Mitotic rounding alters cell geometry to ensure efficient bipolar spindle formation

Area of Science:

• Cell Biology
• Cytoskeleton Dynamics
• Mitosis

Background:

• Accurate animal cell division necessitates precise coordination between the microtubule-based spindle and the actin-based cell cortex.
• The roles of the actin cortex, its mechanics, and cell shape in spindle formation are not fully understood.

Purpose of the Study:

• To dissect the relative roles of actin, cortical mechanics, and cell shape in spindle formation during animal cell division.
• To investigate the impact of cell rounding on spindle morphogenesis and mitotic progression.

Main Methods:

• Perturbation experiments were conducted to alter actin cortex function and cell shape.
• Mitotic cell height was limited using various methods to study confinement effects.
• Spindle assembly, pole splitting, and mitotic progression were monitored.

Main Results:

• The actin cortex is dispensable for rounding and mitotic progression in isolated cells but essential for rounding under confinement.
• Failure to round up leads to defects in spindle assembly, pole splitting, and delayed mitosis.
• These defects are linked to the limited reach of centrosome-nucleated microtubules and can be rescued by increasing microtubule length.

Conclusions:

• Cell rounding, driven by the actin cortex, is critical for unperturbed spindle morphogenesis in confined mitotic cells.
• The findings explain the necessity of cell rounding for proper spindle assembly and timely progression through mitosis.
• This highlights the interplay between cell shape, cortical mechanics, and microtubule dynamics in cell division.