Forces acting on the fission yeast anaphase spindle

Area of Science:

• Cell Biology
• Microscopy
• Genetics

Background:

• The fission yeast mitotic spindle comprises three microtubule sets, including astral microtubules associated with spindle pole bodies.
• During anaphase B, astral microtubules can adopt parallel or convergent configurations.
• Fission yeast mitosis features an extended anaphase B, with spindle elongation crucial for cell division.

Purpose of the Study:

• To investigate the functional significance of astral microtubule configurations during anaphase B.
• To examine bowed spindle morphology in relation to astral microtubule orientation.
• To understand the role of astral microtubules in regulating mitotic spindle dynamics and cell length.

Main Methods:

• Indirect immunofluorescence microscopy was used to visualize mitotic spindles.
• Analysis of spindle morphology in wild-type and genetically modified fission yeast strains (overexpressing weel+ or inactivating cdc25+).
• Comparison of spindle length and astral microtubule configurations under different cellular conditions.

Main Results:

• Anaphase B spindles frequently appeared bowed specifically when astral microtubules were in a convergent orientation.
• Abnormally long spindles (up to 30 µm) in weel+ overexpressing or cdc25+ inactivated cells also exhibited bowing only with convergent astral microtubules.
• Bowed spindles were not observed when astral microtubules were in a parallel configuration.

Conclusions:

• Convergent astral microtubules are associated with bowed mitotic spindles in fission yeast.
• Astral microtubules may exert pulling forces on spindle poles or counteract forces from pole-to-pole microtubules.
• These findings offer insights into the mechanics of spindle elongation and cell length control during mitosis.