Periodic traction in migrating large amoeba of Physarum polycephalum

Area of Science:

• Cell Biology
• Biophysics
• Cytoskeletal Dynamics

Background:

• The slime mould Physarum polycephalum is a model organism for studying cell motility.
• Its locomotion is driven by Ca(2+)-dependent actomyosin contractions within a vein network.
• The actomyosin network exists as a cortical layer and in fibrils, with their distinct roles unclear.

Purpose of the Study:

• To investigate the roles of the cortical actomyosin layer and fibrils in Physarum polycephalum locomotion.
• To understand how different microplasmodial morphologies affect force generation and movement.

Main Methods:

• Birefringence observations to study fibril activity.
• Traction force microscopy to map force generation.
• Analysis of excised Physarum polycephalum microplasmodia with distinct morphologies.

Main Results:

• Three morphologies (amoeboid, chain, hybrid) were observed, all exhibiting oscillations.
• Chain-type Physarum showed novel force patterns with internal contractile rings.
• Forces are primarily transmitted via cortical actomyosin anchorage, while fibrils stabilize invaginated structures and contribute to force by increasing anchorage length.
• Motility was observed only when there was asymmetry in shape or force distribution.

Conclusions:

• Both cortical actomyosin and fibrils play crucial roles in Physarum polycephalum locomotion.
• Fibrils contribute to force generation and structural integrity.
• Asymmetry in shape and/or force distribution is a prerequisite for directed cell movement in Physarum polycephalum.