Dynein-Dynactin-NuMA clusters generate cortical spindle-pulling forces as a multi-arm ensemble

Area of Science:

• Cell Biology
• Molecular Cell Biology
• Cytoskeleton Dynamics

Background:

• Mitotic spindle positioning relies on cortical force-generating machinery pulling astral microtubules.
• The organization of this machinery for efficient force generation is poorly understood, unlike the kinetochore.
• Understanding cortical force generation is crucial for cell division and development.

Purpose of the Study:

• To investigate the molecular mechanisms underlying cortical force generation for spindle positioning.
• To determine the role of Nuclear Mitotic Apparatus protein (NuMA) in organizing force-generating complexes.
• To elucidate how diffusion-prone cortical components generate substantial spindle-pulling forces.

Main Methods:

• Development of a light-induced reconstitution system in human cells.
• Analysis of induced cortical targeting of NuMA and dynein.
• Investigation of dynein-dynactin recruitment, microtubule binding, and cluster formation.

Main Results:

• Induced cortical targeting of NuMA, but not dynein alone, is sufficient for spindle pulling.
• NuMA recruits dynein-dynactin, binds microtubules, and facilitates dynein-based microtubule gliding.
• Cortical NuMA assembles focal structures (Dynein-Dynactin-NuMA clusters) that generate cooperative forces for spindle positioning.

Conclusions:

• Cortical NuMA is a key organizer of spindle-pulling forces, assembling DDN clusters.
• These DDN clusters function as the core machinery for spindle positioning, analogous to the kinetochore.
• NuMA's clustering activity is essential for spindle positioning but not spindle-pole focusing.