Fetal and neonatal exposure to the endocrine disruptor methoxychlor causes epigenetic alterations in adult ovarian genes

Simulated microgravity-induced epigenetic changes in human lymphocytes

Real space flight and modeled microgravity conditions result in changes in the expression of genes that control important cellular functions. However, the mechanisms for microgravity-induced gene expression changes are not clear. The epigenetic changes of DNA methylation and chromatin histones modifications are known to regulate gene expression. The objectives of this study were to investigate whether simulated microgravity alters (a) the DNA methylation and histone acetylation, and (b) the expression of DNMT1, DNMT3a, DNMT3b, and HDAC1 genes that regulate epigenetic events. To achieve these objectives, human T-lymphocyte cells were grown in a rotary cell culture system (RCCS) that simulates microgravity, and in parallel under normal gravitational conditions as control. The microgravity-induced DNA methylation changes were detected by methylation sensitive-random amplified polymorphic DNA (MS-RAPD) analysis of genomic DNA. The gene expression was measured by Quantitative Real-time PCR. The expression of DNMT1, DNMT3a, and DNMT3b was found to be increased at 72 h, and decreased at 7 days in microgravity exposed cells. The MS-RAPD analysis revealed that simulated microgravity exposure results in DNA hypomethylation and mutational changes. Gene expression analysis revealed microgravity exposure time-dependent decreased expression of HDAC1. Decreased expression of HDAC1 should result in increased level of acetylated histone H3, however a decreased level of acetylated H3 was observed in microgravity condition, indicating thereby that other HDACs may be involved in regulation of H3 deacetylation. The findings of this study suggest that epigenetic events could be one of the mechanistic bases for microgravity-induced gene expression changes and associated adverse health effects.

Early homeostatic disturbances of human growth and maturation by endocrine disrupters

PURPOSE OF REVIEW

We attempt to delineate and integrate aspects of growth and development that could be affected by endocrine disrupters [endocrine-disrupting compounds (EDC)], an increasing public health concern.

RECENT FINDINGS

Epidemiological and experimental data substantiate that fetal and early postnatal life are critical periods of exposure to endocrine disrupters, with possible transgenerational effects. The EDC effects include several disorders of the reproductive system throughout life (abnormalities of sexual differentiation, infertility or subfertility and some neoplasia) and disorders of energy balance (obesity and metabolic syndrome). The mechanisms are consistent with the concept of 'developmental origin of adult disease'. They could involve cross-talk between the factors controlling reproduction and those controlling energy balance, both in the hypothalamus and peripherally.

SUMMARY

Due to ubiquity of endocrine disrupters and lifelong stakes of early exposure, individual families should be provided by pediatricians with recommendations following the precautionary principle, that is prevention or attenuation of conditions possibly detrimental to health before the evidence of such adverse effects is complete and undisputable.

Epigenetic regulation of the expression of genes involved in steroid hormone biosynthesis and action

Steroid hormones participate in organ development, reproduction, body homeostasis, and stress responses. The steroid machinery is expressed in a development- and tissue-specific manner, with the expression of these factors being tightly regulated by an array of transcription factors (TFs). Epigenetics provides an additional layer of gene regulation through DNA methylation and histone tail modifications. Evidence of epigenetic regulation of key steroidogenic enzymes is increasing, though this does not seem to be a predominant regulatory pathway. Steroid hormones exert their action in target tissues through steroid nuclear receptors belonging to the NR3A and NR3C families. Nuclear receptor expression levels and post-translational modifications regulate their function and dictate their sensitivity to steroid ligands. Nuclear receptors and TFs are more likely to be epigenetically regulated than proteins involved in steroidogenesis and have secondary impact on the expression of these steroidogenic enzymes. Here we review evidence for epigenetic regulation of enzymes, transcription factors, and nuclear receptors related to steroid biogenesis and action.

DNA methylation levels in the 5' flanking region of the vitellogenin I gene in liver and brain of adult zebrafish (Danio rerio)--sex and tissue differences and effects of 17alpha-ethinylestradiol exposure

Vitellogenin is produced in the liver of sexually mature female fish in response to endogenous estrogens. Exogenous estrogens also induce synthesis of vitellogenin in the liver of male and juvenile fish and vitellogenin is a frequently used biomarker for estrogen exposure. The epigenetic state, e.g. histone acetylation and DNA methylation, in the region of a gene or in its 5' flanking region influences the gene expression. DNA methylation positions in multicellular eukaryotes are mostly found on cytosine bases located 5' to guanine, i.e. in CpG sites. Here, we have for the first time analyzed the DNA methylation levels of three CpG sites located in the 5' flanking region of the vitellogenin I gene in liver and brain from adult zebrafish (Danio rerio) utilizing Pyrosequencing technology. This sequencing technique allows determination of methylation levels of multiple individual CpG sites. Our purpose was to assess any differences in methylation levels related to sex, tissue and exposure to estrogen. Out of the seven vitellogenin genes identified in the zebrafish, vitellogenin I is the most highly expressed during vitellogenesis. We found that the methylation levels of all three CpG sites were higher in male liver than in female liver. In brain, which does not express vitellogenin, females and males showed similar, high methylation levels in the analyzed CpG positions. Exposure of adult zebrafish to 17alpha-ethinylestradiol (100 ng/L) for 14 days decreased the methylation levels in the 5' flanking region of vitellogenin I in the liver in both females and males. These results suggest that induced expression of vitellogenin in fish following exposure to estrogens might involve alterations in DNA methylation.