Characterization of a Murine Hypomorphic Allele of the Spindle Checkpoint Gene Bub1 and its Role in Tumorigenesis

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  • March 20, 2019
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  • Schliekelman, Mark Jason
    • Affiliation: School of Medicine, Curriculum in Genetics and Molecular Biology
Abstract
  • Bub1 is a serine/threonine kinase originally described as a core component of the spindle assembly checkpoint (SAC) mechanism in yeast. We produced mice harboring a Bub1 mutant allele lacking exons 2 and 3, resulting in a hypomorphic mutant expressed at less than 5% of wt levels. Despite this significant reduction, homozygous mutant animals are viable on a mixed 129P2/B6 or FVB background but display increased tumorigenesis with aging, whereas mice with a C57Bl/6J background die perinatally. Bub1 mutant murine embryonic fibroblasts (MEFs) display defects in chromosome congression to the metaphase plate, severe chromosome missegregation and aneuploidy accompanied by high levels of premature senescence. Mutant MEFs have a robust SAC in response to nocodazole treatment, but an impaired response to Taxol. The significant reduction in SAC response to Taxol but not nocodazole, coupled with the reduced binding of BubR1 but not Mad2, indicates that Bub1 is particularly critical for the SAC response to a lack of tension on kinetochores. In light of the tumor suppressor p53’s role in induction of senescence and prevention of aneuploidy, we assessed inactivation of p53 in Bub1 mutant MEFs. p53 loss eliminates increased senescence in Bub1Δ2-3/Δ2-3 MEFs, but does restore proliferation in Bub1Δ2-3/Δ2-3 MEF cultures or rescue perinatal lethality of Bub1Δ2-3/Δ2-3 animals. Despite its role as a guardian of genomic integrity, p53 inactivation does not increase aneuploidy in Bub1 mutant cells.
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  • In Copyright
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  • Van Dyke, Terry A.
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  • October 19, 2010

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