Dictyostelium cell shape generation requires myosin II

Area of Science:

• Cell Biology
• Biophysics
• Developmental Biology

Background:

• Myosin II is crucial for various non-muscle cell functions like movement and cytokinesis.
• Conventional imaging reveals minimal morphological differences in Dictyostelium amoebae lacking myosin II (mhcA-).

Purpose of the Study:

• To investigate the role of myosin II in three-dimensional (3D) cell shape generation using side-view microscopy (SVM).
• To differentiate 3D shape changes from pseudopod formation and determine myosin II's necessity for these processes.

Main Methods:

• Side-view microscopy (SVM) to observe cell morphology in 3D.
• Analysis of wild-type and mhcA- Dictyostelium amoebae under adhered and suspension conditions.
• Characterization of F-actin distribution and organelle exclusion in vertically extended cell regions.

Main Results:

• Wild-type cells exhibit extensive 3D shape changes, often extending vertically above the substrate, unlike mhcA- cells.
• Vertically extended regions in wild-type cells are not enriched in F-actin and do not exclude organelles, distinguishing them from pseudopods.
• mhcA- cells form F-actin-rich pseudopods and spread laterally but fail to extend vertically.
• Suspended mhcA- cells rapidly become spherical, while wild-type cells retain their irregular 3D shape, indicating myosin II's role in maintaining shape independent of substrate.

Conclusions:

• Myosin II is required for generating and maintaining three-dimensional cell shape in Dictyostelium amoebae.
• The mechanism of 3D shape generation is distinct from pseudopod formation.
• Cells lacking myosin II can attach and spread on a substrate but cannot generate or maintain complex 3D structures without it.