Spontaneous deletions and reciprocal translocations in Saccharomyces cerevisiae: influence of ploidy

Abstract

SummaryStudying spontaneous chromosomal rearrangements throws light on the rules underlying the genome reshaping events occurring in eukaryotic cells, which are part of the evolutionary process. In Saccharomyces cerevisiae, translocation and deletion processes have been frequently described in haploids, but little is known so far about these processes at the diploid level. Here we investigated the nature and the frequency of the chromosomal rearrangements occurring at this ploidy level. Using a positive selection screen based on a particular mutated allele of the URA2 gene, spontaneous diploid revertants were selected and analysed. Surprisingly, the diploid state was found to be correlated with a decrease in chromosome rearrangement frequency, along with an increase in the complexity of the rearrangements occurring in the target gene. The presence of short DNA tandem repeat sequences seems to be a key requirement for deletion and reciprocal translocation processes to occur in diploids. After discussing the differences between the haploid and diploid levels, some mechanisms possibly involved in chromosome shortening and arm exchange are suggested.

The Ty1 LTR-retrotransposon population in Saccharomyces cerevisiae genome: dynamics and sequence variations during mobility

“…In 62 of the revertants, the ATCase‐reactivating rearrangement corresponds to deletion events (27 revertants), translocation events (two revertants) and duplication events (33 revertants). All these categories have been described previously in the FL100 background (Welcker et al , 2000; Schacherer et al , 2004; Tourrette et al , 2007).…”

“…Chromosomal rearrangements can restore ATCase expression, resulting in Ura + revertants. In an FL100 background, this positive screening has been found to act as a real transposon‐trap, because up to 70% of the rearrangements selected consisted of de novo integrase‐mediated Ty1 insertions (Roelants et al , 1995; Tourrette et al , 2007).…”

Ploidy influences cellular responses to gross chromosomal rearrangements in saccharomyces cerevisiae

“…Unfortunately, haploid strains could not be generated from diploids carrying segmental deletions and nonreciprocal translocations. In fact, these rearrangements involve essential genes, which result in non-viable haploid strains [20,21]. Meiosis was therefore induced in the diploid mutant strains carrying an aneuploidy or a segmental duplication.…”

“…Several types of GCRs were selected depending on the ploidy context. Although aneuploidy and nonreciprocal translocation have been isolated in diploid strains, single gene duplication occurs only in haploids [19-21]. By contrast, segmental duplication and deletion have been described in both contexts [21-23].…”

“…Although aneuploidy and nonreciprocal translocation have been isolated in diploid strains, single gene duplication occurs only in haploids [19-21]. By contrast, segmental duplication and deletion have been described in both contexts [21-23]. To analyze the effects of ploidy on cellular responses, haploid and diploid revertants carrying the same GCRs were selected by inducing meiosis in diploid mutants or crossing haploid revertants with a strain bearing the URA2 mutated allele.…”