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Microtubule-associated coiled-coil protein Ssm4 is involved in the meiotic development in fission yeast
A Yamashita1, Y Watanabe, M Yamamoto
1Department of Biophysics and Biochemistry, Graduate School of Science, University of Tokyo, Japan.
Background:
In fission yeast, an RNA species named meiRNA is specifically required for the promotion of the first meiotic division. To dissect the function of this RNA and its partner RNA-binding protein Mei2, we screened for high-copy-number suppressors of the arrest prior to the first meiotic division caused by loss of meiRNA.
Results:
Analysis of one of the suppressors, named ssm4, suggested that it encodes a coiled-coil protein carrying a microtubule-binding motif at its N-terminus. Expression of ssm4 was restricted to cells undergoing meiosis. Disruption of ssm4 affected neither vegetative growth nor conjugation, but resulted in frequent generation of asci carrying less than four spores. Tagged Ssm4 could colocalize with microtubules in mitotic cells, and was seen to localize at spindles during both the first and the second meiotic division. The microtubule-binding motif was essential for the association of Ssm4 with microtubules and for its function during meiosis, but not for the suppression of loss of meiRNA. Ssm4 appeared to possess a potential to migrate to the nucleus.
Conclusions:
Ssm4 is a microtubule-colocalizing protein that plays a role specifically in meiosis. Ssm4 appears to modify the structure or the function of nuclear microtubules in order to promote the meiotic nuclear division.
Insights
Ssm4 is a meiosis-specific protein that binds microtubules and is essential for proper nuclear division in fission yeast. Its function is crucial for ensuring the correct number of spores per ascus during meiosis.
Area of Science:
- Cell Biology
- Molecular Biology
- Genetics
Background:
- MeiRNA is essential for the first meiotic division in fission yeast.
- Mei2 is an RNA-binding protein partner of meiRNA.
- Loss of meiRNA causes cell cycle arrest before meiosis.
Purpose of the Study:
- To identify suppressors of meiRNA-deficiency-induced meiotic arrest.
- To characterize the function of the identified suppressor gene, ssm4.
- To elucidate the role of Ssm4 protein in meiotic nuclear division.
Main Methods:
- High-copy-number suppressor screen in fission yeast.
- Gene disruption and analysis of meiotic phenotypes.
- Fluorescence microscopy to track Ssm4 localization with microtubules and spindles.
- Analysis of the role of the N-terminal microtubule-binding motif.
Main Results:
- Identified ssm4 as a suppressor, encoding a coiled-coil protein with an N-terminal microtubule-binding motif.
- ssm4 expression is meiosis-specific; its disruption causes abnormal spore formation (fewer than four spores per ascus).
- Ssm4 localizes to microtubules and spindles during both meiotic divisions; the microtubule-binding motif is crucial for meiotic function.
Conclusions:
- Ssm4 is a novel microtubule-associated protein specifically involved in meiosis.
- Ssm4 is essential for promoting meiotic nuclear division, likely by modifying nuclear microtubules.
- The protein's localization and function are critical for correct meiotic progression and spore formation.