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Identification of a new class of negative regulators affecting sporulation-specific gene expression in yeast
1Waksman Institute of Microbiology, Rutgers, the State University of New Jersey, Piscataway 08854-8020, USA.
Abstract:
We characterized two yeast loci, MDS3 and PMD1, that negatively regulate sporulation. Initiation of sporulation is mediated by the meiotic activator IME1, which relies on MCK1 for maximal expression. We isolated the MDS3-1 allele (encoding a truncated form of Mds3p) as a suppressor that restores IME1 expression in mck1 mutants. mds3 null mutations confer similar suppression phenotypes as MDS3-1, indicating that Mds3p is a negative regulator of sporulation and the MDS3-1 allele confers a dominant-negative phenotype. PMD1 is predicted to encode a protein sharing significant similarity with Mds3p. mds3 pmd1 double mutants are better suppressors of mck1 than is either single mutant, indicating that Mds3p and Pmd1p function synergistically. Northern blot analysis revealed that suppression is due to increased IME1 transcript accumulation. The roles of Mds3p and Pmd1p are not restricted to the MCK1 pathway because mds3 pmd1 mutations also suppress IME1 expression defects associated with MCK1-independent sporulation mutants. Furthermore, mds3 pmd1 mutants express significant levels of IME1 even in vegetative cells and this unscheduled expression results in premature sporulation. These phenotypes and interactions with RAS2-Val19 suggest that unscheduled derepression of IME1 is probably due to a defect in recognition of nutritional status.
Insights
Two yeast genes, MDS3 and PMD1, negatively regulate sporulation by controlling IME1 expression. Mutations in these genes restore sporulation in certain mutants, indicating their role in nutrient sensing.
Area of Science:
- Molecular and Cellular Biology
- Yeast Genetics
- Developmental Biology
Background:
- Sporulation initiation in yeast is regulated by the meiotic activator IME1.
- IME1 expression is dependent on MCK1 for maximal activity.
- Understanding negative regulators of sporulation is crucial for deciphering developmental pathways.
Purpose of the Study:
- To identify and characterize genes that negatively regulate yeast sporulation.
- To investigate the role of MDS3 and PMD1 in controlling IME1 expression.
- To elucidate the mechanism by which MDS3 and PMD1 affect sporulation under different conditions.
Main Methods:
- Genetic screening for suppressors of mck1 mutants.
- Isolation and characterization of MDS3-1 allele and mds3 null mutations.
- Construction and analysis of mds3 pmd1 double mutants.
- Northern blot analysis to quantify IME1 transcript levels.
- Phenotypic analysis of sporulation and IME1 expression in vegetative cells.
Main Results:
- MDS3 and PMD1 were identified as negative regulators of sporulation.
- MDS3-1 allele and mds3 null mutations restore IME1 expression in mck1 mutants.
- Mds3p and Pmd1p function synergistically, and their mutations suppress MCK1-independent defects.
- mds3 pmd1 mutants exhibit increased IME1 transcript accumulation and premature sporulation, even in vegetative cells.
- These phenotypes suggest a defect in nutritional status recognition.
Conclusions:
- MDS3 and PMD1 are key negative regulators of yeast sporulation, acting through IME1.
- These genes play a role beyond the MCK1 pathway, influencing sporulation in response to nutritional cues.
- Dysregulation of MDS3 and PMD1 leads to unscheduled IME1 expression and premature sporulation, highlighting their importance in developmental control.