The leading edge is a lipid diffusion barrier.

The researchers used migrating keratocytes as a model system for cell protrusion. They labeled the outer membrane leaflet with carbocyanine dyes to track lipid movement. Sequential TIRF and epi-fluorescent imaging captured lipid diffusion in the dorsal and ventral lamellipodium membranes. They compared diffusion rates in different regions of the cell membrane during protrusion. The study employed global diffusion analysis to quantify lateral mobility of lipids. Cytochalasin treatment was used to disrupt actin polymerization and assess its effect on lipid diffusion. They analyzed whether membrane microdomains played a role in the observed diffusion barrier. The methods combined live-cell imaging with pharmacological interventions to test their hypothesis.

Lateral mobility of lipids in the outer membrane leaflet was significantly reduced at the leading edge during protrusion. Global diffusion analysis revealed a clear diffusion barrier at the leading edge region. Carbocyanine dye movement was slower in the dorsal lamellipodium compared to the ventral region. The study found no evidence supporting the involvement of membrane microdomains in this effect. Cytochalasin treatment abolished the observed diffusion barrier, indicating actin's role. The results suggest that actin filaments stabilize membrane components at the leading edge. The diffusion barrier was specific to the region where actin polymerization occurs. These findings support the idea that actin-membrane interactions trap regulatory proteins.

The study's findings suggest that actin polymerization creates a diffusion barrier at the leading edge. The observed lipid immobilization supports the idea of actin-membrane interactions stabilizing membrane components. The authors propose that densely packed molecular complexes mediate this interaction. Cytochalasin treatment confirmed the dependence of the diffusion barrier on actin. The results indicate that actin filaments may trap regulatory proteins in a positive-feedback loop. The absence of membrane microdomain involvement suggests alternative stabilization mechanisms. These conclusions align with the observed effects of actin disruption on lipid mobility. The findings support the hypothesis that actin dynamics regulate membrane component positioning.