Cell lineage asymmetry in Schizosaccharomyces pombe: unilateral transmission of a high-frequency state for mating-type switching in diploid pedigrees

Summary

Sporulation was followed in diploid pedigrees of the fission yeast Schizosacharomyces pombe of the genotype h ⁹⁰ //h ^−U. From the pattern of dividing cells and asci over 6–8 cell cyles information was gathered on the underlying laws regulating mating-type switching in this year. The results are discussed in relation to the introduction and transmission of double-strand breaks at the smt signal dose to the mat1 cassette. Such cuts have previously been reported as being a prerequisite for mating-type switching. The general criteria appear as follows. Each cell giving rise to a switch carries a cut at smt. A newly switched cassette is not associated with a cut. The sister cell to a newly switched cell retains bot the original cassette and the double-strand cut. Most of the time a “virgin” cell without the cut divides unequally so that one and only one of the daugthers obtains a cut. The consequence of these criteria is that long series of switch after switch in the same direction (“recurrent swtiching”) were observed in the pedigrees.