Suppression, Estrogen receptor (ER) activity

50-41-9

PYTMYKVIJXPNBD-UHFFFAOYSA-N

Clomiphene citrate (1:1)

Clomiphene citrate Clomid Ethanamine, 2-[4-(2-chloro-1,2-diphenylethenyl)phenoxy]-N,N-diethyl-, 2-hydroxy-1,2,3-propanetricarboxylate (1:1) 1-[p-(β-Diethylaminoethoxy)phenyl]-1,2-diphenyl-2-chloroethylene citrate 2-[4-(2-Chloro-1,2-diphenylethenyl)phenoxy]-N,N-diethylethanamine 2-hydroxy-1,2,3-propanetricarboxylic acid (1:1) 2-[p-(2-Chloro-1,2-diphenylvinyl)phenoxy]triethylamine dihydrogen citrate Chloramiphene clomifen dihydrogen citrate Clomifendihydrogencitrat Clomifene citrate Clomiphene dihydrogen citrate Clomivid Clomphid Clostilbegit Clostilbegyt dihidrogenocitrato de clomifeno dihydrogenocitrate de clomifen Dyneric Fertivet Genozym Ikaclomin Ikaclomine NSC 35770 Pergotime Racemic clomiphene citrate Serophene Triethylamine, 2-[p-(2-chloro-1,2-diphenylvinyl)phenoxy]-, citrate Triethylamine, 2-[p-(2-chloro-1,2-diphenylvinyl)phenoxy]-, citrate (1:1)

DTXSID8020337

10540-29-1

NKANXQFJJICGDU-QPLCGJKRSA-N

Tamoxifen

OHT Ethanamine, 2-[4-[(1Z)-1,2-diphenyl-1-butenyl]phenoxy]-N,N-dimethyl- (Z)-2-[4-(1,2-Diphenyl-1-butenyl)phenoxy]-N,N-dimethylethanamine Ethanamine, 2-[4-(1,2-diphenyl-1-butenyl)phenoxy]-N,N-dimethyl-, (Z)- Ethanamine, 2-[4-[(1Z)-1,2-diphenyl-1-buten-1-yl]phenoxy]-N,N-dimethyl- Ethylamine, 2-[p-(1,2-diphenyl-1-butenyl)phenoxy]-N,N-dimethyl-, (Z)- Mammaton Novaldex Tamoxifen and its salts tamoxifene tamoxifeno trans-Tamoxifen Z-Tamoxifen TAM

DTXSID1034187

84449-90-1

GZUITABIAKMVPG-UHFFFAOYSA-N

Raloxifene

RAL Methanone, [6-hydroxy-2-(4-hydroxyphenyl)benzo[b]thien-3-yl][4-[2-(1-piperidinyl)ethoxy]phenyl]-

DTXSID3023550

13311-84-7

MKXKFYHWDHIYRV-UHFFFAOYSA-N

Flutamide

Propanamide, 2-methyl-N-[4-nitro-3-(trifluoromethyl)phenyl]- 4-Nitro-3-(trifluoromethyl)isobutyranilide 4'-Nitro-3'-trifluoromethylisobutyranilide Eulexin Flucinom Flutamid flutamida m-Propionotoluidide, α,α,α-trifluoro-2-methyl-4'-nitro- N-(Isopropylcarbonyl)-4-nitro-3-trifluoromethylaniline Niftholide Niftolide NSC 147834 NSC 215876

DTXSID7032004

50471-44-8

FSCWZHGZWWDELK-UHFFFAOYNA-N

FSCWZHGZWWDELK-UHFFFAOYSA-N

Vinclozolin

2,4-Oxazolidinedione, 3-(3,5-dichlorophenyl)-5-ethenyl-5-methyl- (.+-.)-Vinclozolin BAS 352-04F N-3,5-Dichlorophenyl-5-methyl-5-vinyl-1,3-oxazolidine-2,4-dione N-3,5-Dichlorophenyl-5-methyl-5-vinyloxazolidine-2,4-dione N-3,5-Dichlorphenyl-5-methyl-5-vinyl-1,3-oxazolidin-2,4-dion N-3,5-diclorofenil-5-metil-5-vinil-1,3-oxazolidina-2,4-diona Ornalin Ranilan Ronilan Ronilan 50WP

DTXSID4022361

117-81-7

BJQHLKABXJIVAM-UHFFFAOYNA-N

BJQHLKABXJIVAM-UHFFFAOYSA-N

Di(2-ethylhexyl) phthalate

1,2-Benzenedicarboxylic acid, bis(2-ethylhexyl) ester DEHP 1,2-Benzedicarboxylic acid, bis(2-ethyl-hexyl) ester 1,2-Benzenedicarboxylic acid bis(2-ethylhexyl) ester 1,2-Benzenedicarboxylic acid, 1,2-bis(2-ethylhexyl) ester 1,2-Benzenedicarboxylic acid,bis(2-ethylhexylester) Bis(2-ethylhexyl) 1,2-benzenedicarboxylate Bis(2-ethylhexyl) o-phthalate bis(2-ethylhexyl) phthalate Bis(2-ethylhexyl)phthalat Bis(2-ethylhexyl)phthalate Bisoflex 81 Bisoflex DOP Corflex 400 Di(2-ethylhexyl)phthalate Di(isooctyl) phthalate Di-2-ethylhexlphthalate Di-2-ethylhexyl phthalate DI-2-ETHYLHEXYL-PHTHALATE Diacizer DOP Diethylhexyl phthalate Dioctylphthalate DOF Ergoplast FDO Ergoplast FDO-S ETHYLHEXYL PHTHALATE Eviplast 80 Eviplast 81 Fleximel Flexol DOD Flexol DOP ftlalato de bis(2-etilhexilo) Garbeflex DOP-D 40 Good-rite GP 264 Hatco DOP Jayflex DOP Kodaflex DEHP Kodaflex DOP Monocizer DOP NSC 17069 Palatinol AH Palatinol AH-L Phtalate de Bis (Ethyle-2-Hexyle) Phtalate de bis(2-ethylhexyle) PHTHALATE, BIS(2-ETHYLHEXYL) Phthalic acid di(2-ethylhexyl) ester Phthalic acid, bis(2-ethylhexyl) ester PHTHALIC ACID, BIS(2-ETHYLHEXYL)ESTER PHTHALSAEURE-BIS-(2-AETHYLHEXYL)-ESTER Pittsburgh PX 138 Plasthall DOP Reomol D 79P Sansocizer DOP Sansocizer R 8000 Sconamoll DOP Staflex DOP Truflex DOP Vestinol AH Vinycizer 80 Vinycizer 80K Witcizer 312

DTXSID5020607

PR:000007204

PR estrogen receptor

FMA:67338

FMA Mature sperm cell

GO:0030284

GO estrogen receptor activity

HP:0008669

HP Abnormal spermatogenesis

WIKI decreased

WIKI abnormal

Clomiphene citrate (1:1)

2022-02-26T23:24:20

Tamoxifen

2016-11-29T18:42:27

Raloxifene

2016-11-29T18:42:27

Flutamide Flutamide is a selective androgen receptor (AR) antagonist (Simard et al 1986) that has been shown to induce shorter male AGD in rats after in utero exposure (Foster & Harris 2005; Hass et al 2007; Kita et al 2016; McIntyre et al 2001; Mylchreest et al 1999; Scott et al 2007; Welsh et al 2007).

2016-11-29T18:42:27

2025-08-14T05:22:07

Vinclozolin

2020-05-14T11:28:31

Bis(2-ethylhexyl) phthalate

2016-11-29T18:42:08

WCS_9606

common toxicological species human

10116

NCBI rat

10095

NCBI mice

WikiUser_17

mammals

WikiUser_28

Vertebrates

Suppression, Estrogen receptor (ER) activity

Molecular

Estrogen receptors are produced in all vertebrates and located in either the cell cytoplasm or nucleus(Bondesson et al., 2015; Eick and Thornton, 2011). Estrogen receptors are localized either in cytoplasm, or on the cell surface.   Site of action: Stressors (e.g., clomiphene) act on neuronal cell in the hypothalamus, where it inhibits hypothalamic Estrogen Receptors selectively. Responses at the macromolecular level: Stressors activate the Estrogen Receptor α in the presence of lower level of estrogen and partially blocks the same for higher level of estrogen and works as antagonist for the Estrogen Receptor β(Trost and Khera, 2014). Stressors appear to act in the brain's pituitary gland to secrete an increased amount of gonadotropins hormone (GnRH) in hypothalamus leading towards increased GnRH level in blood. Estrogen Receptor α: ERα (Estrogen Receptor α or NR3A1 or ESR1) - A nuclear receptor and it is activated by the estrogen (sex hormone). Estrogen located at chromosome number 6 ( 6q25.1) Estrogen Receptor β:  ERβ (Estrogen Receptor β or NR3A2 or  ESR2) – This is also nuclear receptor and is activated by the sex hormone estrogen which is located at chromosome number 14 (14q23.2). I ERβ has an N-terminal DNA binding domain and C-terminal ligand binding domain. This  is localized to the nucleus, cytoplasm, and mitochondria. Selective estrogen receptor modulators (SERM) inhibits the ERβ. Drugs used as SERM are clomiphene, tamoxifen, raloxifene etc. Biological compartments:  Estrogen receptors (ER) are present in the plasma membrane. Both ERα and ERβ have diverse functions depending on cells and organs. ERs have also been located in cytoplasmic organelles including mitochondria and the endoplasmic reticulum(Levin, 2009).   General role in biology: Estrogen receptors (both estrogen receptor alpha (ERα) and estrogen receptor beta (ERβ) binds the estrogens to promote the biological functions of estrogens. Depending upon a balance between ERα and ERβ activities in target organs, estrogen signaling is selectively stimulated or inhibited (Welboren et al., 2009). ERβ has a high degree of sequence homology with the classical estrogen receptor (ERα). Interestingly, ERβ is detected in many tissues, including those previously assumed to be estrogen insensitive. In tissues where both ERs are expressed, such as the hypothalamus, uterus, mammary glands, and immune system, ERα promotes proliferation whereas ERβ has pro-apoptotic and pro-differentiating functions(Morani et al., 2008). ERα is present mainly in ovary (thecal cells) where as ERβ is found mainly in  ovary (granulosa cells)(Paterni et al., 2014). ERα and ERβ is identical approximately 97% in the DNA-binding domain and approximately 56% in the ligand-binding domain(Dahlman-Wright et al., 2006).

Radioreceptor assay/The estrogen receptor binding assay (using Rat Uterine Cytosol): This assay identifies chemicals that have the potential to interact with the estrogen receptor (ER) in vitro.  Principle of this particular assay is based on the competitive protein-binding methods. A radiolabelled ligand and an unlabelled ligand are presented together to a specific receptor. The radioactivity measurement provides the quantitative estimation of the bound and unbound fraction of the ligand with the receptor. All cytosolic estrogen receptor subtypes that are expressed in the specific tissue, including ERα and ERβ are used for the determination of estrogen receptor binding. This assay is simple and rapid to perform when optimal conditions for binding are determined. Assay determines if a ligand/chemical can interact and displace the endogenous hormone 17β-estradiol (Freyberger et al., 2010). An estrogen receptor (ER) transcription assay using fluorescent probes can trace the suppression of estrogen receptor signalling (Han et al., 2024). Levels of estrogen receptor protein can be assessed via immunohistochemical methods (Barnes et al., 1996).

Life Stage: Non-specific as occurs in many lifestages. Sex: Applies to both males and females. Taxonomic: Largely studied in laboratory mammals, plausible for all vertebrates as estrogen receptors have been evolutionarily conserved.

CL:0000540

CL neuron

High Mixed

High

Not Otherwise Specified

High High High

Adashi, E. Y., Hsueh, A. J., & Yen, S. S. (1980). Alterations induced by clomiphene in the concentrations of oestrogen receptors in the uterus, pituitary gland and hypothalamus of female rats. J Endocrinol. , 87(3), 383-92. Barnes DM, Harris WH, Smith P, Millis RR, Rubens RD. 1996. Immunohistochemical determination of oestrogen receptor: comparison of different methods of assessment of staining and correlation with clinical outcome of breast cancer patients. British Journal of Cancer. 74(9):1445-1451.  Bharti, S., Misro, M., & Rai, U. (2013). Clomiphene citrate potentiates the adverse effects of estrogen on rat testis and down-regulates the expression of steroidogenic enzyme genes. Fertility and sterility, 99(1), 140-148. e5. Bondesson, M., Hao, R., Lin, C.-Y., Williams, C., & Gustafsson, J.-Å. (2015). Estrogen receptor signaling during vertebrate development. Biochimica et Biophysica Acta (BBA)-Gene Regulatory Mechanisms, 1849(2), 142-151. Bussenot, I., Parinaud, J., Clamagirand, C., Vieitez, G., & Pontonnier, G. (1990). Effect of clomiphene cirate on oestrogen secretion by human granulosa cells in culture. Human Reproduction, 5(5), 533-536. Dahlman-Wright, K., Cavailles, V., Fuqua, S. A., Jordan, V. C., Katzenellenbogen, J. A., Korach, K. S., et al. (2006). International union of pharmacology. LXIV. Estrogen receptors. Pharmacological reviews, 58(4), 773-781. Dominguez, R., & Micevych, P. (2010). Estradiol rapidly regulates membrane estrogen receptor alpha levels in hypothalamic neurons. J Neurosci, 30(38), 12589-96. doi:30/38/12589 [pii]10.1523/JNEUROSCI.1038-10.2010. Eick, G. N., & Thornton, J. W. (2011). Evolution of steroid receptors from an estrogen-sensitive ancestral receptor. Molecular and cellular endocrinology, 334(1-2), 31-38. Freyberger, A., Wilson, V., Weimer, M., Tan, S., Tran, H. S., & Ahr, H. J. (2010). Assessment of a robust model protocol with accelerated throughput for a human recombinant full length estrogen receptor-alpha binding assay: protocol optimization and intralaboratory assay performance as initial steps towards validation. Reprod Toxicol, 30(1), 50-9. doi:S0890-6238(10)00003-1 [pii]. Han K, Choi G, Kim TJ. 2024. Fluorescence-based techniques for investigating estrogen receptor dynamics. BMB Reports 2024 57(11):472-483. Kerin, J. F., Liu, J. H., Phillipou, G., & Yen, S. S. (1985). Evidence for a hypothalamic site of action of clomiphene citrate in women. J Clin Endocrinol Metab. , 61(2), 65-68. Kettel, L. M., Roseff, S. J., Berga, S. L., Mortola, J. F., & Yen, S. S. (1993). Hypothalamic-pituitary-ovarian response to clomiphene citrate in women with polycystic ovary syndrome. Fertil Steril. , 59(3), 532-38. Koch, Y., Dikstein, S., Superstine, E., & Sulman, F. G. (1971). THE EFFECT OF PROMETHAZINE AND CLOMIPHENE ON GONADOTROPHIN SECRETION IN THE RAT. Journal of Endocrinology, 49(1), 13-17. doi:10.1677/joe.0.0490013. Kurosawa, T., Hiroi, H., Momoeda, M., Inoue, S., & Taketani, Y. (2010). Clomiphene citrate elicits estrogen agonistic/antagonistic effects differentially via estrogen receptors αand β. Endocrine journal, 57(6), 517-521. Levin, E. R. (2009). Plasma membrane estrogen receptors. Trends in Endocrinology & Metabolism, 20(10), 477-482. Morani, A., Warner, M., & Gustafsson, J. Å. (2008). Biological functions and clinical implications of oestrogen receptors alfa and beta in epithelial tissues. Journal of internal medicine, 264(2), 128-142. Oride, A., Kanasaki, H., Tumurbaatar, T., Zolzaya, T., Okada, H., Hara, T., et al. (2020). Effects of the Fertility Drugs Clomiphene Citrate and Letrozole on Kiss-1 Expression in Hypothalamic Kiss-1-Expressing Cell Models. Reproductive sciences (Thousand Oaks, Calif.), 27. doi:10.1007/s43032-020-00154-1. Paterni, I., Granchi, C., Katzenellenbogen, J. A., & Minutolo, F. (2014). Estrogen receptors alpha (ERα) and beta (ERβ): subtype-selective ligands and clinical potential. Steroids, 90, 13-29. Sutaria, U., Crooke, A., Bertrand, P., & Hodgson, C. (1980). Clomiphene citrate and human chorionic gonadotropin in the treatment of anovulatory infertility. International Journal of Gynecology & Obstetrics, 18(6), 435-437. Taheripanah, R., Kabir-Salmani, M., Favayedi, M., Zamaniyan, M., Malih, N., & Taheripanah, A. (2020). Effects of clomiphene citrate plus estradiol or progesterone on endometrial ultrastructure: An RCT. International Journal of Reproductive BioMedicine, 18(3), 201. Trost, L. W., & Khera, M. (2014). Alternative treatment modalities for the hypogonadal patient. Current urology reports, 15(7), 1-12. Wahab, O. A., Princely, A. C., Oluwadamilare, A. A., Ore-Oluwapo, D. O., Blessing, A. O., & Alfred, E. F. (2019). Clomiphene citrate ameliorated lead acetate-induced reproductive toxicity in male Wistar rats. JBRA assisted reproduction, 23(4), 336-343. doi:10.5935/1518-0557.20190038. Welboren, W.-J., Sweep, F. C., Span, P. N., & Stunnenberg, H. G. (2009). Genomic actions of estrogen receptor?: what are the targets and how are they regulated? Endocrine-related cancer, 16(4), 1073. Italics indicate edits from John Frisch July 2026.  A full list of updates can be found in the Change Log on the View History page.     AOPWiki 2016-11-29T18:41:28

2026-07-28T10:42:04

Epigenetic modification process

Cellular

Epigenetic modifications are the processes that involve changes in gene expression without modifying the DNA sequence (Shaw, 2006). The main processes are DNA methylation, histone modification, alterations of factors involved in nucleosomes assembly and remodeling, and gene regulation by non-coding RNAs (Rodríguez-Paredes & Esteller, 2011). DNA methylation is the addition of methyl groups in a CpG dinucleotide by DNA methyltransferases (DNMTs), resulting in the regulation of the expression of that gene (Sharma et al., 2010). DNA methylation usually affects the gene promoter, leading to the inhibition of gene transcription (Lee et al., 2020). In mammals, the DNMT family includes five proteins: DNMT1, DNMT2, DNMT3A, DNMT3B, and DNMT3L (DNMT3-like) (Bestor, 2000). The other important epigenetic process is histone modifications. Histones are proteins involved in DNA packaging into nucleosomes. The modifications on the tails of histones modify the chromatin formation, affecting gene accessibility (Greer & Shi, 2012). In particular, eukaryotic cells have 5 main families of histones, and histone H3 has an important role in the epigenetics (Shechter et al., 2007). Histones can undergo methylation, acetylation or phosphorylation (Ilango et al., 2020). Methylation of histones is carried out by histone methyltransferases and demethylation by histone demethylases. Based on the different lysine that is methylated, there could be the activation or the repression of transcription. For example, if lysine 4, 36 or 79 undergo methylation there will be as consequence the activation of transcription (Kouzarides, 2007), whereas lysines 9 or 27 methylation is linked to transcriptional repression (Raha et al., 2011). Furthermore, also the number of methyl groups is an important factor in the transcriptional effect. Lysine 9 di- and tri-methylation is associated with repression, whereas lysine 4 mono-methylation is associated with transcriptional activation (Lachner et al., 2001; Rosenfeld et al., 2009). Modification of the acetylation status of histones is under the control of histone acetyltransferases (HATs) that carry out acetylation, which can be reverted by histone deacetylases (HDACs). Histone acetylation instead is usually associated to an increased transcription, due to the removal of positive charges and therefore the relaxion of the chromatin (euchromatin), whereas histone deacetylation is related to transcription repression, due to the formation of heterochromatin (Watson et al., 2014). There is also emerging evidence of a crosstalk between methylated DNA regions and histone deacetylation (Lee et al., 2020). Indeed, histone deacetylases are part of a multiprotein transcription repression complex and they are associated to Sin3A and methyl-CpG binding proteins (MeCPs). MeCPs are able to bind to CpG islands which are methylated and to interact with Sin3A, that in turns interacts with histone deacetylases, leading to transcriptional repression (Bird & Wolffe, 1999, Cho et al., 2004; Song et al., 2013). Finally, non-coding RNAs, like lncRNA, sncRNA, miRNA, siRNA and piRNA, are some of the main players in epigenetics (Rajagopal et al., 2020). They are RNA transcripts that will not be translated into proteins, but they modulate gene expression by inhibiting target mRNA transcripts or by favoring their degradation (Esteller, 2011). They are involved in the development of several diseases, including cancer (Esteller, 2011). Between them, lncRNAs are characterized by different actions, such as histone modification and transcriptional regulation (Jiang et al., 2020).

Histone methylation Histone methylation can be detected directly by measuring histone methyltransferase activity/inhibition on specific histones using commercially available kits or indirectly as detection of specific histone methylation levels by western blotting with antibodies raised against specific histone modifications. DNA methylation (Urdinguio et al, 2009) Site-specific DNA methylation Bisulfite genomic sequencing of multiple clones is a DNA-methylation assay that entails initial modification of DNA by sodium bisulphite, converting all unmethylated, but not methylated, cytosines to uracil, and subsequent genomic sequencing. This assay constitutes one of the gold standards for DNA-methylation analysis, but is time consuming and expensive. Methylation-specific PCR uses bisulfite modified DNA and subsequent amplification with primers that are specific for methylated versus unmethylated DNA. This method is fast and cheap, but is not quantitative and requires previous knowledge of the DNA-methylation pattern. MethyLight is a high-throughput quantitative methylation assay that uses fluorescence-based real-time PCR technology. This technique also uses bisulfite modified DNA. Pyrosequencing is a DNA-sequencing method in which light is emitted as a result of an enzymatic reaction each time a nucleotide is incorporated into the growing DNA chain. Methylation-dependent DNA sequence variation, after sodium bisulphite treatment, is treated as a single nucleotide polymorphism. Genome-wide DNA methylation DNA-methylation arrays involve the modified DNA being hybridisied after bisulfite treatment to previously designed arrays and each methylation data point is represented by fluorescent signals from the M (methylated) and U (unmethylated) alleles printed in the platform. The arrays are imaged using a BeadArray Reader. This technique is reliable and automatised, but is limited to the CpG sites present in the array. Methylated DNA immunoprecipitation (methyl-DIP) involves immunoprecipitation with anti-5- methylcytosine antibodies followed by hybridisation to genomic microarrays or ultrasequencing, allowing the identification of methyl-CpG rich sequences. This method allows wide coverage of the human genome, but is expensive and requires a caerful bioinformatic analysis. Global DNA-methylation quantification High-performance capillary electrophoresis (HPCE) provides reliable measure of the total 5- methylcytosine DNA content starting with small amounts of sample, but requires specialised machinery. High performance liquid chromatography (HPLC) provides a reliable measure of the total 5- methylcytosine DNA content but requires important amounts of sample and specialised machinery. In situ DNA-methylation imaging Immunostaining with anti-5-methylcytosine antibodies requires the use of other markers to map the stained regions and has variability depending on the antibody badge. miRNAs and LncRNA A broad spectrum of methods is available in miRNAs lncRNA research, ranging from computational annotation of lncRNA genes to molecular and cellular analyses of the function of individual lncRNA. Description of these methods and methodological details are provided in a series of methods and protocols published in Methods in Molecular Biology by Humana Press (2006 and 2021) In Vivo measurements of epigenetic biomarkers Zebrafish has been proposed as a model for gene expression assessment of epigenetic biomarkers (Torres et al. 2021). In this model, morphological abnormalities and epigenetic changes were assessed at 80 hours-post fertilization, including DNA global methylation and gene expression of both DNA and histone epigenetic modifications

Epigenetic modulation is widely involved in developmental processes, differentiation, and reprogramming of stem cells, as well as a variety of human diseases. Dysregulation of epigenetic control is involved in several pathologies (Feinberg, 2007). Large amount of data accumulated in cancer epigenetics where epigenetic alterations contribute to cancer initiation and progression (Jones and Baylin, 2007; Esteller, 2008) Life Stage: All life stages as epigenetic modifications affecting gene expression occur in all life stages. Sex: Applies to both males and females. Taxonomic: Epigenetic modifications occur across a vast array of taxa including bacteria, plants, and animals (Liu et al. 2025).

High Unspecific

High

All life stages

High Moderate Bestor TH. The DNA methyltransferases of mammals. Hum Mol Genet 2000; 9: 2395–402. Bird, A. P., & Wolffe, A. P. (1999). Methylation-induced repression--belts, braces, and chromatin. Cell, 99(5), 451-454. https://doi.org/10.1016/s0092-8674(00)81532-9 Cho, K. S., Elizondo, L. I., & Boerkoel, C. F. (2004). Advances in chromatin remodeling and human disease. Current opinion in genetics & development, 14(3), 308-315. https://doi.org/10.1016/j.gde.2004.04.015 Esteller M. Epigenetics in cancer. N Engl J Med 2008; 358: 1148–59. Esteller M. (2011). Non-coding RNAs in human disease. Nature reviews. Genetics, 12(12), 861-874. <a href="https://doi.org/10.1038/nrg3074" style="color:#0563c1; text-decoration:underline">https://doi.org/10.1038/nrg3074</a> Feinberg AP. Phenotypic plasticity and the epigenetics of human disease. Nature 2007; 447: 433–40. Greer, E. L., & Shi, Y. (2012). Histone methylation: a dynamic mark in health, disease and inheritance. Nature reviews. Genetics, 13(5), 343-357. https://doi.org/10.1038/nrg3173 Ilango, S., Paital, B., Jayachandran, P., Padma, P. R., & Nirmaladevi, R. (2020). Epigenetic alterations in cancer. Frontiers in bioscience (Landmark edition), 25(6), 1058-1109. https://doi.org/10.2741/4847 Jiang, W., Xia, J., Xie, S., Zou, R., Pan, S., Wang, Z. W., Assaraf, Y. G., & Zhu, X. (2020). Long non-coding RNAs as a determinant of cancer drug resistance: Towards the overcoming of chemoresistance via modulation of lncRNAs. Drug resistance updates : reviews and commentaries in antimicrobial and anticancer chemotherapy, 50, 100683. <a href="https://doi.org/10.1016/j.drup.2020.100683" style="color:#0563c1; text-decoration:underline">https://doi.org/10.1016/j.drup.2020.100683</a> Jones PA, Baylin SB. The epigenomics of cancer. Cell 2007; 128: 683–92. Kouzarides T. (2007). Chromatin modifications and their function. Cell, 128(4), 693-705. https://doi.org/10.1016/j.cell.2007.02.005 Lachner, M., O'Carroll, D., Rea, S., Mechtler, K., & Jenuwein, T. (2001). Methylation of histone H3 lysine 9 creates a binding site for HP1 proteins. Nature, 410(6824), 116-120. https://doi.org/10.1038/35065132 Lee, H. T., Oh, S., Ro, D. H., Yoo, H., & Kwon, Y. W. (2020). The Key Role of DNA Methylation and Histone Acetylation in Epigenetics of Atherosclerosis. Journal of lipid and atherosclerosis, 9(3), 419-434. <a href="https://doi.org/10.12997/jla.2020.9.3.419" style="color:#0563c1; text-decoration:underline">https://doi.org/10.12997/jla.2020.9.3.419</a> Liu X, Nisa KUI, Kong W, Lang Z, and Niu Q. 2025. DNA methylation and histone modifications: conserved, divergent, and synergistic epigenetic regulation across plants and animals.  Epigenetics Insights 18: e015. Long Non-Coding RNAs, Methods and Protocols (2021). Eds. Lin Zhang, Xiaowen Hu, Humana New York, NY,  <a href="https://doi.org/10.1007/978-1-0716-1697-0" style="color:#0563c1; text-decoration:underline">https://doi.org/10.1007/978-1-0716-1697-0</a> MicroRNA Protocols. Methods and Protocols (2006).  Ed. Shao-Yao Ying, Humana New York, NY, doi.org/10.1385/1597451231 Raha, P., Thomas, S., & Munster, P. N. (2011). Epigenetic modulation: a novel therapeutic target for overcoming hormonal therapy resistance. Epigenomics, 3(4), 451-470. https://doi.org/10.2217/epi.11.72 Rajagopal, T., Talluri, S., Akshaya, R. L., & Dunna, N. R. (2020). HOTAIR LncRNA: A novel oncogenic propellant in human cancer. Clinica chimica acta; international journal of clinical chemistry, 503, 1-18. https://doi.org/10.1016/j.cca.2019.12.028 Rodríguez-Paredes, M., & Esteller, M. (2011). Cancer epigenetics reaches mainstream oncology. Nature medicine, 17(3), 330-339. https://doi.org/10.1038/nm.2305 Rosenfeld, J. A., Wang, Z., Schones, D. E., Zhao, K., DeSalle, R., & Zhang, M. Q. (2009). Determination of enriched histone modifications in non-genic portions of the human genome. BMC genomics, 10, 143. https://doi.org/10.1186/1471-2164-10-143 Sharma, S., Kelly, T. K., & Jones, P. A. (2010). Epigenetics in cancer. Carcinogenesis, 31(1), 27-36. https://doi.org/10.1093/carcin/bgp220 Shaw R. (2006). The epigenetics of oral cancer. International journal of oral and maxillofacial surgery, 35(2), 101-108. https://doi.org/10.1016/j.ijom.2005.06.014 Shechter, D., Dormann, H. L., Allis, C. D., & Hake, S. B. (2007). Extraction, purification and analysis of histones. Nature protocols, 2(6), 1445-1457. https://doi.org/10.1038/nprot.2007.202 Song, C. X., Szulwach, K. E., Dai, Q., Fu, Y., Mao, S. Q., Lin, L., Street, C., Li, Y., Poidevin, M., Wu, H., Gao, J., Liu, P., Li, L., Xu, G. L., Jin, P., & He, C. (2013). Genome-wide profiling of 5-formylcytosine reveals its roles in epigenetic priming. Cell, 153(3), 678-691. https://doi.org/10.1016/j.cell.2013.04.001 Torres T, Ruivo R, Santos MM. Epigenetic biomarkers as tools for chemical hazard assessment: Gene expression profiling using the model Danio rerio. Sci Total Environ. 2021 Jun 15;773:144830. doi: 10.1016/j.scitotenv.2020.144830. Epub 2021 Jan 29. PMID: 33592472. Urdinguio RG, Sanchez-Mut JV, Esteller M. Epigenetic mechanisms in neurological diseases: genes, syndromes, and therapies. Lancet Neurol 2009; 8: 1056–72 Watson, J.D., Baker, T.A., Gann, A., Levine, M., Losik, R. (2014). Molecular biology of the gene (Seventh ed.). Boston: Pearson/CSH Press. ISBN 978-0-321-76243-6. Italics indicate edits from John Frisch July 2026.  A full list of updates can be found in the Change Log on the View History page. AOPWiki 2023-07-27T05:44:01

2026-07-28T10:49:51

Impaired, Spermatogenesis

Organ

Spermatogenesis is a multiphase process of cellular transformation that produces mature male gametes known as sperm for sexual reproduction (Xu et al., 2015). The process of spermatogenesis can be broken down into 3 phases: the mitotic proliferation of spermatogonia, meiosis, and post-meiotic differentiation(spermiogenesis) (Boulanger et al., 2015). Spermatogenesis can be impaired within these phases or due to external factors such as chemical exposures or the gonadal tissue environment. For example, zebrafish and fathead minnow exposed to flutamide, an antiandrogen, have shown signs of impaired spermatogenesis such as spermatocyte degradation(Jensen et al., 2004, Yin et al., 2017).

Impairment of spermatogenesis can be measured and detected in a multitude of ways. One example of this is qualitative histological assessments (Jensen et al., 2004). Through histology, sperm morphology can be examined and quantified through the number and stage of the sperm. Sperm morphology, overall quantity, and quantity within each stage can be ways to detect impaired spermatogenesis(Uhrin et al., 2000, Xie et al., 2020). Additionally, sperm quality can also be another assessment of impaired spermatogenesis such as sperm motility, velocity, ATP content, and lipid peroxidation(Gage et al., 2004, Xia et al., 2018, Chen et al., 2015). Impaired spermatogenesis can also be seen by measuring sperm density(Chen et al., 2015).

Taxonomic Applicability: Largely studied in lab mammals; plausible for all sexually reproductive animals that have sperm. Many invertebrates that reproduce sexually produce sperm, although a diversity of reproductive strategies exist in invertebrates including parthenogenesis  (Picard et al. 2021). Life Stage Applicability: Only applicable for sexually mature adults Sex Applicability: Only applicable to males In vitro data is used to support these domains.

UBERON:0000473

UBERON testis

High Male

High

Adult, reproductively mature

High

Boulanger, G., Cibois, M., Viet, J., Fostier, A., Deschamps, S., Pastezeur, S., Massart, C., Gschloessl, B., Gautier-Courteille, C., & Paillard, L. (2015). Hypogonadism Associated with Cyp19a1 (Aromatase) Posttranscriptional Upregulation in Celf1 Knockout Mice. Molecular and cellular biology, 35(18), 3244–3253. <a href="https://doi.org/10.1128/MCB.00074-15">https://doi.org/10.1128/MCB.00074-15</a> Chen, J., Xiao, Y., Gai, Z., Li, R., Zhu, Z., Bai, C., Tanguay, R. L., Xu, X., Huang, C., & Dong, Q. (2015). Reproductive toxicity of low level bisphenol A exposures in a two-generation zebrafish assay: Evidence of male-specific effects. Aquatic toxicology (Amsterdam, Netherlands), 169, 204–214. https://doi.org/10.1016/j.aquatox.2015.10.020 Golshan, M. & S.M.H. Alvai (2019) “Androgen signaling in male fishes: Examples of anti-androgenic chemicals that cause reproductive disorders”, Theriogenology, Vol. 139, Elsevier, pp. 58-71. https://doi.org/10.1016/j.theriogenology.2019.07.020  Jensen, K.M. et al. (2004) “Characterization of responses to the antiandrogen flutamide in a short-term reproduction assay with the fathead minnow”, Aquatic Toxicology, Vol. 70(2), Elsevier, pp. 99-110. https://doi.org/10.1016/j.aquatox.2004.06.012  Organisation for Economic Co-operation and Development.  2001. Test No. 416: Two-Generation Reproduction Toxicity, OECD Guidelines for the Testing of Chemicals, Section 4.  https://www.oecd.org/content/dam/oecd/en/publications/reports/2001/01/test-no-416-two-generation-reproduction-toxicity_g1gh2941/9789264070868-en.pdf (retrieved 15 July 2026) Picard MAL, Vicoso B, Bertrand S, Escriva H. 2021. Diversity of Modes of Reproduction and Sex Determination Systems in Invertebrates, and the Putative Contribution of Genetic Conflict. Genes 12(8):1136.    Uhrin, P., Dewerchin, M., Hilpert, M., Chrenek, P., Schöfer, C., Zechmeister-Machhart, M., Krönke, G., Vales, A., Carmeliet, P., Binder, B. R., & Geiger, M. (2000). Disruption of the protein C inhibitor gene results in impaired spermatogenesis and male infertility. The Journal of clinical investigation, 106(12), 1531–1539. <a href="https://doi.org/10.1172/JCI10768">https://doi.org/10.1172/JCI10768</a> US Environmental Protection Agency (EPA).   1998.  Health Effects Test Guidelines OPPTS 870.3800 Reproduction and Fertility Effects https://ntp.niehs.nih.gov/sites/default/files/iccvam/suppdocs/feddocs/epa/epa_870_3800.pdf (retrieved 19 Jan 2026) Xia, H., Zhong, C., Wu, X., Chen, J., Tao, B., Xia, X., Shi, M., Zhu, Z., Trudeau, V. L., & Hu, W. (2018). Mettl3 Mutation Disrupts Gamete Maturation and Reduces Fertility in Zebrafish. Genetics, 208(2), 729–743. https://doi.org/10.1534/genetics.117.300574 Xie, H., Kang, Y., Wang, S., Zheng, P., Chen, Z., Roy, S., & Zhao, C. (2020). E2f5 is a versatile transcriptional activator required for spermatogenesis and multiciliated cell differentiation in zebrafish. PLoS genetics, 16(3), e1008655. https://doi.org/10.1371/journal.pgen.1008655 Xu, K., Wen, M., Duan, W., Ren, L., Hu, F., Xiao, J., Wang, J., Tao, M., Zhang, C., Wang, J., Zhou, Y., Zhang, Y., Liu, Y., & Liu, S. (2015). Comparative analysis of testis transcriptomes from triploid and fertile diploid cyprinid fish. Biology of reproduction, 92(4), 95. <a href="https://doi.org/10.1095/biolreprod.114.125609">https://doi.org/10.1095/biolreprod.114.125609</a> Yin, P. et al. (2017) “Diethylstilbestrol, flutamide and their combination impaired the spermatogenesis of male adult zebrafish through disrupting HPG axis, meiosis and apoptosis”, Aquatic Toxicology, Vol. 185, Elsevier, pp. 129-137. https://doi.org/10.1016/j.aquatox.2017.02.013 Italics indicate edits from John Frisch July 2026.  A full list of updates can be found in the Change Log on the View History page. AOPWiki 2020-04-16T12:02:39

2026-07-28T10:54:39

<upstream-id>74888601-f114-49f1-ac7c-6b21db7d12cd</upstream-id> <downstream-id>0afb9eb3-b27c-44bd-9270-cfb29ff6f960</downstream-id> Estrogen receptors (ER) are nuclear transcription factors involved in regulation of many physiological processes in vertebrates through signalling.  There are two main types of estrogen receptors, estrogen receptor alpha (ERα) and estrogen receptor beta (ERβ) receptors.  Binding by estrogen activates estrogen receptor activity.  Suppression of estrogen receptor activity occurs when a stressor hinders estrogen binding to estrogen receptors or when estrogen levels are diminished, resulting in lowered estrogen receptor activity. Epigenetic modifications are alterations that affect gene expression without altering the underlying gene sequence.  Among some of the more common processes that lead to epigenetic modifications are DNA methylation and alteration of histone proteins.  DNA methylation involves addition of methyl groups to DNA which causes increased or decreased gene expression.  Histone proteins are small proteins that assist gene expression, DNA repair, and DNA replication; histones can be modified by the addition of methyl, acetyl, or phosphate groups, which accelerates or slows DNA expression, repair, and replication.

This Key Event Relationship was part of an Environmental Protection Agency effort to develop AOPs that establish scientifically supported causal linkages between alternative endpoints measured using new approach methodologies (NAMs) and guideline apical endpoints measured in Tier 1 and Tier 2 test guidelines (U.S. EPA, 2025) employed by the Endocrine Disruptor Screening Program (EDSP). A series of key events that represent significant, measurable, milestones connecting molecular initiation to apical endpoints indicative of adversity were identified based on scientific review articles and empirical studies. Additionally, scientific evidence supporting the causal relationships between each pair of key events was assembled and evaluated.   The present effort focused primarily on empirical studies with mammals.   Empirical studies are focused on suppression of estrogen receptors and resulting epigenetic modifications, in support of development of AOP 651. Authors of KER 3833 did a further evaluation of published peer-reviewed literature to provide additional evidence in support of the key event relationship.  The literature used to support this KER began with the test guidelines and followed to primary, secondary, and/or tertiary works concerning the relevant underlying biology.  In addition, search engines were used to target journal articles with terms ‘estrogen receptor suppression’, ‘estrogen’, and ‘epigenetic modifications’ order to locate representative empirical studies that support the key event relationship.   Following initial human effort AOP development, artificial Intelligence (AI)-assisted literature search and synthesis, using EPA-AI GPT5, was used to identify additional literature, and draft Uncertainties and Inconsistencies content of this KER page. Additionally, EPA-AI GPT5 was also used to  check for additional text improvement in other sections. All content generated through this process were reviewed and verified by the KER author against literature sources, prior to inclusion.

Endocrine-disrupting compounds have been widely studied, with resulting disruptions to estrogen receptor activity.  Estrogen receptors have been evolutionarily conserved in vertebrates, and are key signallers in a variety of pathways.    Suppression of estrogen receptor activity leads to modification of downstream pathways of gene expression, including the levels of gene expression leading to proteins responsible for epigenetic modifications such as DNA methylation and the alteration of histone proteins.

<table cellspacing="0" class="Table" style="border-collapse:collapse; width:683px"> <tbody> <tr> <td style="background-color:#d9d9d9; border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:1px solid black; vertical-align:top; width:102px"> Species </td> <td style="background-color:#d9d9d9; border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:1px solid black; vertical-align:top; width:58px"> Duration </td> <td style="background-color:#d9d9d9; border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:1px solid black; vertical-align:top; width:121px"> Dose </td> <td style="background-color:#d9d9d9; border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:1px solid black; vertical-align:top; width:75px"> Suppression ER? </td> <td style="background-color:#d9d9d9; border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:1px solid black; vertical-align:top; width:89px"> Epigenetic modifications? </td> <td style="background-color:#d9d9d9; border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:1px solid black; vertical-align:top; width:155px"> Summary </td> <td style="background-color:#d9d9d9; border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:1px solid black; vertical-align:top; width:82px"> Citation </td> </tr> <tr> <td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top; width:102px"> Mice (Mus musculus) </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:58px"> 5 weeks </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:121px"> 20-40 ug/kg body weight zearalenone (ZEA). </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:75px"> yes </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:89px"> yes </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:155px"> Suppressed ER indicated by statistically significant decreased ERα protein in testes at all doses leading to epigenetic modifications indicated by statistically significant decrease in methylation markers 5mC and 5hmC at all doses and statistically significant increase in the histone methylation marker H3K27 at all doses. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:82px"> Gao et al. (2019) </td> </tr> <tr> <td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top; width:102px"> Mice (Mus musculus) </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:58px"> 5 weeks </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:121px"> 1–10 mg/kg body weight carbendazim (CBZ). </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:75px"> yes </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:89px"> yes </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:155px"> Suppressed ER indicated by statistically significant decreased ERα protein in testes at all doses leading to epigenetic modifications indicated by statistically significant decrease in methylation markers 5mC at all doses and 5hmC at high dose and statistically significant increase in the histone methylation marker H3K27 at all doses. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:82px"> Liu et al. (2019) </td> </tr> <tr> <td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top; width:102px"> Mice (Mus musculus) </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:58px"> 56 days after birth </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:121px"> 20-40 ug/kg body weight zearalenone (ZEA). </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:75px"> yes </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:89px"> yes </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:155px"> Suppressed ER in offspring indicated by statistically significant decreased ERα protein in testes at high dose leading to epigenetic modifications indicated by statistically significant decrease in methylation marker 5hmC at high dose and statistically significant increase in the histone methylation marker H3K27 at high dose. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:82px"> Men et al. (2019) </td> </tr> <tr> <td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top; width:102px"> Mice (Mus musculus) </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:58px"> 6 weeks </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:121px"> 50 mg/kg/body weight/day Bisphenol A (BPA) </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:75px"> yes </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:89px"> yes </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:155px"> Suppressed ER in offspring indicated by statistically significant decreased ERα and ERβ protein in testes leading to epigenetic modifications indicated by statistically significant change in histone mRNA, protein and methylation. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:82px"> Ryu et al. (2022) </td> </tr> </tbody> </table>

<ul> <li>Uncertainties in attribution to Estrogen receptors suppression. <ul style="list-style-type:circle"> <li>Estrogen receptors are only one class of nuclear receptor that alters gene expression of pathways associated with epigenetic modifications such as DNA methylation and histone modifications in humans and laboratory rodents (Romagnolo et al. 2014); therefore it can be difficult to attribute epigenetic modifications solely to suppression of estrogen receptor activity, particularly for studies conducted with stressors that are not highly specific to ER.</li> </ul> </li> <li>Complications due to heterogeneity in tissue type. <ul style="list-style-type:circle"> <li>Tissue contains a variety of cell types, particularly reproductive tissue with various ages in germ cells.  Care should be taken not to attribute a global pattern in epigenetic modification when there are heterogeneous cell-types present, which can be mitigated by single cell type studies in humans and laboratory rodents (Cui et al. 2025).</li> </ul> </li> </ul>

High Unspecific

Moderate

All life stages

High Moderate

Life Stage: All life stages as estrogen receptor signalling leading to epigenetic modifications affecting gene expression occur in all life stages. Sex: Applies to both males and females. Taxonomic: Largely studied in lab mammals; plausible for all vertebrates as estrogen receptors have been evolutionarily conserved, and epigenetic modifications are an inherent feature of DNA replication (Romagnolo et al. 2014; Fishman and Tauber 2024; Cui et al. 2025; Liu et al. 2025).

Cui Y, Deng J, Zhang Y, Du L, Jiang F, Li C, Chen W, Zhang H, He Z. 2025. Epigenetic regulation by DNA methylation, histone modifications and chromatin remodeling complexes in controlling spermatogenesis and their dysfunction with male infertility. Cellular and Molecular Life Sciences 82(1): 343.  Fishman B, Tauber E. 2024.  Epigenetics and seasonal timing in animals: a concise review. Journal of Comparative Physiology A: Neuroethology, Sensory, Neural, and Behavioral Physiology 210(4): 565-574.   Gao Y, Zhao Y, Zhang H, Zhang P, Liu J, Feng Y, Men Y, Li L, Shen W, Sun Z, Min L. 2019.  Pubertal exposure to low doses of zearalenone disrupting spermatogenesis through ERα related genetic and epigenetic pathways. Toxicology Letters. 315: 31-38. Liu J, Zhang P, Zhao Y, Zhang H. 2019.  Low dose carbendazim disrupts mouse spermatogenesis might be through estrogen receptor related histone and DNA methylation. Ecotoxicology and Environmental Safety 176: 242-249.  Liu X, Nisa KUI, Kong W, Lang Z, and Niu Q. 2025. DNA methylation and histone modifications: conserved, divergent, and synergistic epigenetic regulation across plants and animals.  Epigenetics Insights 18: e015. Men Y, Zhao Y, Zhang P, Zhang H, Gao Y, Liu J, Feng Y, Li L, Shen W, Sun Z, Min L. 2019.  Gestational exposure to low-dose zearalenone disrupting offspring spermatogenesis might be through epigenetic modifications. Basic and Clinical Pharmacology and Toxicology 125(4): 382-393. Romagnolo DF, Zempleni J, Selmin OI. 2014. Nuclear receptors and epigenetic regulation: opportunities for nutritional targeting and disease prevention. Advances in Nutrition 5(4):373-385. Ryu DY, Pang WK, Adegoke EO, Rahman MS, Park YJ, Pang MG. 2022.  Abnormal histone replacement following BPA exposure affects spermatogenesis and fertility sequentially. Environment International 170: 107617.  U.S. Environmental Protection Agency.  2025.  EDSP Test Guidelines and Guidance Document. https://www.epa.gov/test-guidelines-pesticides-and-toxic-substances/edsp-test-guidelines-and-guidance-document (retrieved 25 July 2025). Italics indicate edits from John Frisch July 2026.  A full list of updates can be found in the Change Log on the View History page.   AOPWiki 2026-07-28T10:22:17

2026-07-28T11:13:54

<upstream-id>0afb9eb3-b27c-44bd-9270-cfb29ff6f960</upstream-id> <downstream-id>ef0cfd4f-f15d-408f-851b-c7f4a06f934b</downstream-id> Epigenetic modifications are alterations that affect gene expression without altering the underlying gene sequence.  Among some of the more common processes that lead to epigenetic modifications are DNA methylation and alteration of histone proteins.  DNA methylation involves addition of methyl groups to DNA which causes increased or decreased gene expression.  Histone proteins are small proteins that assist gene expression, DNA repair, and DNA replication; histones can be modified by the addition of methyl, acetyl, or phosphate groups, which accelerates or slows DNA expression, repair, and replication.  Spermatogenesis is the process in which germ cells develop into mature sperm in testes in male animals and hermaphrodites.  Impaired spermatogenesis can result in lower mature sperm counts, problems in proper sperm function such as sperm motility, or other sperm abnormalities.  Epigenetic modifications alter the levels of gene expression for loci expressing proteins involved in sperm development, impairing spermatogenesis.

This Key Event Relationship was part of an Environmental Protection Agency effort to develop AOPs that establish scientifically supported causal linkages between alternative endpoints measured using new approach methodologies (NAMs) and guideline apical endpoints measured in Tier 1 and Tier 2 test guidelines (U.S. EPA, 2025) employed by the Endocrine Disruptor Screening Program (EDSP). A series of key events that represent significant, measurable, milestones connecting molecular initiation to apical endpoints indicative of adversity were identified based on scientific review articles and empirical studies. Additionally, scientific evidence supporting the causal relationships between each pair of key events was assembled and evaluated.   The present effort focused primarily on empirical studies with mammals.   Empirical studies are focused on epigenetic modifications and resulting impaired spermatogenesis, in support of development of AOP 651. Authors of KER 3834 did a further evaluation of published peer-reviewed literature to provide additional evidence in support of the key event relationship.  The literature used to support this KER began with the test guidelines and followed to primary, secondary, and/or tertiary works concerning the relevant underlying biology.  In addition, search engines were used to target journal articles with ‘epigenetic modifications’, ‘sperm motility’, and ‘sperm abnormalities’ in order to locate representative empirical studies that support the key event relationship.   Following initial human effort AOP development, artificial Intelligence (AI)-assisted literature search and synthesis, using EPA-AI GPT5, was used to identify additional literature, and draft Uncertainties and Inconsistencies content of this KER page. Additionally, EPA-AI GPT5 was also used to  check for additional text improvement in other sections. All content generated through this process were reviewed and verified by the KER author against literature sources, prior to inclusion.

Epigenetic modification of DNA located in germ cells alters the levels of gene expression for loci expressing proteins involved in sperm development, with resulting impaired spermatogenesis causing lower sperm counts, problems in sperm function, and other sperm abnormalities (for review of normal epigenetic modifications in spermatogenesis, see Gunes and Kulac (2013), for review of how disruption of epigenetic modifications disrupts spermatogenesis, see Cui et al. (2025)).

<table cellspacing="0" class="Table" style="border-collapse:collapse; width:683px"> <tbody> <tr> <td style="background-color:#d9d9d9; border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:1px solid black; vertical-align:top; width:95px"> Species </td> <td style="background-color:#d9d9d9; border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:1px solid black; vertical-align:top; width:58px"> Duration </td> <td style="background-color:#d9d9d9; border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:1px solid black; vertical-align:top; width:113px"> Dose </td> <td style="background-color:#d9d9d9; border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:1px solid black; vertical-align:top; width:86px"> Epigenetic modfications? </td> <td style="background-color:#d9d9d9; border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:1px solid black; vertical-align:top; width:109px"> Impaired spermatogenesis? </td> <td style="background-color:#d9d9d9; border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:1px solid black; vertical-align:top; width:147px"> Summary </td> <td style="background-color:#d9d9d9; border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:1px solid black; vertical-align:top; width:76px"> Citation </td> </tr> <tr> <td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top; width:95px"> Mice (Mus musculus) </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:58px"> 5 weeks </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:113px"> 20-40 ug/kg body weight zearalenone (ZEA). </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:86px"> yes </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:109px"> yes </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:147px"> Epigenetic modifications indicated by statistically significant decrease in methylation markers 5mC and 5hmC at all doses and statistically significant increase in the histone methylation marker H3K27 at all doses leading to impaired spermatogenesis indicated by statistically significant decrease in sperm motility at high dose and statistically significant increase in abnormal acrosome integrity and spermatozoa abnormality at all doses. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:76px"> Gao et al. (2019) </td> </tr> <tr> <td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top; width:95px"> Mice (Mus musculus) </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:58px"> 5 weeks </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:113px"> 1–10 mg/kg body weight carbendazim (CBZ). </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:86px"> yes </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:109px"> yes </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:147px"> Epigenetic modifications indicated by statistically significant decrease in methylation markers 5mC at all doses and 5hmC at high dose and statistically significant increase in the histone methylation marker H3K27 at all doses leading to impaired spermatogenesis indicated by statistically significant decrease in sperm motility at all doses and statistically significant decrease in  spermatozoa count at high dose. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:76px"> Liu et al. (2019) </td> </tr> <tr> <td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top; width:95px"> Mice (Mus musculus) </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:58px"> 56 days after birth </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:113px"> 20-40 ug/kg body weight zearalenone (ZEA). </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:86px"> yes </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:109px"> yes </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:147px"> Epigenetic modifications in offspring indicated by statistically significant decrease in methylation marker 5hmC at high dose and statistically significant increase in the histone methylation marker H3K27 at high dose leading to impaired spermatogenesis indicated by statistically significant decrease in sperm motility at all doses, statistically significant decrease in  spermatozoa count at high dose, and statistically significant increase in abnormal acrosome integrity at high dose. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:76px"> Men et al. (2019) </td> </tr> <tr> <td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top; width:95px"> Mice (Mus musculus) </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:58px"> 6 weeks </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:113px"> 50 mg/kg/body weight/day Bisphenol A (BPA) </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:86px"> yes </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:109px"> yes </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:147px"> Epigenic modifications indicated by statistically significant change in histone mRNA, protein and methylation leading to impaired spermatogenesis indicated by statistically significant decrease in sperm motility, concentration, and hyperactivity. </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:76px"> Ryu et al. (2022) </td> </tr> </tbody> </table>

<ul> <li>Complications due to heterogeneity in tissue type. <ul style="list-style-type:circle"> <li>Tissue contains a variety of cell types, particularly reproductive tissue with various ages in germ cells.  Care should be taken not to attribute a global pattern in epigenetic modification when there are heterogeneous cell-types present, which can be mitigated by single cell type studies in humans and laboratory rodents (Cui et al. 2025).</li> </ul> </li> <li>Complications due to multiple epigenetic effects. <ul style="list-style-type:circle"> <li>Interactions among DNA methylation, histone modifications, and other epigenetic modifications can make it difficult to attribute impaired spermatogenesis to a particular epigenetic effect in humans and laboratory rodents (Cui et al. 2025).</li> </ul> </li> </ul>

High Male

Moderate

Adult, reproductively mature

High Moderate

Life Stage: Adult, reproductively mature for process producing fully functional sperm. Sex: Applies to males as related to sperm. Taxonomic: Largely studied in lab mammals; plausible for all sexually reproductive animals that have sperm.

Cui Y, Deng J, Zhang Y, Du L, Jiang F, Li C, Chen W, Zhang H, He Z. 2025.  Epigenetic regulation by DNA methylation, histone modifications and chromatin remodeling complexes in controlling spermatogenesis and their dysfunction with male infertility. Cellular and Molecular Life Sciences 82(1): 343.  Gao Y, Zhao Y, Zhang H, Zhang P, Liu J, Feng Y, Men Y, Li L, Shen W, Sun Z, Min L. 2019.  Pubertal exposure to low doses of zearalenone disrupting spermatogenesis through ERα related genetic and epigenetic pathways. Toxicology Letters. 315: 31-38. Gunes S, Kulac T.  2013.  The role of epigenetics in spermatogenesis. Turkish Journal of Urology 39(3): 181-187. Liu J, Zhang P, Zhao Y, Zhang H. 2019.  Low dose carbendazim disrupts mouse spermatogenesis might be through estrogen receptor related histone and DNA methylation. Ecotoxicology and Environmental Safety 176: 242-249.  Men Y, Zhao Y, Zhang P, Zhang H, Gao Y, Liu J, Feng Y, Li L, Shen W, Sun Z, Min L. 2019.  Gestational exposure to low-dose zearalenone disrupting offspring spermatogenesis might be through epigenetic modifications. Basic and Clinical Pharmacology and Toxicology 125(4): 382-393. Ryu DY, Pang WK, Adegoke EO, Rahman MS, Park YJ, Pang MG. 2022.  Abnormal histone replacement following BPA exposure affects spermatogenesis and fertility sequentially. Environment International 170: 107617.  U.S. Environmental Protection Agency.  2025.  EDSP Test Guidelines and Guidance Document. https://www.epa.gov/test-guidelines-pesticides-and-toxic-substances/edsp-test-guidelines-and-guidance-document (retrieved 25 July 2025). Italics indicate edits from John Frisch July 2026.  A full list of updates can be found in the Change Log on the View History page.   AOPWiki 2026-07-28T10:22:38

2026-07-28T11:18:52

Suppression, Estrogen receptor (ER) activity leads to Impaired, Spermatogenesis via epigenetic modifications

Suppression ER activity leads to Impaired, Spermatogenesis

John Frisch

Of the content populated in the AOP-Wiki: John R. Frisch and Travis Karschnik, General Dynamics Information Technology; Daniel L. Villeneuve, US Environmental Protection Agency, Risk Assessment Support Division; Scott Lynn, US Environmental Protection Agency, Office of Chemical Safety and Pollution Prevention.

BY-SA

2.8

Estrogen receptors (ER) are nuclear transcription factors involved in regulation of many physiological processes in vertebrates through signalling.  There are two main classic types of nuclear estrogen receptors, estrogen receptor alpha (ERα) and estrogen receptor beta (ERβ) receptors and a more recently discovered membrane receptor, G protein-coupled estrogen receptor 1 (GPER1; Chen et al. (2022)).  Binding by estrogen activates estrogen receptor activity.  Suppression of estrogen receptor activity occurs when a stressor hinders estrogen binding to estrogen receptors or when estrogen levels are diminished, resulting in lowered estrogen receptor activity. Epigenetic modifications are alterations that affect gene expression without altering the underlying gene sequence.  Among some of the more common processes that lead to epigenetic modifications are DNA methylation and alteration of histone proteins.  DNA methylation involves addition of methyl groups to DNA which causes increased or decreased gene expression.  Histone proteins are small proteins that assist gene expression, DNA repair, and DNA replication; histones can be modified by the addition of methyl, acetyl, or phosphate groups, which accelerates or slows DNA expression, repair, and replication. Spermatogenesis is the process in which germ cells develop into mature sperm in testes in male animals.  Impaired spermatogenesis can result in lower mature sperm counts, problems in proper sperm function such as sperm motility, or other sperm abnormalities.  For review of normal epigenetic modifications in spermatogenesis, see Gunes and Kulac (2013), for review of how disruption of epigenetic modifications disrupts spermatogenesis, see Cui et al. (2025). This AOP contributes to the scientific understanding of the mechanistic foundations for linking suppression of estrogen receptor activity to the adverse outcome impaired spermatogenesis, with sperm motility, morphology, and abnormalities representing apical endpoints in guideline tests associated with the Endocrine Disruptor Screening Program (US EPA 1998; OECD 2001).   This AOP was part of an Environmental Protection Agency effort to develop AOPs that establish scientifically supported causal linkages between alternative endpoints measured using new approach methodologies (NAMs) and guideline apical endpoints measured in Tier 1 and Tier 2 test guidelines (U.S. EPA, 2025) employed by the Endocrine Disruptor Screening Program (EDSP).  A series of key events that represent significant, measurable, milestones connecting molecular initiation to apical endpoints indicative of adversity were identified based on scientific review articles and empirical studies. Additionally, scientific evidence supporting the causal relationships between each pair of key events was assembled and evaluated. The present effort focused primarily on empirical studies with laboratory mammals.

The scope of the aforementioned EPA project was to develop AOP(s) relevant to apical endpoints employed in the test guidelines, based on mechanisms consistent with empirical studies. The literature used to support this AOP and its constituent pages began with the test guidelines and followed to primary, secondary, and/or tertiary works concerning the relevant underlying biology. KE and KER page creation and re-use was determined using Handbook principles where page re-use was preferred.   <img alt="" src="https://aopwiki.org/system/dragonfly/production/2024/07/16/2spzwstnyk_Citation_workflow_graphic.png" style="height:729px; width:592px" />

Clomiphene citrate (a stressor) at 10-10 - 10-12 M concentrations exhibits approximately 30% of the estrogenic activity which is same from 17β-estradiol (at 10-10 M) in ERα-expressing cells where as no activity in ERβ cells. Clomiphene citrate at the concentration of  10-10 M reveals weak estrogen agonist activity in the presence of 17 β -estradiol (E2) at the concentration of 10-14 M in ERα-expressing cells, and no activity was found in ERβ cells. Clomiphene citrate at lower doses (10-10 - 10-12 M), but not higher doses (10-6 - 10-8 M) showed estrogenic activity via ERα. However, clomiphene citrate at concentrations between 10-6 M and 10-12 M did not reveal any estrogenic activity via ERβ. In the presence of E2, clomiphene citrate worked as either as an agonist or an antagonist through ERα depending on the concentrations of E2.  Clomiphene citrate worked as antagonistic when it is combined with the higher E2 concentrations and worked as agonistic with the lower E2 concentrations. On the other hand, via ER β, clomiphene citrate acted as an estrogen antagonist irrespective of the concentration of E2. (Kurosawa et al., 2010).

Impairment of spermatogenesis is an adverse outcome monitored in Endocrine Disruptor Screening Program (EDSP) protocol (US EPA 1998; OECD 2001), assessed by sperm motility, morphology, and abnormalities.

adjacent

Not Specified

Moderate adjacent

Not Specified

Moderate

High Male

Moderate

Adult, reproductively mature

High Moderate

<table cellspacing="0" class="Table" style="border-collapse:collapse"> <tbody> <tr> <td colspan="2" style="background-color:#d0cece; border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:1px solid black; vertical-align:top"> 1. Support for Biological Plausibility of Key Event Relationships: Is there a mechanistic relationship between KEup and KEdown consistent with established biological knowledge? </td> </tr> <tr> <td style="background-color:#d0cece; border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top"> Key Event Relationship (KER) </td> <td style="background-color:#d0cece; border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top"> Level of Support   Strong = Extensive understanding of the KER based on extensive previous documentation and broad acceptance. Moderate = Support of essentiality from empirical studies, with some uncertainty in how tightly upstream events are linked to downstream events. </td> </tr> <tr> <td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top"> Relationship 3833: Suppression, Estrogen receptor (ER) activity leads to epigenetic modifications </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top"> Moderate support.  The relationship between suppression of estrogen receptor activity and epigenetic modifications is broadly accepted and supported by animal data, particularly laboratory mammal data.   Given the complexity of molecular-level interactions, it is difficult to link suppression of ER signalling to specific epigenetic modifications. </td> </tr> <tr> <td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top"> Relationship 3834: Epigenetic modifications leads to impaired, Spermatogenesis </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top"> Moderate support.  The relationship between epigenetic modifications  and impaired spermatogenesis is broadly accepted and supported by animal data, particularly laboratory mammal data. Although specific epigenetic modifications have been linked to specific spermatogenesis impairments, it is difficult to establish causality.  </td> </tr> <tr> <td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top"> Overall </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top"> Moderate support.  Extensive understanding of the relationships between events from empirical studies from animals, particularly laboratory mammals. </td> </tr> </tbody> </table> Life Stage: Adult, reproductively mature for process producing fully functional sperm. Sex: Applies to males as related to sperm. Taxonomic: Largely studied in laboratory mammals, plausible for all vertebrates as estrogen receptors have been evolutionarily conserved.

<table cellspacing="0" class="Table" style="background:white; border-collapse:collapse; width:775px"> <tbody> <tr> <td colspan="2" style="background-color:#d0cece; border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top"> 2. Essentiality of Key Events: Are downstream KEs and/or the AO prevented if an upstream KE is blocked? </td> </tr> <tr> <td style="background-color:#d0cece; border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top"> Key Event (KE) </td> <td style="background-color:#d0cece; border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top"> Level of Support Strong = Direct evidence from specifically designed experimental studies illustrating essentiality and direct relationship between key events. </td> </tr> <tr> <td style="background-color:white; border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top"> MIE 1046 Suppression, Estrogen receptor (ER) activity </td> <td style="background-color:white; border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top"> Strong support.  Suppression of estrogen receptor activity leads to epigenetic modifications.   Evidence is available from exposure to endocrine-disrupting compounds and toxicants.  Best evidence for essentiality for estrogen receptor activity is from stressor exposure studies decreasing estrogen receptor activity leading to altered histone messenger RNA, protein and methylation. </td> </tr> <tr> <td style="background-color:white; border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top"> KE 2152 Epigenetic modifications </td> <td style="background-color:white; border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top"> Strong support.  Epigenetic modifications lead to impaired spermatogenesis.   Evidence is available from exposure to endocrine-disrupting compounds and toxicants.  Best evidence for essentiality of epigenetic modifications is from studies showing a specific epigenetic modification leading to a specific impairment of spermatogenesis (reviewed by Cui et al. 2025).  </td> </tr> <tr> <td style="background-color:white; border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top"> AO 1758 Impaired, Spermatogenesis </td> <td style="background-color:white; border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top"> This is the final event of the AOP. </td> </tr> <tr> <td style="background-color:white; border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top"> Overall </td> <td style="background-color:white; border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top"> Strong support.  Direct evidence from empirical studies from animals, particularly laboratory mammals for all key events. </td> </tr> </tbody> </table>

<table cellspacing="0" class="Table" style="border-collapse:collapse"> <tbody> <tr> <td colspan="2" style="background-color:#d0cece; border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top"> 3. Empirical Support for Key Event Relationship: Does empirical evidence support that a change in KEup leads to an appropriate change in KEdown? </td> </tr> <tr> <td style="background-color:#d0cece; border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top"> Key Event Relationship (KER) </td> <td style="background-color:#d0cece; border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top"> Level of Support  Strong =  Experimental evidence from exposure to toxicant shows consistent change in both events across taxa and study conditions.  </td> </tr> <tr> <td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top"> Relationship 3833: Suppression, Estrogen receptor (ER) activity leads to epigenetic modifications </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top"> Strong support.  Suppression of estrogen receptor activity leads to epigenetic modifications.  Evidence is available from endocrine disruptor and toxicant studies.  Suppression of estrogen receptor activity occurred earlier in the time-course of exposure than epigenetic modifications, and the concentrations of stressors that suppressed estrogen receptor activity were equal to or lower than the concentrations that led to epigenetic modifications.  Therefore, the data support a causal relationship.  </td> </tr> <tr> <td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top"> Relationship 3834: Epigenetic modifications leads to impaired, Spermatogenesis </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top"> Strong support. Epigenetic modifications leads to impaired spermatogenesis.  Evidence is available from endocrine disruptor and toxicant studies.  Epigenetic modifications occurred earlier in the time-course of exposure than impaired spermatogenesis, and the concentrations of stressors that caused epigenetic modifications were equal to or lower than the concentrations that led to impaired spermatogenesis.  Therefore, the data support a causal relationship. </td> </tr> <tr> <td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top"> Overall </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top"> Strong support.  Evidence from empirical studies shows consistent relationships in upstream and downstream events, with upstream events occurring earlier in the time-course of exposure and at equal or lower concentrations than downstream events, supporting causal relationships. </td> </tr> </tbody> </table>

<div> <table class="table table-bordered table-fullwidth"> <thead> <tr> <th>Modulating Factor (MF)</th> <th>Influence or Outcome</th> <th>KER(s) involved</th> </tr> </thead> <tbody> <tr> <td> </td> <td> </td> <td> </td> </tr> </tbody> </table> </div>

Chen P, Li B, Ou-Yang L.  2022.  Role of estrogen receptors in health and disease. Frontiers in Endrocrinology 13:839005.  Cui Y, Deng J, Zhang Y, Du L, Jiang F, Li C, Chen W, Zhang H, He Z. 2025.  Epigenetic regulation by DNA methylation, histone modifications and chromatin remodeling complexes in controlling spermatogenesis and their dysfunction with male infertility. Cellular and Molecular Life Sciences 82(1): 343.  Gunes S, Kulac T.  2013.  The role of epigenetics in spermatogenesis. Turkish Journal of Urology 39(3): 181-187. Organisation for Economic Co-operation and Development.  2001. Test No. 416: Two-Generation Reproduction Toxicity, OECD Guidelines for the Testing of Chemicals, Section 4.  https://www.oecd.org/content/dam/oecd/en/publications/reports/2001/01/test-no-416-two-generation-reproduction-toxicity_g1gh2941/9789264070868-en.pdf (retrieved 15 July 2026) U.S. Environmental Protection Agency.  1998.  Health Effects Test Guidelines OPPTS 870.3800 Reproduction and Fertility Effects.  https://ntp.niehs.nih.gov/sites/default/files/iccvam/suppdocs/feddocs/epa/epa_870_3800.pdf (retrieved 24 December 2025) U.S. Environmental Protection Agency.  2025.  EDSP Test Guidelines and Guidance Document. https://www.epa.gov/test-guidelines-pesticides-and-toxic-substances/edsp-test-guidelines-and-guidance-document (retrieved 25 July 2025).   AOPWiki 2026-07-28T10:11:21

2026-07-28T11:22:31