Mechanistic insights into central spindle assembly mediated by the centralspindlin complex

Area of Science:

• Cell Biology
• Molecular Biology
• Structural Biology

Background:

• The central spindle is essential for regulating the division plane during cytokinesis in animal cells.
• The heterotetrameric centralspindlin complex bundles microtubules to form the central spindle, but its assembly mechanism is not well understood.

Purpose of the Study:

• To elucidate the detailed mechanism of centralspindlin complex formation and its role in central spindle assembly.
• To investigate the role of specific charged residues and liquid-liquid phase separation in centralspindlin function.

Main Methods:

• Determined crystal structures of the molecular backbone of ZEN-4/CYK-4 centralspindlin from *Caenorhabditis elegans*.
• Investigated the propensity for liquid-liquid phase separation of the centralspindlin complex.
• Assessed the in vitro microtubule bundling activity and in vivo central spindle assembly.

Main Results:

• The crystal structures revealed the detailed mechanism of centralspindlin complex formation.
• Centralspindlin exhibits an intrinsic propensity for liquid-liquid phase separation.
• Specific basic residues on ZEN-4 and acidic residues on CYK-4 are critical for condensation, microtubule bundling, and in vivo central spindle assembly.

Conclusions:

• Centralspindlin complex formation and function are driven by charge-driven macromolecular condensation.
• The findings provide key insights into the mechanism of central spindle assembly mediated by centralspindlin.