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Genetic analysis of the sam mutations, which induce sexual development with no requirement for nutritional starvation
S Katayama1, F Ozoe, R Kurokawa
1Department of Applied Bioscience and Biotechnology, Faculty of Life and Environmental Science, Shimane University, Matsue, Japan.
Abstract:
The cAMP pathway and the Ras pathway are the two major pathways to sexual development in the fission yeast Schizosaccharomyces pombe. To understand the cAMP pathway or the related pathway, we analyzed mutants that display a phenotype similar to cyr1-, that is, hyper-sporulation. Nine mutants termed sam (sporulation abnormal mutant), which are highly inclined to sexual development despite the presence of nitrogen sources, were partially characterized. Cyclic AMP was detected in all nine sam mutant cells, and over-expression of the adenylyl cyclase gene (cyr1) failed to suppress the hyper-sporulation phenotype of these sam mutants, suggesting that none of the sam mutants were likely to be allelic to cyr1. Epistatic tests of sam mutants showed that they were divided into two dominant and seven recessive mutants. Dominants were able to make spores in sam/sam+ heterodiploid cells upon abundant nutrients. Both two dominant mutants bypassed the inability to make spores in ras1 deficient diploid cells, suppressed the deficiency to execute sporulation in byr2 deficient diploid cells, but failed to suppress the byr1 deficiency. Two dominant mutations seem not to occur within the byr2 gene.
Insights
Researchers identified nine "sporulation abnormal" (sam) mutants in fission yeast, revealing new insights into sexual development pathways. These mutants exhibit hyper-sporulation, independent of nutrient availability, suggesting novel regulatory mechanisms.
Area of Science:
- Molecular Biology
- Genetics
- Yeast Biology
Background:
- Sexual development in fission yeast (Schizosaccharomyces pombe) is primarily regulated by the cAMP and Ras pathways.
- Understanding these pathways is crucial for deciphering developmental regulation.
- The cyr1 mutant exhibits hyper-sporulation, serving as a reference phenotype.
Purpose of the Study:
- To investigate novel genes and pathways involved in regulating sexual development in Schizosaccharomyces pombe.
- To characterize mutants exhibiting a hyper-sporulation phenotype, similar to cyr1 mutants.
Main Methods:
- Isolation and partial characterization of nine 'sporulation abnormal' (sam) mutants.
- Measurement of intracellular cyclic AMP levels.
- Complementation tests, including over-expression of adenylyl cyclase (cyr1).
- Epistatic analysis using heterodiploid cells with known mutations (ras1, byr2, byr1).
Main Results:
- Nine sam mutants were identified, all showing hyper-sporulation independent of nitrogen sources.
- Cyclic AMP was detected in all sam mutants, and cyr1 over-expression did not suppress the phenotype, indicating they are not allelic to cyr1.
- Mutants were classified into two dominant and seven recessive.
- The two dominant mutants bypassed ras1 deficiency, suppressed byr2 deficiency, but not byr1 deficiency, suggesting they act upstream or parallel to byr2 and downstream of byr1.
Conclusions:
- The identified sam mutants represent novel genetic components regulating sexual development in fission yeast.
- The dominant sam mutations likely do not reside within the byr2 gene, pointing to new regulatory interactions.
- These findings contribute to a deeper understanding of the interplay between cAMP, Ras, and other pathways governing yeast sexual differentiation.