Getting the actin filaments straight: nucleation-release or treadmilling?

Area of Science:

• Cell Biology
• Biophysics
• Cytoskeleton Dynamics

Background:

• Actin filament dynamics are essential for cell locomotion in metazoans.
• Previous models, like 'nucleation-release,' proposed short, non-oriented filaments in lamellipodia based on caged actin probe experiments.
• Recent structural data challenge this model, suggesting long actin filaments with graded lengths.

Purpose of the Study:

• To re-evaluate models of actin-based cell motility in light of new structural data.
• To investigate the role of actin filament organization and dynamics in lamellipodia movement.
• To reconcile conflicting experimental findings regarding filament length and organization.

Main Methods:

• Analysis of structural data from keratocyte cytoskeletons.
• Integration of previous findings on cytoskeleton-substrate interactions.
• Comparative analysis of different actin dynamics models.

Main Results:

• Recent structural data are inconsistent with the 'nucleation-release' model.
• The data support a model involving treadmilling of long actin filaments of varying lengths.
• The cell cytoskeleton remains stationary relative to the substrate during movement.

Conclusions:

• The 'nucleation-release' model for keratocyte motility is likely incorrect.
• Long actin filaments undergoing treadmilling are more consistent with observed structures.
• Lateral filament flow is a potential mechanism driving lamellipodia motility, reconciling structural data and cell movement.