Different frameshift mutation spectra in non-repetitive DNA of MutSalpha- and MutLalpha-deficient fission yeast cells

Area of Science:

• * Molecular Biology
• * Genetics
• * Yeast Genetics

Background:

• * DNA mismatch repair (MMR) pathways are crucial for maintaining genomic stability by correcting errors during DNA replication.
• * Deficiencies in MMR proteins can lead to increased mutation rates and are associated with various diseases, including cancer.
• * Understanding the specific roles of MMR proteins and associated nucleases in mutation types is essential for comprehending genome instability.

Purpose of the Study:

• * To establish and utilize a frameshift reversion assay in Schizosaccharomyces pombe for detecting nucleotide deletions and insertions.
• * To investigate the impact of mutations in mismatch repair (MMR) genes (msh2, msh6, mlh1, pms1) and DNA nuclease genes (rad2, exo1) on frameshift mutation rates.
• * To characterize the specific types of mutations (e.g., 1bp deletions, 2bp insertions) that accumulate in different mutant strains.

Main Methods:

• * Development of a frameshift reversion assay in the fission yeast Schizosaccharomyces pombe.
• * Analysis of frameshift mutation rates in various MMR mutants (msh2, msh6, mlh1, pms1) and DNA nuclease mutants (rad2, exo1).
• * Characterization of mutation types, including 1bp deletions and 2bp insertions (CG to (CG)(2)), in different genetic backgrounds.

Main Results:

• * Frameshift mutation rates were significantly increased in MMR mutants (msh2, msh6, mlh1, pms1) and DNA nuclease mutants (rad2, exo1) compared to wild type.
• * MutSalpha-deficient strains (msh2, msh6) predominantly accumulated 1bp deletions.
• * MutLalpha-deficient strains (mlh1, pms1) accumulated significantly more 2bp CG insertions, and this accumulation depended on MutSalpha, Rad2, and Exo1 presence.

Conclusions:

• * The established frameshift reversion assay effectively detects deletions and insertions in Schizosaccharomyces pombe.
• * MMR and DNA nuclease pathways play critical roles in preventing specific types of frameshift mutations.
• * The accumulation of (CG)(2) duplications in MutLalpha-deficient strains is dependent on the coordinated action of MutSalpha, Rad2, and Exo1.