Genome-wide genetic analysis of polyploidy in yeast

Abstract

Polyploidy, increased sets of chromosomes, occurs during development, cellular stress, disease and evolution. Despite its prevalence, little is known about the physiological alterations that accompany polyploidy. We previously described 'ploidy-specific lethality', where a gene deletion that is not lethal in haploid or diploid budding yeast causes lethality in triploids or tetraploids. Here we report a genome-wide screen to identify ploidy-specific lethal functions. Only 39 out of 3,740 mutations screened exhibited ploidy-specific lethality. Almost all of these mutations affect genomic stability by impairing homologous recombination, sister chromatid cohesion, or mitotic spindle function. We uncovered defects in wild-type tetraploids predicted by the screen, and identified mechanisms by which tetraploidization affects genomic stability. We show that tetraploids have a high incidence of syntelic/monopolar kinetochore attachments to the spindle pole. We suggest that this defect can be explained by mismatches in the ability to scale the size of the spindle pole body, spindle and kinetochores. Thus, geometric constraints may have profound effects on genome stability; the phenomenon described here may be relevant in a variety of biological contexts, including disease states such as cancer.

Transformation, genomic instability and senescence mediated by platelet/megakaryocyte glycoprotein Ibα

“…The remarkably high level of DSBs in HFF-GpIba cells (Figure 4) is consistent with their elevated levels of p53 and differs somewhat from the situation in yeast where DSBs are increased only in tetraploids exposed to exogenous stress (Storchova et al, 2006). Genotoxicity in GpIba overexpressing cells could also arise as a direct result of tetraploidy and/or from dysmorphic nuclear changes (Figures 4 and 5).…”

“…These tumors, along with in vitro maintained cells, eventually reacquired apparently diploid genomes (Figures 2b and c), suggesting that long-term tetraploidy is actually detrimental (Andalis et al, 2004;Comai, 2005;Storchova et al, 2006). Our finding that (c) The Oncomine database was queried for DNA microarray studies documenting the overexpression of GpIba in primary human tumor samples.…”

“…Transcriptional profiling showed that 107 genes were differentially expressed between diploid and tetraploid Rat1a-GpIba cells. Although it seems likely that this group plays a role in promoting, maintaining or responding to tetraploidy, it was notable for its lack of genes functioning in homologous recombination, sister chromatid cohesion or mitotic spindle function, which are implicated in the survival of yeast tetraploids and in the assembly of Drosophila mitotic spindles (Storchova et al, 2006;Goshima et al, 2007). This discrepancy may reflect more the way by which these critical genes were identified than in actual functional differences.…”

The mitotic checkpoint kinase NEK2A regulates kinetochore microtubule attachment stability

“…In addition to providing a physical link between chromosomes and spindle microtubules, the kinetochore has an active function in orchestrating chromosome movements through microtubule motors and correcting spindle microtubule attachment to kinetochore via checkpoint sensors located at or near it (Yao et al, 2000;Ke et al, 2003;Fang and Fang 2007). Recent studies show that CIN results from high incidence of aberrant kinetochore microtubule attachments such as syntelic attachment (Storchova et al, 2006), which promotes tumorigenesis in p53-null cells (Fujiwara et al, 2005). An outstanding question is how kinetochore microtubule attachment errors are generated and corrected during cell division.…”

Depletion of Endonuclease G Selectively Kills Polyploid Cells

“…Recently, Storchova et al identified 39 gene deletions in a genome-wide screen that lead to ploidy-specific lethality in S. cerevisiae. 20 Most of these genes that are indispensable for the survival of polyploid cells are required for genomic stability, meaning that their absence impairs homologous recombination, sister chromatid cohesion, or mitotic spindle function. As the group of identified ploidy-specific lethal mutations is remarkably small and specific, Storchova et al suggest that altered genomic stability is the major physiological change accompanying polyploidization in budding yeast.…”