Locally excitable Cdc42 signals steer cells during chemotaxis

Area of Science:

• Cell Biology
• Biochemistry
• Molecular Biology

Background:

• Neutrophils and amoeboid cells navigate via chemotaxis, directing movement towards attractants.
• Small GTPases like Ras, Rac, Cdc42, and RhoA are known regulators of chemotaxis, but their precise roles in spatiotemporal control of cell polarization and steering remain unclear.

Purpose of the Study:

• To elucidate the spatiotemporal roles of Ras, Rac, Cdc42, and RhoA small GTPases in directing neutrophil-like cell chemotaxis and polarization.
• To investigate the mechanism by which local signaling events control cell turning and directionality.

Main Methods:

• Utilized neutrophil-like PLB-985 cells expressing fluorescence biosensors for GTPase activity.
• Employed spatiotemporal photorelease of chemoattractant to stimulate directed cell migration.
• Investigated the role of actin polymerization inhibition in uncovering GTPase activity dynamics.

Main Results:

• Local Cdc42 signals, but not Rac, RhoA, or Ras, were observed to precede cell turning during chemotaxis.
• Pre-existing local Cdc42 activity predicted future migration direction even in unpolarized cells under uniform stimulation.
• Inhibition of actin polymerization revealed recurring local Cdc42 activity pulses, indicative of excitable compass behavior.
• Cdc42 antagonizes RhoA, maintaining a steep gradient, while Ras and Rac form shallow gradients during migration.

Conclusions:

• Locally excitable Cdc42 signals are the primary drivers of chemotactic steering and de novo cell polarization.
• Cdc42 acts as a key compass mechanism, integrating local cues to direct cell movement.