FMNL formins boost lamellipodial force generation

Area of Science:

• Cell Biology
• Molecular Biology
• Biophysics

Background:

• Cell migration relies on lamellipodium protrusion, driven by actin networks.
• Arp2/3 complex-dependent branching is considered vital for lamellipodium stability and force generation.

Purpose of the Study:

• To investigate the role of formins FMNL2 and FMNL3 in actin nucleation and elongation within lamellipodia.
• To determine the contribution of FMNL2/3 to cell migration velocity, lamellipodial structure, and force generation.

Main Methods:

• In vitro actin nucleation and elongation assays for FMNL2/3.
• Gene inactivation of FMNL2/3 in melanoma cells and fibroblasts.
• CRISPR/Cas9-mediated depletion of FMNL2/3.
• Analysis of lamellipodial protrusion velocity, actin filament density, bundling, and ultrastructure.
• Measurement of lamellipodium protrusion forces and cell migration in viscous media.

Main Results:

• FMNL2 and FMNL3 nucleate and elongate actin filaments with complementary activities in vitro.
• Loss of FMNL2/3 function reduces lamellipodial width, actin filament density, and bundling.
• FMNL2/3 inactivation abolishes lamellipodium protrusion forces and alters ultrastructural organization.
• FMNL2/3 depletion reduces cell migration velocity and the ability to move against viscous media.

Conclusions:

• Formin FMNL2/3 activity is essential for generating protrusion forces in lamellipodia.
• FMNL formins contribute to cell migration independently of Arp2/3 complex-dependent actin branching.
• These findings highlight a critical role for formins in the biophysical mechanisms of cell motility.