To the extent possible under law, AOP-Wiki has waived all copyright and related or neighboring rights to KE:1885

Event: 1885

Key Event Title

The KE title should describe a discrete biological change that can be measured. It should generally define the biological object or process being measured and whether it is increased, decreased, or otherwise definably altered relative to a control state. For example “enzyme activity, decreased”, “hormone concentration, increased”, or “growth rate, decreased”, where the specific enzyme or hormone being measured is defined. More help

Inhibition of Plxna2

Short name
The KE short name should be a reasonable abbreviation of the KE title and is used in labelling this object throughout the AOP-Wiki. The short name should be less than 80 characters in length. More help
Inhibition of Plxna2

Biological Context

Structured terms, selected from a drop-down menu, are used to identify the level of biological organization for each KE. Note, KEs should be defined within a particular level of biological organization. Only KERs should be used to transition from one level of organization to another. Selection of the level of biological organization defines which structured terms will be available to select when defining the Event Components (below). More help

Cell term

Further information on Event Components and Biological Context may be viewed on the attached pdf.The biological context describes the location/biological environment in which the event takes place.  For molecular/cellular events this would include the cellular context (if known), organ context, and species/life stage/sex for which the event is relevant. For tissue/organ events cellular context is not applicable.  For individual/population events, the organ context is not applicable. More help

Organ term

Further information on Event Components and Biological Context may be viewed on the attached pdf.The biological context describes the location/biological environment in which the event takes place.  For molecular/cellular events this would include the cellular context (if known), organ context, and species/life stage/sex for which the event is relevant. For tissue/organ events cellular context is not applicable.  For individual/population events, the organ context is not applicable. More help

Key Event Components

Further information on Event Components and Biological Context may be viewed on the attached pdf.Because one of the aims of the AOP-KB is to facilitate de facto construction of AOP networks through the use of shared KE and KER elements, authors are also asked to define their KEs using a set of structured ontology terms (Event Components). In the absence of structured terms, the same KE can readily be defined using a number of synonymous titles (read by a computer as character strings). In order to make these synonymous KEs more machine-readable, KEs should also be defined by one or more “event components” consisting of a biological process, object, and action with each term originating from one of 22 biological ontologies (Ives, et al., 2017; See List). Biological process describes dynamics of the underlying biological system (e.g., receptor signalling). The biological object is the subject of the perturbation (e.g., a specific biological receptor that is activated or inhibited). Action represents the direction of perturbation of this system (generally increased or decreased; e.g., ‘decreased’ in the case of a receptor that is inhibited to indicate a decrease in the signalling by that receptor).Note that when editing Event Components, clicking an existing Event Component from the Suggestions menu will autopopulate these fields, along with their source ID and description. To clear any fields before submitting the event component, use the 'Clear process,' 'Clear object,' or 'Clear action' buttons. If a desired term does not exist, a new term request may be made via Term Requests. Event components may not be edited; to edit an event component, remove the existing event component and create a new one using the terms that you wish to add. More help

Key Event Overview

AOPs Including This Key Event

All of the AOPs that are linked to this KE will automatically be listed in this subsection. This table can be particularly useful for derivation of AOP networks including the KE. Clicking on the name of the AOP will bring you to the individual page for that AOP. More help
AOP Name Role of event in AOP Point of Contact Author Status OECD Status
Inhibition of Fyna leading to increased mortality KeyEvent Vid Modic (send email) Under development: Not open for comment. Do not cite


This is a structured field used to identify specific agents (generally chemicals) that can trigger the KE. Stressors identified in this field will be linked to the KE in a machine-readable manner, such that, for example, a stressor search would identify this as an event the stressor can trigger. NOTE: intermediate or downstream KEs in one AOP may function as MIEs in other AOPs, meaning that stressor information may be added to the KE description, even if it is a downstream KE in the pathway currently under development.Information concerning the stressors that may trigger an MIE can be defined using a combination of structured and unstructured (free-text) fields. For example, structured fields may be used to indicate specific chemicals for which there is evidence of an interaction relevant to this MIE. By linking the KE description to a structured chemical name, it will be increasingly possible to link the MIE to other sources of chemical data and information, enhancing searchability and inter-operability among different data-sources and knowledgebases. The free-text section “Evidence for perturbation of this MIE by stressor” can be used both to identify the supporting evidence for specific stressors triggering the MIE as well as to define broad chemical categories or other properties that classify the stressors able to trigger the MIE for which specific structured terms may not exist. More help

Taxonomic Applicability

Latin or common names of a species or broader taxonomic grouping (e.g., class, order, family) can be selected from an ontology. 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
zebrafish Danio rerio High NCBI

Life Stages

The structured ontology terms for life-stage are more comprehensive than those for taxa, but may still require further description/development and explanation in the free text section. More help
Life stage Evidence
Larvae High

Sex Applicability

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

Key Event Description

A description of the biological state being observed or measured, the biological compartment in which it is measured, and its general role in the biology should be provided. For example, the biological state being measured could be the activity of an enzyme, the expression of a gene or abundance of an mRNA transcript, the concentration of a hormone or protein, neuronal activity, heart rate, etc. The biological compartment may be a particular cell type, tissue, organ, fluid (e.g., plasma, cerebrospinal fluid), etc. The role in the biology could describe the reaction that an enzyme catalyses and the role of that reaction within a given metabolic pathway; the protein that a gene or mRNA transcript codes for and the function of that protein; the function of a hormone in a given target tissue, physiological function of an organ, etc. Careful attention should be taken to avoid reference to other KEs, KERs or AOPs. Only describe this KE as a single isolated measurable event/state. This will ensure that the KE is modular and can be used by other AOPs, thereby facilitating construction of AOP networks. More help

Plexins (Plxns) are the receptors encoded by the nine members of the plexin gene family, they are primary transducers of vertebrate semaphorin (Sema) signals. The nine vertebrate plexins are subdivided into four subfamilies comprising four type A plexins, three type B plexins, plexin C1 (PlEXC1) and plexin D1(Neufeld & Kessler, 2008; Tamagnone et al., 1999). The plexins are transmembrane receptors distinguished by the presence of a split gTPase-activating (gAP) cytoplasmic domain (Oinuma et al., 2004). Semaphorins are members of a large gene family of secreted and membrane-anchored proteins containing more than 20 vertebrate genes. There are eight subclasses of Semas. Semas 1 and 2 are found in invertebrates, 3–7 are found in vertebrates, and Sema V is found in the genome of non neurotropic DNA viruses. They were initially characterized as axon guidance factors and are divided into eight subfamilies. The nine receptors belonging to the plexin family function as semaphorin receptors (Neufeld & Kessler, 2008). Semas were initially discovered with respect to their role as repulsive guidance cues for migrating axons, although it is now appreciated that they have much broader roles in development. Semas and Plxns have tissue-specific expression patterns, and many Semas can signal through multiple Plxn family members (Luo et al., 1993). Plxna2 is predicted to have semaphorin receptor activity. Involved in optic vesicle formation, predicted to localize to integral component of plasma membrane and semaphorin receptor complex. Is expressed in several structures, including brain; hatching gland; olfactory field; optic vesicle; and retina and is critical to zebrafish eye development. Orthologous to human PLXNA2 (plexin A2)(ZFIN Gene: Plxna2, n.d.).

Sema-Plxn signaling regulates cellular processes such as cytoskeletal dynamics, proliferation, and differentiation. However, the receptor-proximal signaling mechanisms driving Sema-Plxn signal transduction are only partially understood. Plxn tyrosine phosphorylation is thought to play an important role in these signaling events as receptor and nonreceptor tyrosine kinases have been shown to interact with Plxn receptors (St. Clair et al., 2018). Phosphorylation is one of the fundamental mechanisms of cell signaling and regulation of cell growth, proliferation, differentiation, metabolism, neural function, etc (Hanrs & Hunter2, n.d.; Johnson & Lewis, 2010; Mellado et al., 2001). Tyrosine phosphorylation is a pivotal post-translational protein modification that regulates intracellular signalling. Therefore, phosphorylation of tyrosines in the intracellular domain of plex-ins could determine or modify their interactions with additional signal transducers (Franco & Luca Tamagnone, 2008).

How It Is Measured or Detected

One of the primary considerations in evaluating AOPs is the relevance and reliability of the methods with which the KEs can be measured. The aim of this section of the KE description is not to provide detailed protocols, but rather to capture, in a sentence or two, per method, the type(s) of measurements that can be employed to evaluate the KE and the relative level of scientific confidence in those measurements. Methods that can be used to detect or measure the biological state represented in the KE should be briefly described and/or cited. These can range from citation of specific validated test guidelines, citation of specific methods published in the peer reviewed literature, or outlines of a general protocol or approach (e.g., a protein may be measured by ELISA).Key considerations regarding scientific confidence in the measurement approach include whether the assay is fit for purpose, whether it provides a direct or indirect measure of the biological state in question, whether it is repeatable and reproducible, and the extent to which it is accepted in the scientific and/or regulatory community. Information can be obtained from the OECD Test Guidelines website and the EURL ECVAM Database Service on Alternative Methods to Animal Experimentation (DB-ALM). ?

Phosphorylation changes of Plxna2 tyrosine can be detected  directly using western blot and indirectly by using ELISA method to measure plxna2 activity. There are several antibodies available commercially. 

In one study, Fyn kinase dependent phosphorylation of plxna2 was measured with western blotting using α-Fyn (rabbit mAb, 1 : 2000; Cell Signaling Technology), α-Flag M2 (mouse mAb, 1 : 2000; Sigma-Aldrich Corp.), α-phosphotyrosine 4G10 (mouse mAb; 1 : 1000; EMD Millipore, Billerica, MA, USA), and α-Src pY416 (rabbit mAb, 1 : 5000; Cell Signaling Technology). The following secondary antibodies were used: α-rabbit-HRP (goat IgG, 1 : 15 000; EMD Millipore), α-mouse-HRP (goat IgG, 1 : 5000; EMD Millipore), or for immunoprecipitation samples, α-mouse- HRP Light Chain Specific (goat IgG, 1 : 10 000, Jackson ImmunoResearch Laboratories, West Grove, PA, USA) (St. Clair et al., 2018).

Domain of Applicability

This free text section should be used to elaborate on the scientific basis for the indicated domains of applicability and the WoE calls (if provided). While structured terms may be selected to define the taxonomic, life stage and sex applicability (see structured applicability terms, above) of the KE, the structured terms may not adequately reflect or capture the overall biological applicability domain (particularly with regard to taxa). Likewise, the structured terms do not provide an explanation or rationale for the selection. The free-text section on evidence for taxonomic, life stage, and sex applicability can be used to elaborate on why the specific structured terms were selected, and provide supporting references and background information.  More help

Key event described here has been primarily established in zebrafish models (Emerson et al., 2017; St. Clair et al., 2018).


List of the literature that was cited for this KE description. Ideally, the list of references, should conform, to the extent possible, with the OECD Style Guide ( (OECD, 2015). More help

Emerson, S. E., St. Clair, R. M., Waldron, A. L., Bruno, S. R., Duong, A., Driscoll, H. E., Ballif, B. A., McFarlane, S., & Ebert, A. M. (2017). Identification of target genes downstream of semaphorin6A/PlexinA2 signaling in zebrafish. Developmental Dynamics, 246(7), 539–549.

Franco, M., & Luca Tamagnone, &. (2008). review Tyrosine phosphorylation in semaphorin signalling: shifting into overdrive. EMBO Reports, 9, 865–871.

Hanrs, S. K., & Hunter2, T. (n.d.). The eukaryotic protein kinase superfamily: idnase. (catalytic) domam structure and classification.

Johnson, L. N., & Lewis, R. J. (2010). ChemInform Abstract: Structural Basis for Control by Phosphorylation. ChemInform, 32(40), no--no.

Luo, Y., Raible, D., & Raper, J. A. (1993). Collapsin : A Protein in Brain That Induces the Collapse and Paralysis of Neuronal Growth Cones. 75(1984), 217–227.

Mellado, M., Rodríguez-Frade, J. M., Mañes, S., & Martínez-A., C. (2001). Chemokine signaling and functional responses: The role of receptor dimerization and TK pathway activation. Annual Review of Immunology, 19, 397–421.

Neufeld, G., & Kessler, O. (2008). The semaphorins: Versatile regulators of tumour progression and tumour angiogenesis. Nature Reviews Cancer, 8(8), 632–645.

Oinuma, I., Ishikawa, Y., Katoh, H., & Negishi, M. (2004). The Semaphorin 4D receptor Plexin-B1 is a GTPase activating protein for R-Ras. Science, 305(5685), 862–865.

St. Clair, R. M., Emerson, S. E., D’Elia, K. P., Marion, W. E., Schmoker, A. M., Ebert, A. M., & Ballif, B. A. (2018). Fyn-dependent phosphorylation of PlexinA1 and PlexinA2 at conserved tyrosines is essential for zebrafish eye development. FEBS Journal, 285(1), 72–86.

Tamagnone, L., Artigiani, S., Chen, H., He, Z., Ming, G. L., Song, H. J., Chedotal, A., Winberg, M. L., Goodman, C. S., Poo, M. M., Tessier-Lavigne, M., & Comoglio, P. M. (1999). Plexins are a large family of receptors for transmembrane, secreted, and GPI-anchored semaphorins in vertebrates. Cell, 99(1), 71–80.

ZFIN Gene: plxna2. (n.d.). Retrieved March 15, 2021, from