A cytokinetic ring-driven cell rotation achieves Hertwig's rule in early development

Area of Science:

• Cell biology
• Developmental biology
• Biophysics

Background:

• Hertwig's rule describes cell division along the longest axis, typically governed by the mitotic spindle.
• Early cell divisions in some organisms present exceptions to this rule.

Purpose of the Study:

• Investigate the mechanism correcting spindle misalignment during early cell division in Caenorhabditis elegans.
• Determine if the observed mechanism is conserved in other cell types.

Main Methods:

• Theoretical modeling
• Live-cell imaging in Caenorhabditis elegans embryos
• Experiments with compressed mouse zygotes

Main Results:

• Microtubule-based forces initially align the mitotic spindle with the short cell axis, violating Hertwig's rule.
• The constricting cytokinetic ring generates inward forces that rotate the cell.
• This rotation corrects spindle-cell axis misalignment, aligning the spindle with the long axis.

Conclusions:

• A novel cytokinetic ring-driven mechanism ensures adherence to Hertwig's rule by actively rotating the cell.
• This mechanism is conserved in early cell divisions of systems where cells can rotate within a confining environment, such as mouse zygotes.