Three types of actomyosin rings within a common cytoplasm exhibit distinct modes of contractility

Area of Science:

• Cell Biology
• Biophysics
• Cytoskeletal Dynamics

Background:

• Actomyosin rings are essential for cell division, wound healing, and shape changes.
• These rings are composed of conserved proteins like non-muscle myosin II (NMMII) and actin filaments (F-actin).
• The unifying mechanism of actomyosin ring closure across diverse cellular contexts remains unclear.

Purpose of the Study:

• To investigate the mechanisms of contractile force generation in different actomyosin rings.
• To compare ring closure kinetics, protein dynamics, and force generation across distinct cellular events.
• To develop a physical model for understanding actomyosin ring mechanics.

Main Methods:

• Studied three actomyosin ring types in C. elegans oogenic germline: GSC mitotic cytokinesis, meiotic compartment apoptosis, and oocyte cellularization.
• Quantified ring closure kinetics, protein density, and abundance dynamics.
• Developed and applied a physical model linking filament interactions, material properties, and protein distribution to ring closure kinematics.

Main Results:

• Each studied actomyosin ring exhibited unique closure kinetics and protein dynamics.
• The mechanism of contractile force generation varied among the different ring types.
• The physical model successfully related protein density (anillin, NMMII) to ring closure kinematics.
• Model fitting provided estimates for experimentally inaccessible parameters, like asymmetric protein distribution along F-actin.

Conclusions:

• Actomyosin ring closure is not governed by a single unifying mechanism.
• The role of non-muscle myosin II (NMMII) varies depending on its distribution and motor activity along actin filaments.
• The degree of contractility and the influence of material properties differ significantly among various actomyosin ring types.