Microtubule pivoting enables mitotic spindle assembly in S. cerevisiae

Area of Science:

• Cell Biology
• Cytoskeletal Dynamics
• Mitotic Spindle Assembly

Background:

• Bipolar spindle assembly requires antiparallel microtubule organization in the midzone.
• Microtubule motors generate forces for pole separation, but their efficiency is limited by initial parallel interactions and modest preferences for antiparallel alignment.
• The geometric bias favoring parallel interactions and the role of microtubule pivoting at spindle poles remain understudied.

Purpose of the Study:

• To directly measure the intrinsic pivoting flexibility of microtubules around yeast spindle poles.
• To investigate the importance of microtubule pivoting in vivo during early spindle assembly and pole separation.
• To determine if modifying microtubule-pole interface flexibility affects spindle organization and function.

Main Methods:

• Quantitative measurement of microtubule pivoting dynamics around isolated yeast spindle poles.
• Genetic engineering of mutants affecting the microtubule-anchoring pole component, Spc110, to alter pivoting flexibility.
• In vivo assessment of the impact of engineered flexibility on timely pole separation during spindle assembly.

Main Results:

• Pivoting flexibility of microtubules around spindle poles can be modulated by mutating Spc110.
• Engineering different flexibilities demonstrated the in vivo importance of pivoting for timely pole separation.
• Passive thermal pivoting facilitates initial microtubule contact between adjacent poles.

Conclusions:

• Microtubule pivoting at the spindle pole is a critical mechanism for overcoming geometric constraints during bipolar spindle formation.
• Modulating microtubule-pole interface flexibility directly influences the efficiency of pole separation.
• While passive pivoting initiates microtubule contact, active minus end-directed forces are necessary for achieving antiparallel alignment required for cell division.