Filopodium retraction is controlled by adhesion to its tip

Area of Science:

• Cell Biology
• Biophysics
• Microbiology

Background:

• Filopodia are crucial for cell sensing, migration, and adhesion.
• Pathogens exploit filopodia for cellular invasion.
• Filopodial dynamics offer insights into elementary adhesion and signaling events.

Purpose of the Study:

• To investigate the forces controlling filopodial retraction.
• To characterize the relationship between ligand density and filopodial stall force.
• To understand how microbial components influence filopodial dynamics.

Main Methods:

• Utilized functionalized beads and optical tweezers to measure single filopodium retraction forces.
• Applied beads coated with β1 integrin ligand (Yersinia Invasin) and carboxyl groups.
• Tested the effect of Shigella type three secretion systems on filopodial stall force.

Main Results:

• Filopodial stall force is dependent on bead coating and ligand density.
• Forces ranged from 8 pN (Yersinia Invasin) to 15 pN (carboxyl groups).
• A small number of clustered Shigella type three secretion systems induced stall forces of 10 pN.

Conclusions:

• The number of receptor-ligand interactions at the filopodial tip dictates maximal retraction force.
• Discrete, clustered receptors are sufficient to generate substantial retraction stall forces.
• Filopodial retraction force is primarily determined by the number and density of ligand-receptor interactions.