Interphase microtubules determine the initial alignment of the mitotic spindle

Area of Science:

• Cell Biology
• Cytoskeleton Dynamics
• Mitosis

Background:

• In fission yeast (Schizosaccharomyces pombe), interphase microtubules (MTs) position the nucleus, which dictates the cell division plane.
• The mechanism by which the mitotic spindle orients relative to this plane for accurate chromosome segregation remains unclear.
• Previous hypotheses suggested astral MTs and a spindle orientation checkpoint (SOC) regulate spindle alignment.

Purpose of the Study:

• To investigate the role of interphase microtubules in spindle orientation during mitosis in Schizosaccharomyces pombe.
• To determine if a spindle orientation checkpoint (SOC) exists and influences spindle alignment.
• To elucidate the mechanism of initial spindle alignment with the cell division plane.

Main Methods:

• Single-cell assay to track spindle position throughout mitosis.
• Observation of spindle dynamics in fission yeast (Schizosaccharomyces pombe).

Main Results:

• No evidence supporting the existence of a spindle orientation checkpoint (SOC) was found.
• Nascent spindles are highly aligned with the cell's longitudinal axis at mitosis onset.
• Spindle alignment is achieved by growing along the axis of adjacent interphase microtubules.
• Spindle misalignment can lead to anucleate cells if spindle elongation is hindered.

Conclusions:

• Interphase microtubules play a crucial role in determining the initial alignment of the mitotic spindle.
• This alignment is mediated by the interaction between interphase microtubules and the spindle pole body.
• The study proposes a novel function for interphase microtubules in orienting the spindle for cell division.