@article{9049, abstract = {Diffusiophoretic motion of colloids and macromolecules under salt gradients exhibits a logarithmic-sensing, i.e. the particle velocity is proportional to the spatial gradient of the logarithm of the salt concentration, as VDP = DDP∇logc. Here we explore experimentally the implications of this log-sensing behavior, on the basis of a hydrogel microfluidic device allowing to build spatially and temporally controlled gradients. We first demonstrate that the non-linearity of the salt-taxis leads to a trapping of particles under concentration gradient oscillations via a rectification of the motion. As an alternative, we make use of the high sensitivity of diffusiophoretic migration to vanishing salt concentration due to the log-sensing: in a counter-intuitive way, a vanishing gradient can lead to measurable velocity provided that the solute concentration is low enough, thus keeping ∇c/c finite. We show that this leads to a strong segregation of particles in osmotic shock configuration, resulting from a step change of the salt concentration at the boundaries. These various phenomena are rationalized on the basis of a theoretical description for the time-dependent Smoluchowski equation for the colloidal density.}, author = {Palacci, Jérémie A and Cottin-Bizonne, Cécile and Ybert, Christophe and Bocquet, Lydéric}, issn = {1744-6848}, journal = {Soft Matter}, number = {4}, pages = {980--994}, publisher = {Royal Society of Chemistry}, title = {{Osmotic traps for colloids and macromolecules based on logarithmic sensing in salt taxis}}, doi = {10.1039/c1sm06395b}, volume = {8}, year = {2012}, } @article{922, abstract = {We study theoretically the morphologies of biological tubes affected by various pathologies. When epithelial cells grow, the negative tension produced by their division provokes a buckling instability. Several shapes are investigated: varicose, dilated, sinuous, or sausagelike. They are all found in pathologies of tracheal, renal tubes, or arteries. The final shape depends crucially on the mechanical parameters of the tissues: Young's modulus, wall-to-lumen ratio, homeostatic pressure. We argue that since tissues must be in quasistatic mechanical equilibrium, abnormal shapes convey information as to what causes the pathology. We calculate a phase diagram of tubular instabilities which could be a helpful guide for investigating the underlying genetic regulation.}, author = {Hannezo, Edouard B and Prost, Jacques and Joanny, Jean}, journal = {Physical Review Letters}, number = {1}, publisher = {American Physical Society}, title = {{Mechanical instabilities of biological tubes}}, doi = {10.1103/PhysRevLett.109.018101}, volume = {109}, year = {2012}, } @article{9499, abstract = {EMBRYONIC FLOWER1 (EMF1) is a plant-specific gene crucial to Arabidopsis vegetative development. Loss of function mutants in the EMF1 gene mimic the phenotype caused by mutations in Polycomb Group protein (PcG) genes, which encode epigenetic repressors that regulate many aspects of eukaryotic development. In Arabidopsis, Polycomb Repressor Complex 2 (PRC2), made of PcG proteins, catalyzes trimethylation of lysine 27 on histone H3 (H3K27me3) and PRC1-like proteins catalyze H2AK119 ubiquitination. Despite functional similarity to PcG proteins, EMF1 lacks sequence homology with known PcG proteins; thus, its role in the PcG mechanism is unclear. To study the EMF1 functions and its mechanism of action, we performed genome-wide mapping of EMF1 binding and H3K27me3 modification sites in Arabidopsis seedlings. The EMF1 binding pattern is similar to that of H3K27me3 modification on the chromosomal and genic level. ChIPOTLe peak finding and clustering analyses both show that the highly trimethylated genes also have high enrichment levels of EMF1 binding, termed EMF1_K27 genes. EMF1 interacts with regulatory genes, which are silenced to allow vegetative growth, and with genes specifying cell fates during growth and differentiation. H3K27me3 marks not only these genes but also some genes that are involved in endosperm development and maternal effects. Transcriptome analysis, coupled with the H3K27me3 pattern, of EMF1_K27 genes in emf1 and PRC2 mutants showed that EMF1 represses gene activities via diverse mechanisms and plays a novel role in the PcG mechanism.}, author = {Kim, Sang Yeol and Lee, Jungeun and Eshed-Williams, Leor and Zilberman, Daniel and Sung, Z. Renee}, issn = {1553-7404}, journal = {PLoS Genetics}, number = {3}, publisher = {Public Library of Science}, title = {{EMF1 and PRC2 cooperate to repress key regulators of Arabidopsis development}}, doi = {10.1371/journal.pgen.1002512}, volume = {8}, year = {2012}, } @article{9497, abstract = {The regulation of eukaryotic chromatin relies on interactions between many epigenetic factors, including histone modifications, DNA methylation, and the incorporation of histone variants. H2A.Z, one of the most conserved but enigmatic histone variants that is enriched at the transcriptional start sites of genes, has been implicated in a variety of chromosomal processes. Recently, we reported a genome-wide anticorrelation between H2A.Z and DNA methylation, an epigenetic hallmark of heterochromatin that has also been found in the bodies of active genes in plants and animals. Here, we investigate the basis of this anticorrelation using a novel h2a.z loss-of-function line in Arabidopsis thaliana. Through genome-wide bisulfite sequencing, we demonstrate that loss of H2A.Z in Arabidopsis has only a minor effect on the level or profile of DNA methylation in genes, and we propose that the global anticorrelation between DNA methylation and H2A.Z is primarily caused by the exclusion of H2A.Z from methylated DNA. RNA sequencing and genomic mapping of H2A.Z show that H2A.Z enrichment across gene bodies, rather than at the TSS, is correlated with lower transcription levels and higher measures of gene responsiveness. Loss of H2A.Z causes misregulation of many genes that are disproportionately associated with response to environmental and developmental stimuli. We propose that H2A.Z deposition in gene bodies promotes variability in levels and patterns of gene expression, and that a major function of genic DNA methylation is to exclude H2A.Z from constitutively expressed genes.}, author = {Coleman-Derr, Devin and Zilberman, Daniel}, issn = {1553-7404}, journal = {PLoS Genetics}, number = {10}, publisher = {Public Library of Science}, title = {{Deposition of histone variant H2A.Z within gene bodies regulates responsive genes}}, doi = {10.1371/journal.pgen.1002988}, volume = {8}, year = {2012}, } @article{9528, abstract = {Accumulating evidence points toward diverse functions for plant chromatin. Remarkable progress has been made over the last few years in elucidating the mechanisms for a number of these functions. Activity of the histone demethylase IBM1 accurately targets DNA methylation to silent repeats and transposable elements, not to genes. A genetic screen uncovered the surprising role of H2A.Z-containing nucleosomes in sensing precise differences in ambient temperature and consequent gene regulation. Precise maintenance of chromosome number is assured by a histone modification that suppresses inappropriate DNA replication and by centromeric histone H3 regulation of chromosome segregation. Histones and noncoding RNAs regulate FLOWERING LOCUS C, the expression of which quantitatively measures the duration of cold exposure, functioning as memory of winter. These findings are a testament to the power of using plants to research chromatin organization, and demonstrate examples of how chromatin functions to achieve biological accuracy, precision, and memory.}, author = {Huff, Jason T. and Zilberman, Daniel}, issn = {0959-437X}, journal = {Current Opinion in Genetics and Development}, number = {2}, pages = {132--138}, publisher = {Elsevier}, title = {{Regulation of biological accuracy, precision, and memory by plant chromatin organization}}, doi = {10.1016/j.gde.2012.01.007}, volume = {22}, year = {2012}, } @article{966, abstract = {Motivated by recent experiments on Ba3NiSb2O 9, we investigate possible quantum spin liquid ground states for spin S=1 Heisenberg models on the triangular lattice. We use variational Monte Carlo techniques to calculate the energies of microscopic spin liquid wave functions where spin is represented by three flavors of fermionic spinon operators. These energies are compared with the energies of various competing three-sublattice ordered states. Our approach shows that the antiferromagnetic Heisenberg model with biquadratic term and single-ion anisotropy does not have a low-temperature spin liquid phase. However, for an SU(3)-invariant model with sufficiently strong ring-exchange terms, we find a paired chiral quantum spin liquid with a Fermi surface of deconfined spinons that is stable against all types of ordering patterns we considered. We discuss the physics of this exotic spin liquid state in relation to the recent experiment and suggest new ways to test this scenario.}, author = {Bieri, Samuel and Maksym Serbyn and Senthil, Todadri S and Lee, Patrick}, journal = {Physical Review B - Condensed Matter and Materials Physics}, number = {22}, publisher = {American Physical Society}, title = {{Paired chiral spin liquid with a Fermi surface in S=1 model on the triangular lattice}}, doi = {10.1103/PhysRevB.86.224409}, volume = {86}, year = {2012}, } @article{2968, abstract = {Little is known about the stability of trophic relationships in complex natural communities over evolutionary timescales. Here, we use sequence data from 18 nuclear loci to reconstruct and compare the intraspecific histories of major Pleistocene refugial populations in the Middle East, the Balkans and Iberia in a guild of four Chalcid parasitoids (Cecidostiba fungosa, Cecidostiba semifascia, Hobbya stenonota and Mesopolobus amaenus) all attacking Cynipid oak galls. We develop a likelihood method to numerically estimate models of divergence between three populations from multilocus data. We investigate the power of this framework on simulated data, and-using triplet alignments of intronic loci-quantify the support for all possible divergence relationships between refugial populations in the four parasitoids. Although an East to West order of population divergence has highest support in all but one species, we cannot rule out alternative population tree topologies. Comparing the estimated times of population splits between species, we find that one species, M. amaenus, has a significantly older history than the rest of the guild and must have arrived in central Europe at least one glacial cycle prior to other guild members. This suggests that although all four species may share a common origin in the East, they expanded westwards into Europe at different times. © 2012 Blackwell Publishing Ltd.}, author = {Lohse, Konrad and Barton, Nicholas H and Melika, George and Stone, Graham}, journal = {Molecular Ecology}, number = {18}, pages = {4605 -- 4617}, publisher = {Wiley-Blackwell}, title = {{A likelihood based comparison of population histories in a parasitoid guild}}, doi = {10.1111/j.1365-294X.2012.05700.x}, volume = {21}, year = {2012}, } @misc{13075, abstract = {Little is known about the stability of trophic relationships in complex natural communities over evolutionary timescales. Here, we use sequence data from 18 nuclear loci to reconstruct and compare the intraspecific histories of major Pleistocene refugial populations in the Middle East, the Balkans and Iberia in a guild of four Chalcid parasitoids (Cecidostiba fungosa, C. semifascia, Hobbya stenonota and Mesopolobus amaenus) all attacking Cynipid oak galls. We develop a likelihood method to numerically estimate models of divergence between three populations from multilocus data. We investigate the power of this framework on simulated data, and - using triplet alignments of intronic loci - quantify the support for all possible divergence relationships between refugial populations in the four parasitoids. Although an East to West order of population divergence has highest support in all but one species, we cannot rule out alternative population tree topologies. Comparing the estimated times of population splits between species, we find that one species, M. amaenus, has a significantly older history than the rest of the guild and must have arrived in central Europe at least one glacial cycle prior to other guild members. This suggests that although all four species may share a common origin in the East, they expanded westwards into Europe at different times.}, author = {Lohse, Konrad and Barton, Nicholas H and Stone, Graham and Melika, George}, publisher = {Dryad}, title = {{Data from: A likelihood-based comparison of population histories in a parasitoid guild}}, doi = {10.5061/DRYAD.0G0FS}, year = {2012}, } @article{13407, abstract = {We show that diamagnetic particles can be remotely manipulated by a magnet by the reversible adsorption of dual-responsive, light-switchable/superparamagnetic nanoparticles down to their surface. Adsorption occurs upon exposure to UV light, and can be reversed thermally or by ambient light. The dynamic self-assembly of thin films of the dual-responsive nanoparticles induces attractive interactions between diamagnetic particles. We demonstrate that catalytic amounts of the dual-responsive nanoparticles are sufficient to magnetically guide and deliver the diamagnetic particles to desired locations, where they can then be released by disassembling the dynamic layers of superparamagnetic nanoparticles with visible light.}, author = {Chovnik, Olga and Balgley, Renata and Goldman, Joel R. and Klajn, Rafal}, issn = {1520-5126}, journal = {Journal of the American Chemical Society}, keywords = {Colloid and Surface Chemistry, Biochemistry, General Chemistry, Catalysis}, number = {48}, pages = {19564--19567}, publisher = {American Chemical Society}, title = {{Dynamically self-assembling carriers enable guiding of diamagnetic particles by weak magnets}}, doi = {10.1021/ja309633v}, volume = {134}, year = {2012}, } @article{13408, abstract = {Well-defined metallic nanobowls can be prepared by extending the concept of a protecting group to colloidal synthesis. Magnetic nanoparticles are employed as “protecting groups” during the galvanic replacement of silver with gold. The replacement reaction is accompanied by spontantous dissociation of the protecting groups, leaving behind metallic nanobowls.}, author = {Ridelman, Yonatan and Singh, Gurvinder and Popovitz-Biro, Ronit and Wolf, Sharon G. and Das, Sanjib and Klajn, Rafal}, issn = {1613-6829}, journal = {Small}, keywords = {Biomaterials, Biotechnology, General Materials Science, General Chemistry}, number = {5}, pages = {654--660}, publisher = {Wiley}, title = {{Metallic nanobowls by galvanic replacement reaction on heterodimeric nanoparticles}}, doi = {10.1002/smll.201101882}, volume = {8}, year = {2012}, }