Upstream eventDepolymerization, Microtubule
Key Event Relationship Overview
AOPs Referencing Relationship
|AOP Name||Directness||Weight of Evidence||Quantitative Understanding|
|Chemical binding to tubulin in oocytes leading to aneuploid offspring||directly leads to||Moderate|
|Homo sapiens||Homo sapiens||Moderate||NCBI|
|Sea urchin sp.||unidentified sea urchin||Moderate||NCBI|
Life Stage Applicability
How Does This Key Event Relationship Work
Spindle organization and function requires normal microtubule dynamics. When microtubule polymerization is affected (i.e., depolymerization), spindle organization and function is impaired.
Weight of Evidence
Microtubules polymerization is critical to 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).
Empirical Support for Linkage
Include consideration of temporal concordance here
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. (1984) 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. (2010), 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. (2003) showed that 1 uM 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 or 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
Is it known how much change in the first event is needed to impact the second? Are there known modulators of the response-response relationships? Are there models or extrapolation approaches that help describe those relationships?
Limited quantitative understanding. However, data from Salmon et al. (1984) establish a dose-response relationship for both endpoints and two chemical agents, which could thus be modeled.
Evidence Supporting Taxonomic Applicability
Data were produced in sea urchins, mice and humans eggs and embryos. This KER should be applicable to any eukaryotic organism.
Wadsworth et al. Variations on a theme: spindle assembly in diverse cells. Protoplasma 2011, 248, 439-446.
Walczak CE and R Heald. Mechanisms of mitotic spindle assembly and function. Int. Reviews Cytology 2008, 265, 111-158.
Wittman et al. The spindle: a dynamic assembly of microtubules and motors. Nature Cell Biology 2011, 3, e28-234.