Key Event Overview
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AOPs Including This Key Event
|AOP Name||Event Type||Essentiality|
|Chemical binding to tubulin in oocytes leading to aneuploid offspring||KE|
Level of Biological Organization
How this Key Event works
The majority of work for this key event has been conducted in mouse oocytes in vitro. The key event is altered chromosome dynamics at metaphase/anaphase transition. Normal chromosome dynamics refers to the proper alignment and separation of the chromosomes at metaphase and anaphase, respectively. Altered chromosome dynamics refers to the incorrect separation of chromosomes involving an abnormal spindle and a defective cell cycle checkpoint [reviewed in Marchetti et al. 2015].
In oocytes, the meiotic cell division is characterized by unique features with respect to the mitotic process, including: (1) the process by which the meiotic spindle is formed; (2) chromosome organization in bivalents (homologous pairs) with sister kinetochores acting as a functional unit; (3) the role of homologous recombination to ensure proper biorientation and stability of the bivalent structure; (4) the direct entry of oocytes into the second meiotic division, following the first anaphase; and, (5) the lack of chromatin decondensation and formation of the nuclear membrane.
How it is Measured or Detected
Altered chromosome dynamics at metaphase/anaphase is generally assessed by confocal microscopy on fixed or live cells [Shen et al. 2005; Eichenlaub-Ritter et al. 2007; Schuh and Ellenberg 2007]. Antibodies against centromeric proteins and multicolour fluorescence in situ hybridization (FISH) are useful approaches to follow chromosome congression: for example, distances between kinetochores and spindle midzone are used to evaluate the dynamics of chromosome congression; interkinetochore distances may be measured to verify a correct biorientation [Shen et al. 2005; Eichenlaub-Ritter et al. 2007; Schuh and Ellenberg 2007; McGuinness et al. 2009; Lane et al. 2012].
Consider the following criteria when describing each method: 1. Is the assay fit for purpose? Yes 2. Is the assay directly or indirectly (i.e. a surrogate) related to a key event relevant to the final adverse effect in question? Directly 3. Is the assay repeatable? Yes 4. Is the assay reproducible? Yes
Evidence Supporting Taxonomic Applicability
Detailed studies are available reporting defects of chromosome congression after in vitro exposure of mouse oocytes to spindle poisons [Shen et al. 2005; Eichenlaub-Ritter et al. 2007].
Eichenlaub-Ritter U, Winterscheidt U, Vogt E, Shen Y, Tinneberg HR, Sorensen R. 2007. 2-methoxyestradiol induces spindle aberrations, chromosome congression failure, and nondisjunction in mouse oocytes. Biol Reprod 76:784-793.
Lane SI, Yun Y, Jones KT. 2012. Timing of anaphase-promoting complex activation in mouse oocytes is predicted by microtubule-kinetochore attachment but not by bivalent alignment or tension. Development 139:1947-1955.
Marchetti A, Massarotti A, Yauk CL, Pacchierotti F, Russo A. Submitted. The adverse outcome pathway (AOP) for chemical binding to tubulin in oocytes leading to aneuploid offspring. Environ Mol Mutagen.
McGuinness BE, Anger M, Kouznetsova A, Gil-Bernabe AM, Helmhart W, Kudo NR, Wuensche A, Taylor S, Hoog C, Novak B, Nasmyth K. 2009. Regulation of APC/C activity in oocytes by a Bub1-dependent spindle assembly checkpoint. Curr Biol 19:369-380.
Schuh M, Ellenberg J. 2007. Self-organization of MTOCs replaces centrosome function during acentrosomal spindle assembly in live mouse oocytes. Cell 130:484-498.
Shen Y, Betzendahl I, Sun F, Tinneberg HR, Eichenlaub-Ritter U. 2005. Non-invasive method to assess genotoxicity of nocodazole interfering with spindle formation in mammalian oocytes. Reprod Toxicol 19:459-471.