The pedigree pattern of mating-type switching in Schizosaccharomyces pombe

Area of Science:

• * Molecular biology
• * Genetics
• * Cell biology

Background:

• * Previous observations in Schizosaccharomyces pombe indicated that only one of two parallel divisions in sister cells can be accompanied by a mating type switch, termed Miyata's rule.
• * This rule has been investigated in diploid cells heterozygous for the mat2-Pm-B102 allele.

Purpose of the Study:

• * To confirm Miyata's rule in pedigrees of diploid Schizosaccharomyces pombe cells.
• * To investigate the chromosomal level operation of Miyata's rule.
• * To model the mechanism of mating type switching based on cell cycle progression.

Main Methods:

• * Analysis of pedigrees of diploid Schizosaccharomyces pombe cells heterozygous for the mat2-Pm-B102 allele.
• * Observation of mating type switching events in individual chromosomes of sister cells.
• * Fitting a deterministic 3-step model to the frequency distribution of conjugation in four-lined cells (minipedigrees).

Main Results:

• * Miyata's rule was confirmed in the studied pedigrees.
• * The rule was observed to operate at the individual chromosome level, with simultaneous single-switch events occurring on different chromosomes in sister cells.
• * A 3-step model, coupled to the cell cycle, was fitted to empirical data, suggesting two successive precursory states for the switching signal.

Conclusions:

• * Miyata's rule is a robust phenomenon in Schizosaccharomyces pombe mating type determination.
• * The switching mechanism involves chromosomal events and is linked to the cell cycle.
• * The ultimate precursor to a mating type switch is likely a double-strand break at the smt locus.