Key Event Title
|Level of Biological Organization|
Key Event Components
|chromosome movement towards spindle pole||chromosome||abnormal|
Key Event Overview
AOPs Including This Key Event
|AOP Name||Role of event in AOP|
|Tubulin binding and aneuploidy||KeyEvent|
|All life stages||Moderate|
Key Event Description
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., 2016].
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 or enhanced polarizing microscopy on fixed or live cells [Schatten et al., 1985; 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; Mogessie and Schuh, 2017]. A quantitative description of microtubule dynamics and chromosome movement has also been obtained by time-lapse movies of mitotic cells expressing green fluorescence protein (GFP)-conjugate-tubulin [He and Cimini, 2016; Silkworth et al., 2012].
Domain of Applicability
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, Hu et al., 2018]. These studies showed that even exposure to low doses of spindle poisons, such as nocodazole, induced significant spindle abnormalities that manifested as loss of spindle organization, reduced spindle length at both meiosis I and II and congressional failure among other [Shen et al., 2005; Eichenlaub-Ritter et al., 2007]. Studies on altered chromosome dynamics in human oocytes are scarce. Long-term confocal imaging of chromosome dynamics in 50 human oocytes, collected from women undergoing intracytoplasmic sperm injection showed tri-directional anaphase and other types of chromosomal misalignment in many of them [Haverfield et al., 2017].
Evidence for Perturbation by Stressor
After in vitro exposure, bipolar spindle formation and chromosome alignment at the metaphase plate are severely disturbed in oocytes. Six hr later, the percentage of aneuploid oocytes is significantly increased about the control level (Eichenlaub-RItter et al 2007).
All tested concentrations induce spindle abnormalities in vitro. The lowest effective concentration for chromosome congression defects is 40 nM. The dose-response relationship are congruent with the proposed AOP (Shen et al 2005)
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.
Haverfield J, Dean NL, Noel D, Remillard-Labrosse G, Paradis V, Kadoch IJ, FitzHarris G. 2017. Tri-directional anaphases as a novel chromosome segregation defect in human oocytes. Hum Reprod 32:1293-1303.
He B, Cimini D. 2016. Using photoactivable GFP to study microtubule dynamics and chromosome segregation. Methods Mol Biol 1413:15-31.
Hu L-L, Zhou X, Zhang H-L, Wu L-L, Tang L-S, Chen L-L, Duan JL. 2018. Exposure to podophyllotoxin inhibits oocyte meiosis by disturbing meiotic spindle formation. Sci Report 8:10145.
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 F, Massarotti A, Yauk CL, Pacchierotti F, Russo A. 2016. The adverse outcome pathway (AOP) for chemical binding to tubulin in oocytes leading to aneuploid offspring. Environ Mol Mutagen 57:87-113.
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.
Mogessie B, Schuh M. 2017. Actin protects mammalian eggs against chromosome segregation errors. Science 357, eaal1647.
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.
Silkworth WT, Nardi IK, Paul R, Mogilner A, Cimini D (2012) Timing of centrosome separation is important for accurate chromosome segregation. Mol Cell Biol 23:401-411.