Explore the vast range of titles available.

Eukaryotic cells are large enough to detect signals and then orient to them by differentiating the signal strength across the length and breadth of the cell. Amoebae, fibroblasts, neutrophils and growth cones all behave in this way. Little is known however about cell motion and searching behavior in the absence of a signal. Is individual cell motion best characterized as a random walk? Do individual cells have a search strategy when they are beyond the range of the signal they would otherwise move toward? Here we ask if single, isolated, Dictyostelium and Polysphondylium amoebae bias their motion in the absence of external cues. We placed single well-isolated Dictyostelium and Polysphondylium cells on a nutrient-free agar surface and followed them at 10 sec intervals for approximately 10 hr, then analyzed their motion with respect to velocity, turning angle, persistence length, and persistence time, comparing the results to the expectation for a variety of different types of random motion. We find that amoeboid behavior is well described by a special kind of random motion: Amoebae show a long persistence time ( approximately 10 min) beyond which they start to lose their direction; they move forward in a zig-zag manner; and they make turns every 1-2 min on average. They bias their motion by remembering the last turn and turning away from it. Interpreting the motion as consisting of runs and turns, the duration of a run and the amplitude of a turn are both found to be exponentially distributed. We show that this behavior greatly improves their chances of finding a target relative to performing a random walk. We believe that other eukaryotic cells may employ a strategy similar to Dictyostelium when seeking conditions or signal sources not yet within range of their detection system.

On October 23 the FDA issued an Emergency Use Authorization for peramivir for the treatment of suspected or confirmed cases of 2009 H1N1 influenza. Drs. Debra Birnkrant and Edward Cox discuss the limited data on safety and efficacy and the criteria for emergency use of peramivir. On October 23, 2009, Food and Drug Administration (FDA) Commissioner Margaret Hamburg issued an Emergency Use Authorization (EUA) for peramivir for intravenous injection (BioCryst Pharmaceuticals). Peramivir is an unapproved investigational neuraminidase inhibitor that may be effective in treating certain hospitalized adult and pediatric patients with suspected or confirmed cases of 2009 H1N1 influenza. The EUA allows health care providers to use peramivir, subject to specified conditions. This is the first EUA that has been issued for an unapproved drug. The legal standard for the authorization of an EUA during a declared public health emergency requires a finding that it is . . .

The diffusion coefficient of the transcription factor LacI within living Escherichia coli has been measured directly by in vivo tracking to be D =0.4  μ m 2 /s. At this rate, simple models of diffusion lead to the expectation that LacI and other proteins will rapidly homogenize throughout the cell. Here, we test this expectation of spatial homogeneity by single‐molecule visualization of LacI molecules non‐specifically bound to DNA in fixed cells. Contrary to expectation, we find that the distribution depends on the spatial location of its encoding gene. We demonstrate that the spatial distribution of LacI is also determined by the local state of DNA compaction, and that E. coli can dynamically redistribute proteins by modifying the state of its nucleoid. Finally, we show that LacI inhomogeneity increases the strength with which targets located proximally to the LacI gene are regulated. We propose a model for intranucleoid diffusion that can reconcile these results with previous measurements of LacI diffusion, and we discuss the implications of these findings for gene regulation in bacteria and eukaryotes. The steady‐state spatial distribution of the lac repressor transcription factor is found to depend on the location of the encoding gene and the compaction of the surrounding DNA. This has important implications for global gene regulation and genome organization. Synopsis The steady‐state spatial distribution of the lac repressor transcription factor is found to depend on the location of the encoding gene and the compaction of the surrounding DNA. This has important implications for global gene regulation and genome organization. The steady‐state spatial distribution of the canonical lac repressor transcription factor, LacI, is not homogeneous in E. coli . The spatial distribution of LacI depends upon the location of the encoding gene and the compaction state of DNA, which changes in response to growth conditions. When DNA becomes highly condensed, proteins are excluded from the nucleoid volume. These observations suggest mechanisms driving the spatial organization of the E. coli genome and regulation of global transcription patterns.

Cells use protein-DNA and protein-protein interactions to regulate transcription. A biophysical understanding of this process has, however, been limited by the lack of methods for quantitatively characterizing the interactions that occur at specific promoters and enhancers in living cells. Here we show how such biophysical information can be revealed by a simple experiment in which a library of partially mutated regulatory sequences are partitioned according to their in vivo transcriptional activities and then sequenced en masse. Computational analysis of the sequence data produced by this experiment can provide precise quantitative information about how the regulatory proteins at a specific arrangement of binding sites work together to regulate transcription. This ability to reliably extract precise information about regulatory biophysics in the face of experimental noise is made possible by a recently identified relationship between likelihood and mutual information. Applying our experimental and computational techniques to the Escherichia coli lac promoter, we demonstrate the ability to identify regulatory protein binding sites de novo, determine the sequence-dependent binding energy of the proteins that bind these sites, and, importantly, measure the in vivo interaction energy between RNA polymerase and a DNA-bound transcription factor. Our approach provides a generally applicable method for characterizing the biophysical basis of transcriptional regulation by a specified regulatory sequence. The principles of our method can also be applied to a wide range of other problems in molecular biology.

We report on a microfluidic particle-separation device that makes use of the asymmetric bifurcation of laminar flow around obstacles. A particle chooses its path deterministically on the basis of its size. All particles of a given size follow equivalent migration paths, leading to high resolution. The microspheres of 0.8, 0.9, and 1.0 micrometers that were used to characterize the device were sorted in 40 seconds with a resolution of ~10 nanometers, which was better than the time and resolution of conventional flow techniques. Bacterial artificial chromosomes could be separated in 10 minutes with a resolution of ~12%.

We describe a method for tracking RNA molecules in Escherichia coli that is sensitive to single copies of mRNA, and, using the method, we find that individual molecules can be followed for many hours in living cells. We observe distinct characteristic dynamics of RNA molecules, all consistent with the known life history of RNA in prokaryotes: localized motion consistent with the Brownian motion of an RNA polymer tethered to its template DNA, free diffusion, and a few examples of polymer chain dynamics that appear to be a combination of chain fluctuation and chain elongation attributable to RNA transcription. We also quantify some of the dynamics, such as width of the displacement distribution, diffusion coefficient, chain elongation rate, and distribution of molecule numbers, and compare them with known biophysical parameters of the E. coli system.

Motile eukaryotic cells migrate with directional persistence by alternating left and right turns, even in the absence of external cues. For example, Dictyostelium discoideum cells crawl by extending distinct pseudopods in an alternating right-left pattern. The mechanisms underlying this zig-zag behavior, however, remain unknown. Here we propose a new Excitable Cortex and Memory (EC&M) model for understanding the alternating, zig-zag extension of pseudopods. Incorporating elements of previous models, we consider the cell cortex as an excitable system and include global inhibition of new pseudopods while a pseudopod is active. With the novel hypothesis that pseudopod activity makes the local cortex temporarily more excitable--thus creating a memory of previous pseudopod locations--the model reproduces experimentally observed zig-zag behavior. Furthermore, the EC&M model makes four new predictions concerning pseudopod dynamics. To test these predictions we develop an algorithm that detects pseudopods via hierarchical clustering of individual membrane extensions. Data from cell-tracking experiments agrees with all four predictions of the model, revealing that pseudopod placement is a non-Markovian process affected by the dynamics of previous pseudopods. The model is also compatible with known limits of chemotactic sensitivity. In addition to providing a predictive approach to studying eukaryotic cell motion, the EC&M model provides a general framework for future models, and suggests directions for new research regarding the molecular mechanisms underlying directional persistence.

A new paradigm for accelerating evaluation of investigational therapies during public health emergencies caused by emerging infectious diseases could permit therapies shown to be safe and effective to reach patients as soon as possible. Life-threatening emerging or reemerging infectious diseases increasingly inspire demands for access to novel, often untested therapies. Recent concern about transmission of the Middle East respiratory syndrome coronavirus (MERS-CoV) in Asia underscores the need to rapidly evaluate investigational therapies during outbreaks, identify those that actually benefit patients, and protect against those that cause harm. Although a traditional sequence of studies in animals followed by phased clinical trials works well for many therapeutics, that process may be too slow during public health emergencies. We propose establishing a new paradigm for accelerating evaluation of investigational therapies during public health emergencies so that therapies . . .

Background Behavioural and mental disorders have become a public health crisis; averting mental ill-health in early years can achieve significant longer-term health benefits and cost savings. This study assesses whether the Enhancing Social-Emotional Health and Wellbeing in the Early Years (E-SEE-Steps)—a proportionate universal delivery model comprising the Incredible Babies book (IY-B) and the Incredible Years Infant (IY-I) and Toddler (IY-T) parenting programmes is cost-effective compared to services as usual (SAU) for the primary caregiver, child and dyad. Methods Using UK data for 339 primary caregivers from the E-SEE trial, we conducted a within-trial economic evaluation assessing the cost-effectiveness of E-SEE Steps. Health outcomes were expressed in quality-adjusted life-years (QALY) and costs in UK pounds sterling (2018–19). Missing data were populated via multiple imputation and costs and QALYs discounted at 3.5% per annum. Cost-effectiveness results were conducted for primary caregivers, children and dyad using econometric modelling to control for patient co-variables. Uncertainty was explored through scenario and sensitivity analyses. Results The average cost of E-SEE Steps intervention was £458.50 per dyad. E-SEE Steps was associated with modest gains in primary caregiver HRQoL but minor decrements in child HRQoL compared to SAU. For primary caregivers, E-SEE Steps was more effective (0.034 QALYs) and more costly (£446) compared to SAU, with a corresponding incremental cost-effectiveness ratio (ICER) of £13,011 per QALY. In children, E-SEE Steps was strictly dominated with poorer outcomes (-0.005 QALYs) and greater costs (£178) relative to SAU. QALY gains in primary caregivers exceeded those QALY losses found in children, meaning E-SEE Steps was more effective (0.031 QALYs) and costly (£621) for the dyad (ICER: £20,062 per QALY). All scenario analyses found E-SEE Steps cost-effective for the dyad at a £30,000 per QALY threshold. Sensitivity analyses found significant cost reductions from expansions in programme delivery and attendance. Conclusions E-SEE Steps achieved modest health gains in primary caregivers but small negative effects on children and was more costly than SAU. E-SEE Steps appears cost-effective for the dyad, but the results should be interpreted with caution given the potential detrimental impact on children. Trial registration ISRCTN11079129 ; Pre participant trial enrolment, 11/05/2015

We show that genomic-length DNA molecules imaged in nanochannels have an extension along the channel that scales linearly with the contour length of the polymer, in agreement with the scaling arguments developed by de Gennes for self-avoiding confined polymers. This fundamental relationship allows us to measure directly the contour length of single DNA molecules confined in the channels, and the statistical analysis of the dynamics of the polymer in the nanochannel allows us to compute the SD of the mean of the extension. This statistical analysis allows us to measure the extension of λ DNA multimers with a 130-nm SD in 1 min.