400 research outputs found
Circadian clocks optimally adapt to sunlight for reliable synchronization
Circadian oscillation provides selection advantages through synchronization
to the daylight cycle. However, a reliable clock must be designed through two
conflicting properties: entrainability to synchronize internal time with
periodic stimuli such as sunlight, and regularity to oscillate with a precise
period. These two aspects do not easily coexist because better entrainability
favors higher sensitivity, which may sacrifice the regularity. To investigate
conditions for satisfying the two properties, we analytically calculated the
optimal phase-response curve with a variational method. Our result indicates an
existence of a dead zone, i.e., a time period during which input stimuli
neither advance nor delay the clock. A dead zone appears only when input
stimuli obey the time course of actual solar radiation but a simple sine curve
cannot yield a dead zone. Our calculation demonstrates that every circadian
clock with a dead zone is optimally adapted to the daylight cycle.Comment: 24 pages, 7 figure
Fluctuating noise drives Brownian transport
The transport properties of Brownian ratchet was studied in the presence of
stochastic intensity noise (SIN) in both overdamped and underdamped regimes. In
the overdamped case, analytical solution using the matrix continued fraction
method revealed the existence of a maximum current when the noise intensity
fluctuates on intermediate time scale regions. Similar effects were observed
for the underdamped case by Monte Carlo simulations. The optimal
time-correlation for the Brownian transport coincided with the experimentally
observed time-correlation of the extrinsic noise in Esherichia coli gene
expression and implied the importance of environmental noise for molecular
mechanisms.Comment: 22 pages, 8 figure
Enhanced entrainability of genetic oscillators by period mismatch
Biological oscillators coordinate individual cellular components so that they
function coherently and collectively. They are typically composed of multiple
feedback loops, and period mismatch is unavoidable in biological
implementations. We investigated the advantageous effect of this period
mismatch in terms of a synchronization response to external stimuli.
Specifically, we considered two fundamental models of genetic circuits: smooth-
and relaxation oscillators. Using phase reduction and Floquet multipliers, we
numerically analyzed their entrainability under different coupling strengths
and period ratios. We found that a period mismatch induces better entrainment
in both types of oscillator; the enhancement occurs in the vicinity of the
bifurcation on their limit cycles. In the smooth oscillator, the optimal period
ratio for the enhancement coincides with the experimentally observed ratio,
which suggests biological exploitation of the period mismatch. Although the
origin of multiple feedback loops is often explained as a passive mechanism to
ensure robustness against perturbation, we study the active benefits of the
period mismatch, which include increasing the efficiency of the genetic
oscillators. Our findings show a qualitatively different perspective for both
the inherent advantages of multiple loops and their essentiality.Comment: 28 pages, 13 figure
NADase as a target molecule of in vivo suppression of the toxicity in the invasive M-1 group A Streptococcal isolates
<p>Abstract</p> <p>Background</p> <p>NAD-glycohydrolase (NADase) secreted by M-1 group A streptococcal (GAS) isolates are suspected as one of the virulence factors to cause severe invasive disease including streptococcal toxic shock-like syndrome (STSS). M-1 GAS strains were divided into three groups based on NADase activity: high activity, low activity and no activity in our previous report.</p> <p>Results</p> <p>The representative high activity isolates taken from STSS patients showed higher virulence compared with isolates from the low activity group, when used to infect mice. The knockout mutant of the <it>nga </it>gene, which encodes NADase also showed reduced virulence in a mouse infection study. The cloned <it>nga </it>gene was able to significantly complement the lost virulence. In addition, the solution containing purified recombinant IFS, which is an inhibitor of NADase, partially rescued mice infected with <it>S. pyogenes</it>.</p> <p>Conclusions</p> <p>These results indicate that NADase is important for the virulence of <it>S. pyogenes </it>in vivo and is the potential target to suppress the virulence.</p
Myelopathy Caused by Chronic Epidural Hematoma Associated with L1 Osteoporotic Vertebral Collapse: A Case Report and Review of the Literature
Epidural hematoma associated with osteoporotic vertebral collapse has not been reported yet in the literature. We report a case of myelopathy caused by chronic epidural hematoma associated with L1 osteoporotic vertebral collapse and review the relevant literature
Ectopic Calcification as Discernible Manifestation in Neonates with Pseudohypoparathyroidism Type 1a
The diagnosis of pseudohypoparathyroidism type 1a (PHP1a) is challenging, because both the osteodystrophy, such as brachydactyly and round face, and the symptomatic
hypocalcemia usually develop beyond infancy. Although ectopic calcification may be
an early sign of PHP1a, there are no systematic reviews regarding the time of its
appearance. We here report on two PHP1a patients who presented with subcutaneous
calcification in neonatal period
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