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Directional cell locomotion requires symmetry breaking between the front and rear of the cell. How this manifests itself for cells moving in physiological 3D matrices is often elusive. We take inspiration from the scallop theorem proposed by Purcell for micro-swimmers in Newtonian fluids: self-propelled objects undergoing persistent motion at low Reynolds number must follow a cycle of shape changes that breaks temporal symmetry. We report similar concepts for cells crawling in 3D. We quantified cell motion using a combination of 3D live cell imaging, visualisation of the matrix displacement and a minimal model with multipolar expansion. We show that cells embedded in 3D matrix form myosin-driven force dipoles at both sides of the nucleus, that locally and periodically pinch the matrix. The existence of a phase shift between the two dipoles is required for directed cell motion which manifests itself in cycles in the dipole-quadrupole diagram, a formal equivalence to the Purcell cycle. We confirm this mechanism by triggering local dipolar contractions with a laser, which leads to directed motion. Our study reveals that the cell controls its motility by synchronising dipolar forces distributed at front and back. This result opens new strategies to externally control cell motion as well as for the design of micro-crawlers.

The famous scallop theorem proposed by Purcell in 1977 states that self-propelled objects swimming at low Reynolds number must follow a cycle of shape changes that breaks temporal symmetry. This should hold true for crawling cells as well. However a clear mechanism for this symmetry breaking is still elusive. Here we show that cells embedded in 3D matrix form at both sides of the nucleus force dipoles driven by myosin that locally and periodically pinch the matrix. Using a combination of 3D live cell imaging, traction force microscopy and a minimal model with multipolar expansion, we show that the existence of a phase shift between the two dipoles involves mainly the microtubular network and is required for directed cell motion. We confirm this mechanism by triggering local dipolar contractions with a laser, which leads to directed motion. Our study reveals that the cell controls its motility by synchronising dipolar forces distributed at front and back. This result opens new strategies to externally control cell motion.

While cell crawling on 2D substrate often show a spatially polarised shape with clear front and back, such polarisation is elusive for cells moving in 3D. However directional movement requires symmetry breaking and polarisation. Here, we show that cells embedded in 3D matrix form at both sides of the nucleus force-dipoles, driven by myosin, that locally and periodically pinch the matrix. Using a combination of 3D live cell imaging, traction force microscopy and a minimal model with multipolar expansion, we show that the existence of a phase shift between the two dipoles, mediated mainly by the microtubule network, is involved in directed cell motion. We confirm this mechanism by triggering local dipolar contractions with laser ablation leading to directed motion. Our study reveals that the cell controls its motility by synchronising dipolar forces distributed at front and back.

International audience; Estrogens are major regulators of the mammary gland development, notably during puberty, via estrogen receptor (ER) activation, leading to the proliferation and differentiation of mammary cells. In addition to estrogens, the bone morphogenetic proteins (BMPs) family is involved in breast stem cell/progenitor commitment. However, these two pathways that synergistically contribute to the biology of the normal mammary gland have also been described to initiate and/or promote breast cancer development. In addition to intrinsic events, lifestyle habits and exposure to environmental cues are key risk factors for cancer in general, and especially for breast cancer. In the latter case, bisphenol A (BPA), an estrogen-mimetic compound, is a critical pollutant both in terms of the quantities released in our environment and of its known and speculated effects on mammary gland biology. In this review, we summarize the current knowledge on the actions of BMPs and estrogens in both normal mammary gland development and breast cancer initiation, dissemination, and resistance to treatment, focusing on the dysregulations of these processes by BPA but also by other bisphenols, including BPS and BPF, initially considered as safer alternatives to BPA.

Evapotranspiration is one of the most important fluxes of the water budget in semi-arid areas. The estimation of actual crop transpiration is a major issue in those regions due to its remarkable impacts on the precision of irrigation scheduling, crop growth and yield. Rainfed olive trees are adapted to the southern part of the Mediterranean basin even though they are vulnerable to an increased number of drought spells that might occur under current climate change scenarios. This present paper studies both water and energy exchanges over a rainfed olive grove in semi-arid conditions. The hydrological functioning of sparse olive trees is difficult to characterize because of its low LAI. To better understand water exchanges within the Soil Plant Atmosphere continuum and better evaluate the evapotranspiration and its components, we combine data arising from eddy covariance, soil water content measurements and the sap flow method. First, we check the consistency of the evapotranspiration partitioning and water balance over three contrasted years: one wet and two dry. Total evapotranspiration (ET) from eddy covariance method compares well with the sum of the evaporation (E) generated from the surface soil moisture measurements and the transpiration derived from the sap flow method. The top meter soil water balance corresponds roughly to ET during the wet year but for the dry years there is an evidence of extraction by roots below the first meter of soil. Inter-annual variations of the transpiration and associated water stress levels are analyzed by the combined use of different types of eco-physiological (sap flow) as well as remotely sensed variables that can be monitored through proxi-detection (albedo, surface temperature, surface soil moisture). The amount and timing of vegetation stress are consistent throughout the various indicators. Consequently, this consistent set of data can be used to constrain a SVAT land-surface model capable of representing the various features of the water and energy budget for this specific land cover.

International audience

International audience

International audience

Introduction Surgery remains the basic treatment of hepatic hydatid cyst (HHC). However, it is associated with significant morbidity. The aim of our study was to evaluate mortality and morbidity of surgery of the HHC and to highlight the risk factors. Methods A retrospective study was conducted from January 1, 1996 to December 31, 2006. 391 patients hospitalized for HHC and operated in the Department of General Surgery “A” of the Rabta Hospital in Tunis, Tunisia. Results The overall mortality rate was 0.7% while the overall morbidity rate was 20.4%. About 16.6% suffered from specific complications, while 3.8% suffered from non-specific complications. Predictors of morbidity in a univariate analysis included cysts larger than 9 cm, dome cysts, cysts with bilious contents, type II, III, IV or V on ultrasound classification, fissured cysts and intrabiliary rupture of hepatic hydatid cyst. The multivariate study consisted of independent predictors of disease at the site of the liver dome, the cysto-biliary fistula and intrabiliary rupture of hepatic hydatid cyst Conclusion The hepatic hydatid cyst of the dome and the existence of preoperative complications in particular intrabiliary rupture of hepatic hydatid cyst are the main factors of morbidity. A better understanding of these factors allows the surgeon to choose the appropiate surgical technique that is associated with less morbidity.Pan African Medical Journal 2012; 13:29