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Fission yeast minichromosome loss mutants mis cause lethal aneuploidy and replication abnormality
K Takahashi1, H Yamada, M Yanagida
1Department of Biophysics, Faculty of Science, Kyoto University, Japan.
Abstract:
Precise chromosome transmission in cell division cycle is maintained by a number of genes. The attempt made in the present study was to isolate temperature-sensitive (ts) fission yeast mutants that display high loss rates of minichromosomes at permissive or semipermissive temperature (designated mis). By colony color assay of 539 ts strains that contain a minichromosome, we have identified 12 genetic loci (mis1-mis12) and determined their phenotypes at restrictive temperature. Seven of them are related to cell cycle block phenotype at restrictive temperature, three of them in mitosis. Unequal distribution of regular chromosomes in the daughters is extensive in mis6 and mis12. Cells become inviable after rounds of cell division due to missegregation. The phenotype of mis5 is DNA replication defect and hypersensitivity to UV ray and hydroxyurea. mis5+ encodes a novel member of the ubiquitous MCM family required for the onset of replication. The mis5+ gene is essential for viability and functionally distinct from other previously identified members in fission yeast, cdc21+, nda1+, and nda4+. The mis11 mutant phenotype was the cell division block with reduced cell size. Progression of the G1 and G2 phases is blocked in mis11. The cloned mis11+ gene is identical to prp2+, which is essential for RNA splicing and similar to a mammalian splicing factor U2AF65.
Insights
Researchers identified 12 new genes controlling accurate chromosome inheritance in fission yeast. These genes are crucial for cell division, with mutations leading to chromosome missegregation and inviability.
Area of Science:
- Genetics
- Cell Biology
- Molecular Biology
Background:
- Accurate chromosome transmission during cell division is vital for genetic stability.
- Fission yeast is a model organism for studying fundamental cell processes.
Purpose of the Study:
- To isolate and characterize temperature-sensitive (ts) fission yeast mutants with high minichromosome loss rates.
- To identify novel genes involved in chromosome segregation and cell cycle regulation.
Main Methods:
- Screening 539 ts fission yeast strains for minichromosome instability using a colony color assay.
- Phenotypic analysis of mutants at restrictive temperatures, including cell cycle progression and chromosome distribution.
- Gene cloning and characterization of identified mutants.
Main Results:
- Identified 12 genetic loci (mis1-mis12) associated with minichromosome instability.
- Seven mutants exhibited cell cycle arrest, with three specifically affecting mitosis.
- mis6 and mis12 mutants showed extensive unequal chromosome distribution, leading to inviability.
- mis5+ encodes a novel MCM family member essential for DNA replication.
- mis11 mutant displayed cell division block and G1/G2 phase progression defects, with the gene identified as prp2+ involved in RNA splicing.
Conclusions:
- Discovered novel genes essential for precise chromosome transmission and cell cycle regulation in fission yeast.
- mis5+ represents a distinct, essential MCM family member crucial for replication initiation.
- mis11+ (prp2+) highlights a link between RNA splicing and cell cycle progression.