Genome rearrangements are changes to cells chromosomes that can cause pathology. Genome rearrangements common in cells, and arise due to errors in cell duplication. One type, called a large scale rearrangement, is particularly deleterious to a cell;it can change the number of certain genes, can mutate a gene, and can generate unstable chromosomes that continue to rearrange. In humans it is clear that large scale rearrangements indeed cause significant pathology, a most famous case being the Philadelphia Chromosome where parts of Chr22 and Ch9 fuse, forming a gene fusion that causes leukemia. Recent deep sequencing of cancer genomes reveals a bewildering array of large scale changes;in some chromosomes appear to have exploded and pieced back together randomly, in others there are chains of chromosomes joined together. As mentioned, large scale rearrangements also form inherently unstable chromosomes, including dicentrics that contain two centromeres and are thus unstable. One particular rearrangement arises at a high frequency in pancreatic cancer cells. It's called a fold back inversion, where a chromosome fuses with itself such that it should form a dicentric. Why are fold back inversions of particular interest to us? We have developed a budding yeast chromosome instability system allows us to study large scale rearrangements. We have now identified a fold back inversion type chromosome change (that we call an inverted fusion), in yeast, that indeed forms dicentrics. Such fusions appear to occur frequently in the yeast genome, though we do not yet know where or how frequently. We have studied the mechanism of how this yeast inverted fusion/fold back inversion forms, and propose a model we can test. In this proposal, we will identify sequences in yeast that fuse to form dicentrics. This will provide information on how common fusions may be in the human genome. We will study how fusions occur, important for knowing how fusions occur in pancreatic cells and how they are avoided in normal human cells. Finally, we will establish genetic systems in fission yeast and in human cells to study fold back inversions. This will allow us to begin to directly understand how foldback inversion types of rearrangements arise in pancreatic cancer.

Public Health Relevance

Chromosome rearrangements and dicentrics cause human disease, and they form is not well understood. Using budding, fission and human cell systems, we will study how one prominent rearrangement, termed a inverted or fold back inversion, generates dicentric chromosomes. Fold back inversions are particularly of interest as they are common in pancreatic cancer.

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National Institute of General Medical Sciences (NIGMS)
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Molecular Genetics B Study Section (MGB)
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Willis, Kristine Amalee
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University of Arizona
Schools of Arts and Sciences
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Vinton, Peter J; Weinert, Ted (2017) A Slowed Cell Cycle Stabilizes the Budding Yeast Genome. Genetics 206:811-828
Beyer, Tracey; Weinert, Ted (2016) Ontogeny of Unstable Chromosomes Generated by Telomere Error in Budding Yeast. PLoS Genet 12:e1006345
Kaochar, Salma; Shanks, Lisa; Weinert, Ted (2010) Checkpoint genes and Exo1 regulate nearby inverted repeat fusions that form dicentric chromosomes in Saccharomyces cerevisiae. Proc Natl Acad Sci U S A 107:21605-10
Paek, Andrew L; Jones, Hope; Kaochar, Salma et al. (2010) The role of replication bypass pathways in dicentric chromosome formation in budding yeast. Genetics 186:1161-73
Paek, Andrew L; Kaochar, Salma; Jones, Hope et al. (2009) Fusion of nearby inverted repeats by a replication-based mechanism leads to formation of dicentric and acentric chromosomes that cause genome instability in budding yeast. Genes Dev 23:2861-75