Apical Relaxation during Mitotic Rounding Promotes Tension-Oriented Cell Division.

Area of Science:

• Cell biology
• Developmental biology
• Biophysics

Background:

• Tissue tension anisotropy influences cell division orientation.
• Mitotic rounding (MR) involves increased cortical actomyosin tension, seemingly counteracting external forces.
• The mechanism reconciling tissue tension and MR for division orientation is unclear.

Purpose of the Study:

• To investigate how tissue tension dictates cell division orientation during mitotic rounding.
• To elucidate the role of local cortical tension changes in this process.

Main Methods:

• Utilized ascidian embryos for their simple structure and invariant division patterns.
• Observed blastomere behavior during mitosis, focusing on cortical tension dynamics.
• Manipulated extrinsic forces by altering interphasic blastomere contractility and mitotic domain synchrony.

Main Results:

• Blastomeres undergo localized apical cortical tension relaxation during MR.
• This relaxation permits extrinsic pulling forces from interphasic cells to polarize cell shape and division orientation.
• Disrupting extrinsic forces or asynchronous mitotic domains resulted in abnormal division orientations.

Conclusions:

• Apical relaxation during mitotic rounding is a crucial mechanism.
• This process allows tissue tension anisotropy to control stereotypical cell division orientation.
• External forces play a key role in orienting cell division despite mitotic rounding.