Mechanical assessment by magnetocytometry of the cytosolic and cortical cytoskeletal compartments in adherent epithelial cells

This study aims at quantifying the cellular mechanical properties based on a partitioning of the cytoskeleton in a cortical and a cytosolic compartments. The mechanical response of epithelial cells obtained by magnetocytometry - a micromanipulation technique which uses twisted ferromagnetic beads specifically linked to integrin receptors - was purposely analysed using a series of two Voigt bodies. Results showed that the cortical cytoskeleton has a faster response ( approximately 1 s) than the cytosolic compartment ( approximately 30 s). Moreover, the two cytoskeletal compartments have specific mechanical properties, i.e., the cortical (resp. cytosolic) cytoskeleton has a rigidity in the range: 49-85 Pa (resp.: 74-159 Pa) and a viscosity in the range 5-14 Pa.s (resp.: 593-1534 Pa.s), depending on the level of applied stress. Depolymerising actin-filaments strongly modified these values and especially those of the cytosolic compartment. The structural relevance of this two-compartment partitioning was supported by images of F-actin structure obtained on the same cells.     

Mapacalcine Protects Mouse Neurons against Hypoxia by Blocking Cell Calcium Overload

Stroke is one of a major cause of death and adult disability. Despite intense researches, treatment for stroke remains reduced to fibrinolysis, a technique useful for less than 10% of patients. Finding molecules able to treat or at least to decrease the deleterious consequences of stroke is an urgent need. Here, we showed that mapacalcine, a homodimeric peptide purified from the marine sponge Cliona vastifica, is able to protect mouse cortical neurons against hypoxia. We have also identified a subtype of L-type calcium channel as a target for mapacalcine and we showed that the channel has to be open for mapacalcine binding. The two main L-type subunits at the brain level are CaV1.3 and CaV1.2 subunits but mapacalcine was unable to block these calcium channels.Mapacalcine did not interfere with N-, P/Q- and R-type calcium channels. The protective effect was studied by measuring internal calcium level variation triggered by Oxygen Glucose Deprivation protocol, which mimics stroke, or glutamate stimulation. We showed that NMDA/AMPA receptors are not involved in the mapacalcine protection. The protective effect was confirmed by measuring the cell survival rate after Oxygen Glucose Deprivation condition. Our data indicate that mapacalcine is a promising molecule for stroke treatment.     

Prestress and Adhesion Site Dynamics Control Cell Sensitivity to Extracellular Stiffness

This study aims at improving the understanding of mechanisms responsible for cell sensitivity to extracellular environment. We explain how substrate mechanical properties can modulate the force regulation of cell sensitive elements primarily adhesion sites. We present a theoretical and experimental comparison between two radically different approaches of the force regulation of adhesion sites that depends on their either stationary or dynamic behavior. The most classical stationary model fails to predict cell sensitivity to substrate stiffness whereas the dynamic model predicts extracellular stiffness dependence. This is due to a time dependent reaction force in response to actomyosin traction force exerted on cell sensitive elements. We purposely used two cellular models, i.e., alveolar epithelial cells and alveolar macrophages exhibiting respectively stationary and dynamic adhesion sites, and compared their sensitivity to theoretical predictions. Mechanical and structural results show that alveolar epithelial cells exhibit significant prestress supported by evident stress fibers and lacks sensitivity to substrate stiffness. On the other hand, alveolar macrophages exhibit low prestress and exhibit sensitivity to substrate stiffness. Altogether, theory and experiments consistently show that adhesion site dynamics and cytoskeleton prestress control cell sensitivity to extracellular environment with an optimal sensitivity expected in the intermediate range.     

Suitability for classical biological control of Hedychium coronarium in Argentina

BioControl - Hedychium coronarium (Zingiberales: Zingiberaceae), native to the Himalayas and southern China, has become an environmental weed in many countries around the world. Reported in several...     

Alder forests of Numidia (N.E. Algeria): floristic biodiversity, vulnerability and conservation

The phytoecological study of the alder forests of north-east Algeria shows that these habitats with boreal affinities harbour very high species richness (> 400 species) and complex structures, which suggest their ancient origin. They correspond phytosociologically to two syntaxa, the Campanulo alatae-Alnenion glutinosae (riparian alder forests) and the Rusco hypophylli-Alnetum glutinosae (peat-forming alder carrs), respectively. Their degraded state and their regressive dynamics, observed during the 14 years of the study, reveal their precarious situation and their rapid ongoing decline under the influence of human-induced uncontroled disturbances (cutting, burning, draining, dumping…). With regard to their ecological, historical and patrimonial importance, the alder forests of Algerian Numidia should be urgently protected, with the aim of assuring the perennity of their exceptional floristic corteges.     

Recovery of viable cells from rabbit skin biopsies after storage at ?20°C for up to 10?days

Frozen animal tissues are thought to be appropriate for use as a donor for somatic cell nuclear transfer. This makes the freezing for long term storage a valuable tool for breeders needing to protect an animal population that is endangered by sanitary problems or for cryobanking of genetic resources. We report the successful cryopreservation of explants of skin derived from small biopsies from rabbit ear biopsies by using a protocol that can be easily performed by usual breeders, which are not equipped with cooling devices. By optimizing the procedure, we show that small biopsies can be kept at -20°C in a physiological solution containing 10% DMSO for up to 20 days before being deeply frozen in liquid nitrogen for long-term storage. After 10 days of storage at -20°C, the rate of viability of biopsies was similar to the control one (86 and 82% respectively). After 20 days of storage at -20°C, the rate of viability was dramatically lowered (39%), but it still allows to recover a significant population of viable cells from the preserved sample. Being appropriate to places lacking specific device, such a very simple technique may contribute to facilitate genome banking policies dedicated to the management of genetic resources in wild and domestic animals.     

Systematics of <Emphasis Type="Italic">Mycosphaerella</Emphasis> species associated with the invasive weed <Emphasis Type="Italic">Fallopia japonica</Emphasis>, including the potential biological control agent <Emphasis Type="Italic">M. polygoni-cuspidati</Emphasis>

Native to Japan, Fallopia japonica, most frequently referred to as Japanese knotweed, is a highly problematic invasive weed, particularly in the UK and North America. During surveys for natural enemies of this plant in Japan, two species of Mycosphaerella were collected. One of these was identified as M. polygoni-cuspidati, and is redescribed and neotypified. Causing a damaging leaf spot disease of F. japonica throughout its natural range in Japan, it is absent from the host’s exotic range. The restriction of M. polygoni-cuspidati to F. japonica in its center of origin, together with its severe impact on host fitness, indicates that this is a coevolved natural enemy with high potential as a classical biological control agent for the long-term management of this ecologically and economically important weed. In the field, the fungus has a reduced life cycle, with only spermogonia and pseudothecia (ascomata) being formed. Ascospores are the primary source of infection, and studies show that the mycelium from in vitro cultures is also infective and hyphae penetrate mainly via the stomata. A further, undescribed species of Mycosphaerella co-occurs with M. polygoni-cuspidati, here proposed as the new species M. shimabarensis. Both species have been studied using cultural, morphological and molecular phylogenetic methods.