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Updated: Jul 2, 2026
A Deep-sequencing-assisted, Spontaneous Suppressor Screen in the Fission Yeast Schizosaccharomyces pombe
Published on: March 7, 2019
Fis1 deficiency selects for compensatory mutations responsible for cell death and growth control defects
1W Harry Feinstone Department of Molecular Microbiology and Immunology, Johns Hopkins University Bloomberg School of Public Health, Baltimore, MD 21205, USA.
Abstract:
Genetic mutations affecting mitochondrial fission and fusion proteins cause human neurological disorders, but are assumed to be well tolerated in yeast. The conserved mitochondrial fission protein Dnm1/Drp1 is required for normal mitochondrial division, but also promotes cell death in mammals and yeast. Fis1, an outer mitochondrial membrane-anchored receptor for Dnm1/Drp1, also can promote cell death in mammals, but appears to have prosurvival activity in yeast. Here we report that deletion of the FIS1 gene in yeast consistently results in acquisition of a secondary mutation that confers sensitivity to cell death. In several independently derived FIS1 knockouts, tiling arrays and genomic sequencing identified the secondary mutation as a premature termination in the same stress-response gene, WHI2. The WHI2 mutation rescues the mitochondrial respiratory defect (petite formation) caused by FIS1 deficiency, but also causes a failure to suppress cell growth during amino-acid deprivation. Thus, loss of Fis1 drives the selection for specific compensatory mutations that confer defective growth control and cell death regulation, characteristic of human tumor cells. The important long-term survival function of Fis1 that is compensated by WHI2 mutation appears to be independent of fission factor Dnm1/Drp1 and its adaptor Mdv1, but may be mediated through a second adaptor Caf4, as WHI2 is also mutated in a CAF4 knockout.
Insights
Loss of yeast Fis1 protein triggers compensatory WHI2 mutations, impacting cell death and growth control. These mutations rescue mitochondrial defects but impair stress responses, mimicking cancer cell characteristics.
Area of Science:
- Cell Biology
- Genetics
- Molecular Biology
Background:
- Mitochondrial dynamics proteins, like Dnm1/Drp1 and Fis1, are crucial for mitochondrial fission and fusion.
- While Dnm1/Drp1 is conserved in promoting cell death, Fis1's role varies, acting in cell death in mammals but prosurvival in yeast.
- Genetic mutations in these proteins are linked to human neurological disorders.
Purpose of the Study:
- To investigate the consequences of Fis1 gene deletion in yeast.
- To identify secondary mutations that arise in Fis1 knockouts.
- To understand the functional impact of these compensatory mutations on cell death and growth regulation.
Main Methods:
- Yeast genetics: FIS1 gene knockout.
- Genomic analysis: Tiling arrays and genomic sequencing to identify mutations.
- Phenotypic analysis: Assessing mitochondrial respiratory defects (petite formation) and cell growth during amino-acid deprivation.
Main Results:
- Deletion of FIS1 consistently led to secondary mutations in the WHI2 gene.
- The WHI2 mutation caused premature termination, rescuing the petite phenotype associated with FIS1 deficiency.
- However, the WHI2 mutation resulted in impaired growth suppression during amino-acid deprivation.
- Fis1's survival function, compensated by WHI2, appears independent of Dnm1/Drp1 and Mdv1, potentially involving Caf4.
Conclusions:
- Loss of Fis1 imposes selection pressure for compensatory WHI2 mutations in yeast.
- These WHI2 mutations confer defective growth control and cell death regulation, resembling human tumor cells.
- Fis1 plays a critical long-term survival role in yeast, mediated possibly through Caf4, which is compensated by WHI2 mutations.
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