Cytoplasmic flow is a cell size sensor that scales anaphase.

Area of Science:

• Cell biology
• Developmental biology
• Biophysics

Background:

• Early embryogenesis involves rapid cell divisions without growth, leading to decreasing cell size.
• Maintaining cellular structure proportionality is crucial as cell size changes.
• Nuclear envelope reformation (NER) must adapt its position to avoid occurring outside the cell boundary in smaller cells.

Purpose of the Study:

• To investigate the scaling mechanisms that ensure proper nuclear envelope reformation (NER) positioning in early embryogenesis.
• To understand how cellular structures, specifically NER, adapt to decreasing cell size during rapid mitotic cycles.

Main Methods:

• Utilized live-cell imaging and biophysical modeling to analyze chromosome motility and cytoplasmic flows.
• Investigated the role of dynein-mediated cargo transport along astral microtubules.
• Examined the influence of cell geometry and confinement on cytoplasmic flow dynamics.

Main Results:

• Found that nuclear envelope reformation (NER) position scales with cell size.
• Demonstrated that cytoplasmic flows, driven by viscous cytoplasm and dynein-powered cargo transport, scale with cell size.
• Showed that cell confinement influences cytoplasmic flow velocity, acting as a cell geometry sensor.

Conclusions:

• Cytoplasmic flows, acting as a cell geometry sensor, mediate the scaling of NER position with cell size.
• Astral microtubule interactions with the cell boundary alter flow velocity, which in turn affects chromosome separation and NER timing.
• This mechanism ensures nuclear envelope reformation occurs correctly within the cell boundary despite rapid changes in cell size.