The Schizosaccharomyces pombe spindle checkpoint protein mad2p blocks anaphase and genetically interacts with the anaphase-promoting complex

Abstract

The spindle checkpoint monitors mitotic spindle integrity and the attachment of kinetochores to the spindle. Upon sensing a defect the checkpoint blocks cell cycle progression and thereby prevents chromosome missegregation. Previous studies in budding yeast show that the activated spindle checkpoint inhibits the onset of anaphase by an unknown mechanism. One possible target of the spindle checkpoint is anaphase promoting complex (APC), which controls all postmetaphase events that are blocked by spindle checkpoint activation. We have isolated mad2, a spindle checkpoint component in fission yeast, and shown that mad2 overexpression activates the checkpoint and causes a cell cycle arrest at the metaphase-to-anaphase transition. In addition to the observation that mad2-induced arrest can be partially relieved by mitosis-promoting factor inactivation, we present genetic evidence consistent with the hypothesis that the spindle checkpoint imposes a cell cycle arrest by inhibiting APCdependent proteolysis.

The Actomyosin Ring Recruits Early Secretory Compartments to the Division Site in Fission Yeast

“…Thus, to assess the specific contribution of Cdc15p independently from the actomyosin ring, we observed the spatial distribution of the secretory pathway proteins in wild-type and temperaturesensitive cdc15-140 mutant cells arrested in metaphase by overexpressing the spindle assembly checkpoint component Mad2p (He et al, 1997) under the nmt1 promoter (Maundrell, 1990). Briefly, Mad2p overexpression was induced for 20 h at the permissive temperature of 24°C followed by a temperature shift-up for 4 h at 36°C.…”

SAC‐ing mitotic errors: How the spindle assembly checkpoint (SAC) plays defense against chromosome mis‐segregation

“…C: If the spindle checkpoint is not functional, an unattached kinetochore will not promote a cell cycle arrest prior to anaphase, and chromosome mis-segregation may result. [He et al, 1997[He et al, , 1998]. Although fission yeast Mph1p is the structural and functional homologue of budding yeast Mps1p [He et al, 1998;reviewed in Winey and Huneycutt, 2002], Mph1p is not essential for viability or spindle pole body duplication in fission yeast [He et al, 1998].…”

“…Mad2p abundance is also increased in mammary epithelial cells lacking p53, another tumor suppressor [Pati et al, 2004]. Although it is unclear how increased production of Mad2p may contribute to tumorigenesis since overproduction of Mad2p activates the SAC in yeast [He et al, 1997], this situation may be analogous to the requirement for up-regulation of SAC proteins in rapidly dividing tissues.…”

Identification of frequent impairment of the mitotic checkpoint and molecular analysis of the mitotic checkpoint genes, hsMAD2 and p55CDC, in human lung cancers

“…As an initial step, we examined 21 lung cancer cell lines for the presence of mutations in the hsMAD2 gene, a key component in the sensing and executing mechanism that delays the onset of anaphase in response to a spindle defect (Li and Benezra, 1996;Chen et al, 1996;He et al, 1997). In the reverse transcription-polymerase chain reactionsingle strand conformation polymorphism (RT ± PCR ± SSCP) analysis, several lung cancer cell lines exhibited distinct mobility shifts, which could be classi®ed into two groups, i.e., Group 1: SK-LC-10 and ACC-LC-97 and Group 2: PC-1, QG90 and SBC3 (Figure 3).…”