA) (half-maximal inhibitory concentrations < 0.1 mM for both blockers), a slow delayed rectifier K(+) current component that was sensitive to high concentrations of TEA, but insensitive to 4-AP, and a rapidly inactivating A-type K(+) current component that was blocked by high concentrations of 4-AP, but resistant to TEA. The relative contributions of these components to the macroscopic K(+) current were estimated as 57 +/- 5, 25 +/- 6, and 19 +/- 2 %, respectively. Dendrotoxin, a selective blocker of Kv1 channels had only minimal effects on K(+) currents in nucleated patches. Coapplication of the membrane-permeant cAMP analogue 8-(4-chlorophenylthio)-adenosine 3':5'-cyclic monophosphate (cpt-cAMP) and the phosphodiesterase blocker isobutyl-methylxanthine (IBMX) resulted in a selective inhibition of the fast delayed rectifier K(+) current component. This inhibition was absent in the presence of the protein kinase A (PKA) inhibitor H-89, implying the involvement of PKA-mediated phosphorylation. Single-cell reverse transcription-polymerase chain reaction (RT-PCR) analysis revealed a high abundance of Kv3.2 mRNA in OA interneurones, whereas the expression level of Kv3.1 mRNA was markedly lower. Similarly, RT-PCR analysis showed a high abundance of Kv4.3 mRNA, whereas Kv4.2 mRNA was undetectable. This suggests that the fast delayed rectifier K(+) current and the A-type K(+) current component are mediated predominantly by homomeric Kv3.2 and Kv4.3 channels. Selective modulation of Kv3.2 channels in OA interneurones by cAMP is likely to be an important factor regulating the activity of dendritic inhibitory cells in principal neurone-interneurone microcircuits.}, author = {Lien, Cheng and Martina, Marco and Schultz, Jobst and Ehmke, Heimo and Jonas, Peter M}, issn = {0022-3751}, journal = {Journal of Physiology}, number = {Pt 2}, pages = {405 -- 419}, publisher = {Wiley-Blackwell}, title = {{Gating, modulation and subunit composition of voltage-gated K(+) channels in dendritic inhibitory interneurones of rat hippocampus}}, doi = {10.1113/jphysiol.2001.013066}, volume = {538}, year = {2002}, } @article{3800, abstract = {Networks of GABAergic interneurons are of critical importance for the generation of gamma frequency oscillations in the brain. To examine the underlying synaptic mechanisms, we made paired recordings from "basket cells" (BCs) in different subfields of hippocampal slices, using transgenic mice that express enhanced green fluorescent protein (EGFP) under the control of the parvalbumin promoter. Unitary inhibitory postsynaptic currents (IPSCs) showed large amplitude and fast time course with mean amplitude-weighted decay time constants of 2.5, 1.2, and 1.8 ms in the dentate gyrus, and the cornu ammonis area 3 (CA3) and 1 (CA1), respectively (33-34 degrees C). The decay of unitary IPSCs at BC-BC synapses was significantly faster than that at BC-principal cell synapses, indicating target cell-specific differences in IPSC kinetics. In addition, electrical coupling was found in a subset of BC-BC pairs. To examine whether an interneuron network with fast inhibitory synapses can act as a gamma frequency oscillator, we developed an interneuron network model based on experimentally determined properties. In comparison to previous interneuron network models, our model was able to generate oscillatory activity with higher coherence over a broad range of frequencies (20-110 Hz). In this model, high coherence and flexibility in frequency control emerge from the combination of synaptic properties, network structure, and electrical coupling.}, author = {Bartos, Marlene and Vida, Imre and Frotscher, Michael and Meyer, Axel and Monyer, Hannah and Geiger, Jörg and Jonas, Peter M}, issn = {0027-8424}, journal = {PNAS}, number = {20}, pages = {13222 -- 13227}, publisher = {National Academy of Sciences}, title = {{Fast synaptic inhibition promotes synchronized gamma oscillations in hippocampal interneuron networks}}, doi = {10.1073/pnas.192233099}, volume = {99}, year = {2002}, } @article{3801, abstract = {To examine possible interactions between fast depression and modulation of inhibitory synaptic transmission in the hippocampus, we recorded from pairs of synaptically connected basket cells (BCs) and granule cells (GCs) in the dentate gyrus of rat brain slices at 34 degrees C. Multiple-pulse depression (MPD) was examined in trains of 5 or 10 inhibitory postsynaptic currents (IPSCs) evoked at frequencies of 10-100 Hz under several conditions that inhibit transmitter release: block of voltage-dependent Ca2+ channels by Cd2+ (10 microM), activation of gamma-amino-butyric acid type B receptors (GABA(B)Rs) by baclofen (10 microM) and activation of muscarinic acetylcholine receptors (mAchRs) by carbachol (2 microM). All manipulations led to a substantial inhibition of synaptic transmission, reducing the amplitude of the first IPSC in the train (IPSC1) by 72%, 61% and 29%, respectively. However, MPD was largely preserved under these conditions (0.34 in control versus 0.31, 0.50 and 0.47 in the respective conditions at 50 Hz). Similarly, a theta burst stimulation (TBS) protocol reduced IPSC1 by 54%, but left MPD unchanged (0.40 in control and 0.39 during TBS). Analysis of both fractions of transmission failures and coefficients of variation (CV) of IPSC peak amplitudes suggested that MPD had a presynaptic expression site, independent of release probability. In conclusion, different types of presynaptic modulation of inhibitory synaptic transmission converge on a reduction of synaptic strength, while short-term dynamics are largely unchanged.}, author = {Hefft, Stefan and Kraushaar, Udo and Geiger, Jörg and Jonas, Peter M}, issn = {0022-3751}, journal = {Journal of Physiology}, number = {Pt 1}, pages = {201 -- 8}, publisher = {Wiley-Blackwell}, title = {{Presynaptic short-term depression is maintained during regulation of transmitter release at a GABAergic synapse in rat hippocampus}}, doi = {10.1113/jphysiol.2001.013455}, volume = {539}, year = {2002}, } @article{3802, abstract = {The presynaptic Ca2+ signal is a key determinant of transmitter release at chemical synapses. In cortical synaptic terminals, however, little is known about the kinetic properties of the presynaptic Ca2+ channels. To investigate the timing and magnitude of the presynaptic Ca2+ inflow, we performed whole-cell patch-clamp recordings from mossy fiber boutons (MFBs) in rat hippocampus. MFBs showed large high-voltage-activated Ca(2+) currents, with a maximal amplitude of approximately 100 pA at a membrane potential of 0 mV. Both activation and deactivation were fast, with time constants in the submillisecond range at a temperature of approximately 23 degrees C. An MFB action potential (AP) applied as a voltage-clamp command evoked a transient Ca2+ current with an average amplitude of approximately 170 pA and a half-duration of 580 microsec. A prepulse to +40 mV had only minimal effects on the AP-evoked Ca2+ current, indicating that presynaptic APs open the voltage-gated Ca2+ channels very effectively. On the basis of the experimental data, we developed a kinetic model with four closed states and one open state, linked by voltage-dependent rate constants. Simulations of the Ca2+ current could reproduce the experimental data, including the large amplitude and rapid time course of the current evoked by MFB APs. Furthermore, the simulations indicate that the shape of the presynaptic AP and the gating kinetics of the Ca2+ channels are tuned to produce a maximal Ca2+ influx during a minimal period of time. The precise timing and high efficacy of Ca2+ channel activation at this cortical glutamatergic synapse may be important for synchronous transmitter release and temporal information processing.}, author = {Bischofberger, Josef and Geiger, Jörg and Jonas, Peter M}, issn = {0270-6474}, journal = {Journal of Neuroscience}, number = {24}, pages = {10593 -- 10602}, publisher = {Society for Neuroscience}, title = {{Timing and efficacy of Ca(2+) channel activation in hippocampal mossy fiber boutons}}, doi = {10.1523/JNEUROSCI.22-24-10593.2002}, volume = {22}, year = {2002}, } @article{3803, abstract = {Mossy fiber (MF) synapses are key stations for flow of information through the hippocampal formation. A major component of the output of the MF system is directed towards inhibitory interneurons. Recent studies have revealed that the functional properties of MF-interneuron synapses differ substantially from those of MF-CA3 pyramidal neuron synapses. Mossy-fiber-interneuron synapses in the stratum lucidum represent a continuum of functional subtypes, in which the subunit composition of postsynaptic AMPA receptors and NMDA receptors appears to be regulated in a coordinated manner.}, author = {Bischofberger, Josef and Jonas, Peter M}, issn = {0166-2236}, journal = {Trends in Neurosciences}, number = {12}, pages = {600 -- 603}, publisher = {Elsevier}, title = {{TwoB or not twoB: differential transmission at glutamatergic mossy fiber-interneuron synapses in the hippocampus}}, doi = {10.1016/S0166-2236(02)02259-2}, volume = {25}, year = {2002}, } @article{3919, abstract = {Hamilton's concept of local mate competition (LMC) is the standard model to explain female-biased sex ratios in solitary Hymenoptera. In social Hymenoptera, however, LMC has remained controversial, mainly because manipulation of sex allocation by workers in response to relatedness asymmetries is an additional powerful mechanism of female bias. Furthermore, the predominant mating systems in the social insects are thought to make LMC unlikely. Nevertheless, several species exist in which dispersal of males is limited and mating occurs in the nest. Some of these species, such as the ant Cardiocondyla obscurior, have evolved dimorphic males, with one morph being specialized for dispersal and the other for fighting with nest-mate males over access to females. Such life history, combining sociality and alternative reproductive tactics in males, provides a unique opportunity to test the power of LMC as a selective force leading to female-biased sex ratios in social Hymenoptera. We show that, in concordance with LMC predictions, an experimental increase in queen number leads to a shift in sex allocation in favour of non-dispersing males, but does not influence the proportion of disperser males. Furthermore, we can assign this change in sex allocation at the colony level to the queens and rule out worker manipulation.}, author = {Cremer, Sylvia and Heinze, Jürgen}, issn = {0962-8452}, journal = {Proceedings of the Royal Society of London Series B Biological Sciences}, number = {1489}, pages = {417 -- 422}, publisher = {Royal Society, The}, title = {{Adaptive production of fighter males: queens of the ant Cardiocondyla adjust the sex ratio under local mate competition}}, doi = {10.1098/rspb.2001.1892}, volume = {269}, year = {2002}, } @article{3920, abstract = {A particular Solid Injector needle, suitable for GC-MS analyses of small specimens, is described together with its application in a study on ants.}, author = {Turillazzi, Stefano and Sledge, Matthew and Cremer, Sylvia and Heinze, Jürgen}, journal = {Insect Social Life}, pages = {169 -- 175}, publisher = {Elsevier}, title = {{A method for analysing small-size specimens in GC-MS}}, volume = {4}, year = {2002}, } @article{3924, abstract = {Males of the ant Cardiocondyla show a dispersal dimorphism of a winged and wingless morph. The loss of flight has lead to morphological reductions in the wingless (ergatoid) males and also affected body size, eye size and pigmentation. As ergatoid males mate exclusively inside the maternal nest, they underlie increased male-male competition and therefore have also evolved additional changes in behaviour and physiology: in contrast to winged males, ergatoid males are highly aggressive towards each other and their spermatogenesis is prolonged compared to all other hymenopteran males. In addition to these two male morphs, we found males with an intermediate appearance. These "intermorphic" males provide a transitional stage between normal males in most investigated morphological and physiological parameters. As they are produced extremely rarely and only in colonies that switch between pure ergatoid to mixed male production, we argue that they likely represent a developmental mistake. Parallels between the determination of male morphs and female castes (queen-worker dimorphism and worker polymorphism) might help to understand how the large potential of phenotypic plasticity in both sexes of social insects is realised during development.}, author = {Cremer, Sylvia and Lautenschläger, Birgit and Heinze, Jürgen}, issn = {0020-1812}, journal = {Insectes Sociaux}, number = {3}, pages = {221 -- 228}, publisher = {Springer}, title = {{A transitional stage between the ergatoid and winged male morph in the ant Cardiocondyla obscurior}}, doi = {10.1007/s00040-002-8305-z}, volume = {49}, year = {2002}, } @article{3925, abstract = {Males of the tropical ant Cardiocondyla obscurior are either wingless and aggressive or winged and docile, and both compete for access to virgin queens in the nest1, 2. Although the fighter males (ergatoids) attack and kill other ergatoids, they tolerate and even attempt to mate with their winged rivals. Here we show that the winged males avoid the aggression of wingless males by mimicking the chemical bouquet of virgin queens, but that their mating success is not reduced as a result. This example of female mimicry by vigorous males is surprising, as in other species it is typically used as a protective strategy by weaker males, and may explain the coexistence and equal mating success of two male morphs.}, author = {Cremer, Sylvia and Sledge, Matthew and Heinze, Jürgen}, issn = {0028-0836}, journal = {Nature}, pages = {897 -- 897}, publisher = {Nature Publishing Group}, title = {{Chemical mimicry: Male ants disguised by the queen's bouquet}}, doi = {10.1038/419897a}, volume = {419}, year = {2002}, } @article{3995, abstract = {This article is a survey of research areas in which motion plays a pivotal role. The aim of the article is to review current approaches to modeling motion together with related data structures and algorithms, and to summarize the challenges that lie ahead in producing a more unified theory of motion representation that would be useful across several disciplines.}, author = {Agarwal, Pankaj and Guibas, Leonidas and Edelsbrunner, Herbert and Erickson, Jeff and Isard, Michael and Har Peled, Sariel and Hershberger, John and Jensen, Christian and Kavraki, Lydia and Koehl, Patrice and Lin, Ming and Manocha, Dinesh and Metaxas, Dimitris and Mirtich, Brian and Mount, David and Muthukrishnan, Sankara and Pai, Dinesh and Sacks, Elisha and Snoeyink, Jack and Suri, Subhash and Wolefson, Ouri}, issn = {0360-0300}, journal = {ACM Computing Surveys}, number = {4}, pages = {550 -- 572}, publisher = {ACM}, title = {{Algorithmic issues in modeling motion}}, doi = {10.1145/592642.592647}, volume = {34}, year = {2002}, } @article{3996, abstract = {We formalize a notion of topological simplification within the framework of a filtration, which is the history of a growing complex. We classify a topological change that happens during growth as either a feature or noise depending on its lifetime or persistence within the filtration. We give fast algorithms for computing persistence and experimental evidence for their speed and utility.}, author = {Edelsbrunner, Herbert and Letscher, David and Zomorodian, Afra}, issn = {0179-5376}, journal = {Discrete & Computational Geometry}, number = {4}, pages = {511 -- 533}, publisher = {Springer}, title = {{Topological persistence and simplification}}, doi = {10.1007/s00454-002-2885-2}, volume = {28}, year = {2002}, } @article{3998, abstract = {We present results on a two-step improvement of mesh quality in three-dimensional Delaunay triangulations. The first step refines the triangulation by inserting sinks and eliminates tetrahedra with large circumradius over shortest edge length ratio. The second step assigns weights to the vertices to eliminate slivers. Our experimental findings provide evidence for the practical effectiveness of sliver exudation.}, author = {Edelsbrunner, Herbert and Guoy, Damrong}, issn = {0177-0667}, journal = {Engineering with Computers}, number = {3}, pages = {229 -- 240}, publisher = {Springer}, title = {{An experimental study of sliver exudation}}, doi = {10.1007/s003660200020}, volume = {18}, year = {2002}, } @article{4000, abstract = {We present fast implementations of a hybrid algorithm for reporting box and cube intersections. Our algorithm initially takes a divide-and-conquer approach and switches to simpler algorithms for low numbers of boxes. We use our implementations as engines to solve problems about geometric primitives. We look at two such problems in the category of quality analysis of surface triangulations.}, author = {Zomorodian, Afra and Edelsbrunner, Herbert}, issn = {0218-1959}, journal = {International Journal of Computational Geometry and Applications}, number = {1-2}, pages = {143 -- 172}, publisher = {World Scientific Publishing}, title = {{Fast software for box intersections}}, doi = {10.1142/S0218195902000785}, volume = {12}, year = {2002}, } @inproceedings{4003, abstract = {The writhing number measures the global geometry of a closed space curve or knot. We show that this measure is related to the average winding number of its Gauss map. Using this relationship, we give an algorithm for computing the writhing number for a polygonal knot with n edges in time roughly proportional to n(1.6). We also implement a different, simple algorithm and provide experimental evidence for its practical efficiency.}, author = {Agarwal, Pankaj and Edelsbrunner, Herbert and Wang, Yusu}, booktitle = {Proceedings of the 13th annual ACM-SIAM symposium on Discrete algorithms}, isbn = {9780898715132}, location = {San Francisco, CA, USA}, pages = {791 -- 799}, publisher = {SIAM}, title = {{Computing the writhing number of a polygonal knot}}, year = {2002}, } @article{4139, abstract = {Pilot studies in England by Stopka and Macdonald revealed that allogrooming in the Old World wood mouse, Apodemus sylvaticus, is a commodity that males can trade for reproductive benefits with females. This study, which used a combination of field study and observations in experimental enclosures, revealed that specific experimental conditions such as group-size and sex-ratio manipulations have a significant effect on the pattern of allogrooming exchanged between individuals. Furthermore, females from the Czech population were more likely to associate with each other as revealed by the clustering of activity centers of females (i.e., as opposed to almost exclusive ranges in English populations), and also by the higher intensity of allogrooming exchanged between females (i.e., virtually lacking in the previous experiment with English mice). Therefore, geographic variation and specific social conditions seem to be important driving factors for allogrooming behavior. Together with changes in overall grooming patterns, allogrooming between males and females remained invariably asymmetrical over all four experimental groups (i.e., two conditions for each sex) in that males provided more allogrooming to females than they received from them.}, author = {Polechova, Jitka and Stopka, P.}, issn = {0008-4301}, journal = {Canadian Journal of Zoology}, number = {8}, pages = {1383 -- 1388}, publisher = {NRC Research Press}, title = {{Geometry of social relationships in the Old World wood mouse, Apodemus sylvaticus}}, doi = {10.1139/z02-128}, volume = {80}, year = {2002}, } @article{4148, abstract = {Members of the Wnt family have been implicated in a variety of developmental processes including axis formation, Patterning of the central nervous system and tissue morphogenesis. Recent studies have shown that a Wnt signalling pathway similar to that involved in the establishment of planar cell polarity in Drosophila regulates convergent extension movements during zebrafish and Xenopus gastrulation. This finding provides a good starting point to dissect the complex cell biology and genetic regulation of vertebrate gastrulation movements.}, author = {Tada, Masazumi and Concha, Miguel and Heisenberg, Carl-Philipp J}, issn = {1084-9521}, journal = {Seminars in Cell & Developmental Biology}, number = {3}, pages = {251 -- 260}, publisher = {Academic Press}, title = {{Non-canonical Wnt signalling and regulation of gastrulation movements}}, doi = {10.1016/S1084-9521(02)00052-6}, volume = {13}, year = {2002}, } @article{4194, abstract = {Cells at the anterior boundary of the neural plate (ANB) can induce telencephalic gene expression when transplanted to more posterior regions. Here, we identify a secreted Frizzled-related Wnt antagonist, Tic, that is expressed in ANB cells and can cell nonautonomously promote telencephalic gene expression in a concentration-dependent manner. Moreover, abrogation of Tlc function compromises telencephalic development. We also identify Wnt8b as a locally acting modulator of regional fate in the anterior neural plate and a likely target for antagonism by Tic. Finally, we show that tlc expression is regulated by signals that establish early antero-posterior and dorso-ventral ectodermal pattern. From these studies, we propose that local antagonism of Wnt activity within the anterior ectoderm is required to establish the telencephalon.}, author = {Houart, Corinne and Caneparo, Luca and Heisenberg, Carl-Philipp J and Barth, K Anukampa and Take Uchi, Masaya and Wilson, Stephen}, issn = {0896-6273}, journal = {Neuron}, number = {2}, pages = {255 -- 265}, publisher = {Elsevier}, title = {{Establishment of the telencephalon during gastrulation by local antagonism of Wnt signaling}}, doi = {10.1016/S0896-6273(02)00751-1}, volume = {35}, year = {2002}, } @article{4196, abstract = {During vertebrate gastrulation, large cellular rearrangements lead to the formation of the three germ layers, ectoderm, mesoderm and endoderm. Zebrafish offer many genetic and experimental advantages for studying vertebrate gastrulation movements. For instance, several mutants, including silberblick, knypek and trilobite, exhibit defects in morphogenesis during gastrulation. The identification of the genes mutated in these lines together with the analysis of the mutant phenotypes has provided new insights into the molecular and cellular mechanisms that underlie vertebrate gastrulation movements.}, author = {Heisenberg, Carl-Philipp J and Tada, Masazumi}, issn = {1084-9521}, journal = {Seminars in Cell & Developmental Biology}, number = {6}, pages = {471 -- 479}, publisher = {Academic Press}, title = {{Zebrafish gastrulation movements: bridging cell and developmental biology}}, doi = {10.1016/S1084952102001003}, volume = {13}, year = {2002}, } @article{4199, abstract = {Recent studies on vertebrate homologues of the van gogh/strabismus (vang/stbm) gene, a key player in planar cell polarity signalling in Drosophila, show that vang/stbm is involved in patterning and morphogenesis during vertebrate gastrulation where it modulates two distinct Wnt signals.}, author = {Heisenberg, Carl-Philipp J and Tada, Masazumi}, issn = {0960-9822}, journal = {Current Biology}, number = {4}, pages = {R126 -- R128}, publisher = {Cell Press}, title = {{Wnt signalling: A moving picture emerges from van gogh}}, doi = {10.1016/S0960-9822(02)00704-2}, volume = {12}, year = {2002}, }