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Event: 1890

Key Event Title

A descriptive phrase which defines a discrete biological change that can be measured. More help

Decrease (loss of) fetal male germ cells

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. More help

Germ cell loss, male

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Biological Context

Structured terms, selected from a drop-down menu, are used to identify the level of biological organization for each KE. More help

Level of Biological Organization
Cellular

Cell term

The location/biological environment in which the event takes place.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. Further information on Event Components and Biological Context may be viewed on the attached pdf. More help

Organ term

Key Event Components

The KE, as defined by a set structured ontology terms consisting of a biological process, object, and action with each term originating from one of 14 biological ontologies (Ives, et al., 2017; https://aopwiki.org/info_pages/2/info_linked_pages/7#List). Biological process describes dynamics of the underlying biological system (e.g., receptor signalling).Biological process describes dynamics of the underlying biological system (e.g., receptor signaling). 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 signaling 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. Further information on Event Components and Biological Context may be viewed on the attached pdf. 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
Ectopic ATRA in fetal testis leads to reduced sperm count	KeyEvent	Terje Svingen (send email)	Under development: Not open for comment. Do not cite

Taxonomic Applicability

Latin or common names of a species or broader taxonomic grouping (e.g., class, order, family) that help to define the biological applicability domain of the KE.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
human, mouse, rat	human, mouse, rat	Moderate	NCBI

Life Stages

An indication of the the relevant life stage(s) for this KE. More help

Life stage	Evidence
Fetal	High

Sex Applicability

An indication of the the relevant sex for this KE. More help

Term	Evidence
Male	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. More help

Male germ cell apoptosis in the fetal testis

In the fetal testis, apoptosis of XY germ cells (pro-spermatogonia) takes place early during gonad differentiation (Coucouvanis et al, 1993; Nguyen et al, 2020; Rucker 3rd et al, 2000; Wang et al, 1998) and is required to adjust overall germ cell numbers to Sertoli cells within the testis cords (Aitken et al, 2011). Later in development, spermatogonia that have been damaged by, for instance by chemical exposures, are also eliminated by apoptosis (Aitken et al, 2011; Wang et al, 2007). Hence, the process of germ cell apoptosis in integral to reproductive development and a failure to eliminate damaged and excess spermatogonia can result in sterility (Knudson et al, 1995; Rodriguez et al, 1997). Nonetheless, it stands to reason that abnormally high levels of apoptosis during fetal life will result in a smaller spermatogonial stem cell pool, and that this will likely result in diminished reproductive potential (Aitken et al, 2011).

Fetal germ cell loss as Key Event

Although it is normal that a large number of pro-spermatogonia are eliminated by apoptosis during development, excessive loss during the prenatal period would be expected to have a direct consequence for fertility later in life. If all or the majority of pro-spermatogoia are lost, the spermatogonial stem cell pool will be either depleted and/or be of lower quality, and therefore the efficiency of spermatogenesis in the adult testis will be compromised. Hence, loss of germ cells during fetal life, in excess of what is normally ‘programmed’, would be expected to negatively impact adult fertility. It is relevant that spermatogenesis is relatively robust in rodents, compared with humans; in the latter, the number of sperm per ejaculate is only 2 – 4 fold higher than the number at which fertility is significantly reduced (Rahban & Nef, 2020; Working, 1988).

How It Is Measured or Detected

A description of the type(s) of measurements that can be employed to evaluate the KE and the relative level of scientific confidence in those measurements.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). Do not provide detailed protocols. More help

Apoptosis is most routinely detected by DNA ladder assay, TUNEL assay or Comet assay (Majtnerová & Roušar, 2018).

Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay, which detects apoptotic DNA fragmentations (Gorczyca et al, 1992) is available commercially from numerous companies using various staining technologies.

DNA laddering can be used to measure apoptosis at later stages only and is used to detect apoptosis of many cells, as it involves separation of DNA by agarose gel electrophoresis (Gong et al, 1994).

Comet assay, or single cell gel electrophoresis assay, can detect DNA damage at single-cell resolution (Singh et al, 1988). The alkaline Comet Assay is part of OECD Test Guideline 489 (OECD, 2016).

Direct measurements of total germ cell number in animal models can be performed with using various probes and antibodies to germ cell markers that are commercially available and reporter assays using germ cell specific promoter elements driving expression of reporter proteins. These reporter assays can detect the presence of germ cells in a quantitative manner. Examples include reporter mouse line OG2 (Szabó et al, 2002).

Domain of Applicability

A description of the scientific basis for the indicated domains of applicability and the WoE calls (if provided). More help

Fetal male germ cells must enter cell cycle quiescence during fetal life (McLaren, 2001). This process is conserved between mice, rats and humans (Francavilla et al, 1990)