Emergent actin flows explain distinct modes of gliding motility

Area of Science:

• Cell Biology
• Parasitology
• Biophysics

Background:

• Toxoplasma gondii employs gliding motility, distinct from other eukaryotic cell movement mechanisms.
• This motility is believed to be driven by a sub-membrane layer of flowing filamentous (F)-actin.
• The precise mechanisms by which F-actin flow generates diverse gliding patterns remain poorly understood.

Purpose of the Study:

• To investigate the self-organization principles underlying F-actin flow in Toxoplasma gondii.
• To develop a model explaining how emergent F-actin dynamics produce observed gliding behaviors.
• To correlate predicted actin states with experimental observations of parasite motility.

Main Methods:

• Development of a continuum model for emergent F-actin flow within the parasite's confined geometry.
• Inclusion of F-actin turnover dynamics in the theoretical model.
• Experimental observation of live Toxoplasma gondii with drug-stabilized actin bundles.

Main Results:

• The model predicts a steady-state rearward actin transport mode when F-actin turnover is present.
• Absence of F-actin turnover results in predicted actin patches that recirculate along the cell length.
• These predicted actin states align with experimental observations in live parasites.

Conclusions:

• Self-organization of F-actin flow within Toxoplasma gondii's geometry can intrinsically generate distinct motility modes.
• The model provides a framework for understanding how different gliding behaviors emerge from actin dynamics.
• This work elucidates the biophysical basis of parasite gliding motility.