Protrusive growth from giant liposomes driven by actin polymerization.

Cell movement relies on protrusions formed at the leading edge. While actin polymerization beneath the membrane is suspected to drive these structures, the exact mechanism remains unclear. Previous studies have been limited by the complexity of cellular systems. Researchers have explored simplified models to isolate the role of actin. Giant liposomes offer a controlled platform for such investigations. These artificial cells can mimic biological membranes without cellular interference. However, the link between actin polymerization and protrusion formation has not been fully established. Understanding how actin dynamics translate to membrane deformation is a key gap. This study aims to clarify the role of actin in protrusive growth using a model system.

The goal was to determine if actin polymerization alone can drive protrusive growth in a simplified system. The researchers used giant liposomes containing actin to avoid cellular complexity. By controlling actin concentration, they aimed to observe protrusion formation. They introduced KCl via electroporation to trigger polymerization. The study sought to measure deformation rates and compare them to cellular observations. The researchers wanted to confirm if actin polymerization directly causes protrusion. They also aimed to assess the timing of deformation relative to polymerization. This approach allows for isolating actin’s role in protrusion formation.

Giant liposomes were prepared with varying actin concentrations (100 or 200 microM). Electroporation was used to introduce KCl into individual liposomes. Deformation was observed using microscopy techniques. The rate of protrusive growth was measured in micrometers per second. Brownian motion of particles inside the liposomes was tracked. The timing of deformation was compared to polymerization rates in a cuvette. The study focused on liposomes with 200 microM actin for detailed analysis. Observations were made in real time to capture dynamic changes.

Protrusive structures formed in liposomes with 200 microM actin at rates between 0.3 and 0.7 micrometers per second. These rates matched those observed in cell motility studies. Deformation occurred within 30 to 100 seconds, aligning with polymerization times. Brownian motion of particles inside the liposomes nearly stopped during deformation. The timing of deformation correlated with actin polymerization in a cuvette. No protrusions were observed in liposomes with 100 microM actin. The deformation was localized and consistent with actin-driven processes. These findings suggest a direct link between actin polymerization and protrusion formation.

The researchers concluded that actin polymerization in liposomes causes protrusive growth. The deformation rates matched those observed in cells, supporting the model. The cessation of Brownian motion indicates structural changes in the liposome. The timing of deformation aligns with polymerization kinetics in a controlled system. These findings suggest that actin polymerization alone can drive protrusion formation. The study provides evidence for a direct causal relationship between actin and protrusion. The model system used in this study effectively isolates actin’s role in the process. The results support the hypothesis that actin polymerization is sufficient for protrusion formation.