DES Gene Changes and Proposed Mechanisms of Action

image of Mechanisms involved in breast cancer etiology

Exposure to Diethylstilbestrol during Sensitive Life Stages: A legacy of heritable health effects

2013 Study Abstract

The fact that DES causes developmental changes in the second generation through gestational exposure has required evaluation of the mechanisms involved in several target tissues. DES is classified as a carcinogen by the World Health Organization, U.S. Environmental Protection Agency, National Toxicology Program, and the International Agency for Cancer Research. Studies on the genotoxicity of DES in humans have not revealed striking outcomes; to date, it does not change ploidy patterns, cause specific mutations known to induce high risk of breast cancer, or induce loss of heterozygosity of allelic imbalance. In directed in vitro tests, the data on induction of sister chromatid exchange, induction of micronuclei, and unscheduled DNA synthesis, were negative or equivocal. However, DES caused aneuploidy, induced adduct formation in mitochondrial DNA, and altered the ability of microtubules to form.

DES is also known to affect endocrine sensitive tissues and may have hereditary effects due to DNA modifications ; like many other breast cancer risk factors, it may have multiple mechanisms of action, depending on the target tissue. Through molecular studies many potential mechanisms of action have been proposed among them are different genetic and epigenetic pathways that have been implicated in the DES-induced carcinogenesis and reproductive developmental abnormalities seen in humans and animals. These effects appear to occur in specific target tissues and may be related to gene expression of the ER-α at the time of exposure. DES may create an environment conducive to the development of cancer over time.

In mouse models, pre-and neonatal DES exposure induces a wide range of gene expression changes that persist into adulthood. Molecular mechanistic studies have shown that many of the changes caused by DES, including structural and cellular abnormalities, are caused by altered programming of hox and wnt genes which play roles in reproductive tract differentiation. DES potentially inhibits the expression of wnt7a, hoxa10, and hoxa11 during critical periods of reproductive tract development. Changes in hox gene expression have led to abnormalities in tissues that depend on their expression for normal developmental signaling. Down regulation of hoxa11 (which is found in the stroma and epithelial cells of the uterus) may be partly responsible for DES-induced uterine malformations, as similar malformations are seen in hoxa11-null mice. Hoxa10 (which is expressed in the uterine horns) controls uterine organogenesis and its expression is increased in cultured human endometrial cells but repressed in mice after in utero exposure to DES. Female mice exposed to DES in utero had aberrant methylation in the promoter and intron of hoxa10, which persisted into adulthood.

Genetic modifications by DES have also been implicated in the initiation and progression of neoplasms and cancer. Neonatal DES exposure in mice can reprogram uterine differentiation by changing genetic pathways controlling uterine morphogenesis and/or altering gene expression in stem cells. DES affects the methylation patterns of genes that are associated with proliferation (c-jun, c-fos, c-myc, ltf); genes associated with apoptosis (bcl-2, bcl-x); and growth factors associated with proliferation and differentiation (EGF, TGF-α). This change in methylation is referred to as estrogen imprinting. Estrogen imprinting is an epigenetic mechanism where early-life exposure to estrogens (i.e., DES, Bisphenol A) permanently alters DNA methylation and gene expression of estrogen-responsive genes. Once changed, the altered gene profiles can continue to be expressed without further hormonal stimulation.

Proto-oncogenes help regulate normal cell proliferation and differentiation. When these genes are changed through mutation or methylation they can cause neoplastic cell transformation. Studies have shown changes in patterns of expression of estrogen-related proto-oncogenes in the genital tract of female mice exposed to DES. Changes in the proto-oncogenes and growth factors that cause elevations in their expression are associated with increased proliferation in the tissues (like the uterus and vagina) which can lead to cancer. Genetic modifications of the apoptotic genes that cause decreases in apoptosis are also associated with an increased incidence of cancer.

DES treatment affects male mice at the genomic level. DES altered Insl3 mRNA expression in male mice exposed in utero. Emmen et al. found a threefold decrease in Insl3 mRNA, which is expressed in fetal Leydig cells and is associated with the transabdominal phase of testis descent and development of the gubernaculum. This finding may provide a mechanism for DES-induced cryptorchidism. Another group found that gestational DES exposure in C57Bl/6 mice decreased the expression of two transcription factors (GATA4 and ID2) in the testes of adult males. GATA4 (expressed in Sertoli cells, Leydig cells, and other testicular somatic cells) is required for the correct expression of Sry and all the steps in testicular organogenesis that follow. ID2 is associated with the inhibition of differentiation of different cell types, and the decrease in GATA4 and ID2 may be associated with fertility problems later in life.

The research into tissue-specific mechanisms of action for DES is still underway. There are other unique attributes of DES that likely lead to its long-term effects following brief periods of exposure. A study of metabolism and disposition of DES in the pregnant rat, demonstrated enhanced disposition of DES and DES oxidative metabolites to the fetal reproductive tissues vs. liver following a single maternal exposure. Studies in mice demonstrate an accumulation of DES in the fetal reproductive tract, where it can reach levels three times higher than fetal blood . These findings of accumulated DES in reproductive tissues relate specifically to the location of ER-α, the known receptor for DES. The fact that there are multiple metabolic DES products has complicated the understanding of its effects. DES metabolites (especially quinines) are reactive ; they are formed in vivo, bind DNA and have been found in mammary tissue of rat, adult mouse reproductive tract, and mouse fetal tissues. These oxidative metabolites affect CYP gene activation and likely play a role in cancer mediation.

DES is no longer used in the human population which makes research less of a priority for funding organizations. However, for individuals/families already exposed, DES seems to be an initiating event in an initiation/promotion model for hormonal carcinogenesis and there is ample reason to fund research on effects in their unexposed children. Therefore, thoughtful follow-up of all generations and justified/planned use of stored samples (blood) will be critical in the future to determine those at highest risk for adverse health consequences.

Sources

  • Exposure to Diethylstilbestrol during Sensitive Life Stages: A legacy of heritable health effects, Birth defects research. Part C, Embryo today : reviews, NCBI PubMed PMC3817964, 2013 Nov 5.
  • Mechanisms involved in breast cancer etiology featured image PMC3817964/figure/F2.
DES DIETHYLSTILBESTROL RESOURCES

Mechanisms of reduced fertility in DES Hoxa-10 mutant mice

hoxa10-regulation image

An interesting aspect of DES-Hoxa10 regulation is that it appears to be both qualitatively (as defined by the characteristic posterior shift in Hox spatial domains) and quantitatively (lower levels of expression) conserved in murine and human species.

1996 Study Abstract

The establishment of a receptive uterine environment is critical for embryonic survival and implantation. One gene that is expressed in the uterus during the peri-implantation period in mice and is required for female fertility is the homeobox gene Hoxa-10. Here we characterize the peri-implantation defects in Hoxa-10 mutant females and investigate functions of Hoxa-10 in the uterine anlage during morphogenesis and in the adult uterus during pregnancy. Examination of pregnancy in Hoxa-10 mutant females has revealed failure of implantation as well as resorption of embryos in the early postimplantation period. Morphologic analysis of the mutant uterus has demonstrated homeotic transformation of the proximal 25% into oviduct. Histology and molecular markers confirm this anterior transformation. Furthermore, in situ hybridization shows that this region coincides with the anterior limit of embryonic Hoxa-10 expression in the urogenital ducts and a parallel transformation is observed in Hoxa-10 mutant males at the junction of the epididymis and ductus deferens. Female fertility could be compromised by either the homeotic transformation or the absence of Hoxa-10 function in the adult during pregnancy. To distinguish between these two potential mechanisms of infertility, wildtype blastocysts were transferred into mutant uteri distal to the transformed region on day 2.5 of pseudopregnancy. This procedure did not rescue the phenotype, suggesting that adult uterine expression of Hoxa-10 is required during pregnancy. Moreover, when implantation was experimentally delayed, homozygous uteri were able to support survival of blastocysts comparable to wild-type controls, indicating that the requirement for Hoxa-10 is intrinsic to implantation. While expression of LIF and HB-EGF appears unaffected in the mutant uteri, a decrease is observed in the intensity and number of blue dye reactions, an indicator of increased vascular permeability in response to implantation. In addition, mutant uteri exhibited decreased decidualization in response to artificial stimuli. These results show that Hoxa-10 is required during morphogenesis for proper patterning of the reproductive tract and in the adult uterus for peri-implantation events.

Sources and more information
  • Mechanisms of reduced fertility in Hoxa-10 mutant mice: uterine homeosis and loss of maternal Hoxa-10 expression, Development (Cambridge, England), NCBI PubMed PMID: 8787743, 1996 Sep.
  • HOXA10 expression in breast cancer cells featured image credit sciencedirect.
DES DIETHYLSTILBESTROL RESOURCES

Uterine expression of the genes Hoxa10, Hoxa11, and Wnt7a after DES treatment

Estrogen receptor-alpha knockout mice exhibit resistance to the developmental effects of neonatal diethylstilbestrol exposure on the female reproductive tract

2001 Study Abstract

Data indicate that estrogen-dependent and -independent pathways are involved in the teratogenic/carcinogenic syndrome that follows developmental exposure to 17beta-estradiol or diethylstilbestrol (DES), a synthetic estrogen. However, the exact role and extent to which each pathway contributes to the resulting pathology remain unknown.

We employed the alphaERKO mouse, which lacks estrogen receptor-alpha (ERalpha), to discern the role of ERalpha and estrogen signaling in mediating the effects of neonatal DES exposure. The alphaERKO provides the potential to expose DES actions mediated by the second known ER, ERbeta, and those that are ER-independent.

Wild-type and alphaERKO females were treated with vehicle or DES (2 microg/pup/day for Days 1-5) and terminated after 5 days and 2, 4, 8, 12, and 20 months for biochemical and histomorphological analyses. Assays for uterine expression of the genes Hoxa10, Hoxa11, and Wnt7a shortly after treatment indicated significant decreases in DES-treated wild-type but no effect in the alphaERKO. In contrast, the DES effect on uterine expression of Wnt4 and Wnt5a was preserved in both genotypes, suggesting a developmental role for ERbeta.

Adult alphaERKO mice exhibited complete resistance to the chronic effects of neonatal DES exposure exhibited in treated wild-type animals, including atrophy, decreased weight, smooth muscle disorganization, and epithelial squamous metaplasia in the uterus; proliferative lesions of the oviduct; and persistent vaginal cornification.

Therefore, the lack of DES effects on gene expression and tissue differentiation in the alphaERKO provides unequivocal evidence of an obligatory role for ERalpha in mediating the detrimental actions of neonatal DES exposure in the murine reproductive tract.

Sources and more information
  • Estrogen receptor-alpha knockout mice exhibit resistance to the developmental effects of neonatal diethylstilbestrol exposure on the female reproductive tract, Developmental biology, NCBI PubMed PMID: 11784006, 2001 Oct.
  • Estrogen receptor alpha featured image credit wikipedia.
DES DIETHYLSTILBESTROL RESOURCES

Epigenetic mechanism underlies DES-mediated alterations in HOXA10 expression

image of homeobox gene HOXA10 expression

Hypermethylation of homeobox A10 by in utero diethylstilbestrol exposure: an epigenetic mechanism for altered developmental programming

2009 Study Abstract

Diethylstilbestrol (DES) is a nonsteroidal estrogen that induces developmental anomalies of the female reproductive tract. The homeobox gene HOXA10 controls uterine organogenesis, and its expression is altered after in utero DES exposure.

We hypothesized that an epigenetic mechanism underlies DES-mediated alterations in HOXA10 expression. We analyzed the expression pattern and methylation profile of HOXA10 after DES exposure.

Expression of HOXA10 is increased in human endometrial cells after DES exposure, whereas Hoxa10 expression is repressed and shifted caudally from its normal location in mice exposed in utero. Cytosine guanine dinucleotide methylation frequency in the Hoxa10 intron was higher in DES-exposed offspring compared with controls (P = 0.017). The methylation level of Hoxa10 was also higher in the caudal portion of the uterus after DES exposure at the promoter and intron (P < 0.01). These changes were accompanied by increased expression of DNA methyltransferases 1 and 3b. No changes in methylation were observed after in vitro or adult DES exposure.

DES has a dual mechanism of action as an endocrine disruptor; DES functions as a classical estrogen and directly stimulates HOXA10 expression with short-term exposure, however, in utero exposure results in hypermethylation of the HOXA10 gene and long-term altered HOXA10 expression.

We identify hypermethylation as a novel mechanism of DES-induced altered developmental programming.

Discussion

Women exposed to DES in utero commonly demonstrate abnormalities of the reproductive tract. The frequency of müllerian abnormalities is related to the gestational age of exposure and the total dose of DES received. DES is widely used as a model for estrogenic endocrine disruption that continues to be a significant health concern. An association between clear cell adenocarcinoma of the vagina in women and in utero DES exposure has been clearly established, yet the mechanism by which DES leads to carcinogenesis is not understood. In addition, DES-mediated endocrine disruption during gestation results in developmental anomalies that persist into adulthood in both human and laboratory animals.

Hox genes comprise a highly evolutionarily conserved family of proteins, and they act as the principal regulators of tissue identity during development. They also play an essential role in defining multiple anterior-posterior axes in the developing embryo. Alterations in Hox gene expression are known to lead to anomalies in tissues that depend on their expression for proper developmental signaling (3). Thus, it is not surprising that the uterine anomalies seen after DES exposure are accompanied by a change in Hox expression. Specifically, the alterations seen in Hox gene expression after exposure to DES in utero result from a posterior or caudal shift from the normal pattern. The decreased levels of expression of Hoxa10 cranially may allow for the increased Hoxa9 expression that is demonstrated after DES exposure. This alteration of Hoxa10 expression by DES could provide a molecular mechanism by which DES produces reproductive tract anomalies.

DNA methylation has regulated a variety of aspects of cellular physiology, including growth and differentiation, through alterations in gene expression. Specifically, HOXA10 methylation has been associated with several human cancers . Yoshida et al. found that down-regulation of HOXA10 expression in endometrial carcinomas is associated with methylation of the HOXA10 promoter. Wu et al.  reported that aberrant methylation at HOXA10 may be the cause of its lower expression in the endometrium of women with endometriosis. However, altered methylation in an essential developmental gene resulting in permanent reproductive tract anomalies has not been previously reported, nor has a mechanism responsible for these changes been described.

We investigated the frequency of DNA methylation of Hoxa10 upon in uteroDES exposure, and have shown aberrant methylation in the promoter and intron of Hoxa10 and that this altered methylation also persisted into adulthood. Furthermore, we have also shown increased levels of mRNA expression of two important DNMTs, the enzymes responsible for DNA methylation. We speculate that the mechanism by which DNMT expression is up-regulated by DES is mediated by the estrogen receptor (ER). It has been recently been demonstrated that estrogens can alter the expression of at least one of the DNMTs. Furthermore, alterations in HOX gene expression in the uterus are not seen on ER knockout α-mice.

These findings suggest that hypermethylation of the Hoxa10 gene could be the mechanism responsible for the DES-altered developmental programming of the Hoxa10 gene and its associated anomalies. It has been previously reported that DES-induced down-regulation of Hoxa10 or Hoxa11 gene expression is not associated with methylation changes at the proximal promoter. However, we did find differences in levels of DNA methylation in both the promoter and the intron in the DES-treated group in the caudal portions of the uterus. It is possible that the changes in DNA methylation are only observed in the regions of the gene that we explored, which were further 5′ than those previously reported. Our methods of MSP and BSP may also have been more sensitive than those previously used.

We found that, spatially, changes in DNA methylation appeared to be confined to the caudal portion of the uterus. This finding was surprising because expression of Hoxa10 was found to be relatively increased in this portion of the uterus, and not decreased, as is typically seen with increased DNA methylation. We suspect that, rather than silencing gene activity altogether, the mechanism of this epigenetic alteration may be mediated through differential methylation of promoter binding sites for transcriptional repressors. For instance, the promoter sequence we investigated contains a binding site for Yin-Yang 1. Yin-Yang 1 is a zinc finger protein that classically functions as a repressor of Hox gene transcription.

At the same time, we found no significant changes in DNA methylation of HOXA10 in DES-treated HESCs or Ishikawa cells, and these changes were not accompanied by decreased HOXA10 expression. In fact, in vitro treatment with DES resulted in elevated levels of HOXA10 gene expression in these cells, similar to a previous report from our laboratory. Thus, the short-term increase in HOXA10 expression upon DES treatment is likely not related to changes in DNA methylation. Instead, this increase in expression is more likely mediated by the direct estrogen-agonist effect of DES on the ER because HOXA10 has been shown previously to both contain an estrogen response element, and to be regulated by estradiol. On the other hand, changes in DNA methylation may take longer to occur, or alternatively, may only occur during a critical developmental window. The absence of changes in DNA methylation after acute DES exposure in the adult uterus further supports this suggestion.

It has been shown previously that ER-α is necessary to obtain the DES phenotype  because ER-α knockout mice show none of the anatomical or gene expression changes related to chronic DES exposure in utero. The effect of DES is likely mediated through ER-α, given the loss of response in the knockout mouse.

In conclusion, we have shown that aberrant DNA methylation of the Hoxa10 gene is associated with changes in Hoxa10 expression after in utero DES exposure, This change in gene methylation provides a molecular mechanism through which DES results in altered developmental programming of the reproductive tract. With short-term exposure, DES appears to act as a classical estrogen, stimulating Hox gene expression; however, after longer exposure in utero, DES induces a permanent epigenetic effect on the expression of Hox genes through changes in DNA methylation. The mechanism of these changes in DNA methylation involves DES-mediated up-regulation of DNMTs. It has recently become clear that alterations in DNA methylation are associated with a variety of processes, including control of gene expression, change in chromatin structure, gene imprinting, and accompanying transcriptional silencing of affiliated genes. Thus, methylation-induced epigenetic changes play an important role in development. Because DES is a prototypical xenoestrogen, other EDCs may have similar epigenetic effects. Thus, DNA methylation is a novel mechanism by which endocrine disruptors may regulate developmental programming.

Sources and more information
  • Full study (free access) : Hypermethylation of homeobox A10 by in utero diethylstilbestrol exposure: an epigenetic mechanism for altered developmental programming, The Endocrine Society, Volume 150, Issue 7, Pages 3376–3382, 1 July 2009.
  • Featured image Immunohistochemical analysis shows that DES exposure alters Hoxa10 expression in 2-wk-old female mice exposed in utero to DES. A, Location of cranial and caudal sections of the mouse uterus. B, Hoxa10 expression in the cranial and caudal sections of the uterus. DES-treated mice showed increased caudal expression and decreased cranial expression of Hoxa10 in the uterus compared with controls credit NCBI PMC2703508/figure/F2.
DES DIETHYLSTILBESTROL RESOURCES

Neonatal DES treatment reduces Hoxa10 and Hoxa11 expression in the uteri

image of Hoxa10 and Hoxa11 expression in the uteri

Estrogen Receptor-α Knockout Mice Exhibit Resistance to the Developmental Effects of Neonatal Diethylstilbestrol Exposure on the Female Reproductive Tract

Study 2001 Abstract

Data indicate that estrogen-dependent and -independent pathways are involved in the teratogenic/carcinogenic syndrome that follows developmental exposure to 17beta-estradiol or diethylstilbestrol (DES), a synthetic estrogen. However, the exact role and extent to which each pathway contributes to the resulting pathology remain unknown.

We employed the alphaERKO mouse, which lacks estrogen receptor-alpha (ERalpha), to discern the role of ERalpha and estrogen signaling in mediating the effects of neonatal DES exposure. The alphaERKO provides the potential to expose DES actions mediated by the second known ER, ERbeta, and those that are ER-independent.

Wild-type and alphaERKO females were treated with vehicle or DES (2 microg/pup/day for Days 1-5) and terminated after 5 days and 2, 4, 8, 12, and 20 months for biochemical and histomorphological analyses.

Assays for uterine expression of the genes Hoxa10, Hoxa11, and Wnt7a shortly after treatment indicated significant decreases in DES-treated wild-type but no effect in the alphaERKO. In contrast, the DES effect on uterine expression of Wnt4 and Wnt5a was preserved in both genotypes, suggesting a developmental role for ERbeta. Adult alphaERKO mice exhibited complete resistance to the chronic effects of neonatal DES exposure exhibited in treated wild-type animals, including atrophy, decreased weight, smooth muscle disorganization, and epithelial squamous metaplasia in the uterus; proliferative lesions of the oviduct; and persistent vaginal cornification.

Therefore, the lack of DES effects on gene expression and tissue differentiation in the alphaERKO provides unequivocal evidence of an obligatory role for ERalpha in mediating the detrimental actions of neonatal DES exposure in the murine reproductive tract.

Sources and more information
  • Estrogen Receptor-α Knockout Mice Exhibit Resistance to the Developmental Effects of Neonatal Diethylstilbestrol Exposure on the Female Reproductive Tract, Developmental Biology, Researchgate DOI: 10.1006/dbio.2001.0413, November 2001.
  • Neonatal DES treatment reduces Hoxa10 and Hoxa11 expression in the uteri of wild-type but not ␣ ERKO mice featured image credit researchgate.
DES DIETHYLSTILBESTROL RESOURCES

Hox-a10 and Hox-a11 expression potently repressed by perinatal DES exposure

image of des and hox genes

Promoter CpG methylation of Hoxa-10 and Hoxa-11 in mouse uterus not altered upon neonatal diethylstilbestrol exposure

2001 Study Abstract

Mouse abdominal B-like Hoxa genes are expressed and functionally required in the developing reproductive tracts. Mice lacking either Hoxa-10 or Hoxa-11, two of the AbdB Hoxa genes, exhibit abnormal uterine development similar to that induced by in utero diethylstilbestrol (DES) exposure.

Indeed, uterine Hoxa10 and Hoxa11 expression is potently repressed by perinatal DES exposure, providing a potential molecular mechanism for DES-induced reproductive tract malformations.

We have shown previously that DES can permanently alter uterine lactoferrin gene expression through modulation of the lactoferrin promoter methylation pattern. Here we ask whether a similar mechanism also functions to deregulate uterine Hoxa-10 or Hoxa-11 expression during neonatal DES exposure.

We mapped the Hoxa-10 promoter by cloning a 1.485 kb DNA fragment 5′ of the Hoxa-10 exon1a. A 5′ rapid amplification of cDNA ends (RACE) experiment revealed a transcription start site for the a10-1 transcript.

Functional analysis of the proximal 200-bp sequences demonstrated significant promoter activity, confirming the location of the Hoxa-10 promoter. Moreover, methylation assays performed on eight CpGs in Hoxa-10 and 19 CpGs in Hoxa-11 proximal promoters demonstrated that all these CpGs were highly unmethylated in both control and DES-dosed mice from postnatal day 5 to day 30. Significant methylation around Hoxa10 and Hoxa11 promoters was only observed in DES-induced uterine carcinomas in 18-mo-old mice.

Our results suggest that DES-induced downregulations of Hox-a10 or Hox-a11 gene expression are not associated with methylation changes in their proximal promoters and that gene imprinting by developmental DES exposure may be a gene-specific phenomenon.

Sources and more information
  • Promoter CpG methylation of Hox-a10 and Hox-a11 in mouse uterus not altered upon neonatal diethylstilbestrol exposure, Molecular carcinogenesis, NCBI PubMed PMID : 11746833, 2001 Dec.
  • Featured image credit .researchgate.
DES DIETHYLSTILBESTROL RESOURCES

Hoxa-10 gene expression might be repressed by DES during reproductive tract morphogenesis

representation of Hoxa-10-gene

Abdominal B (AbdB) Hoxa genes: regulation in adult uterus by estrogen and progesterone and repression in müllerian duct by the synthetic estrogen diethylstilbestrol (DES)

1998 Study Abstract

Mice deficient for the Abdominal B (AbdB) Hox gene Hoxa-10 exhibit reduced fertility due to defects in implantation. During the peri-implantation period Hoxa-10 is sequentially expressed in the uterine epithelium and stroma. These observations, combined with the stringent regulation of uterine implantation by ovarian steroids, prompted us to test whether estrogen and progesterone directly regulate the expression of Hoxa-10 and other AbdB Hoxa genes.

Here we show that Hoxa-10 expression in the adult uterus is strongly activated by progesterone. This activation is blocked by the progesterone receptor antagonist RU486 and is independent of new protein synthesis. In addition, Hoxa-10 expression is repressed by estrogen in a protein synthesis-independent manner. Analysis of adjacent AbdB Hoxa genes reveals that Hoxa-9 and a-11 are also activated in a colinear fashion by progesterone but differentially regulated by estrogen.

These results suggest that the regulation of AbdB Hox gene expression in the adult uterus by ovarian steroids is a property related to position within the cluster, mediated by the direct action of estrogen and progesterone receptors upon these genes. We next examined whether the embryonic expression of Hoxa10 is regulable by hormonal factors. Previous work has demonstrated that perinatal administration of the synthetic estrogen diethylstilbestrol (DES) to mice and humans produces uterine, cervical, and oviductal malformations. Certain of these phenotypes resemble those in Hoxa-10 knockout mice, suggesting that Hoxa-10 gene expression might be repressed by DES during reproductive tract morphogenesis.

Exposure of the developing female reproductive tract to DES, either in vivo or in organ culture, represses the expression of Hoxa-10 in the Müllerian duct. Thus, these data not only establish a direct link between ovarian steroids and AbdB Hoxa gene expression in the adult uterus, but also provide a potential mechanism for the teratogenic effects of DES on the developing reproductive tract.

Sources and more information
  • Abdominal B (AbdB) Hoxa genes: regulation in adult uterus by estrogen and progesterone and repression in müllerian duct by the synthetic estrogen diethylstilbestrol (DES), Developmental biology, NCBI PubMed, PMID : 9630742, 1998 May.
  • Featured image credit atlasgeneticsoncology.
DES DIETHYLSTILBESTROL RESOURCES

Prenatal Exposure to DES linked to Hypermethylation of Homeobox A10

An Epigenetic Mechanism for Altered Developmental Programming

2009 Study Abstract

Diethylstilbestrol (DES) is a nonsteroidal estrogen that induces developmental anomalies of the female reproductive tract.

Hypermethylation of Homeobox A10 by in Utero Diethylstilbestrol Exposure: An Epigenetic Mechanism for Altered Developmental Programming, Research Gate, publication/24213324, March 2009.

The homeobox gene HOXA10 controls uterine organogenesis, and its expression is altered after in utero DES exposure.

We hypothesized that an epigenetic mechanism underlies DES-mediated alterations in HOXA10 expression. We analyzed the expression pattern and methylation profile of HOXA10 after DES exposure.

Expression of HOXA10 is increased in human endometrial cells after DES exposure, whereas Hoxa10 expression is repressed and shifted caudally from its normal location in mice exposed in utero. Cytosine guanine dinucleotide methylation frequency in the Hoxa10 intron was higher in DES-exposed offspring compared with controls (P = 0.017). The methylation level of Hoxa10 was also higher in the caudal portion of the uterus after DES exposure at the promoter and intron (P < 0.01).

These changes were accompanied by increased expression of DNA methyltransferases 1 and 3b. No changes in methylation were observed after in vitro or adult DES exposure.

DES has a dual mechanism of action as an endocrine disruptor;

  1. DES functions as a classical estrogen and directly stimulates HOXA10 expression with short-term exposure,
  2. however, DES in utero exposure results in hypermethylation of the HOXA10 gene and long-term altered HOXA10 expression.

We identify hypermethylation as a novel mechanism of DES-induced altered developmental programming.

More DES DiEthylStilbestrol Resources