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Ploidy dictates repair pathway choice under DNA replication stress
1Department of Molecular Biology and Genetics, College of Agriculture and Life Sciences, Cornell University, Ithaca, New York 14853, USA.
Genetics
|January 19, 2011
Summary
A defective minichromosome maintenance (MCM) helicase causes replication stress, but only diploid cells show genetic instability (GIN) due to distinct DNA repair pathway choices. Ploidy dictates genome integrity maintenance, revealing a fundamental haplophase-diplophase difference.
Area of Science:
- Cell Biology
- Genetics
- Molecular Biology
Background:
- Replication stress is a critical factor in genome instability and cancer.
- The minichromosome maintenance (MCM) helicase is essential for DNA replication.
- Ploidy, the number of chromosome sets, can influence cellular responses.
Purpose of the Study:
- To investigate the role of ploidy in the cellular response to replication stress caused by a defective MCM helicase allele.
- To elucidate the distinct DNA repair pathways utilized by haploid and diploid cells under replication stress.
- To understand how ploidy impacts genome integrity maintenance.
Main Methods:
- Utilized a defective minichromosome maintenance (MCM) helicase allele in yeast (Saccharomyces cerevisiae).
- Compared the responses of haploid and diploid yeast mutants to replication stress.
- Analyzed DNA repair pathway utilization through genetic and molecular assays.
- Investigated the Mcm4(Chaos3) allele in mouse models for mammary gland tumor predisposition.
Main Results:
- A defective MCM helicase allele caused replication stress in both haploid and diploid yeast.
- Only diploid mutants exhibited G2/M cell cycle delay, severe genetic instability (GIN), and reduced viability.
- Haploid mutants favored fork restart pathways (Rad6-dependent), while diploid mutants utilized double-strand break repair pathways (Rad52 and MRX-dependent).
- The choice of repair pathway was irreversible and independent of repair enzyme availability.
- Ploidy, not mating type heterozygosity, determined the GIN phenotype.
Conclusions:
- Ploidy-specific responses to replication stress are dictated by early events influencing DNA repair pathway choice.
- Defective MCM helicase leads to GIN specifically in certain cell types (diploids), highlighting a fundamental difference between haplophase and diplophase.
- This study uncovers a crucial distinction in genome integrity maintenance strategies between haploid and diploid cells.
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