The nucleus acts as a ruler tailoring cell responses to spatial constraints.

The microscopic environment inside a metazoan organism is highly crowded. Whether individual cells can tailor their behavior to the limited space remains unclear. In this study, we found that cells measure the degree of spatial confinement by using their largest and stiffest organelle, the nucleus. Cell confinement below a resting nucleus size deforms the nucleus, which expands and stretches its envelope. This activates signaling to the actomyosin cortex via nuclear envelope stretch-sensitive proteins, up-regulating cell contractility. We established that the tailored contractile response constitutes a nuclear ruler-based signaling pathway involved in migratory cell behaviors. Cells rely on the nuclear ruler to modulate the motive force that enables their passage through restrictive pores in complex three-dimensional environments, a process relevant to cancer cell invasion, immune responses, and embryonic development.

Temporal change in deep-sea benthic ecosystems: a review of the evidence from recent time-series studies.

Societal concerns over the potential impacts of recent global change have prompted renewed interest in the long-term ecological monitoring of large ecosystems. The deep sea is the largest ecosystem on the planet, the least accessible, and perhaps the least understood. Nevertheless, deep-sea data collected over the last few decades are now being synthesised with a view to both measuring global change and predicting the future impacts of further rises in atmospheric carbon dioxide concentrations. For many years, it was assumed by many that the deep sea is a stable habitat, buffered from short-term changes in the atmosphere or upper ocean. However, recent studies suggest that deep-seafloor ecosystems may respond relatively quickly to seasonal, inter-annual and decadal-scale shifts in upper-ocean variables. In this review, we assess the evidence for these long-term (i.e. inter-annual to decadal-scale) changes both in biologically driven, sedimented, deep-sea ecosystems (e.g. abyssal plains) and in chemosynthetic ecosystems that are partially geologically driven, such as hydrothermal vents and cold seeps. We have identified 11 deep-sea sedimented ecosystems for which published analyses of long-term biological data exist. At three of these, we have found evidence for a progressive trend that could be potentially linked to recent climate change, although the evidence is not conclusive. At the other sites, we have concluded that the changes were either not significant, or were stochastically variable without being clearly linked to climate change or climate variability indices. For chemosynthetic ecosystems, we have identified 14 sites for which there are some published long-term data. Data for temporal changes at chemosynthetic ecosystems are scarce, with few sites being subjected to repeated visits. However, the limited evidence from hydrothermal vents suggests that at fast-spreading centres such as the East Pacific Rise, vent communities are impacted on decadal scales by stochastic events such as volcanic eruptions, with associated fauna showing complex patterns of community succession. For the slow-spreading centres such as the Mid-Atlantic Ridge, vent sites appear to be stable over the time periods measured, with no discernable long-term trend. At cold seeps, inferences based on spatial studies in the Gulf of Mexico, and data on organism longevity, suggest that these sites are stable over many hundreds of years. However, at the Haakon Mosby mud volcano, a large, well-studied seep in the Barents Sea, periodic mud slides associated with gas and fluid venting may disrupt benthic communities, leading to successional sequences over time. For chemosynthetic ecosystems of biogenic origin (e.g. whale-falls), it is likely that the longevity of the habitat depends mainly on the size of the carcass and the ecological setting, with large remains persisting as a distinct seafloor habitat for up to 100 years. Studies of shallow-water analogs of deep-sea ecosystems such as marine caves may also yield insights into temporal processes. Although it is obvious from the geological record that past climate change has impacted deep-sea faunas, the evidence that recent climate change or climate variability has altered deep-sea benthic communities is extremely limited. This mainly reflects the lack of remote sensing of this vast seafloor habitat. Current and future advances in deep-ocean benthic science involve new remote observing technologies that combine a high temporal resolution (e.g. cabled observatories) with spatial capabilities (e.g. autonomous vehicles undertaking image surveys of the seabed).

Hydrodynamic narrowing of tubes extruded from cells.

We discuss the pulling force f required to extrude a lipid tube from a living cell as a function of the extrusion velocity L. The main feature is membrane friction on the cytoskeleton. As recently observed for neutrophils, the tether force exhibits a "shear thinning" response over a large range of pulling velocities, which was previously interpreted by assuming viscoelastic flows of the sliding membrane. Here, we propose an alternative explanation based on purely Newtonian flow: The diameter of the tether decreases concomitantly with the increase of the membrane tension in the lipid tube. The pulling force is found to vary as L(1/3), which is consistent with reported experimental data for various types of cells.

[Factors determining the choice of a modality of treatment by dialysis: a study of nine dialysis centers]. / Facteurs déterminant le choix d'une modalité de traitement par dialyse: une enquête dans neuf centres de dialyse.

BACKGROUND: The objective of this cross-sectional study in a population of 1472 dialysis patients was to identify the main factors involved in the choice of a specific option for dialysis therapy, taking into account three different types of criteria such as medical dependence (DM), nurse care requirement (SI) and independence for dialysis therapy (CA). METHODS: Each patient has been analysed, independently of present treatment modality, according to the above three criteria, namely DM, SI and CA. For each type of parameter, patients have been allocated to one of three levels, each level being established to evaluate whether dialytic treatment should be undertaken as hospital centre dialysis (HDC) or in a facility off the hospital. Level 3 of any one category corresponded to the inability of doing haemodialysis at home (HHD) or in self-care unit (AD). Level 2 included patients who could be treated in AD or by peritoneal dialysis (PD) with the assistance of a nurse. CAPD or HHD were considered as potential treatment modalities only in patients qualifying for level 1 of each criterion. RESULTS: In the patient population as a whole, the following treatment options were observed: HHD 3.6%, CAPD 6%, PD 1.8%, AD 16.3% and HDC 72.2%. For medical dependence (DM) there was a relatively even distribution for the three levels in six centres. In contrast, two centres were characterized by a predominance of DM level 3. Differences in DM levels between centres were greatly reduced when considering separately only those patients who were actually treated by CAPD, HDC and AD. SI levels were more uniformly distributed within all centres, and this was true for HCD and AD patients. When considering CA levels in HDC patients, a large predominance of CA level 3 was observed in all centres whereas CA level 1 was nearly in existent. CONCLUSION: The major finding of this study was that the inability or the refusal of dialysis patients to participate at treatment, independently of medical condition and nurse care requirement, was the main factor in the choice of hospital centre dialysis.