Aop: 106


Each AOP should be given a descriptive title that takes the form “MIE leading to AO”. For example, “Aromatase inhibition [MIE] leading to reproductive dysfunction [AO]” or “Thyroperoxidase inhibition [MIE] leading to decreased cognitive function [AO]”. In cases where the MIE is unknown or undefined, the earliest known KE in the chain (i.e., furthest upstream) should be used in lieu of the MIE and it should be made clear that the stated event is a KE and not the MIE. More help

Chemical binding to tubulin in oocytes leading to aneuploid offspring

Short name
A short name should also be provided that succinctly summarises the information from the title. This name should not exceed 90 characters. More help
Tubulin binding and aneuploidy

Graphical Representation

A graphical summary of the AOP listing all the KEs in sequence, including the MIE (if known) and AO, and the pair-wise relationships (links or KERs) between those KEs should be provided. This is easily achieved using the standard box and arrow AOP diagram (see this page for example). The graphical summary is prepared and uploaded by the user (templates are available) and is often included as part of the proposal when AOP development projects are submitted to the OECD AOP Development Workplan. The graphical representation or AOP diagram provides a useful and concise overview of the KEs that are included in the AOP, and the sequence in which they are linked together. This can aid both the process of development, as well as review and use of the AOP (for more information please see page 19 of the Users' Handbook).If you already have a graphical representation of your AOP in electronic format, simple save it in a standard image format (e.g. jpeg, png) then click ‘Choose File’ under the “Graphical Representation” heading, which is part of the Summary of the AOP section, to select the file that you have just edited. Files must be in jpeg, jpg, gif, png, or bmp format. Click ‘Upload’ to upload the file. You should see the AOP page with the image displayed under the “Graphical Representation” heading. To remove a graphical representation file, click 'Remove' and then click 'OK.'  Your graphic should no longer be displayed on the AOP page. If you do not have a graphical representation of your AOP in electronic format, a template is available to assist you.  Under “Summary of the AOP”, under the “Graphical Representation” heading click on the link “Click to download template for graphical representation.” A Powerpoint template file should download via the default download mechanism for your browser. Click to open this file; it contains a Powerpoint template for an AOP diagram and instructions for editing and saving the diagram. Be sure to save the diagram as jpeg, jpg, gif, png, or bmp format. Once the diagram is edited to its final state, upload the image file as described above. More help


List the name and affiliation information of the individual(s)/organisation(s) that created/developed the AOP. In the context of the OECD AOP Development Workplan, this would typically be the individuals and organisation that submitted an AOP development proposal to the EAGMST. Significant contributors to the AOP should also be listed. A corresponding author with contact information may be provided here. This author does not need an account on the AOP-KB and can be distinct from the point of contact below. The list of authors will be included in any snapshot made from an AOP. More help

Francesco Marchetti 1*, Alberto Massarotti 2, Carole L. Yauk 1, Francesca Pacchierotti 3, Antonella Russo 4

1 Environmental Health Science and Research Bureau, Health Canada, Ottawa, Canada. 2 Dipartimento di Scienze del Farmaco, Università degli Studi del Piemonte Orientale “A. Avogadro”, Novara, Italy. 3 Health Protection Technology Division, Laboratory of Biosafety and Risk Assessment, ENEA CR Casaccia, Rome, Italy. 4 Department of Molecular Medicine, University of Padova, Padova, Italy.

  • Correspondence to: Francesco Marchetti, Environmental Health Science and Research Bureau, Health Canada, Ottawa, ON K1A 0K9, Canada. E-mail:

Point of Contact

Indicate the point of contact for the AOP-KB entry itself. This person is responsible for managing the AOP entry in the AOP-KB and controls write access to the page by defining the contributors as described below. Clicking on the name will allow any wiki user to correspond with the point of contact via the email address associated with their user profile in the AOP-KB. This person can be the same as the corresponding author listed in the authors section but isn’t required to be. In cases where the individuals are different, the corresponding author would be the appropriate person to contact for scientific issues whereas the point of contact would be the appropriate person to contact about technical issues with the AOP-KB entry itself. Corresponding authors and the point of contact are encouraged to monitor comments on their AOPs and develop or coordinate responses as appropriate.  More help
Cataia Ives   (email point of contact)


List user names of all  authors contributing to or revising pages in the AOP-KB that are linked to the AOP description. This information is mainly used to control write access to the AOP page and is controlled by the Point of Contact.  More help
  • Francesco Marchetti
  • Cataia Ives


The status section is used to provide AOP-KB users with information concerning how actively the AOP page is being developed, what type of use or input the authors feel comfortable with given the current level of development, and whether it is part of the OECD AOP Development Workplan and has been reviewed and/or endorsed. “Author Status” is an author defined field that is designated by selecting one of several options from a drop-down menu (Table 3). The “Author Status” field should be changed by the point of contact, as appropriate, as AOP development proceeds. See page 22 of the User Handbook for definitions of selection options. More help
Author status OECD status OECD project SAAOP status
Open for citation & comment EAGMST Under Review 1.11 Included in OECD Work Plan
This AOP was last modified on May 08, 2022 11:33
The date the AOP was last modified is automatically tracked by the AOP-KB. The date modified field can be used to evaluate how actively the page is under development and how recently the version within the AOP-Wiki has been updated compared to any snapshots that were generated. More help

Revision dates for related pages

Page Revision Date/Time
Binding, Tubulin April 20, 2021 10:47
Disruption, Microtubule dynamics November 07, 2019 15:09
Disorganization, Meiotic Spindle April 20, 2021 10:55
Increase, Aneuploid offspring May 27, 2019 14:54
Altered, Meiotic chromosome dynamics May 27, 2019 14:17
Altered, Chromosome number May 27, 2019 14:29
Binding, Tubulin leads to Disruption, Microtubule dynamics May 27, 2019 15:06
Disruption, Microtubule dynamics leads to Disorganization, Meiotic Spindle December 13, 2019 16:16
Disorganization, Meiotic Spindle leads to Altered, Meiotic chromosome dynamics December 13, 2019 16:19
Altered, Meiotic chromosome dynamics leads to Altered, Chromosome number December 13, 2019 16:06
Altered, Chromosome number leads to Increase, Aneuploid offspring December 13, 2019 16:23
Binding, Tubulin leads to Altered, Chromosome number December 13, 2019 16:25
Colchicine November 29, 2016 18:42
Vinblastine sulfate May 27, 2019 15:42
Benomyl November 29, 2016 18:42
Nocodazole November 29, 2016 18:42


In the abstract section, authors should provide a concise and informative summation of the AOP under development that can stand-alone from the AOP page. Abstracts should typically be 200-400 words in length (similar to an abstract for a journal article). Suggested content for the abstract includes the following: The background/purpose for initiation of the AOP’s development (if there was a specific intent) A brief description of the MIE, AO, and/or major KEs that define the pathway A short summation of the overall WoE supporting the AOP and identification of major knowledge gaps (if any) If a brief statement about how the AOP may be applied (optional). The aim is to capture the highlights of the AOP and its potential scientific and regulatory relevance More help

Aneuploidy, an abnormal number of chromosomes, arising during meiosis in germ cells represents the most common chromosomal abnormality at birth and is the leading cause of pregnancy loss in humans. Aneuploidy can affect any chromosome, and data in rodents suggest that neither aneuploid sperm nor aneuploid oocytes are selected against at fertilization. Therefore, an increase in germ cell aneuploidy is expected to result in an increase in aneuploid pregnancies. The etiology of human aneuploidy is still not well understood, although there is strong evidence supporting a preferential occurrence during female meiosis I and a positive correlation with maternal age. There is extensive evidence in animal models that chemicals can induce aneuploidy by interfering with the proper functioning of the meiotic spindle and other aspects of chromosome segregation. Over 15 chemicals have been shown to induce aneuploidy in mammalian oocytes and the majority of these chemicals interfere with microtubule dynamics during meiosis. In addition to these animal studies, there is also one reported case in which environmental exposure to trichlorfon, an organophosphate insecticide, was associated with a cluster of Down syndrome cases among women in a Hungarian community. The present AOP focuses on the induction of aneuploidy in mammalian oocytes as a consequence of chemical binding to tubulin (MIE). In this AOP, chemicals that bind to tubulin lead to the depolymerization of microtubules (KE1). Extensive microtubule depolymerization leads to meiotic spindle disorganization (KE2), which in turns lead to altered chromosome dynamics (KE3) and the generation of aneuploid oocytes (KE4). Aneuploid oocytes can be fertilized and generate aneuploid offspring (AO). There is ample empirical evidence supporting this AOP and the overall weight of evidence is strong.

Background (optional)

This optional subsection should be used to provide background information for AOP reviewers and users that is considered helpful in understanding the biology underlying the AOP and the motivation for its development. The background should NOT provide an overview of the AOP, its KEs or KERs, which are captured in more detail below. Examples of potential uses of the optional background section are listed on pages 24-25 of the User Handbook. More help

Aneuploidy is associated with serious human health effects. Approximately 10–30% of human zygotes, 50% of spontaneous abortions, and 0.3% of human newborns are aneuploid [Hassold et al., 2007; Nagaoka et al., 2012; Webster and Schuh, 2017]. Cytogenetic analyses of human oocytes and preimplantation embryos have reported frequencies of aneuploidy in excess of 50% [Magli et al., 2001; Munne, 2002; Kuliev et al., 2003]. In these studies, the overall aneuploidy frequency is estimated from the analysis of a subset of chromosomes, which may affect the accuracy of the estimate.

Aneuploidy can affect any chromosome [Nagaoka et al., 2012; Webster and Schuh, 2017], although there is evidence that acrocentric chromosomes may be more frequently involved in aneuploidy than metacentric chromosomes [Nicolaidis and Petersen, 1998; Hassold et al., 2007; Gianaroli et al., 2010]. In humans, only trisomies for a few autosomal chromosomes (13, 18 and 21) and aneuploidies of the sex chromosomes are compatible with life. These aneuploidies have important developmental, neurological and reproductive effects. Trisomy 21 or Down syndrome, with an occurrence of ~1/720 births, is the most common genetic abnormality in newborns [Hassold et al., 2007].

The etiology of human aneuploidy is still not well understood, although there is strong evidencesupporting a preferential occurrence during female meiosis I and a positive correlation with maternal age [Hunt and Hassold, 2002; Nagaoka et al., 2012]. The prevalence of chromosome segregation errors during female meiosis is clearly supported by the application of state-of-the-art genomic approaches, such as Comparative Genomic Hybridization (CGH), array-Comparative Genomic Hybridization (aCGH), SNP-arrays [Handyside, 2012; Nagaoka et al., 2012] and next generation sequencing (NGS) [Hou et al., 2013; Kung et al., 2015; Treff et al., 2016].

The present AOP focuses on chemical binding to tubulin that causes depolymerization of microtubules and generation of aneuploid cells. Although this molecular initiating event can occur in any cell, the adverse outcome is the generation of aneuploid conceptuses; therefore, this AOP is specific to germ cells, and in particular, to female germ cells.


Gianaroli L, Magli MC, Cavallini G, Crippa A, Capoti A, Resta S, Robles F, Ferraretti AP. 2010. Predicting aneuploidy in human oocytes: key factors which affect the meiotic process. Hum Reprod 25:2374-2386.

Handyside AH. 2012. Molecular origin of female meiotic aneuploidies. Biochim Biophys Acta 1822:1913-1920.

Hassold T, Hall H, Hunt P. 2007. The origin of human aneuploidy: Where we have been, where we are going. Hum Mol Genet 16: R203–R208.

Hou Y, Fan W, Yan L, Li R, Lian Y, Huang J, Xu L, Tand F, Xiw XS, Qiao J. 2013. Genome analyses of single human oocytes. Cell 155:1492-1506.

Hunt PA, Hassold TJ. 2002. Sex matters in meiosis, Science 296:2181-2183.

Kuliev A, Cieslak J, Ilkevitch Y, Verlinsky Y. 2003. Chromosomal abnormalities in a series of 6,733 human oocytes in preimplantation diagnosis for age-related aneuploidies. Reprod Biomed Online 6:54-59.

Kung A, Munné S, Bankowski B, Coates A, Wells D. 2015. Validation of next-generation sequencing for comprehensive chromosome screening of embryos. Reprod Biomed Online 31:760-769.

Magli MC, Gianaroli L, Ferraretti AP. 2001. Chromosomal abnormalities in embryos. Mol Cell Endocrinol 183:S29-34.

Munne S. 2002. Preimplantation genetic diagnosis of numerical and structural chromosome abnormalities. Reprod Biomed Online 4:183-196.

Nagaoka SI, Hassold TJ, Hunt PA. 2012. Human aneuploidy: Mechanisms and new insights into an age-old problem. Nat Rev Genet 13:493–504.

Nicolaidis P, Petersen MB. 1998. Origin and mechanisms of non-disjunction in human autosomal trisomies. Hum Reprod 13:313-319.

Treff NR, Kirsher RL, Tao X, Garnsey H, Boher C, Silva E, Landis J, Taylor D, Scott RT, Woodruff TK, Duncan FE. 2016. Next Generation Sequencing-based comprehensive chromosome screening in mouse polar bodies, oocytes, and embryos. Biol Reprod 94:76

Webster A, Schuh M. 2017. Mechanisms of aneuploidy in human eggs. Trends Cell Biol 27:55-68.

Summary of the AOP

This section is for information that describes the overall AOP. The information described in section 1 is entered on the upper portion of an AOP page within the AOP-Wiki. This is where some background information may be provided, the structure of the AOP is described, and the KEs and KERs are listed. More help


Molecular Initiating Events (MIE)
An MIE is a specialised KE that represents the beginning (point of interaction between a stressor and the biological system) of an AOP. More help
Key Events (KE)
This table summarises all of the KEs of the AOP. This table is populated in the AOP-Wiki as KEs are added to the AOP. Each table entry acts as a link to the individual KE description page.  More help
Adverse Outcomes (AO)
An AO is a specialised KE that represents the end (an adverse outcome of regulatory significance) of an AOP.  More help
Sequence Type Event ID Title Short name
1 MIE 718 Binding, Tubulin Binding, Tubulin
2 KE 720 Disruption, Microtubule dynamics Disruption, Microtubule dynamics
3 KE 721 Disorganization, Meiotic Spindle Disorganization, Meiotic Spindle
4 KE 752 Altered, Meiotic chromosome dynamics Altered, Meiotic chromosome dynamics
5 KE 723 Altered, Chromosome number Altered, Chromosome number
6 AO 728 Increase, Aneuploid offspring Increase, Aneuploid offspring

Relationships Between Two Key Events (Including MIEs and AOs)

This table summarises all of the KERs of the AOP and is populated in the AOP-Wiki as KERs are added to the AOP. Each table entry acts as a link to the individual KER description page.To add a key event relationship click on either Add relationship: events adjacent in sequence or Add relationship: events non-adjacent in sequence.For example, if the intended sequence of KEs for the AOP is [KE1 > KE2 > KE3 > KE4]; relationships between KE1 and KE2; KE2 and KE3; and KE3 and KE4 would be defined using the add relationship: events adjacent in sequence button.  Relationships between KE1 and KE3; KE2 and KE4; or KE1 and KE4, for example, should be created using the add relationship: events non-adjacent button. This helps to both organize the table with regard to which KERs define the main sequence of KEs and those that provide additional supporting evidence and aids computational analysis of AOP networks, where non-adjacent KERs can result in artifacts (see Villeneuve et al. 2018; DOI: 10.1002/etc.4124).After clicking either option, the user will be brought to a new page entitled ‘Add Relationship to AOP.’ To create a new relationship, select an upstream event and a downstream event from the drop down menus. The KER will automatically be designated as either adjacent or non-adjacent depending on the button selected. The fields “Evidence” and “Quantitative understanding” can be selected from the drop-down options at the time of creation of the relationship, or can be added later. See the Users Handbook, page 52 (Assess Evidence Supporting All KERs for guiding questions, etc.).  Click ‘Create [adjacent/non-adjacent] relationship.’  The new relationship should be listed on the AOP page under the heading “Relationships Between Two Key Events (Including MIEs and AOs)”. To edit a key event relationship, click ‘Edit’ next to the name of the relationship you wish to edit. The user will be directed to an Editing Relationship page where they can edit the Evidence, and Quantitative Understanding fields using the drop down menus. Once finished editing, click ‘Update [adjacent/non-adjacent] relationship’ to update these fields and return to the AOP page.To remove a key event relationship to an AOP page, under Summary of the AOP, next to “Relationships Between Two Key Events (Including MIEs and AOs)” click ‘Remove’ The relationship should no longer be listed on the AOP page under the heading “Relationships Between Two Key Events (Including MIEs and AOs)”. More help

Network View

The AOP-Wiki automatically generates a network view of the AOP. This network graphic is based on the information provided in the MIE, KEs, AO, KERs and WoE summary tables. The width of the edges representing the KERs is determined by its WoE confidence level, with thicker lines representing higher degrees of confidence. This network view also shows which KEs are shared with other AOPs. More help


The stressor field is a structured data field that can be used to annotate an AOP with standardised terms identifying stressors known to trigger the MIE/AOP. Most often these are chemical names selected from established chemical ontologies. However, depending on the information available, this could also refer to chemical categories (i.e., groups of chemicals with defined structural features known to trigger the MIE). It can also include non-chemical stressors such as genetic or environmental factors. Although AOPs themselves are not chemical or stressor-specific, linking to stressor terms known to be relevant to different AOPs can aid users in searching for AOPs that may be relevant to a given stressor. More help
Name Evidence Term
Colchicine High
Vinblastine sulfate High
Benomyl High
Nocodazole High

Life Stage Applicability

Identify the life stage for which the KE is known to be applicable. More help
Life stage Evidence
Adult, reproductively mature High

Taxonomic Applicability

Latin or common names of a species or broader taxonomic grouping (e.g., class, order, family) can be selected. In many cases, individual species identified in these structured fields will be those for which the strongest evidence used in constructing the AOP was available in relation to this KE. More help
Term Scientific Term Evidence Link
Mus musculus Mus musculus High NCBI
Homo sapiens Homo sapiens Moderate NCBI
Hamster Hamster Moderate NCBI

Sex Applicability

The authors must select from one of the following: Male, female, mixed, asexual, third gender, hermaphrodite, or unspecific. More help
Sex Evidence
Female High

Overall Assessment of the AOP

This section addresses the relevant biological domain of applicability (i.e., in terms of taxa, sex, life stage, etc.) and WoE for the overall AOP as a basis to consider appropriate regulatory application (e.g., priority setting, testing strategies or risk assessment). The goal of the overall assessment is to provide a high level synthesis and overview of the relative confidence in the AOP and where the significant gaps or weaknesses are (if they exist). Users or readers can drill down into the finer details captured in the KE and KER descriptions, and/or associated summary tables, as appropriate to their needs.Assessment of the AOP is organised into a number of steps. Guidance on pages 59-62 of the User Handbook is available to facilitate assignment of categories of high, moderate, or low confidence for each consideration. While it is not necessary to repeat lengthy text that appears elsewhere in the AOP description (or related KE and KER descriptions), a brief explanation or rationale for the selection of high, moderate, or low confidence should be made. More help
Attached file: Summary woe


A comprehensive review of the literature (Supplementary Table 1) was conducted to gather the available studies in which the effects of microtubule inhibitors were tested for the induction of aneuploidy in female germ cells. The focus of this AOP is on spindle poisons that bind to tubulin resulting in microtubule depolymerization leading to abnormalities in spindle function and chromosomal dynamic ultimately resulting in an egg with an abnormal number of chromosomes. Although chemicals with different mechanism of actions, such as topoisomerase II inhibitors, also have strong data showing aneugenic activity in female germ cells [Mailhes and Marchetti, 2005; Pacchierotti et al., 2007], chemicals that bind to tubulin represent the largest class for which the aneugenic activity has been evaluated [Marchetti et al., 2016]. Studies providing sufficient information regarding doses, timing of exposure and egg collection, and experimental results were considered to assess the empirical data supporting each of the KEs and KERs. It should be noted that, as mentioned before, few studies have investigated multiple KEs within the same study design and the majority of the data available refers to the induction of aneuploidy. An additional complication is that the MIE and first KE (microtubule depolymerization) are most often assessed in acellular systems rendering the quantitative assessment of the concordance among upstream KEs and downstream KEs complex. However, those few cases where multiple KEs were investigated showed concordance for both dose-related and time-related effects [Shen et al., 2005; Eichenlaub-Ritter et al., 2007]. As a whole, we consider the studies in Supplementary Table 1 to provide extensive and convincing evidence that tubulin-binding chemicals cause microtubule depolymerization and spindle disturbances leading to the generation of aneuploid eggs. Strong in vivo dose-response data on the induction of aneuploid eggs is available for several chemicals, including colchicine, benomyl, and vinblastine [reviewed in Mailhes and Marchetti, 1994; 2005; Pacchierotti et al., 2007]. Data with colchicine is also available to demonstrate that aneuploid eggs are fertilized and that the frequencies of aneuploidy are similar before and after fertilization [Mailhes et al., 1990]. Overall, we consider that the available data provide high support for this AOP as a whole, while empirical support for the different KERs is varied.

Domain of Applicability

The relevant biological domain(s) of applicability in terms of sex, life-stage, taxa, and other aspects of biological context are defined in this section. Biological domain of applicability is informed by the “Description” and “Biological Domain of Applicability” sections of each KE and KER description (see sections 2G and 3E for details). In essence the taxa/life-stage/sex applicability is defined based on the groups of organisms for which the measurements represented by the KEs can feasibly be measured and the functional and regulatory relationships represented by the KERs are operative.The relevant biological domain of applicability of the AOP as a whole will nearly always be defined based on the most narrowly restricted of its KEs and KERs. For example, if most of the KEs apply to either sex, but one is relevant to females only, the biological domain of applicability of the AOP as a whole would be limited to females. While much of the detail defining the domain of applicability may be found in the individual KE and KER descriptions, the rationale for defining the relevant biological domain of applicability of the overall AOP should be briefly summarised on the AOP page. More help

Although the molecular initiating event and a few of the key event can occur in any cell type, the adverso outcome is require these events to occur in the oocyte. Thus, the present AOP should be considered specific to female germ cells exposed in the peri-ovulation period. The majority of data in this AOP were derived from experiments in mice, however, relevant endpoints have been evaluated in a variety of higher and lower eukaryotes. The available results on the induction of aneuploidy by the prototype tubulin-binding chemical colchicine in oocytes of species other than Mus musculus are qualitatively consistent with mouse data, in agreement with the similarities in the mechanism of action across several Phyla and the high degree of homology of tubulin across species. Evidence for microtubule depolymerization and spindle disorganization has been obtained in human oocytes exposed in culture to colchicine. In addition, the similarities in oogenesis between rodents and humans suggest that the MIE and KEs are conserved and would occur in human oocytes also. Therefore, the AOP should apply to any species that produce eggs.

Essentiality of the Key Events

An important aspect of assessing an AOP is evaluating the essentiality of its KEs. The essentiality of KEs can only be assessed relative to the impact of manipulation of a given KE (e.g., experimentally blocking or exacerbating the event) on the downstream sequence of KEs defined for the AOP. Consequently evidence supporting essentiality is assembled on the AOP page, rather than on the independent KE pages that are meant to stand-alone as modular units without reference to other KEs in the sequence.The nature of experimental evidence that is relevant to assessing essentiality relates to the impact on downstream KEs and the AO if upstream KEs are prevented or modified. This includes: Direct evidence: directly measured experimental support that blocking or preventing a KE prevents or impacts downstream KEs in the pathway in the expected fashion. Indirect evidence: evidence that modulation or attenuation in the magnitude of impact on a specific KE (increased effect or decreased effect) is associated with corresponding changes (increases or decreases) in the magnitude or frequency of one or more downstream KEs.When assembling the support for essentiality of the KEs, authors should organise relevant data in a tabular format. The objective is to summarise briefly the nature and numbers of investigations in which the essentiality of KEs has been experimentally explored either directly or indirectly. See pages 50-51 in the User Handbook for further definitions and clarifications.  More help

Not all events within this AOP can be tested for essentiality. This is due to technical limitations at this time. However, there is one study demonstrating the essentiality of proper spindle organization for correct chromosome congression and segregation. Ou et al. [2010] showed that depletion of the microtubule organizing centres (required for spindle organization) leads to increase in the incidence spindle and chromosome dynamic abnormalities. Moreover, studies with mice deficient in specific spindle assembly checkpoint proteins show an increase in the occurrence of high levels of aneuploid oocytes [Leland et al., 2009; McGuinness et al., 2009; reviewed in Mailhes and Marchetti, 2010].

The final step of the AOP requires the transmission of the aneuploid condition from the oocyte to the offspring. Since the available data suggest that there is a narrow window of sensitivity for the induction of aneuploidy by spindle poisons (around the time of resumption of meiosis in preparation for ovulation) it could be possible to wait longer periods of time after the administration of colchicine, or any other of the chemicals listed in this AOP, and demonstrate that under these conditions there is no transmission of aneuploidy to the offspring. However, no such study has been conducted.

Evidence Assessment

The biological plausibility, empirical support, and quantitative understanding from each KER in an AOP are assessed together.  Biological plausibility of each of the KERs in the AOP is the most influential consideration in assessing WoE or degree of confidence in an overall hypothesised AOP for potential regulatory application (Meek et al., 2014; 2014a). Empirical support entails consideration of experimental data in terms of the associations between KEs – namely dose-response concordance and temporal relationships between and across multiple KEs. It is examined most often in studies of dose-response/incidence and temporal relationships for stressors that impact the pathway. While less influential than biological plausibility of the KERs and essentiality of the KEs, empirical support can increase confidence in the relationships included in an AOP. For clarification on how to rate the given empirical support for a KER, as well as examples, see pages 53- 55 of the User Handbook.  More help

Biological plausibility of the KERs is strong. There is clear understanding of the MIE for many of the chemicals listed in this AOP. Both the colchicine- and vinca alkaloid-binding sites on tubulin are characterized in detail. The consequences of chemical binding to tubulin for microtubule dynamics are also qualitatively and quantitatively well understood. It also broadly accepted that microtubule dynamics is essential for proper spindle assembly and function. There is less understanding of why the SAC is unable to prevent meiotic progression in the presence of misaligned chromosomes [Marchetti et al., 2006; Webster and Schuh, 2017] and this represent a key research gap.

Empirical support for the KERs is generally strong, although the empirical evidence and our understanding of the KER between abnormalities in chromosome dynamics and generation of an aneuploidy egg is limited. The strongest empirical support is associated with the indirect KER linking binding of chemicals to tubulin with the induction of aneuploid eggs. Overall, the timescale of events, from the initial biochemical interactions (MIE) occurring within seconds to minutes of exposure, through disruption of spindle (KE2) and chromosome alignment and segregation in meiosis (KE3) occurring in the following hours, to the formation and ovulation of an aneuploid oocyte (KE4) and to its possible fertilization, which would occur later on, is fully coherent and consistent with the timeline of oocyte development and fertilization [Marchetti et al., 2016]. Moreover, examination of the incidence of events occurring across doses for KE2, KE3 and KE4 after in vitro exposure of oocytes to nocodazole [Shen et al., 2005] and 2-methoxyestradiol [Eichenlaub-Ritter et al., 2007] supports the order and linkages between the KEs across the AOP.

The comparison between the lowest effective concentrations inducing each subsequent event is complex because colchicine binding to tubulin and microtubule depolymerization are measured in acellular systems, whereas, spindle disorganization and altered chromosome alignment and segregation are mostly analysed in cultured oocytes, and induction of aneuploid oocytes and zygotes is assessed after treatment of laboratory rodents by intraperitoneal or oral administrations. Cells in culture may respond to chemical exposure with a different sensitivity than whole organisms [Sun et al., 2005], and a comparison between in vitro molar concentrations and mg/kg body weight of in vivo administered doses can be done only roughly, based on many assumptions. Furthermore, few in vitro experiments were aimed at identifying the Lowest Effective Tested Concentration, or were even conducted at multiple concentration levels. In many cases, experiments aimed to test the hypothesis that a given effect was elicited by chemical disruption of a certain process, and to do this, high doses were used. The published work shows that there is progressivity between dose, severity of spindle damage and degree of aneuploidy, from one to several involved chromosomes up to a complete inhibition of chromosome segregation and arrest of oocytes at meiosis I [Russo and Pacchierotti, 1988; Mailhes et al., 1990; Mailhes and Aardema, 1992; Mailhes et al., 1993; Sun et al., 2005; Eichenlaub-Ritter et al., 2007].

Quantitative Understanding

Some proof of concept examples to address the WoE considerations for AOPs quantitatively have recently been developed, based on the rank ordering of the relevant Bradford Hill considerations (i.e., biological plausibility, essentiality and empirical support) (Becker et al., 2017; Becker et al, 2015; Collier et al., 2016). Suggested quantitation of the various elements is expert derived, without collective consideration currently of appropriate reporting templates or formal expert engagement. Though not essential, developers may wish to assign comparative quantitative values to the extent of the supporting data based on the three critical Bradford Hill considerations for AOPs, as a basis to contribute to collective experience.Specific attention is also given to how precisely and accurately one can potentially predict an impact on KEdownstream based on some measurement of KEupstream. This is captured in the form of quantitative understanding calls for each KER. See pages 55-56 of the User Handbook for a review of quantitative understanding for KER's. More help

As described in the previous sections of the AOP, it is well established that chemicals that bind to tubulin affect the polymerization of microtubules triggering abnormalities in the meiotic spindle and the subsequent chromosomal missegregation. There is also sufficient evidence to show that these events increase with dose in a manner that is consistent with this AOP. Binding to tubulin seems to increase linearly with dose, however, microtubule depolymerization must exceed a threshold before abnormalities in the meiotic spindles become apparent. There is also sufficient evidence that there is a threshold for the induction of aneuploidy. However, the precise quantitative relationship has not been established and it may be different for different chemicals. This is because different chemicals may induce different degrees of arrest at the metaphase of the first meiotic division which would prevent the manifestation of the aneuploidy in metaphase II oocytes.

Considerations for Potential Applications of the AOP (optional)

At their discretion, the developer may include in this section discussion of the potential applications of an AOP to support regulatory decision-making. This may include, for example, possible utility for test guideline development or refinement, development of integrated testing and assessment approaches, development of (Q)SARs / or chemical profilers to facilitate the grouping of chemicals for subsequent read-across, screening level hazard assessments or even risk assessment. While it is challenging to foresee all potential regulatory application of AOPs and any application will ultimately lie within the purview of regulatory agencies, potential applications may be apparent as the AOP is being developed, particularly if it was initiated with a particular application in mind. This optional section is intended to provide the developer with an opportunity to suggest potential regulatory applications and describe his or her rationale.To edit the “Considerations for Potential Applications of the AOP” section, on an AOP page, in the upper right hand menu, click ‘Edit.’ This brings you to a page entitled, “Editing AOP.” Scroll down to the “Considerations for Potential Applications of the AOP” section, where a text entry box allows you to submit text. In the upper right hand menu, click ‘Update AOP’ to save your changes and return to the AOP page or 'Update and continue' to continue editing AOP text sections.  The new text should appear under the “Considerations for Potential Applications of the AOP” section on the AOP page. More help

There are no established OECD test guidelines (TG) for measuring aneuploidy in oocytes. However, there are several existing TGs, such as the in vivo and in vitro micronucleus test (OECD TG 474 and OECD TG 487) and the in vivo and in vitro chromosomal aberration test (OECD TG 475 and OECD TG 473), and one specific to spermatogonial cells (OECD TG 483) that although not specifically designed to detect aneuploidy can provide evidence of aneugenic activity. Although it is generally assumed that data obtained in somatic cells can be extrapolated to germ cells to inform regulatory decisions, the availability of germ cell data is critical for the proper classification of products under the Globally Harmonized System (GHS) of classification and labelling [United Nations, 2013]. In addition, the recent International Workshops on Genotoxicity Testing that took place in Tokyo, Japan in November 2017 included a workgroup that addressed the risk of aneugens for human health assessment. As part of the work, the group reviewed all available data for germ cell aneugens in mammals, independently of the mechanism of action. Therefore, the present AOP addresses at topic of high interest among the genotoxicity community and may help in identifying research gaps and direct future work.


List the bibliographic references to original papers, books or other documents used to support the AOP. More help

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.

Leland S, Nagarajan P, Polyzos A, Thomas S, Samaan G, Donnell R, Marchetti F, Venkatachalam S. 2009. Heterozygosity for a Bub1 mutation causes female-specific germ cell aneuploidy in mice. Proc Natl Acad Sci USA 106:12776-12781.

Mailhes JB, Marchetti F. 1994. Chemically-induced aneuploidy in mammalian oocytes. Mutat Res 320:87-111.

Mailhes JB, Marchetti F. 2005. Mechanisms and chemically-induced aneuploidy in rodent germ cells. Cytogenet Genome Research 111:384-391.

Mailhes JB, Marchetti F. 2010. Advances in understanding the genetic causes and mechanisms of female germ cell aneuploidy. Exp Rev Obst Gyn 5:687–706.

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.

Mailhes JB, Carabatsos MJ, Young D, London SN, Bell M, Albertini DF. 1999. Taxol-induced meiotic maturation delay, spindle defects, and aneuploidy in mouse oocytes and zygotes. Mutat Res 423:79-90

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-Bernabé 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.

OECD. 2016. Test No. 473: In Vitro Mammalian Chromosomal Aberration Test, OECD Publishing, Paris.

OECD. 2016. Test No. 474: Mammalian Erythrocyte Micronucleus Test, OECD Publishing, Paris.

OECD. 2016. Test No. 475: Mammalian Bone Marrow Chromosomal Aberration Test, OECD Publishing, Paris.

OECD. 2016. Test No. 483: Mammalian Spermatogonial Chromosomal Aberration Test, OECD Publishing, Paris.

OECD. 2016. Test No. 487: In Vitro Mammalian Cell Micronucleus Test, OECD Publishing, Paris.

Ou XH, Li S, Xu BZ, Wang ZB, Quan S, Li M, Zhang QH, Ouyang YC, Schatten H, Xing FQ, Sun QY. 2010. p38α 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.

Pacchierotti F, Adler ID, Eichenlaub-Ritter U, Mailhes JB. 2007. Gender effects on the incidence of aneuploidy in mammalian germ cells. Environ Res 104:46-69.

Russo A, Pacchierotti F. 1988. Meiotic arrest and aneuploidy induced by vinblastine in mouse oocytes. Mutat Res 202:215–221.

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.

Sun F, Betzendahl I, Pacchierotti F, Ranaldi R, Smitz J, Cortvrindt R, Eichenlaub-Ritter U. 2005. Aneuploidy in mouse metaphase II oocytes exposed in vivo and in vitro in preantral follicle culture to nocodazole. Mutagenesis 20:65–75.

United Nations  2013. Globally Harmonized System of Classification and Labelling of Chemicals (GHS), Fifth revised edition ed., New York and Geneva.

Webster A, Schuh M. 2017. Mechanisms of aneuploidy in human eggs. Trends Cell Biol 27:55-68