Upstream eventDisorganization, Spindle
Altered, Meiotic chromosome dynamics
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|
Life Stage Applicability
|All life stages||Moderate|
Key Event Relationship Description
Incorrect spindle organization refers to lack of the bipolar organization of the spindle within the cell. This bipolar organization is required to assure that chromosomes will align correctly to the metaphase plate prior to equal division between the daughter cells. Alternatively, incorrect spindle formation can lead to shorter spindle fibers and/or incorrect length of these fibers, which leads to chromosome misalignment.
In this KER, chemicals that cause spindle disorganization lead to altered meiotic chromosome dynamics. The relationship between spindle disorganization and altered chromosome dynamics can occur in both somatic and in germ cells; however, this relationship focuses on female meiotic chromosomes because of the differences in how the meiotic spindle is assembled in oocytes with respect to other cell types (i.e., lack of centrioles and dependency on microtubule organizing centers). Interestingly, some studies investigating the effects of protein deficiencies in mouse oocytes provide direct evidence of the events involved in the KER [McGuinnes et al., 2009; Ou et al., 2010; Baumann et al., 2017]. For example, targeting deletion of Bub1 in mouse oocytes caused dysregulation of spindle assembly and leads to defective chromosome congression [McGuinness et al., 2009]. After depletion of p38a in mouse oocytes, a MTCO component, aberrant spindle organization, including defective or multipolar spindles are more than 3 times more frequent than in control mice, while there is an 8-fold increase in chromosome congression defects [Ou et al., 2010]. Finally, in a study carried out using an oocyte conditional pericentrin knockout mouse model and live cell imaging, alterations in spindle size have been observed, together with delay in meiotic spindle formation following in vitro culture of cumulus-enclosed oocytes. These abnormalities were associated with a significant increase in the number of unattached kinetochores and merotelic attachments, as well as, an increase in misaligned and uncongressed chromosomes [Baumann et al., 2017].
Evidence Supporting this KER
Moderate, based on strong biological plausibility and weak emprical evidence.
The weight of evidence for this KER is moderate. It is well understood that the proper organization of the meiotic spindle is necessary in order for chromosomes to correctly align. This process has been extensively described in the literature. For a recent comprehensive review on this topic, please see Bennabi et al. .
Although it is very common to measure spindle abnormalities (i.e., spindle disorganization), few studies have examined meiotic chromosome dynamics. Thus, there are insufficient empirical data examining the concordance between spindle abnormalities and chromosome dynamics.
However, two in vitro studies on mouse eggs have investigated spindle abnormalities and chromosome congression defects within individual studies (i.e., both endpoints measured). These studies used nocodazole and 2-methoxyestradiol to demonstrate that there is a temporal and dose-response related consistency among the events; i.e., downstream KEs are occurring at higher doses and later time points than upstream KEs [Shen et al., 2005; Eichenlaub-Ritter et al., 2007]. Further evidence supporting this KER has been collected in somatic cells, especially in vitro (reviewed in Silkworth and Cimini, 2012).
Uncertainties and Inconsistencies
There is not extensive empirical data this KER, however, the available data does not show inconsistencies.
Quantitative Understanding of the Linkage
Although there are no inconsistent results reported, it is important to note that very few studies have measured chromosome dynamics in oocytes in general. Thus, there is a large amount of uncertainty surrounding the qualitative and quantitative association between these two endpoints.
As noted above, very few studies have examined both KE2 and KE3 under the same experimental conditions, especially in oocytes. In addition, spindle abnormalities (KEupstream) and altered chromosome dynamics (KEdownstream) in oocytes treated with tubulin binding chemicals have not been quantitated by detailed dose-response relationships. Thus, the dataset is too limited to allow defining a response-response relationship between KEupstream and KEdownstream. A study on mouse oocytes treated in vitro with nocodazole [Shen et al., 2005] showed that KEdownstream occurred at a dose higher than doses inducing KEustream, suggesting that a certain level of spindle abnormalities (KEupstream) is to be reached before altered chromosome dynamics (KEdownstream) occur, but data are too limited to draw a firm conclusion on the shape of the response-response relationship.
Spindle formation (KEupstream) and chromosome congression on the metaphase plate (KEdownstream) are highly dynamic processes. In mouse oocytes, the first meiotic spindle is assembled in 3–4 h, and 3 more hours are needed for it to migrate to the cortex [Wei et al., 2018]. During the following 2 hours, chromosome congress at the spindle equator by a trial and error process connecting kinetochores with kinetochore fibres. The establishment of complete and correct connections is monitored by checkpoint mechanisms that control anaphase triggering. Live imaging studies of oocytes treated with tubulin binding chemicals are not available that could allow the timing of changes in KEdownstream in relation to the start of changes in KEupstream. However, live imaging studies under impaired spindle assembly conditions [Yi et al., 2019] suggest that spindle disorganization (KEupstream) induces altered chromosome dynamics (KEdownstream) in a matter of minutes. Alterations may last for hours, if spindle damage is sustained by continuous chemical exposure. In fact, anaphase onset may be delayed by hours when oocytes are exposed to spindle disrupting chemicals [Mailhes et al., 1993; Mailhes and Marchetti, 1994].
Known modulating factors
Due to the lack of solid evidence about the response-response relationship modulating factors cannot be identified in this KER.
Known Feedforward/Feedback loops influencing this KER
To our knowledge, there are no feedback loops influencing this KER.
Domain of Applicability
Although this KER has only been measured in mouse oocytes, the process of meiosis, spindle formation and chromosome congression in eggs is thought to be similar across mammalian species.
Baumann C, Wang X, Yang L, Viveiros MM. 2017. Error-prone meiotic division and subfertility in mice with oocyte-conditional knockdown of pericentrin. J Cell Sci 130:1251-1262.
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.
Mailhes JB, Marchetti F. 1994. Chemically-induced aneuploidy in mammalian oocytes. Mutat Res 320:87-111.
Mailhes JB, Aardema MJ, Marchetti F. 1993. Investigation of aneuploidy induction in mouse oocytes following exposure to vinblastine-sulfate, pyrimethamine, diethylstilbestrol diphosphate, or chloral hydrate. Environ Mol Mutagen 22:107–114.
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.
Ou XH, Li S, Xu BZ, Wang ZB, Quan S, Li M, Zhang QH, Ouyang YC, Schatten H, Xing FQ, Sun QY. 2010. p38alpha MAPK is a MTOC-associated protein regulating spindle assembly, spindle length and accurate chromosome segregation during mouse oocyte meiotic maturation. Cell Cycle 9:4130-4143
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, Cimini D. 2012. Transient defects of mitotic spindle geometry and chromosome segregation errors. Cell Div 7:19.
Yi Z-Y, Liang Q-X, Meng T-G, Li J, Dong M-Z, Hou Y, Ouyang Y-C, Zhang C-H, Schatten H, Sun Q-Y, Qiao J, Qian WP. 2019. PKCβ1 regulates meiotic cell cycle in mouse oocyte. Cell Cycle, DOI: 10.1080/15384101.2018.1564492
Wei Z, Greaney J, Zhou C, Homer H. 2018. Cdk1 inactivation induces post-anaphase-onset spindle migration and membrane protrusion required for extreme asymmetry in mouse oocytes. Nature Comm 9:4029. DOI: 10.1038/s41467-018-06510-9.