Upstream eventDepolymerization, Microtubule
Key Event Relationship Overview
AOPs Referencing Relationship
|AOP Name||Adjacency||Weight of Evidence||Quantitative Understanding|
|Chemical binding to tubulin in oocytes leading to aneuploid offspring||adjacent||Moderate|
|Homo sapiens||Homo sapiens||Moderate||NCBI|
|Sea urchin sp.||unidentified sea urchin||Moderate||NCBI|
Life Stage Applicability
Key Event Relationship Description
Spindle organization and function requires normal microtubule dynamics. When microtubule polymerization is affected (i.e., depolymerization), spindle organization and function is impaired.
Evidence Supporting this KER
The weight of evidence for this KER is moderate. Microtubule polymerization is critical for the appropriate functioning of the spindle. Mitotic and meiotic spindles differ in how they are assembled. In mitotic cells, spindle organization is controlled by centrioles [Walczak and Heald, 2008; Wadsworth et al., 2011; Wittman et al., 2011]. However, centrioles are absent in mammalian oocytes [Manandhar et al., 2005] and meiotic spindle is organized by multiple microtubule organizing centers (MTOCs). Gradually, MTOCs coalesce and surround the chromosomes and subsequently elongate in a typical barrel-shape bipolar spindle [Schuh and Ellenberg, 2007; Clift and Schuh, 2015], similar to the mitotic spindle. Assembly, elongation and function of the spindle requires proper microtubule dynamics. If microtubules become depolymerized, it affects the structural integrity of the spindle resulting in abnormal spindles that are characterized by reduction in microtubule density, loss of barrel shape, mono- or multi-polar spindle, and reduced distance between the poles [Ibanez et al., 2003; Shen et al., 2005; Eichenlaub-Ritter et al., 2007; Xu et al., 2012]. The normal biology underlying the critical role of proper microtubule polymerization for the appropriate structure and function of spindle is well established, and it is widely understood that chemicals that alter microtubule dynamics cause spindle disorganization [Manandhar et al., 2005; Schuh and Ellenberg, 2007].
Several papers have explored the temporal and incidence relationship between microtubule depolymerization and appearance of spindle abnormalities, providing empirical evidence to support this KER in a variety of species. For example, Salmon et al.  showed that within 20 seconds of colchicine or colcemid administration in sea urchin embryos, microtubule depolymerization occurs. This leads to spindle abnormalities at the same concentration that occurs a few minutes later. In Liu et al. , in vitro culturing of human oocytes in the presence of 10 uM colchicine prevented microtubule polymerization and because of this, meiotic spindle did not form (i.e., exposure led to failure to progress to meiosis II supporting temporal concordance). Ibanez et al.  showed that 1 µM colcemid caused microtubule depolymerization that led to smaller spindles and lower microtubule density in mouse oocytes within 15 minutes of exposure, demonstrating temporal and incidence concordance.
Uncertainties and Inconsistencies
There are not a lot of studies that have explored these two events within the same experiment. Thus, the empirical evidence is not based on a large number of papers. However, the papers that are available are of sound experimental design that address both time and incidence relationships, and span three species.
Quantitative Understanding of the Linkage
Limited quantitative understanding. However, data from Salmon et al.  establish a dose-response relationship for both endpoints and two chemical agents, which could thus be modeled.
Known modulating factors
Known Feedforward/Feedback loops influencing this KER
Domain of Applicability
Data were produced in sea urchins, mice and human eggs and embryos. This KER should be applicable to any eukaryotic organism.
Clift D, Schuh M. 2015. A three-step MTOC fragmentation mechanism facilitate bipolar spindle assembly in mouse oocytes. Nat Commun 6:7217.
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.
Ibanez E, Albertini DF, Overstrom EW. 2003. Demecolcine-induced oocyte enucleation for somatic cell cloning: Coordination between cell-cycle egress, kinetics of cortical cytoskeletal interactions, and second polar body extrusion. Biol Reprod 68:1249–1258.
Liu S, Li Y, Feng HL, Yan JH, Li M, Ma SY, Chen ZJ. 2010. Dynamic modulation of cytoskeleton during in vitro maturation in human oocytes. Am J Obstet Gynecol 151:e1–7.
Manandhar G, Schatten H, Sutovsky P. 2005. Centrosome reduction during gametogenesis and its significance. Biol Reprod 72:2-13.
Salmon ED, McKeel M, Hays T. 1984. Rapid rate of tubulin dissociation from microtubules in the mitotic spindle in vivo measured by blocking polymerization with colchicine. J Cell Biol 99:1066-1075.
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.
Wadsworth P, Lee WL, Murata T, Baskin TI. 2011. Variations on a theme: spindle assembly in diverse cells. Protoplasma 248:439-446.
Walczak CE and R Heald. 2008. Mechanisms of mitotic spindle assembly and function. Int. Rev Cytol 265:111-158.
Wittman T, Hyman A, Desai A. 2011. The spindle: a dynamic assembly of microtubules and motors. Nat Cell Biol 3:e28-234.
Xu XL, Ma W, Zhu YB, Wang C, Wang BY, An N, An L, Liu Y, Wu ZH, Tian JH. 2012. The microtubule-associated protein ASPM regulates spindle assembly and meiotic progression in mouse oocytes. PLoS One 7:e49303.