Bacterial Filament Systems: Toward Understanding Their Emergent Behavior and Cellular Functions.

Bacteria use homologs of eukaryotic cytoskeletal filaments to conduct many different tasks, controlling cell shape, division, and DNA segregation. These filaments, combined with factors that regulate their polymerization, create emergent self-organizing machines. Here, we summarize the current understanding of the assembly of these polymers and their spatial regulation by accessory factors, framing them in the context of being dynamical systems. We highlight how comparing the in vivo dynamics of the filaments with those measured in vitro has provided insight into the regulation, emergent behavior, and cellular functions of these polymeric systems.

Unveiling the Therapeutic Potential of Vitamin-E in Preventing Inflammation and Stromal Congestion in Alcoholic Liver Injury.

OBJECTIVES: The objective of the research was to investigate and assess how effective Vitamin E is in preventing or reducing liver inflammation and stromal congestion associated with alcoholic liver injury. STUDY DESIGN: This is a laboratory-based experimental study. METHODOLOGY: A total of 18 domestic rabbits were divided into groups A, B, and C. Group A was the control group and treated with normal saline as a placebo. Groups B and C were given 30% ethanol in a daily dose of 30 ml/kg/day. Additionally, group C was treated with vitamin E at 50 mg/kg/day. All three groups were sub-divided into two sub-groups I and II on the basis of experimental duration of eight weeks and four weeks respectively. The subgroups with eight weeks of experimental time duration were categorized as "category E8" and subgroups with an experimental duration of four weeks were categorized as "category E4". Liver tissue samples from each animal were subjected to staining using hematoxylin and eosin (H&E) stain for histological staining in order to assess portal inflammation and to measure the sizes of hepatic sinusoids and central veins to evaluate hepatic congestion. RESULTS: A statistically significant variance was observed in the size of central veins, hepatic sinusoids, and invasion of inflammatory cells in portal areas across and between the groups within categories E4 and E8. Animals treated with vitamin E exhibited lower invasion of inflammatory cells and larger central veins and sinusoids compared to those not treated with vitamin E. CONCLUSION: Vitamin E may have a significant role in reducing or limiting the infiltration of inflammatory cells and could help prevent hepatic congestion in cases of alcoholic liver injury.

Spatiotemporal dynamics of actomyosin networks.

Rhodamine-phalloidin-labeled actin filaments were visualized gliding over a skeletal heavy meromyosin (HMM)-coated surface. Experiments at low filament densities showed that when two filaments collided, their paths were affected in a manner that depended on collision angle. Some collisions resulted in complete alignment of the filament paths; in others, the filaments crossed over one another. Filament crossover or alignment was equally probable at ∼40° contact angle. Filaments often underwent significant bending during collision and analysis of filament shape indicated an energy requirement of ∼13 kBT. Experiments were performed over a wide range of HMM surface density and actin filament bulk concentration. Actin filament gliding speed and path persistence plateaued above a critical HMM surface density, and at high (micromolar) actin filament concentrations, filament motion became dramatically aligned in a common direction. Spatiotemporal features of alignment behavior were determined by correlation analysis, supported by simulations. The thermal drift of individual filament tracks was suppressed as the population became more oriented. Spatial correlation analysis revealed that long-range alignment was due to incremental recruitment rather than fusion of locally ordered seed domains. The global alignment of filament movement, described by an "order parameter," peaked at optimal actin concentrations and myosin surface densities, in contrast to previous predictions of a critical phase transition. Either hydrodynamic coupling or exchange of filaments between the surface bound and adjacent bulk phase layers might degrade order at high actin filament concentration, and high HMM surface densities might decrease alignment probability during collisions. Our results are compatible with generation of long-range order from mechanical interaction between individual actin filaments. Furthermore, we show that randomly oriented myosin motors align relatively short, submicrometer actin filaments into motile surface domains that extend over many tens of micrometers and these patterns persist for several minutes.

MreB filaments align along greatest principal membrane curvature to orient cell wall synthesis.

MreB is essential for rod shape in many bacteria. Membrane-associated MreB filaments move around the rod circumference, helping to insert cell wall in the radial direction to reinforce rod shape. To understand how oriented MreB motion arises, we altered the shape of Bacillus subtilis. MreB motion is isotropic in round cells, and orientation is restored when rod shape is externally imposed. Stationary filaments orient within protoplasts, and purified MreB tubulates liposomes in vitro, orienting within tubes. Together, this demonstrates MreB orients along the greatest principal membrane curvature, a conclusion supported with biophysical modeling. We observed that spherical cells regenerate into rods in a local, self-reinforcing manner: rapidly propagating rods emerge from small bulges, exhibiting oriented MreB motion. We propose that the coupling of MreB filament alignment to shape-reinforcing peptidoglycan synthesis creates a locally-acting, self-organizing mechanism allowing the rapid establishment and stable maintenance of emergent rod shape.