937 research outputs found
Coupling of actin hydrolysis and polymerization: Reduced description with two nucleotide states
The polymerization of actin filaments is coupled to the hydrolysis of
adenosine triphosphate (ATP), which involves both the cleavage of ATP and the
release of inorganic phosphate. We describe hydrolysis by a reduced two-state
model with a cooperative cleavage mechanism, where the cleavage rate depends on
the state of the neighboring actin protomer in a filament. We obtain
theoretical predictions of experimentally accessible steady state quantities
such as the size of the ATP-actin cap, the size distribution of ATP-actin
islands, and the cleavage flux for cooperative cleavage mechanisms.Comment: 6 page
Chronic Lunar Dust Exposure on Rat Cornea: Evaluation by Gene Expression Profiling
Lunar dust is capable of entering habitats and vehicle compartments by sticking to spacesuits or other objects that are transferred into the spacecraft from the lunar surface and has been reported to cause irritation upon exposure. During the Apollo missions, crewmembers reported irritation specifically to the skin and eyes after contamination of the lunar and service modules. It has since been hypothesized that ocular irritation and abrasion might occur as a result of such exposure, impairing crew vision. Recent work has shown that both ultrafine and unground lunar dust exhibited minimal irritancy of the ocular surface (i.e., cornea); however, the assessment of the severity of ocular damage resulting from contact of lunar dust particles to the cornea has focused only on macroscopic signs of mechanical irritancy and cytotoxicity. Given the chemical reactive properties of lunar dust, exposure of the cornea may contribute to detrimental effects at the molecular level including but not limited to oxidative damage. Additionally, low level chronic exposures may confound any results obtained in previous acute studies. We report here preliminary results from a tissue sharing effort using 10weekold Fischer 344 male rats chronically exposed to filtered air or jet milled lunar dust collected during Apollo 14 using a JaegerNYU noseonly chamber for a total of 120 hours (6 hours daily, 5 days a week) over a 4week period. RNA was isolated from corneas collected from rats at 1 day and 7 days after being exposed to concentrations of 0, 20, and 60 mg/m3 of lunar dust. Microarray analysis was performed using the Affymetrix GeneChip Rat Genome 230 2.0 Array with Affymetrix Expression Console and Transcriptome Analysis Console used for normalization and secondary analysis. An Ingenuity iReport"TM" was then generated for canonical pathway identification. The number of differentially expressed genes identified increases with dose compared to controls suggesting a more severe response to the lunar dust insult at higher levels. Pathways of interests that have been identified in all exposed samples include oxidative stress response, mitochondrial dysfunction, fibrosis, epithelial healing, TGF-Beta signaling, and extracellular matrix remodeling. Several biological processes related to cell migration, cellular proliferation, and eye development were also identified to be altered by exposure to lunar dust. Our preliminary results suggest that even a chronic insult of lunar dust as low as 20 mg/m(exp 3) elicits a molecular response in cornea tissue. Lunar dust on the surface of the moon would have the added properties of ionization and activation potentially leading to further damage to the cornea and greater sensitivity to any other environmental insult such as exposure to radiation. Additional studies are required to fully assess the risk of vision impairment and the mechanistic responses initiated in cornea exposed to lunar dust as well as the potential for longterm effects to astronaut healt
Curved Tails in Polymerization-Based Bacterial Motility
The curved actin ``comet-tail'' of the bacterium Listeria monocytogenes is a
visually striking signature of actin polymerization-based motility. Similar
actin tails are associated with Shigella flexneri, spotted-fever Rickettsiae,
the Vaccinia virus, and vesicles and microspheres in related in vitro systems.
We show that the torque required to produce the curvature in the tail can arise
from randomly placed actin filaments pushing the bacterium or particle. We find
that the curvature magnitude determines the number of actively pushing
filaments, independent of viscosity and of the molecular details of force
generation. The variation of the curvature with time can be used to infer the
dynamics of actin filaments at the bacterial surface.Comment: 8 pages, 2 figures, Latex2
Interleukin‐22 and CD160 play additive roles in the host mucosal response to Clostridium difficile infection in mice
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/110834/1/imm12414.pd
Sensorimotor Predictors of Post-Landing Functional Task Performance
Spaceflight drives adaptive changes in healthy individuals appropriate for sensorimotor function in a microgravity environment. These changes are maladaptive for return to earth's gravity. The inter-individual variability of sensorimotor decrements is striking, although poorly understood. The goal of this study is to identify a set of behavioral, neuroimaging and genetic measures that can potentially be used to predict early performance following G-transitions such as return to Earth on a set of sensorimotor tasks. Astronauts are being recruited who previously participated in sensorimotor field tests and/or dynamic posturography (MedB) within R+1 days following long-duration spaceflight
Tightness of slip-linked polymer chains
We study the interplay between entropy and topological constraints for a
polymer chain in which sliding rings (slip-links) enforce pair contacts between
monomers. These slip-links divide a closed ring polymer into a number of
sub-loops which can exchange length between each other. In the ideal chain
limit, we find the joint probability density function for the sizes of segments
within such a slip-linked polymer chain (paraknot). A particular segment is
tight (small in size) or loose (of the order of the overall size of the
paraknot) depending on both the number of slip-links it incorporates and its
competition with other segments. When self-avoiding interactions are included,
scaling arguments can be used to predict the statistics of segment sizes for
certain paraknot configurations.Comment: 10 pages, 6 figures, REVTeX
Production of Y(1S) Mesons from chib Decays in pp(bar) Collisions at sqrt(s)=1.8 TeV
We have reconstructed the radiative decays and in collisions
at TeV, and measured the fraction of mesons
that originate from these decays. For mesons with
GeV/, the fractions that come from and
decays are and
, respectively. We have derived the fraction of
directly produced mesons to be .Comment: 13 Pages, 2 figure
Inclusive jet cross section in collisions at TeV
The inclusive jet differential cross section has been measured for jet
transverse energies, , from 15 to 440 GeV, in the pseudorapidity region
0.10.7. The results are based on 19.5 pb of data
collected by the CDF collaboration at the Fermilab Tevatron collider. The data
are compared with QCD predictions for various sets of parton distribution
functions. The cross section for jets with GeV is significantly
higher than current predictions based on O() perturbative QCD
calculations. Various possible explanations for the high- excess are
discussed.Comment: 8 pages with 2 eps uu-encoded figures Submitted to Physical Review
Letter
Search for charged Higgs decays of the top quark using hadronic tau decays
We present the result of a search for charged Higgs decays of the top quark,
produced in collisions at 1.8 TeV. When the charged
Higgs is heavy and decays to a tau lepton, which subsequently decays
hadronically, the resulting events have a unique signature: large missing
transverse energy and the low-charged-multiplicity tau. Data collected in the
period 1992-1993 at the Collider Detector at Fermilab, corresponding to
18.70.7~pb, exclude new regions of combined top quark and charged
Higgs mass, in extensions to the standard model with two Higgs doublets.Comment: uuencoded, gzipped tar file of LaTeX and 6 Postscript figures; 11 pp;
submitted to Phys. Rev.
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