529 research outputs found
Morphogen-defined patterning of Escherichia coli enabled by an externally tunable band-pass filter
<p>Abstract</p> <p>Background</p> <p>Gradients of morphogens pattern cell fate â a phenomenon that is especially important during development. A simple model system for studying how morphogens pattern cell behavior would overcome difficulties inherent in the study of natural morphogens <it>in vivo</it>. A synthetic biology approach to building such a system is attractive.</p> <p>Results</p> <p>Using an externally-tunable band-pass filter paradigm, we engineered <it>Escherichia coli </it>cells to function as a model system for the study of how multiple morphogens can pattern cell behavior. We demonstrate how our system exhibits behavior such as morphogen crosstalk and how the cells' growth and fluorescence can be patterned in a number of complex patterns. We extend our cell patterning from 2D cultures on the surface of plates to 3D cultures in soft agarose medium.</p> <p>Conclusion</p> <p>Our system offers a convenient, well-defined model system for fundamental studies on how multiple morphogen gradients can affect cell fate and lead to pattern formation. Our design principles could be applied to eukaryotic cells to develop other models systems for studying development or for enabling the patterning of cells for applications such as tissue engineering and biomaterials.</p
Cumulative Step-size Adaptation on Linear Functions: Technical Report
The CSA-ES is an Evolution Strategy with Cumulative Step size Adaptation,
where the step size is adapted measuring the length of a so-called cumulative
path. The cumulative path is a combination of the previous steps realized by
the algorithm, where the importance of each step decreases with time. This
article studies the CSA-ES on composites of strictly increasing with affine
linear functions through the investigation of its underlying Markov chains.
Rigorous results on the change and the variation of the step size are derived
with and without cumulation. The step-size diverges geometrically fast in most
cases. Furthermore, the influence of the cumulation parameter is studied.Comment: Parallel Problem Solving From Nature (2012
Cumulative Step-size Adaptation on Linear Functions
The CSA-ES is an Evolution Strategy with Cumulative Step size Adaptation,
where the step size is adapted measuring the length of a so-called cumulative
path. The cumulative path is a combination of the previous steps realized by
the algorithm, where the importance of each step decreases with time. This
article studies the CSA-ES on composites of strictly increasing functions with
affine linear functions through the investigation of its underlying Markov
chains. Rigorous results on the change and the variation of the step size are
derived with and without cumulation. The step-size diverges geometrically fast
in most cases. Furthermore, the influence of the cumulation parameter is
studied.Comment: arXiv admin note: substantial text overlap with arXiv:1206.120
K-SPMM: a database of murine spermatogenic promoters modules & motifs
BACKGROUND: Understanding the regulatory processes that coordinate the cascade of gene expression leading to male gamete development has proven challenging. Research has been hindered in part by an incomplete picture of the regulatory elements that are both characteristic of and distinctive to the broad population of spermatogenically expressed genes. DESCRIPTION: K-SPMM, a database of murine Spermatogenic Promoters Modules and Motifs, has been developed as a web-based resource for the comparative analysis of promoter regions and their constituent elements in developing male germ cells. The system contains data on 7,551 genes and 11,715 putative promoter regions in Sertoli cells, spermatogonia, spermatocytes and spermatids. K-SPMM provides a detailed portrait of promoter site components, ranging from broad distributions of transcription factor binding sites to graphical illustrations of dimeric modules with respect to individual transcription start sites. Binding sites are identified through their similarities to position weight matrices catalogued in either the JASPAR or the TRANSFAC transcription factor archives. A flexible search function allows sub-populations of promoters to be identified on the basis of their presence in any of the four cell-types, their association with a list of genes or their component transcription-factor families. CONCLUSION: This system can now be used independently or in conjunction with other databases of gene expression as a powerful aid to research networks of co-regulation. We illustrate this with respect to the spermiogenically active protamine locus in which binding sites are predicted that align well with biologically foot-printed protein binding domains. AVAILABILITY
Parentsâ report of canadian elementary school childrenâs physical activity and screen time during the COVID-19 pandemic: A longitudinal study
COVID-19 public health protocols have altered childrenâs daily routines, limiting their physical activity opportunities. The purpose of this study was to examine how the COVID-19 pandemic affected childrenâs (ages 10â12 years) physical activity and screen time, and to explore the impact of gender, socioeconomic status (SES), and public health constraints (i.e., facility use and social interaction) on the changes in childrenâs health behaviors. Online surveys were disseminated to parents at two time points: before COVID-19 (May 2019 to February 2020) and during COVID-19 (November to December 2020). Wilcoxon signed-rank tests were used to assess changes in physical activity and screen time, and for subgroup analyses. Parents (n = 95) reported declines in childrenâs physical activity (Z = â2.53, p. = 0.01, d = 0.18), and increases in weekday (Z = â4.61, p \u3c 0.01, d = 0.33) and weekend screen time (Z = â3.79, p \u3c 0.01, d = 0.27). Significant changes in physical activity and screen time behaviors were identified between gender, SES, and facility use groups. All social interaction groups underwent significant changes in screen time. Overall, COVID-19 protocols have negatively influenced childrenâs physical activity and screen time. Due to the negative consequences of inactivity and excessive screen time, resources must be made available to support families during the pandemic
In Vitro Recombination of Non-Homologous Genes Can Result in Gene Fusions that Confer a Switching Phenotype to Cells
Regulation of protein activity is central to the complexity of life. The ability to regulate protein activity through exogenously added molecules has biotechnological/biomedical applications and offers tools for basic science. Such regulation can be achieved by establishing a means to modulate the specific activity of the protein (i.e. allostery). An alternative strategy for intracellular regulation of protein activity is to control the amount of protein through effects on its production, accumulation, and degradation. We have previously demonstrated that the non-homologous recombination of the genes encoding maltose binding protein (MBP) and TEM1 ÎČ-lactamase (BLA) can result in fusion proteins in which ÎČ-lactamase enzyme activity is allosterically regulated by maltose. Here, through use of a two-tiered genetic selection scheme, we demonstrate that such recombination can result in genes that confer maltose-dependent resistance to ÎČ-lactam even though they do not encode allosteric enzymes. These âphenotypic switchâ genes encode fusion proteins whose accumulation is a result of a specific interaction with maltose. Phenotypic switches represent an important class of proteins for basic science and biotechnological applications in vivo
Deciphering the folding kinetics of transmembrane helical proteins
Nearly a quarter of genomic sequences and almost half of all receptors that
are likely to be targets for drug design are integral membrane proteins.
Understanding the detailed mechanisms of the folding of membrane proteins is a
largely unsolved, key problem in structural biology. Here, we introduce a
general model and use computer simulations to study the equilibrium properties
and the folding kinetics of a -based two helix bundle fragment
(comprised of 66 amino-acids) of Bacteriorhodopsin. Various intermediates are
identified and their free energy are calculated toghether with the free energy
barrier between them. In 40% of folding trajectories, the folding rate is
considerably increased by the presence of non-obligatory intermediates acting
as traps. In all cases, a substantial portion of the helices is rapidly formed.
This initial stage is followed by a long period of consolidation of the helices
accompanied by their correct packing within the membrane. Our results provide
the framework for understanding the variety of folding pathways of helical
transmembrane proteins
Transition to superfluid turbulence governed by an intrinsic parameter
Hydrodynamic flow in both classical and quantum fluids can be either laminar
or turbulent. To describe the latter, vortices in turbulent flow are modelled
with stable vortex filaments. While this is an idealization in classical
fluids, vortices are real topologically stable quantized objects in
superfluids. Thus superfluid turbulence is thought to hold the key to new
understanding on turbulence in general. The fermion superfluid 3He offers
further possibilities owing to a large variation in its hydrodynamic
characteristics over the experimentally accessible temperatures. While studying
the hydrodynamics of the B phase of superfluid 3He, we discovered a sharp
transition at 0.60Tc between two regimes, with regular behaviour at
high-temperatures and turbulence at low-temperatures. Unlike in classical
fluids, this transition is insensitive to velocity and occurs at a temperature
where the dissipative vortex damping drops below a critical limit. This
discovery resolves the conflict between existing high- and low-temperature
measurements in 3He-B: At high temperatures in rotating flow a vortex loop
injected into superflow has been observed to expand monotonically to a single
rectilinear vortex line, while at very low temperatures a tangled network of
quantized vortex lines can be generated in a quiescent bath with a vibrating
wire. The solution of this conflict reveals a new intrinsic criterion for the
existence of superfluid turbulence.Comment: Revtex file; 5 pages, 2 figure
Genetic Selection for Enhanced Folding In Vivo Targets the Cys14-Cys38 Disulfide Bond in Bovine Pancreatic Trypsin Inhibitor
The periplasm provides a strongly oxidizing environment; however, periplasmic expression of proteins with disulfide bonds is often inefficient. Here, we used two different tripartite fusion systems to perform in vivo selections for mutants of the model protein bovine pancreatic trypsin inhibitor (BPTI) with the aim of enhancing its expression in Escherichia coli. This trypsin inhibitor contains three disulfides that contribute to its extreme stability and protease resistance. The mutants we isolated for increased expression appear to act by eliminating or destabilizing the Cys14-Cys38 disulfide in BPTI. In doing so, they are expected to reduce or eliminate kinetic traps that exist within the well characterized in vitro folding pathway of BPTI. These results suggest that elimination or destabilization of a disulfide bond whose formation is problematic in vitro can enhance in vivo protein folding. The use of these in vivo selections may prove a valuable way to identify and eliminate disulfides and other rate-limiting steps in the folding of proteins, including those proteins whose in vitro folding pathways are unknown. Antioxid. Redox Signal. 14, 973-984.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90494/1/ars-2E2010-2E3712.pd
GLUE-IT and PEDEL-AA: new programmes for analyzing protein diversity in randomized libraries
There are many methods for introducing random mutations into nucleic acid sequences. Previously, we described a suite of programmes for estimating the completeness and diversity of randomized DNA libraries generated by a number of these protocols. Our programmes suggested some empirical guidelines for library design; however, no information was provided regarding library diversity at the protein (rather than DNA) level. We have now updated our web server, enabling analysis of translated libraries constructed by site-saturation mutagenesis and error-prone PCR (epPCR). We introduce GLUE-Including Translation (GLUE-IT), which finds the expected amino acid completeness of libraries in which up to six codons have been independently varied (according to any user-specified randomization scheme). We provide two tools for assisting with experimental design: CodonCalculator, for assessing amino acids corresponding to given randomized codons; and AA-Calculator, for finding degenerate codons that encode user-specified sets of amino acids. We also present PEDEL-AA, which calculates amino acid statistics for libraries generated by epPCR. Input includes the parent sequence, overall mutation rate, library size, indel rates and a nucleotide mutation matrix. Output includes amino acid completeness and diversity statistics, and the number and length distribution of sequences truncated by premature termination codons. The web interfaces are available at http://guinevere.otago.ac.nz/stats.html
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