8,298 research outputs found
Complexity in cancer stem cells and tumor evolution: towards precision medicine
In this review, we discuss recent advances on the plasticity of cancer stem
cells and highlight their relevance to understand the metastatic process and to
guide therapeutic interventions. Recent results suggest that the strict
hierarchical structure of cancer cell populations advocated by the cancer stem
cell model must be reconsidered since the depletion of cancer stem cells leads
the other tumor cells to switch back into the cancer stem cell phenotype. This
plasticity has important implications for metastasis since migrating cells do
not need to be cancer stem cells in order to seed a metastasis. We also discuss
the important role of the immune system and the microenvironment in modulating
phenotypic switching and suggest possible avenues to exploit our understanding
of this process to develop an effective strategy for precision medicine.Comment: 2 Figures, to appear in Seminars in Cancer Biology, Available online
23 February 201
Energy-Efficient selective activation in Femtocell Networks
Provisioning the capacity of wireless networks is difficult when peak load is significantly higher than average load, for example, in public spaces like airports or train stations. Service providers can use femtocells and small cells to increase local capacity, but deploying enough femtocells to serve peak loads requires a large number of femtocells that will remain idle most of the time, which wastes a significant amount of power.
To reduce the energy consumption of over-provisioned femtocell networks, we formulate a femtocell selective activation problem, which we formalize as an integer nonlinear optimization problem. Then we introduce GREENFEMTO, a distributed femtocell selective activation algorithm that deactivates idle femtocells to
save power and activates them on-the-fly as the number of users increases. We prove that GREENFEMTO converges to a locally Pareto optimal solution and demonstrate its performance using extensive simulations of an LTE wireless system. Overall, we find that GREENFEMTO requires up to 55% fewer femtocells to serve a given user load, relative to an existing femtocell power-saving procedure, and comes within 15% of a globally optimal solution
Conformational mechanism for the stability of microtubule-kinetochore attachments
Regulating the stability of microtubule(MT)-kinetochore attachments is
fundamental to avoiding mitotic errors and ensure proper chromosome segregation
during cell division. While biochemical factors involved in this process have
been identified, its mechanics still needs to be better understood. Here we
introduce and simulate a mechanical model of MT-kinetochore interactions in
which the stability of the attachment is ruled by the geometrical conformations
of curling MT-protofilaments entangled in kinetochore fibrils. The model allows
us to reproduce with good accuracy in vitro experimental measurements of the
detachment times of yeast kinetochores from MTs under external pulling forces.
Numerical simulations suggest that geometrical features of MT-protofilaments
may play an important role in the switch between stable and unstable
attachments
Legal determinants of external finance revisited : the inverse relationship between investor protection and societal well-being
This paper investigates relationships between corporate governance traditions and quality of life as measured by a number of widely reported indicators. It provides an empirical analysis of indicators of societal health in developed economies using a classification based on legal traditions. Arguably the most widely cited work in the corporate governance literature has been the collection of papers by La Porta et al. which has shown, inter alia, statistically significant relationships between legal traditions and various proxies for investor protection. We show statistically significant relationships between legal traditions and various proxies for societal health. Our comparative evidence suggests that the interests of investors may not be congruent with the interests of wider society, and that the criteria for judging the effectiveness of approaches to corporate governance should not be restricted to financial metrics
Volume changes during active shape fluctuations in cells
Cells modify their volume in response to changes in osmotic pressure but it
is usually assumed that other active shape variations do not involve
significant volume fluctuations. Here we report experiments demonstrating that
water transport in and out of the cell is needed for the formation of blebs,
commonly observed protrusions in the plasma membrane driven by cortex
contraction. We develop and simulate a model of fluid mediated membrane-cortex
deformations and show that a permeable membrane is necessary for bleb formation
which is otherwise impaired. Taken together our experimental and theoretical
results emphasize the subtle balance between hydrodynamics and elasticity in
actively driven cell morphological changes.Comment: Phys. Rev. Lett. in press. 13 pages 4 figures, 9 supplementary
figure
Cholesterol impairment contributes to neuroserpin aggregation
Intraneural accumulation of misfolded proteins is a common feature of several
neurodegenerative pathologies including Alzheimer's and Parkinson's diseases,
and Familial Encephalopathy with Neuroserpin Inclusion Bodies (FENIB). FENIB is
a rare disease due to a point mutation in neuroserpin which accelerates protein
aggregation in the endoplasmic reticulum (ER). Here we show that cholesterol
depletion induced either by prolonged exposure to statins or by inhibiting the
sterol regulatory binding-element protein (SREBP) pathway also enhances
aggregation of neuroserpin proteins. These findings can be explained
considering a computational model of protein aggregation under non-equilibrium
conditions, where a decrease in the rate of protein clearance improves
aggregation. Decreasing cholesterol in cell membranes affects their biophysical
properties, including their ability to form the vesicles needed for protein
clearance, as we illustrate by a simple mathematical model. Taken together,
these results suggest that cholesterol reduction induces neuroserpin
aggregation, even in absence of specific neuroserpin mutations. The new
mechanism we uncover could be relevant also for other neurodegenerative
diseases associated with protein aggregation.Comment: 7 figure
Mechanical Properties of Growing Melanocytic Nevi and the Progression to Melanoma
Melanocytic nevi are benign proliferations that sometimes turn into malignant
melanoma in a way that is still unclear from the biochemical and genetic point
of view. Diagnostic and prognostic tools are then mostly based on dermoscopic
examination and morphological analysis of histological tissues. To investigate
the role of mechanics and geometry in the morpholgical dynamics of melanocytic
nevi, we study a computation model for cell proliferation in a layered
non-linear elastic tissue. Numerical simulations suggest that the morphology of
the nevus is correlated to the initial location of the proliferating cell
starting the growth process and to the mechanical properties of the tissue. Our
results also support that melanocytes are subject to compressive stresses that
fluctuate widely in the nevus and depend on the growth stage. Numerical
simulations of cells in the epidermis releasing matrix metalloproteinases
display an accelerated invasion of the dermis by destroying the basal membrane.
Moreover, we suggest experimentally that osmotic stress and collagen inhibit
growth in primary melanoma cells while the effect is much weaker in metastatic
cells. Knowing that morphological features of nevi might also reflect geometry
and mechanics rather than malignancy could be relevant for diagnostic purpose
Ecological effects of the European barbel Barbus barbus (L., 1758) (Cyprinidae) invasion on native barbel populations in the Tiber River basin (Italy)
The purpose of this study was to investigate the effects of the European barbel Barbus barbus (L., 1758) invasion in the Tiber River basin (Italy) on the native Tiber barbel Barbus tyberinus Bonaparte, 1839, verifying whether the co-occurrence played a negative impact on growth rate and relative weight. Fish census data were collected during three periods (2000–2005, 2006–2010, 2011–2015) at 158 sampling sites. Since its first record in 1998, European barbel rapidly spread in the study area: it was present in more than 20% of the monitoring sites, where it is leading to the gradual replacement of Tiber barbel by widening its distribution in the Tiber River and in the downstream reaches of the main tributaries. By contrast, Tiber barbel has suffered from this competition, as demonstrated by the fact that the mean value of the relative weight was significantly higher where European barbel was absent. The results obtained suggested that this non-native species could be a serious threat to the conservation status of endemic Tiber barbel, and constitute the premise to underpin conservation strategies aiming to preserve native freshwater biodiversity
You're the Coach: A Guide for Parents of New Drivers, December 8, 2015
This publication is a guide for parents and guardians of teenagers learning to drive. It should be used with the Iowa Driver’s Manual to aid you in instructing your new driver about how to safely and responsibly operate a motor vehicle. Since the task of driving is affected by changing conditions, this manual does not attempt to cover all situations that may arise
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