Estrogen-dependent transcriptional activation and vitellogenin gene memory

Self-organization of plasticity and specialization in a primitively social insect

Biological systems have the capacity to not only build and robustly maintain complex structures but also to rapidly break up and rebuild such structures. Here, using primitive societies of Polistes wasps, we show that both robust specialization and rapid plasticity are emergent properties of multi-scale dynamics. We combine theory with experiments that, after perturbing the social structure by removing the queen, correlate time-resolved multi-omics with video recordings. We show that the queen-worker dimorphism relies on the balance between the development of a molecular queen phenotype in all insects and colony-scale inhibition of this phenotype via asymmetric interactions. This allows Polistes to be stable against intrinsic perturbations of molecular states while reacting plastically to extrinsic cues affecting the whole society. Long-term stability of the social structure is reinforced by dynamic DNA methylation. Our study provides a general principle of how both specialization and plasticity can be achieved in biological systems. A record of this paper's transparent peer review process is included in the supplemental information.

Personality and gonadal development as sources of individual variation in response to GnRH challenge in female great tits

Seasonal timing of reproduction is a key life-history trait, but we know little about the mechanisms underlying individual variation in female endocrine profiles associated with reproduction. In birds, 17β-oestradiol is a key reproductive hormone that links brain neuroendocrine mechanisms, involved in information processing and decision-making, to downstream mechanisms in the liver, where egg-yolk is produced. Here, we test, using a simulated induction of the reproductive system through a Gonadotropin-Releasing Hormone (GnRH) challenge, whether the ovary of pre-breeding female great tits responds to brain stimulation by increasing oestradiol. We also assess how this response is modified by individual-specific traits like age, ovarian follicle size, and personality, using females from lines artificially selected for divergent levels of exploratory behaviour. We show that a GnRH injection leads to a rapid increase in circulating concentrations of oestradiol, but responses varied among individuals. Females with more developed ovarian follicles showed stronger responses and females from lines selected for fast exploratory behaviour showed stronger increases compared to females from the slow line, indicating a heritable component. This study shows that the response of the ovary to reproductive stimulation from the brain greatly varies among individuals and that this variation can be attributed to several commonly measured individual traits, which sheds light on the mechanisms shaping heritable endocrine phenotypes.

Environmental epigenomics: Current approaches to assess epigenetic effects of endocrine disrupting compounds (EDC's) on human health

Environmental Epigenomics is a developing field to study the epigenetic effect on human health from exposure to environmental factors. Endocrine disrupting chemicals have been detected primarily in pharmaceutical drugs, personal care products, food additives, and food containers. Exposure to endocrine-disrupting chemicals (EDCs) has been associated with a high incidence and prevalence of many endocrine-related disorders in humans. Nevertheless, further evidence is needed to establish a correlation between exposure to EDC and human disorders. Conventional detection of EDCs is based on chemical structure and concentration sample analysis. However, substantial evidence has emerged, suggesting that cell exposure to EDCs leads to epigenetic changes, independently of its chemical structure with non-monotonic low-dose responses. Consequently, a paradigm shift in toxicology assessment of EDCs is proposed based on a comprehensive review of analytical techniques used to evaluate the epigenetic effects. Fundamental insights reported elsewhere are compared in order to establish DNA methylation analysis as a viable method for assessing endocrine disruptors beyond the conventional study approach of chemical structure and concentration analysis.

[The new paradigm of the developmental origin of health and diseases (DOHaD)--Epigenetics and environment: evidence and missing links]

According to the new paradigm of the Developpemental Origins of Health and Disease (DOHaD), the environmental factors to which an individual is exposed throughout his life can leave an epigenetic footprint on the genome. A crucial period is the early development, where the epigenome is particularly sensitive to the effects of the environment, and during which the individual builds up his health capital that will enable him to respond more or less well to the vagaries of life. The research challenge is to decipher the modes of action and the epigenetic mechanisms put into play by environmental factors that lead to increased disease susceptibility or resilience. The challenge for health is to translate these scientific discoveries into action through, among others, the establishment of preventive recommendations to slow down the growing incidence of non communicable diseases.

Temporal variation in the estrogenicity of a sewage treatment plant effluent and its biological significance

Daily variation in the estrogenic activity of effluent released by a modern sewage treatment plant (STP) was measured and its effects on the physiology, behavior, and reproductive success of male fish were evaluated. As measured by an estrogen receptor binding assay, the daily estrogenic activity of this effluent was both high and extremely variable (42 +/- 25.4 [mean +/- SD] ng 17beta-estradiol (E2) equivalents/L; n = 18). Liver VTG mRNA expression in male fathead minnows (FHM) covaried with the binding assay estimates, suggesting that these fluctuations are biologically relevant. Tests which exposed male FHMs to either fluctuating levels of E2, a constant concentration of E2 (time-weighted to reflect average concentrations), or control (no E2) demonstrated that while the estrogenic activity of this effluent was detrimental to male spawning success, the fact that its concentration varied in a daily manner was without additional influence. The variability of the effluent's estrogenicity suggests that studies concerned with the effects of STP effluents should collect multiple daily samples and then test them on an appropriate time-weighted basis.

Estrogen receptor alpha regulates expression of the breast cancer 1 associated ring domain 1 (BARD1) gene through intronic DNA sequence

We have used a chromatin immunoprecipitation (ChIP)-based cloning strategy to isolate and identify genes associated with estrogen receptor alpha (ERalpha) in MCF-7 human breast cancer cells. One of the gene regions isolated was a 288bp fragment from the ninth intron of the breast cancer 1 associated ring domain (BARD1) gene. We demonstrated that ERalpha associated with this region of the endogenous BARD 1 gene in MCF-7 cells, that ERalpha bound to three of five ERE half sites located in the 288bp BARD1 region, and that this 288bp BARD1 region conferred estrogen responsiveness to a heterologous promoter. Importantly, treatment of MCF-7 cells with estrogen increased BARD1 mRNA and protein levels. These findings demonstrate that ChIP cloning strategies can be utilized to successfully isolate regulatory regions that are far removed from the transcription start site and assist in identifying cis elements involved in conferring estrogen responsiveness.

Epigenetics, evolution, endocrine disruption, health, and disease

Endocrine-disrupting chemicals (EDCs) in the environment have been linked to human health and disease. This is particularly evident in compounds that mimic the effects of estrogens. Exposure to EDCs early in life can increase risk levels of compromised physical and mental health. Epigenetic mechanisms have been implicated in this process. Transgenerational consequences of EDC exposure is also discussed in both a proximate (mechanism) and ultimate (evolution) context as well as recent work suggesting how such transmission might become incorporated into the genome and subject to selection. We suggest a perspective for exploring and ultimately coming to understand diseases that may have environmental or endocrine origins.

Environmental signaling: what embryos and evolution teach us about endocrine disrupting chemicals

The term "endocrine disrupting chemicals" is commonly used to describe environmental agents that alter the endocrine system. Laboratories working in this emerging field-environmental endocrine research-have looked at chemicals that mimic or block endogenous vertebrate steroid hormones by interacting with the hormone's receptor. Environmental chemicals known to do this do so most often with receptors derived from the steroid/thyroid/retinoid gene family. They include ubiquitous and persistent organochlorines, as well as plasticizers, pharmaceuticals, and natural hormones. These chemicals function as estrogens, antiestrogens, and antiandrogens but have few, if any, structural similarities. Therefore, receptor-based or functional assays have the best chance of detecting putative biological activity of environmental chemicals. Three nuclear estrogen receptor forms-alpha, beta, and gamma-as well as multiple membrane forms and a possible mitochondrial form have been reported, suggesting a previously unknown diversity of signaling pathways available to estrogenic chemicals. Examples of environmental or ambient estrogenization occur in laboratory experiments, zoo animals, domestic animals, wildlife, and humans. Environmentally estrogenized phenotypes may differ depending upon the time of exposure-i.e., whether the exposure occurred at a developmental (organizational and irreversible) or postdevelopmental (activational and reversible) stage. The term "estrogen" must be defined in each case, since steroidal estrogens differ among themselves and from synthetic or plant-derived chemicals. An "estrogen-like function" seems to be an evolutionarily ancient signal that has been retained in a number of chemicals, some of which are vertebrate hormones. Signaling, required for symbiosis between plants and bacteria, may be viewed, therefore, as an early example of hormone cross-talk. Developmental feminization at the structural or functional level is an emerging theme in species exposed, during embryonic or fetal life, to estrogenic compounds. Human experience as well as studies in experimental animals with the potent estrogen diethylstilbestrol provide informative models. Advances in the molecular genetics of sex differentiation in vertebrates facilitate mechanistic understanding. Experiments addressing the concept of gene imprinting or induction of epigenetic memory by estrogen or other hormones suggest a link to persistent, heritable phenotypic changes seen after developmental estrogenization, independent of mutagenesis. Environmental endocrine science provides a new context in which to examine the informational content of ecosystem-wide communication networks. As common features come to light, this research may allow us to predict environmentally induced alterations in internal signaling systems of vertebrates and some invertebrates and eventually to explicate environmental contributions to human reproductive and developmental health.

A composite regulatory element in the first intron of the estrogen-responsive very low density apolipoprotein II gene

During periods of egg laying in the chicken, when circulating levels of estrogen are increased, the liver-specific estrogen-dependent very low density apolipoprotein II (apoVLDLII) gene is expressed. This expression takes place primarily at the level of transcription, driven by two estrogen response elements that reside in the promoter. In transient transfection assays, expression is increased fourfold when the first intron is added to the promoter construct, indicating that 75% of the regulation comes from intron A. Using in vitro DNase I footprinting, six protein-binding sites were revealed throughout the first intron. The functional significance of these binding sites was evaluated by mutation and transient transfection. Two of the protein-binding regions were shown to increase transcription. Site-specific mutations introduced at either the +66 to +86 or +112 to +129 sites disrupted trans-factor binding and reduced the estrogen-dependent expression by 45% and 34%, respectively. A plasmid containing both mutations resulted in a 43% decrease in expression, indicating that the contributions of these regions are not additive. Competition with known sequences in electrophoretic mobility shift assays suggested that the +66 to +86 site binds a chicken member of the nuclear receptor transcription factor family.