Microtubule Dynamics Scale with Cell Size to Set Spindle Length and Assembly Timing

Area of Science:

• Cell Biology
• Developmental Biology
• Biophysics

Background:

• Embryonic cell divisions produce progressively smaller cells, necessitating adaptation of intracellular structures like the mitotic spindle.
• The correlation between mitotic spindle size and cell size is observed, but the underlying scaling mechanisms are not well understood.

Purpose of the Study:

• To investigate the mechanisms of mitotic spindle size scaling during embryonic cell divisions.
• To determine how spindle assembly timing is maintained across successive cell divisions.

Main Methods:

• Live cell imaging of mitotic spindle dynamics in Caenorhabditis elegans and Paracentrotus lividus embryos.
• In silico modeling to predict the effects of microtubule growth rate and cell volume on spindle scaling.
• In vivo experiments to validate computational predictions by modulating cell volume and microtubule growth rate.

Main Results:

• A common scaling mechanism was identified where the growth rate of spindle microtubules scales proportionally with cell volume, explaining spindle shortening.
• Spindle assembly timing remains constant across successive embryonic cell divisions, irrespective of cell size.
• Modulating cell volume or microtubule growth rate in vivo resulted in proportional changes in spindle size, confirming the model's predictions.

Conclusions:

• The scalability of microtubule growth rate in response to varying cell size is a key mechanism for adapting mitotic spindle length.
• This mechanism ensures appropriate spindle size for cell division and maintains consistent spindle assembly timing throughout early development.