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MIF2 is required for mitotic spindle integrity during anaphase spindle elongation in Saccharomyces cerevisiae
M T Brown1, L Goetsch, L H Hartwell
1Department of Genetics, University of Washington, Seattle 98195.
Abstract:
The function of the essential MIF2 gene in the Saccharomyces cerevisiae cell cycle was examined by overepressing or creating a deficit of MIF2 gene product. When MIF2 was overexpressed, chromosomes missegregated during mitosis and cells accumulated in the G2 and M phases of the cell cycle. Temperature sensitive mutants isolated by in vitro mutagenesis delayed cell cycle progression when grown at the restrictive temperature, accumulated as large budded cells that had completed DNA replication but not chromosome segregation, and lost viability as they passed through mitosis. Mutant cells also showed increased levels of mitotic chromosome loss, supersensitivity to the microtubule destabilizing drug MBC, and morphologically aberrant spindles. mif2 mutant spindles arrested development immediately before anaphase spindle elongation, and then frequently broke apart into two disconnected short half spindles with misoriented spindle pole bodies. These findings indicate that MIF2 is required for structural integrity of the spindle during anaphase spindle elongation. The deduced Mif2 protein sequence shared no extensive homologies with previously identified proteins but did contain a short region of homology to a motif involved in binding AT rich DNA by the Drosophila D1 and mammalian HMGI chromosomal proteins.
Insights
The essential MIF2 gene is crucial for maintaining spindle integrity during cell division in yeast. Disrupting MIF2 leads to chromosome missegregation and cell cycle arrest, highlighting its role in mitosis.
Area of Science:
- Cell Biology
- Genetics
- Molecular Biology
Background:
- The Saccharomyces cerevisiae MIF2 gene plays a critical role in cell cycle regulation.
- Understanding its function is essential for comprehending chromosome segregation fidelity.
Purpose of the Study:
- To investigate the function of the essential MIF2 gene during the cell cycle in Saccharomyces cerevisiae.
- To elucidate the role of MIF2 in mitosis and spindle integrity.
Main Methods:
- Gene overexpression and deficit creation in Saccharomyces cerevisiae.
- Isolation and characterization of temperature-sensitive mif2 mutants.
- Microscopic analysis of cell cycle progression, chromosome segregation, and spindle morphology.
- Assessment of mitotic chromosome loss and drug sensitivity.
Main Results:
- Overexpression of MIF2 resulted in chromosome missegregation and G2/M phase accumulation.
- Temperature-sensitive mif2 mutants exhibited delayed cell cycle progression, failed chromosome segregation post-DNA replication, and reduced viability.
- mif2 mutants displayed increased mitotic chromosome loss, hypersensitivity to microtubule-destabilizing drugs, and aberrant spindles.
- Spindles in mif2 mutants arrested before anaphase elongation and frequently fragmented, indicating a loss of structural integrity.
Conclusions:
- MIF2 is essential for maintaining the structural integrity of the spindle apparatus during anaphase spindle elongation.
- The Mif2 protein may interact with DNA, potentially influencing chromosomal stability.
- The findings suggest MIF2 is a key regulator of mitotic progression and chromosome segregation.