The macroscopic effects of microscopic heterogeneity

Over the past decade, advances in super-resolution microscopy and particle-based modeling have driven an intense interest in investigating spatial heterogeneity at the level of single molecules in cells. Remarkably, it is becoming clear that spatiotemporal correlations between just a few molecules can have profound effects on the signaling behavior of the entire cell. While such correlations are often explicitly imposed by molecular structures such as rafts, clusters, or scaffolds, they also arise intrinsically, due strictly to the small numbers of molecules involved, the finite speed of diffusion, and the effects of macromolecular crowding. In this chapter we review examples of both explicitly imposed and intrinsic correlations, focusing on the mechanisms by which microscopic heterogeneity is amplified to macroscopic effect.Comment: 20 pages, 5 figures. To appear in Advances in Chemical Physic

Cohesin acetyltransferase Esco2 is a cell viability factor and is required for cohesion in pericentric heterochromatin

Genetic deletion of murine Esco2 (an acetylase known to establish cohesin during S-phase and genetically linked to Roberts syndrome) results in embryonic lethality that can be molecularly linked to novel and specific functions of Esco2 at pericentric heterochromatin

Self-Organization of the Escherichia coli Chemotaxis Network Imaged with Super-Resolution Light Microscopy

Photoactivated localization microscopy analysis of chemotaxis receptors in bacteria suggests that the non-random organization of these proteins results from random self-assembly of clusters without direct cytoskeletal involvement or active transport

A Review of Mixed Strain Clostridium difficile Colonization and Infection

Given that Clostridium difficile is not part of the normal human microbiota, if multiple strains are to accumulate in the colon implies successive exposure events and/or persistent colonization must occur. Evidence of C. difficile infection (CDI) with more than one strain was first described in 1983. Despite the availability of increasingly discriminatory bacterial fingerprinting methods, the described rate of dual strain recovery in patients with CDI has remained stable at ∼5–10%. More data are needed to determine when dual strain infection may be harmful. Notably, one strain may block the establishment of and infection by another. In humans, patients colonized by non-toxigenic C. difficile strain are at a lower risk of developing CDI. Further studies to elucidate the interaction between co-infecting or colonizing and infecting C. difficile strains may help identify potential exploitable mechanisms to prevent CDI

Nutritionally Enhanced Staple Food Crops

Crop biofortification is a sustainable and cost-effective strategy to address malnutrition in developing countries. This review synthesizes the progress toward developing seed micronutrient-dense cereals and legumes cultivars by exploiting natural genetic variation using conventional breeding and/or transgenic technology, and discusses the associated issues to strengthen crop biofortification research and development. Some major QTL for seed iron and zinc, seed phosphorus, and seed phytate in common bean, rice,J;md wheat have been mapped. An iron reductase QTL associated with seed-iron ~QTL is found in common bean where the genes coding for candidate enzymes involved in phytic acid synthesis have also been mapped. Candidate genes for Ipa co segregate with mutant phenotypes identified in rice and soybean. The Gpe-B1 locus in wild emmer wheat accelerates senescence and increases nutrient remobilization from leaves to developing seeds, and another gene named TtNAM-B1 affecting these traits has been cloned. Seed iron-dense common bean and rice in Latin America; seed iron-dense common bean in eastern and southern Africa;....

Gibbs measures and dismantlable graphs

We model physical systems with "hard constraints" by the space Hom(G; H) of homomorphisms from a locally finite graph G to a fixed finite constraint graph H. Two homomorphisms are deemed to be adjacent if they differ on a single site of G. We investigat

Oral Disinfectants Inhibit Protein-Protein Interactions Mediated by the Anti-Apoptotic Protein Bcl-x(L) and Induce Apoptosis in Human Oral Tumor Cells

Chlorhexidine and alexidine have long been used as oral disinfectants by humans. Both compounds inhibit protein-protein interactions mediated by the anti-apoptotic protein Bcl-xL at physiologically relevant concentrations and induce apoptosis in a series of tumor cell lines derived from the tongue and pharynx (see picture). Inhibition of protein-protein interactions is a potential mode of action of drugs in current human use. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Optimized back-focal-plane interferometry directly measures forces of optically trapped particles

Back-focal-plane interferometry is used to measure displacements of optically trapped samples with very high spatial and temporal resolution. However, the technique is closely related to a method that measures the rate of change in light momentum. It has long been known that displacements of the interference pattern at the back focal plane may be used to track the optical force directly, provided that a considerable fraction of the light is effectively monitored. Nonetheless, the practical application of this idea has been limited to counter-propagating, low-aperture beams where the accurate momentum measurements are possible. Here, we experimentally show that the connection can be extended to single-beam optical traps. In particular, we show that, in a gradient trap, the calibration product κ·β (where κ is the trap stiffness and 1/β is the position sensitivity) corresponds to the factor that converts detector signals into momentum changes; this factor is uniquely determined by three construction features of the detection instrument and does not depend, therefore, on the specific conditions of the experiment. Then, we find that force measurements obtained from back-focal-plane displacements are in practice not restricted to a linear relationship with position and hence they can be extended outside that regime. Finally, and more importantly, we show that these properties are still recognizable even when the system is not fully optimized for light collection. These results should enable a more general use of back-focal-plane interferometry whenever the ultimate goal is the measurement of the forces exerted by an optical trap