Contrasting mutation patterns in haploid and diploid cells from two yeast species

Area of Science:

• Evolutionary biology
• Genetics
• Molecular biology

Background:

• Mutation rates exhibit significant variation across taxa, influenced by natural selection.
• The drift barrier hypothesis suggests selection is less effective against mutator alleles in smaller populations, potentially increasing mutation rates.
• Rare cell types within a population may experience less selection on DNA replication and repair, leading to elevated mutation rates.

Purpose of the Study:

• To test the prediction that mutation rates are elevated in rare cell types.
• To investigate the influence of ploidy state (haploid vs. diploid) on mutation rates and spectra.
• To differentiate between inherent mutagenicity of a cell state and selection acting on cell type rarity.

Main Methods:

• Mutation accumulation experiments were conducted on haploid and diploid cells of the fission yeast Schizosaccharomyces pombe.
• Comparative analysis of mutation rates and spectra between haploid and diploid states.
• Utilizing yeast species where different ploidy levels represent rare cell types in natural populations.

Main Results:

• Schizosaccharomyces pombe showed a higher mutation rate in diploids, the rare cell type in this species.
• This finding is consistent with the hypothesis that mutation rates are elevated in rare cell types.
• The spectrum of mutations was also influenced by the ploidy state in both yeast species studied.

Conclusions:

• The study provides evidence supporting the drift barrier hypothesis's extension to cell type rarity.
• Limits to selection on mutation rates can manifest as variation within species, influenced by ploidy and population dynamics.
• The findings highlight the role of population structure and cell type frequency in shaping genome evolution.