Temperature dependence of estrogen binding: importance of a subzone in the ligand binding domain of a novel piscine estrogen receptor

ORFeus: a computational method to detect programmed ribosomal frameshifts and other non-canonical translation events

BACKGROUND

In canonical protein translation, ribosomes initiate translation at a specific start codon, maintain a single reading frame throughout elongation, and terminate at the first in-frame stop codon. However, ribosomal behavior can deviate at each of these steps, sometimes in a programmed manner. Certain mRNAs contain sequence and structural elements that cause ribosomes to begin translation at alternative start codons, shift reading frame, read through stop codons, or reinitiate on the same mRNA. These processes represent important translational control mechanisms that can allow an mRNA to encode multiple functional protein products or regulate protein expression. The prevalence of these events remains uncertain, due to the difficulty of systematic detection.

RESULTS

We have developed a computational model to infer non-canonical translation events from ribosome profiling data.

CONCLUSION

ORFeus identifies known examples of alternative open reading frames and recoding events across different organisms and enables transcriptome-wide searches for novel events.

Biological-Activity-Based Prioritization of Antidepressants in Wastewater in England and Japan

Antidepressants are one of the most commonly prescribed pharmaceuticals. Although they have been frequently detected in aquatic environments around the globe, little is known regarding their adverse effects on humans and aquatic organisms. Recently, an in vitro monoamine transporter inhibition assay was developed to detect transporter-inhibitory activities of antidepressants in wastewater in Japan. However, it was unclear which antidepressants were responsible for transporter-inhibitory activities in wastewater. Herein, the per capita consumption of 32 antidepressants, their excretion of unchanged parent compounds, per capita water consumption, removal rate during wastewater treatment processes, and potency values from the monoamine transporter inhibition assay were used to prioritize antidepressants of concern in effluent wastewater in England and Japan. In both countries, sertraline and O-desmethylvenlafaxine had the highest contribution to inhibitory activities against the human serotonin transporter (hSERT) and zebrafish SERT (zSERT), respectively. It was found that the antidepressants inhibited the zSERT more strongly than the hSERT. The inhibitory activities found against the zSERT in wastewater in England and Japan were higher than thresholds for abnormal behavior in fish. The antidepressants prioritized in this study provide insight into launching environmental monitoring and ecotoxicological studies of antidepressants.

Analyses of adult transcriptomes from four different populations of the spongy moth, Lymantria dispar L., from China and the USA

The spongy moth Lymantria dispar, formerly known as the gypsy moth, is a forest pest that occurs as two different biotypes: the European spongy moth (ESM), Lymantria dispar dispar, which is distributed in Europe and North America; and the Asian spongy moth (ASM), which consists of subspecies Lymantria dispar asiatica and Lymantria dispar japonica and is distributed in China, Russia, Korea, and Japan. The Asian biotype is classified as a quarantine pest by the U.S. Department of Agriculture because of the superior flight ability of adult females compared to females of the European biotype. To identify genes that potentially account for differences in female flight capability between the two biotypes, we assembled and compared transcriptional profiles of two North American populations of ESM and two Chinese populations of ASM, including samples of unmated female adults and females after mating and oviposition. Of 129,286 unigenes identified, 306 were up-regulated in ASM samples relative to ESM, including genes involved in egg production. In contrast, 2309 unigenes were down-regulated in ASM samples, including genes involved in energy production. Although a previous study found that ASM female flight was reduced after oviposition, a comparison of gene expression before and after mating and oviposition did not reveal any genes which were consistently up- or down-regulated in the two ASM populations.

Organization and phylogenetic relationships of the mitochondrial genomes of Speiredonia retorta and other lepidopteran insects

In this study, we analyzed the complete mitochondrial genome (mitogenome) of Speiredonia retorta, which is a pest and a member of the Lepidoptera order. In total, the S. retorta mitogenome was found to contain 15,652 base pairs encoding 13 protein-coding genes (PCGs), 22 tRNAs, 2 rRNAs, as well as an adenine (A) + thymine (T)-rich region. These findings were consistent with the mitogenome composition of other lepidopterans, as we identified all 13 PCGs beginning at ATN codons. We also found that 11 PCGs terminated with canonical stop codons, whereas cox2 and nad4 exhibited incomplete termination codons. By analyzing the mitogenome of S. retorta using Bayesian inference (BI) and maximum likelihood (ML) models, we were able to further confirm that this species is a member of the Erebidae family.

From gametogenesis to spawning: How climate-driven warming affects teleost reproductive biology

Ambient temperature modulates reproductive processes, especially in poikilotherms such as teleosts. Consequently, global warming is expected to impact the reproductive function of fish, which has implications for wild population dynamics, fisheries and aquaculture. In this extensive review spanning tropical and cold-water environments, we examine the impact of higher-than-optimal temperatures on teleost reproductive development and physiology across reproductive stages, species, generations and sexes. In doing so, we demonstrate that warmer-than-optimal temperatures can affect every stage of reproductive development from puberty through to the act of spawning, and these responses are mediated by age at spawning and are associated with changes in physiology at multiple levels of the brain-pituitary-gonad axis. Response to temperature is often species-specific and changes with environmental history/transgenerational conditioning, and the amplitude, timing and duration of thermal exposure within a generation. Thermally driven changes to physiology, gamete development and maturation typically culminate in poor sperm and oocyte quality, and/or advancement/delay/inhibition of ovulation/spermiation and spawning. Although the field of teleost reproduction and temperature is advanced in many respects, we identify areas where research is lacking, especially for males and egg quality from "omics" perspectives. Climate-driven warming will continue to disturb teleost reproductive performance and therefore guide future research, especially in the emerging areas of transgenerational acclimation and epigenetic studies, which will help to understand and project climate change impacts on wild populations and could also have implications for aquaculture.

Estrogen therapy offsets thermal impairment of vitellogenesis, but not zonagenesis, in maiden spawning female Atlantic salmon (Salmo salar)

In female Atlantic salmon (Salmo salar), exposure to warm summer temperatures causes a reduction in plasma 17β-estradiol (E2), which impairs downstream vitellogenesis and zonagenesis, and reduces egg fertility and embryo survival. The aim of the present study was to determine whether E2-treatment could offset thermal impairment of endocrine function and maintain egg quality in maiden (first-time-spawning) S. salar reared at 22 °C. Treatment with E2 at 22 °C stimulated vitellogenin (vtg) gene expression and subsequent protein synthesis which promoted oocyte growth and increased egg size relative to untreated fish at 14 and 22 °C. However, E2-treatment at 22 °C was not associated with an increase in egg fertility and embryo survival relative to untreated fish at 22 °C, despite the positive effects of E2-treatment on vitellogenesis and oocyte growth. As there was no evidence to suggest that the estrogen receptor alpha expression was suppressed by high temperature, this could be due to the lack of stimulation on zonagenesis by E2-treatment observed at high temperature during oocyte development. Our results demonstrate that treatment with E2 is not able to maintain zonagenesis or egg quality in maiden S. salar at high temperature, even when vtg gene expression, protein synthesis and subsequent oocyte growth is promoted. This implies that the mechanisms regulating zonagenesis, but not vitellogenesis are impaired at elevated temperature in female S. salar broodstock, and highlights the remarkable complexity of thermally induced endocrine disruption in fish.

Reporter cell lines to evaluate the selectivity of chemicals for human and zebrafish estrogen and peroxysome proliferator activated γ receptors

Zebrafish is increasingly used as an animal model to study the effects of environmental nuclear receptors (NRs) ligands. As most of these compounds have only been tested on human NRs, it is necessary to measure their effects on zebrafish NRs. Estrogen receptors (ER) α and β and peroxysome proliferator activated receptor (PPAR) γ are main targets of environmental disrupting compounds (EDCs). In humans there are two distinct nuclear ERs (hERα and hERβ), whereas the zebrafish genome encodes three ERs, zfERα, zfERβ1, and zfERβ2. Only one isoform of PPARγ is expressed in both humans and zebrafish. In this review, we described reporter cell lines that we established to study the interaction of EDCs with human and zebrafish ERs and PPARγ. Using these cell lines, we observed that zfERs are thermo-sensitive while zfPPARγ is not. We also showed significant differences in the ability of environmental and synthetic ligands to modulate activation of zfERs and zfPPARγ in comparison to hERs and hPPARγ. Some environmental estrogens (bisphenol A, mycoestrogens) which are hER panagonists displayed greater potency for zfERα as compared to zfERβs. hERβ selective agonists (8βVE2, DPN, phytoestrogens) also displayed zfERα selectivity. Among hERα selective synthetic agonists, 16α-LE2 was the most zfERα selective compound. Almost all zfPPARγ environmental ligands (halogenated bisphenol A derivatives, phthalates, perfluorinated compounds) displayed similar affinity for human and zebrafish PPARγ while pharmaceutical hPPARγ agonists like thiazolidones are not recognized by zfPPARγ. Altogether, our studies show that all hERs and hPPARγ ligands do not control in a similar manner the transcriptional activity of zfERs and zfPPARγ and point out that care has to be taken in transposing the results obtained using the zebrafish as a model for human physiopathology.

Selectivity of natural, synthetic and environmental estrogens for zebrafish estrogen receptors

Zebrafish, Danio rerio, is increasingly used as an animal model to study the effects of pharmaceuticals and environmental estrogens. As most of these estrogens have only been tested on human estrogen receptors (ERs), it is necessary to measure their effects on zebrafish ERs. In humans there are two distinct nuclear ERs (hERα and hERβ), whereas the zebrafish genome encodes three ERs, zfERα and two zfERβs (zfERβ1 and zfERβ2). In this study, we established HeLa-based reporter cell lines stably expressing each of the three zfERs. We first reported that estrogens more efficiently activate the zfERs at 28°C as compared to 37°C, thus reflecting the physiological temperature of zebrafish in wildlife. We then showed significant differences in the ability of agonist and antagonist estrogens to modulate activation of the three zfER isotypes in comparison to hERs. Environmental compounds (bisphenol A, alkylphenols, mycoestrogens) which are hER panagonists and hERβ selective agonists displayed greater potency for zfERα as compared to zfERβs. Among hERα selective synthetic agonists, PPT did not activate zfERα while 16α-LE2 was the most zfERα selective compound. Altogether, these results confirm that all hER ligands control in a similar manner the transcriptional activity of zfERs although significant differences in selectivity were observed among subtypes. The zfER subtype selective ligands that we identified thus represent new valuable tools to dissect the physiological roles of the different zfERs. Finally, our work also points out that care has to be taken in transposing the results obtained using the zebrafish as a model for human physiopathology.

Differing species responsiveness of estrogenic contaminants in fish is conferred by the ligand binding domain of the estrogen receptor

Exposure to estrogenic endocrine disrupting chemicals (EDCs) induces a range of adverse effects, notably on reproduction and reproductive development. These responses are mediated via estrogen receptors (ERs). Different species of fish may show differences in their responsiveness to environmental estrogens but there is very limited understanding on the underlying mechanisms accounting for these differences. We used custom developed in vitro ERα reporter gene assays for nine fish species to analyze the ligand- and species-specificity for 12 environmental estrogens. Transcriptonal activities mediated by estradiol-17β (E2) were similar to only a 3-fold difference in ERα sensitivity between species. Diethylstilbestrol was the most potent estrogen (∼ 10-fold that of E2) in transactivating the fish ERαs, whereas equilin was about 1 order of magnitude less potent in all species compared to E2. Responses of the different fish ERαs to weaker environmental estrogens varied, and for some considerably. Medaka, stickleback, bluegill and guppy showed higher sensitivities to nonylphenol, octylphenol, bisphenol A and the DDT-metabolites compared with cyprinid ERαs. Triclosan had little or no transactivation of the fish ERαs. By constructing ERα chimeras in which the AF-containing domains were swapped between various fish species with contrasting responsiveness and subsequent exposure to different environmental estrogens. Our in vitro data indicate that the LBD plays a significant role in accounting for ligand sensitivity of ERα in different species. The differences seen in responsiveness to different estrogenic chemicals between species indicate environmental risk assessment for estrogens cannot necessarily be predicted for all fish by simply examining receptor activation for a few model fish species.

Description of new mitochondrial genomes (Spodoptera litura, Noctuoidea and Cnaphalocrocis medinalis, Pyraloidea) and phylogenetic reconstruction of Lepidoptera with the comment on optimization schemes

We newly sequenced mitochondrial genomes of Spodoptera litura and Cnaphalocrocis medinalis belonging to Lepidoptera to obtain further insight into mitochondrial genome evolution in this group and investigated the influence of optimal strategies on phylogenetic reconstruction of Lepidoptera. Estimation of p-distances of each mitochondrial gene for available taxonomic levels has shown the highest value in ND6, whereas the lowest values in COI and COII at the nucleotide level, suggesting different utility of each gene for different hierarchical group when individual genes are utilized for phylogenetic analysis. Phylogenetic analyses mainly yielded the relationships (((((Bombycoidea + Geometroidea) + Noctuoidea) + Pyraloidea) + Papilionoidea) + Tortricoidea), evidencing the polyphyly of Macrolepidoptera. The Noctuoidea concordantly recovered the familial relationships (((Arctiidae + Lymantriidae) + Noctuidae) + Notodontidae). The tests of optimality strategies, such as exclusion of third codon positions, inclusion of rRNA and tRNA genes, data partitioning, RY recoding approach, and recoding nucleotides into amino acids suggested that the majority of the strategies did not substantially alter phylogenetic topologies or nodal supports, except for the sister relationship between Lycaenidae and Pieridae only in the amino acid dataset, which was in contrast to the sister relationship between Lycaenidae and Nymphalidae in Papilionoidea in the remaining datasets.

Mitochondrial myopathy associated with a novel 5522G>A mutation in the mitochondrial tRNA(Trp) gene

We report a novel pathogenic mutation of the mitochondrial transfer RNA (tRNA) gene for tryptophan in a patient with isolated myopathy and persistently elevated creatine kinase. Muscle studies revealed ragged red fibres and decreased activity of respiratory chain complex I and cytochrome c oxidase (COX). Sequencing of the 22 mitochondrial tRNA genes revealed a mutation m.5522G>A, which alters a conserved base pairing in the D-stem of the tRNA for tryptophan. The mutation was heteroplasmic with a mutational load between 88 and 99% in COX-negative fibres. This case contributes to the genetic heterogeneity of mitochondrial diseases caused by mutations in mitochondrial tRNA genes.

Decreased mitochondrial OGG1 expression is linked to mitochondrial defects and delayed hepatoma cell growth

Many solid tumor cells exhibit mitochondrial respiratory impairment; however, the mechanisms of such impairment in cancer development remain unclear. Here, we demonstrate that SNU human hepatoma cells with declined mitochondrial respiratory activity showed decreased expression of mitochondrial 8-oxoguanine DNA glycosylase/lyase (mtOGG1), a mitochondrial DNA repair enzyme; similar results were obtained with human hepatocellular carcinoma tissues. Among several OGG1-2 variants with a mitochondrial-targeting sequence (OGG1-2a, -2b, -2c, -2d, and -2e), OGG1-2a was the major mitochondrial isoform in all examined hepatoma cells. Interestingly, hepatoma cells with low mtOGG1 levels showed delayed cell growth and increased intracellular reactive oxygen species (ROS) levels. Knockdown of OGG1-2 isoforms in Chang-L cells, which have active mitochondrial respiration with high mtOGG1 levels, significantly decreased cellular respiration and cell growth, and increased intracellular ROS. Overexpression of OGG1-2a in SNU423 cells, which have low mtOGG1 levels, effectively recovered cellular respiration and cell growth activities, and decreased intracellular ROS. Taken together, our results suggest that mtOGG1 plays an important role in maintaining mitochondrial respiration, thereby contributing to cell growth of hepatoma cells.

Analysis of mitochondrial gene expression

Dictyostelium provides a well-established model system for the study of mitochondrial biology and disease. A complete mitochondrial transcription and RNA-processing map has been generated, while the start site for transcription and the responsible RNA polymerase have also been identified, as have the major cotranscriptional cleavage sites that generate the mature mitochondrial RNA molecules. Here we describe the methods deployed to study mitochondrial gene transcription and RNA processing in Dictyostelium.

Mitochondrial DNA transmission and confounding mitochondrial influences in cloned cattle and pigs

Although somatic cell nuclear transfer (SCNT) is a powerful tool for production of cloned animals, SCNT embryos generally have low developmental competency and many abnormalities. The interaction between the donor nucleus and the enucleated ooplasm plays an important role in early embryonic development, but the underlying mechanisms that negatively impact developmental competency remain unclear. Mitochondria have a broad range of critical functions in cellular energy supply, cell signaling, and programmed cell death; thus, affect embryonic and fetal development. This review focuses on mitochondrial considerations influencing SCNT techniques in farm animals. Donor somatic cell mitochondrial DNA (mtDNA) can be transmitted through what has been considered a "bottleneck" in mitochondrial genetics via the SCNT maternal lineage. This indicates that donor somatic cell mitochondria have a role in the reconstructed cytoplasm. However, foreign somatic cell mitochondria may affect the early development of SCNT embryos. Nuclear-mitochondrial interactions in interspecies/intergeneric SCNT (iSCNT) result in severe problems. A major biological selective pressure exists against survival of exogenous mtDNA in iSCNT. Yet, mtDNA differences in SCNT animals did not reflect transfer of proteomic components following proteomic analysis. Further study of nuclear-cytoplasmic interactions is needed to illuminate key developmental characteristics of SCNT animals associated with mitochondrial biology.

Detection of mitochondrial DNA mutations in nonmuscle invasive bladder cancer

BACKGROUND

Mitochondrial DNA (mtDNA) mutations have been recently described in various tumors; however, data focusing on bladder cancer are scarce. To understand the significance of mtDNA mutations in bladder cancer development, we investigated the mtDNA alterations in bladder cancer cases.

METHODS

We studied the mtDNA in 38 bladder tumors and 21 microdissected normal bladder tissue samples. Mitochondrial genes ATPase6, CytB, ND1, and D310 region were amplified by polymerase chain reaction and then sequenced.

RESULTS

We detected 40 mutations in our patient population. Our findings indicate that G8697A, G14905A, C15452A, and A15607G mutations are frequent in bladder cancers (p<0.05). In addition, the incidence of A3480G, T4216C, T14798C, and G9055A mutations were higher in patients with bladder tumors.

CONCLUSIONS

In conclusion, the high incidence of mtDNA mutations in bladder cancer suggests that mitochondria could play an important role in carcinogenesis and mtDNA could be a valuable marker for early bladder cancer diagnosis.

Mitochondrial involvement in drug-induced liver injury

Mitochondrial dysfunction is a major mechanism of liver injury. A parent drug or its reactive metabolite can trigger outer mitochondrial membrane permeabilization or rupture due to mitochondrial permeability transition. The latter can severely deplete ATP and cause liver cell necrosis, or it can instead lead to apoptosis by releasing cytochrome c, which activates caspases in the cytosol. Necrosis and apoptosis can trigger cytolytic hepatitis resulting in lethal fulminant hepatitis in some patients. Other drugs severely inhibit mitochondrial function and trigger extensive microvesicular steatosis, hypoglycaemia, coma, and death. Milder and more prolonged forms of drug-induced mitochondrial dysfunction can also cause macrovacuolar steatosis. Although this is a benign liver lesion in the short-term, it can progress to steatohepatitis and then to cirrhosis. Patient susceptibility to drug-induced mitochondrial dysfunction and liver injury can sometimes be explained by genetic or acquired variations in drug metabolism and/or elimination that increase the concentration of the toxic species (parent drug or metabolite). Susceptibility may also be increased by the presence of another condition, which also impairs mitochondrial function, such as an inborn mitochondrial cytopathy, beta-oxidation defect, certain viral infections, pregnancy, or the obesity-associated metabolic syndrome. Liver injury due to mitochondrial dysfunction can have important consequences for pharmaceutical companies. It has led to the interruption of clinical trials, the recall of several drugs after marketing, or the introduction of severe black box warnings by drug agencies. Pharmaceutical companies should systematically investigate mitochondrial effects during lead selection or preclinical safety studies.

Temperature effects on sex determination and ontogenetic gene expression of the aromatases cyp19a and cyp19b, and the estrogen receptors esr1 and esr2 in atlantic halibut (Hippoglossus hippoglossus)

The aromatase (CYP19) and estrogen receptor (ESR) play important roles in the molecular mechanism of sex determination and differentiation of lower vertebrates. Several studies have proven these mechanisms to be temperature sensitive, which can influence the direction of phenotypic gender development. A temperature study was conducted to examine the effect of temperature on the sex differentiation in farmed Atlantic halibut. Sexually undifferentiated larvae were exposed to 7 degrees C, 10 degrees C, or 13 degrees C during gonadal differentiation. Temperature effects on the transcription rate of the aromatase genes cyp19a (ovary type) and cyp19b (brain type) and the ESR genes esr1 and esr2 were examined by quantitative real-time PCR. With increasing temperatures, both cyp19a mRNA levels and the female incidence showed a decreasing trend, thus strongly indicating a relation between the expression of cyp19a and morphological ovary differentiation. In contrast to cyp19a, the levels of cyp19b, esr1, and esr2 mRNA strongly increased in all temperature groups throughout the study period, and did not show obvious temperature-related expression patterns. The present data provide evidence that posthatching temperature exposure significantly affects the expression of cyp19a mRNA during the developmental period and that high temperature possibly influences genetic sex determination in Atlantic halibut. Though, the female incidence never exceeded 50%, suggesting that only the homogametic (XX) female is thermolabile. So whereas temperature treatment is not likely suitable for direct feminization in halibut, the possibility for high-temperature production of XX neomales for broodstock to obtain all-female offspring by crossing with XX females is suggested.

Limited species differences in estrogen receptor alpha-medicated reporter gene transactivation by xenoestrogens

Estrogen receptors (ERs) play an important role in estrogen function. However, it is well known that there are species differences in amino acid sequences of the ligand binding domains. Here, we report on the analysis of species differences in ER-dependent transactivation with some chemicals using reporter gene assays. Full-length ER cDNAs from human, rat, chicken, alligator (Caiman), whiptail lizard, African clawed frog and rainbow trout were prepared from hepatic mRNA by the RT-PCR method and inserted into expression plasmids. Both expression and reporter plasmids were transiently transfected into HeLa cells, and then the estrogenic effects of chemicals were analyzed in terms of induction of luciferase activity. No species differences in transactivation were found among human, rat, chicken, alligator, whiptail lizard and African clawed frog ERs. However, thermo-dependent alteration in susceptibility to 17-beta-estradiol was observed with the rainbow trout ER because of thermo-dependence of estrogen binding.

Engineering a novel secretion signal for cross-host recombinant protein expression

Protein secretion is conferred by a hydrophobic secretion signal usually located at the N-terminal of the polypeptide. We report here, the identification of a novel secretion signal (SS) that is capable of directing the secretion of recombinant proteins from both prokaryotes and eukaryotes. Secretion of fusion reporter proteins was demonstrated in Escherichia coli, Saccharomyces cerevisiae and six different eukaryotic cells. Estrogen-inducibility and secretion of fusion reporter protein was demonstrated in six common eukaryotic cell lines. The rate of protein secretion is rapid and its expression profile closely reflects its intracellular concentration of mRNA. In bacteria and yeast, protein secretion directed by SS is dependent on the growth culture condition and rate of induction. This secretion signal allows a flexible strategy for the production and secretion of recombinant proteins in numerous hosts, and to conveniently and rapidly study protein expression.

Characterization of the 5'-flanking region of the rat gene for mitochondrial transcription factor A (Tfam)

Mitochondrial transcription factor A (Tfam) is essential for the initiation of transcription and the replication of mitochondrial DNA (mtDNA). The 5'-upstream region of the rat Tfam gene was isolated from rat genomic DNA by extending the 5' sequence of newly identified Tfam cDNA using PCR-based Genome Walker. The identified rat Tfam gene showed little sequence homology with the upstream region of human Tfam. No typical TATA or potential nuclear respiratory factor 1 (NRF-1) binding site was found, whereas three potential binding sites for Sp1 and one for NRF-2 were present in the proximal upstream region. Transfection of the Tfam 5'-upstream region ligated to luciferase into rat skeletal muscle L6 cells demonstrated that the promoter activity was 10 times higher than that of control vectors. Despite the absence of the NRF-1 consensus binding sequence, co-transfection of human NRF-1 expression vector increased the Tfam promoter activity 2-fold. The gel mobility shift assays for NRF-1 demonstrated that NRF-1 could bind to the proximal region of the promoter between -112 and +49. The addition of 50 mM glucose for 24 h increased Tfam promoter activity by up to 2-fold, but 100 microM H(2)O(2) for 24 h repressed the activity to 40% of the control. From these results, the sequence presented here is that of authentic rat Tfam promoter and it is hoped that it will prove useful in studies of mtDNA transcription and replication.

Reciprocal mutagenesis between human alpha(L349, M528) and rainbow trout (M317, I496) estrogen receptor residues demonstrates their importance in ligand binding and gene expression at different temperatures

Several fish proteins exhibit compromised function at temperatures outside of their normal physiological range. In this study, the effect of temperature on the ligand binding and the transactivation abilities of the rainbow trout estrogen receptor (rtER) and human estrogen receptor alpha (hER alpha) were examined. Saturation analysis and gene expression assays, using GST-ER and Gal4-ER fusion proteins consisting of the D, E and F domains of human (hER alpha def) and rainbow trout (rtERdef) receptors, show that GST-rtERdef E2 binding affinity and transactivation ability decrease with increasing temperature. A comparison of the amino acid sequence differences between their ligand binding pockets identified two conservative amino acid residue substitutions in rtER (M317, I496) and hER alpha (L349, M528). The effect of these substitutions on ligand binding and transactivation were examined by constructing reciprocal mutants, which effectively exchanged the binding pockets between rtER and hER alpha. The rtERdef M317L:I496M double mutant exhibited increased E2 binding affinity and transactivation ability at higher temperatures, and displayed hER alpha phenotypic behavior for the phytoestrogen, coumestrol. The hER alpha def L349M:M528I double mutant also exhibited a modest trend towards adopting the rtER phenotype. These studies demonstrate that conservative changes in residue hydrophobicity and volume can significantly affect ER ligand binding and transactivation ability in a temperature-dependent manner. The lack of a complete exchange of phenotypes between rtER and hER alpha indicates that factors outside of the ligand binding pocket are also involved.

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 novel piscine vitellogenin gene: structural and functional analyses of estrogen-inducible promoter

The Oreochromis aureus vitellogenin, OaVtg, gene spans 9 kb and contains 34 exons. Its transcription start site is located 15 bp upstream of the translational start codon. Although the OaVtg promoter has a nonconsensus TATA, transient transfection assay showed that this promoter is capable of driving basal transcription. Two imperfect estrogen response elements: EREp (proximal) and EREd (distal) are located in the promoter at - 532 and - 1352, respectively. In competition gel mobility-shift assays, only EREp exhibited specific binding of the recombinant estrogen receptor protein, GST-C/D OaER. Another imperfect ERE (EREexon2) was detected within exon 2 of the OaVtg gene. This is a novel finding for a vitellogenin (Vtg) gene. EREexon2 similarly showed specific recognition of GST-C/D OaER. Both EREp and EREexon2 showed comparable binding affinities as consensus ERE. In transient transfections, the OaVtg promoter, EREp and EREd elicited significant increase in estrogen-dependent synthesis of CAT protein. Hence, we propose that the non-consensus OaVtg EREs contribute to the estrogen-dependent regulation of the OaVtg gene in vivo.