Direct observation and rational design of nucleation behavior in addressable self-assembly

To optimize a self-assembly reaction, it is essential to understand the factors that govern its pathway. Here, we examine the influence of nucleation pathways in a model system for addressable, multicomponent self-assembly based on a prototypical “DNA-brick” structure. By combining temperature-dependent dynamic light scattering and atomic force microscopy with coarse-grained simulations, we show how subtle changes in the nucleation pathway profoundly affect the yield of the correctly formed structures. In particular, we can increase the range of conditions over which self-assembly occurs by using stable multisubunit clusters that lower the nucleation barrier for assembling subunits in the interior of the structure. Consequently, modifying only a small portion of a structure is sufficient to optimize its assembly. Due to the generality of our coarse-grained model and the excellent agreement that we find with our experimental results, the design principles reported here are likely to apply generically to addressable, multicomponent self-assembly.This work was supported by the Engineering and Physical Sciences Research Council (Program Grant EP/I001352/1), the European Regional Development Fund (100185665), Fraunhofer Attract Funding (601683), and the National Institutes of Health (Grant F32GM116231)

Colliding clouds of strongly interacting spin-polarized fermions

Motivated by a recent experiment at MIT, we consider the collision of two clouds of spin-polarized atomic Fermi gases close to a Feshbach resonance. We explain why two dilute gas clouds, with underlying attractive interactions between their constituents, bounce off each other in the strongly interacting regime. Our hydrodynamic analysis, in excellent agreement with experiment, gives strong evidence for a metastable many-body state with effective repulsive interactions.Comment: 6 pages, 5 figure

Wolbachia Utilizes Host Microtubules and Dynein for Anterior Localization in the Drosophila Oocyte

To investigate the role of the host cytoskeleton in the maternal transmission of the endoparasitic bacteria Wolbachia, we have characterized their distribution in the female germ line of Drosophila melanogaster. In the germarium, Wolbachia are distributed to all germ cells of the cyst, establishing an early infection in the cell destined to become the oocyte. During mid-oogenesis, Wolbachia exhibit a distinct concentration between the anterior cortex and the nucleus in the oocyte, where many bacteria appear to contact the nuclear envelope. Following programmed rearrangement of the microtubule network, Wolbachia dissociate from this anterior position and become dispersed throughout the oocyte. This localization pattern is distinct from mitochondria and all known axis determinants. Manipulation of microtubules and cytoplasmic Dynein and Dynactin, but not Kinesin-1, disrupts anterior bacterial localization in the oocyte. In live egg chambers, Wolbachia exhibit movement in nurse cells but not in the oocyte, suggesting that the bacteria are anchored by host factors. In addition, we identify mid-oogenesis as a period in the life cycle of Wolbachia in which bacterial replication occurs. Total bacterial counts show that Wolbachia increase at a significantly higher rate in the oocyte than in the average nurse cell, and that normal Wolbachia levels in the oocyte depend on microtubules. These findings demonstrate that Wolbachia utilize the host microtubule network and associated proteins for their subcellular localization in the Drosophila oocyte. These interactions may also play a role in bacterial motility and replication, ultimately leading to the bacteria's efficient maternal transmission

Can Life develop in the expanded habitable zones around Red Giant Stars?

We present some new ideas about the possibility of life developing around sub-giant and red giant stars. Our study concerns the temporal evolution of the habitable zone. The distance between the star and the habitable zone, as well as its width, increases with time as a consequence of stellar evolution. The habitable zone moves outward after the star leaves the main sequence, sweeping a wider range of distances from the star until the star reaches the tip of the asymptotic giant branch. If life could form and evolve over time intervals from $5 \times 10^8$ to $10^9$ years, then there could be habitable planets with life around red giant stars. For a 1 M$_{\odot}$ star at the first stages of its post main-sequence evolution, the temporal transit of the habitable zone is estimated to be of several 10$^9$ years at 2 AU and around 10$^8$ years at 9 AU. Under these circumstances life could develop at distances in the range 2-9 AU in the environment of sub-giant or giant stars and in the far distant future in the environment of our own Solar System. After a star completes its first ascent along the Red Giant Branch and the He flash takes place, there is an additional stable period of quiescent He core burning during which there is another opportunity for life to develop. For a 1 M$_{\odot}$ star there is an additional $10^9$ years with a stable habitable zone in the region from 7 to 22 AU. Space astronomy missions, such as proposed for the Terrestrial Planet Finder (TPF) and Darwin should also consider the environments of sub-giants and red giant stars as potentially interesting sites for understanding the development of life

Advantageous GOES IR results for ash mapping at high latitudes: Cleveland eruptions 2001

The February 2001 eruption of Cleveland Volcano, Alaska allowed for comparisons of volcanic ash detection using two-band thermal infrared (10–12 μm) remote sensing from MODIS, AVHRR, and GOES 10. Results show that high latitude GOES volcanic cloud sensing the range of about 50 to 65°N is significantly enhanced. For the Cleveland volcanic clouds the MODIS and AVHRR data have zenith angles 6–65 degrees and the GOES has zenith angles that are around 70 degrees. The enhancements are explained by distortion in the satellite view of the cloud\u27s lateral extent because the satellite zenith angles result in a “side-looking” aspect and longer path lengths through the volcanic cloud. The shape of the cloud with respect to the GOES look angle also influences the results. The MODIS and AVHRR data give consistent retrievals of the ash cloud evolution over time and are good corrections for the GOES data

Osteocyte-Specific Deletion of the α2δ1 Auxiliary Voltage Sensitive Calcium Channel Subunit

Context: Skeletal unloading due to disuse, disease, or aging increases bone loss and the risk of skeletal fracture. Conversely, mechanical loading is anabolic to the skeleton, promoting skeletal integrity through increased bone formation. As calcium influx is the first measurable response of bone cells to mechanical stimuli, voltage sensitive calcium channels (VSCCs) play a critical role in bone formation. Given VSCC activity is influenced by its auxiliary α2δ1 subunit, regulating the gating kinetics of the channel’s pore-forming (α1) subunit and forward trafficking of VSCCs to cell membranes, the α2δ1 subunit may govern anabolic bone responses. Objective & Design: We hypothesized that osteocyte-specific α2δ1 deletion in a mouse model would impair skeletal development, decrease bone formation and mechanosensitivity. Methods: Generation of an osteocyte-specific α2δ1 knockout was accomplished by crossing mice (C57BL/6) harboring LoxP sequences flanking Cacna2d1, the gene encoding α2δ1, with mice expressing Cre recombinase under the control of the Dmp1 (10Kb) promoter (Cacna2d1fl/fl, Dmp1-Cre+). To assess skeletal phenotype and mechanosensitivity, longitudinal whole body and site-specific DXA, in vivo μCT (10wk old), and two weeks of tibial loading (16wks) will be conducted before femurs are collected at 20 wks for mechanical testing, ex vivo μCT, and quantitative histomorphometry. Results & Conclusion: Preliminary analyses show no differences in whole body or site-specific BMD and BMC values between mice over time, suggesting osteocyte-specific α2δ1 deletion may not influence skeletal development. However, key differences in mechanosensitivity following tibial loading are expected given the potential role of α2δ1 in mechanically-induced bone formation

Simultaneous cognate epitope recognition by bovine CD4 and CD8 T cells is essential for primary expansion of antigen-specific cytotoxic T-cells following ex vivo stimulation with a candidate Mycobacterium avium subsp. paratuberculosis peptide vaccine

Studies in cattle show CD8 cytotoxic T cells (CTL), with the ability to kill intracellular bacteria, develop following stimulation of monocyte-depleted peripheral blood mononuclear cells (mdPBMC) with antigen-presenting cells (APC, i.e. conventional dendritic cells [cDC] and monocyte-derived DC [MoDC]) pulsed with MMP, a membrane protein from Mycobacterium avium subsp. paratuberculosis (Map) encoded byMAP2121c. CTL activity was diminished if CD4 T cells were depleted from mdPBMC before antigen (Ag) presentation by APC, suggesting simultaneous cognate recognition of MMP epitopes presented by MHC I and MHC II molecules to CD4 and CD8 T cells is essential for development of CTL activity. To explore this possibility, studies were conducted with mdPBMC cultures in the presence of monoclonal antibodies (mAbs) specific for MHC class I and MHC class II molecules. The CTL response of mdPBMC to MMP-pulsed APC was completely blocked in the presence of mAbs to both MHC I and II molecules and also blocked in the presence of mAbs to either MHC I or MHC II alone. The results demonstrate simultaneous cognate recognition of Ag by CD4 and CD8 T cells is essential for delivery of CD4 T cell help to CD8 T cells to elicit development of CTL