Effect of habitat quality on the ecological behaviour of a temperate-living primate: time-budget adjustments

Barbary macaques, like other non-human primates living in highly seasonal temperate environments, display high monthly variations in their diet. In addition, their diet changes according to the habitat type they colonize and to the degree of habitat degradation due to resource exploitation by local people, in particular through pastoralism. We studied the time-budget adjustments of wild Barbary macaques in three cedar–oak forests impacted by different intensities of grazing pressure from goats and sheep. We examined how diet variations influenced the time monkeys spent in their activities and their day range lengths (i.e. their energy costs). At three studied sites, diet composition and time budgets showed marked seasonal variations. Diet composition had a strong influence on monkeys’ time budget. In the forest where pastoralism was the highest, diet included a greater proportion of underground resources, shrub fruit and acorns, which led to an increase in the time spent foraging and moving, as well as an important increase in day range lengths. Energy costs were therefore higher in a degraded environment than in a suitable habitat. The monkeys living in forests subjected to pastoralism took advantage of increased day lengths to spend more time searching for food. However, in the forest with the highest pastoralism pressure, although monkeys spent more time foraging, they spent less time feeding than monkeys at the other sites. In addition, they appeared to have reached the limits of the available time they could devote to these activities, as their diurnal resting time was at its lowest level over several months. Temperature variations did not appear to modify monkeys’ time budgets. In the least favourable habitat, saving time from resting activity allowed monkeys to maintain a relatively high level of social activity, partly linked to rearing constraints.     

Mechanotransduction down to individual actin filaments

The actin cytoskeleton plays an essential role in a cell's ability to generate and sense forces, both internally and in interaction with the outside world. The transduction of mechanical cues into biochemical reactions in cells, in particular, is a multi-scale process which requires a variety of approaches to be understood. This review focuses on understanding how mechanical stress applied to an actin filament can affect its assembly dynamics. Today, experiments addressing this issue at the scale of individual actin filaments are emerging and bring novel insight into mechanotransduction. For instance, recent data show that actin filaments can act as mechanosensors, as an applied tension or curvature alters their conformation and their affinity for regulatory proteins. Filaments can also transmit mechanical tension to other proteins, which consequently change the way they interact with the filaments to regulate their assembly. These results provide evidence for mechanotransduction at the scale of individual filaments, showing that forces participate in the regulation of filament assembly and organization. They bring insight into the elementary events coupling mechanics and biochemistry in cells. The experiments presented here are linked to recent technical developments, and certainly announce the advent of more exciting results in the future.     

CDC42 switches IRSp53 from inhibition of actin growth to elongation by clustering of VASP

Filopodia explore the environment, sensing soluble and mechanical cues during directional motility and tissue morphogenesis. How filopodia are initiated and spatially restricted to specific sites on the plasma membrane is still unclear. Here, we show that the membrane deforming and curvature sensing IRSp53 (Insulin Receptor Substrate of 53 kDa) protein slows down actin filament barbed end growth. This inhibition is relieved by CDC42 and counteracted by VASP, which also binds to IRSp53. The VASP:IRSp53 interaction is regulated by activated CDC42 and promotes high‐density clustering of VASP, which is required for processive actin filament elongation. The interaction also mediates VASP recruitment to liposomes. In cells, IRSp53 and VASP accumulate at discrete foci at the leading edge, where filopodia are initiated. Genetic removal of IRSp53 impairs the formation of VASP foci, filopodia and chemotactic motility, while IRSp53 null mice display defective wound healing. Thus, IRSp53 dampens barbed end growth. CDC42 activation inhibits this activity and promotes IRSp53‐dependent recruitment and clustering of VASP to drive actin assembly. These events result in spatial restriction of VASP filament elongation for initiation of filopodia during cell migration, invasion, and tissue repair.     

On-line characterization of monoclonal antibody variants by liquid chromatography-mass spectrometry operating in a two-dimensional format

Recombinant monoclonal antibodies (MAbs) have become one of the most rapidly growing classes of biotherapeutics in the treatment of human disease. MAbs are highly heterogeneous proteins, thereby requiring a battery of analytical technologies for their characterization. However, incompatibility between separation and subsequent detection is often encountered. Here we demonstrate the utility of a generic on-line liquid chromatography–mass spectrometry (LC-MS) method operated in a two-dimensional format toward the rapid characterization of MAb charge and size variants. Using a single chromatographic system capable of running two independent gradients, up to six fractions of interest from an ion exchange (IEC) or size exclusion (SEC) separation can be identified by trapping and desalting the fractions onto a series of reversed phase trap cartridges with subsequent on-line analysis by mass spectrometry. Analysis of poorly resolved and low-level peaks in the IEC or SEC profile was facilitated by preconcentrating fractions on the traps using multiple injections. An on-line disulfide reduction step was successfully incorporated into the workflow, allowing more detailed characterization of modified MAbs by providing chain-specific information. The system is fully automated, thereby enabling high-throughput analysis with minimal sample handling. This technology provides rapid data turnaround time, a much needed feature during product characterization and development of multiple biotherapeutic proteins.     

Intracellular regulation of heterotrimeric G-protein signaling modulates vascular smooth muscle cell contraction

The contractile function of vascular smooth muscle cells within the media of resistance arterioles is tightly connected to the role of these blood vessels in the maintenance of blood pressure homeostasis. Thus, much effort has been made to understand the intracellular signaling pathways that control vascular smooth muscle cell contractility with the aim that this knowledge will provide important clues for reducing the impact of uncontrolled blood pressure in our society. A key set of surface receptors, the G-protein coupled receptors, has been widely associated with the regulation of vascular smooth muscle cell contractility. Indeed, many of the current treatments for hypertension involve selective inhibition of these receptors. More recently, we have begun to understand the cellular mechanisms whereby G-protein coupled pathways are connected to the contractile machinery of the vascular smooth muscle cells. What has emerged is a view where there are multiple intracellular control points for G-protein signaling that coordinate and focus the extracellular stimuli into meaningful physiologic responses. This work will examine some of the recent advances in our understanding of G-protein signaling and its regulation of contractile function in vascular smooth muscle cells.     

Dissociation of the vacuolar and macroautophagic cytopathology from the cytotoxicity induced by the lipophilic local anesthetic bupivacaine

Local anesthetics, like many other cationic drugs, induce a vacuolar and macroautophagic cytopathology that has been observed in vivo and in various cell types; some also induce cytotoxicity of mitochondrial origin (apoptosis and necrosis) and it is not known whether the 2 types of toxicity overlap or interact. We compared bupivacaine with a more hydrophilic agent, lidocaine, for morphological, functional, and toxicological responses in a previously exploited nonneuronal system, primary smooth muscle cells. Bupivacaine induced little vacuolization (≥2.5?mmol/L, 4?h), but elicited autophagic accumulation (≥0.5?mmol/L, 4?h) and was massively cytotoxic at 2.5-5?mmol/L (4-24?h), the latter effect being unabated by the V-ATPase inhibitor bafilomycin A1. Lidocaine exerted little cytotoxicity at and below 5?mmol/L for 24?h, but intensely induced the V-ATPase-dependent vacuolar and autophagic cytopathology. Bupivacaine was more potent than lidocaine in disrupting mitochondrial potential, as judged by Mitotracker staining (significant proportions of cells affected in the 1-5 and 5-10?mmol/L concentration ranges, respectively). The addition of mitochondrial-inactivating toxins antimycin A and oligomycin to lidocaine (2.5?mmol/L) reproduced the profile of bupivacaine action (low intensity of vacuolization and retained autophagic accumulation). The high potency of bupivacaine as a mitochondrial toxicant eclipses the benign vacuolar and autophagic response seen with more hydrophilic local anesthetics.     

When mother knows best: A population genetic model of transgenerational versus intragenerational plasticity

Many organisms exhibit phenotypic plasticity; producing alternate phenotypes depending on the environment. Individuals can be plastic (intragenerational or direct plasticity), wherein individuals of the same genotype produce different phenotypes in response to the environments they experience. Alternatively, an individual's phenotype may be under the control of its parents, usually the mother (transgenerational or indirect plasticity), so that mother's genotype determines the phenotype produced by a given genotype of her offspring. Under what conditions does plasticity evolve to have intragenerational as opposed to transgenerational genetic control? To explore this question, we present a population genetic model for the evolution of transgenerational and intragenerational plasticity. We hypothesize that the capacity for plasticity incurs a fitness cost, which is borne either by the individual developing the plastic phenotype or by its mother. We also hypothesize that individuals are imperfect predictors of future environments and their capacity for plasticity can lead them occasionally to make a low‐fitness phenotype for a particular environment. When the cost, benefit and error parameters are equal, we show that there is no evolutionary advantage to intragenerational over transgenerational plasticity, although the rate of evolution of transgenerational plasticity is half the rate for intragenerational plasticity, as predicted by theory on indirect genetic effects. We find that transgenerational plasticity evolves when mothers are better predictors of future environments than offspring or when the fitness cost of the capacity for plasticity is more readily borne by a mother than by her developing offspring. We discuss different natural systems with either direct intragenerational plasticity or indirect transgenerational plasticity and find a pattern qualitatively in accord with the predictions of our model.