Polycomb group (PcG) proteins play important roles in maintaining the silent state of HOX genes. Recent studies have implicated histone methylation in long-term gene silencing. However, a connection between PcG-mediated gene silencing and histone methylation has not been established. Here we report the purification and characterization of an EED-EZH2 complex, the human counterpart of the Drosophila ESC-E(Z) complex. We demonstrate that the complex specifically methylates nucleosomal histone H3 at lysine 27 (H3-K27). Using chromatin immunoprecipitation assays, we show that H3-K27 methylation colocalizes with, and is dependent on, E(Z) binding at an Ultrabithorax (Ubx) Polycomb response element (PRE), and that this methylation correlates with Ubx repression. Methylation on H3-K27 facilitates binding of Polycomb (PC), a component of the PRC1 complex, to histone H3 amino-terminal tail. Thus, these studies establish a link between histone methylation and PcG-mediated gene silencing.

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Polycomb group (PcG) proteins maintain the transcriptional silence of target genes through many cycles of cell division. Here, we provide evidence for the sequential binding of PcG proteins at a Polycomb response element (PRE) in proliferating cells in which the sequence-specific DNA binding Pho and Phol proteins directly recruit E(z)-containing complexes, which in turn methylate histone H3 at lysine 27 (H3mK27). This provides a tag that facilitates binding by a Pc-containing complex. In wing imaginal discs, these PcG proteins also are present at discrete locations at or downstream of the promoter of a silenced target gene, Ubx. E(z)-dependent H3mK27 is also present near the Ubx promoter and is needed for Pc binding. The location of E(z)- and Pc-containing complexes downstream of the Ubx transcription start site suggests that they may inhibit transcription by interfering with assembly of the preinitiation complex or by blocking transcription initiation or elongation.

BackgroundPolybrominated diphenyl ethers (PBDEs) are widely used flame retardant compounds that are persistent and bioaccumulative and therefore have become ubiquitous environment contaminants. Animal studies suggest that prenatal PBDE exposure may result in adverse neurodevelopmental effects.ObjectiveIn a longitudinal cohort initiated after 11 September 2001, including 329 mothers who delivered in one of three hospitals in lower Manhattan, New York, we examined prenatal PBDE exposure and neurodevelopment when their children were 12–48 and 72 months of age.MethodsWe analyzed 210 cord blood specimens for selected PBDE congeners and assessed neurodevelopmental effects in the children at 12–48 and 72 months of age; 118, 117, 114, 104, and 96 children with available cord PBDE measurements were assessed at 12, 24, 36, 48, and 72 months, respectively. We used multivariate regression analyses to evaluate the associations between concentrations of individual PBDE congeners and neurodevelopmental indices.ResultsMedian cord blood concentrations of PBDE congeners 47, 99, and 100 were 11.2, 3.2, and 1.4 ng/g lipid, respectively. After adjustment for potential confounders, children with higher concentrations of BDEs 47, 99, or 100 scored lower on tests of mental and physical development at 12–48 and 72 months. Associations were significant for 12-month Psychomotor Development Index (BDE-47), 24-month Mental Development Index (MDI) (BDE-47, 99, and 100), 36-month MDI (BDE-100), 48-month full-scale and verbal IQ (BDE-47, 99, and 100) and performance IQ (BDE-100), and 72-month performance IQ (BDE-100).ConclusionsThis epidemiologic study demonstrates neurodevelopmental effects in relation to cord blood PBDE concentrations. Confirmation is needed in other longitudinal studies.

Polybrominated diphenyl ethers (PBDEs) and 2,2',4,4',5,5'-hexabromobiphenyl (BB-153) are chemicals known as brominated flame retardants. We have assessed the exposure status of the United States population to PBDEs and BB-153 and explored associations with demographic information, including participants' age, sex, and race/ethnicity. A total of 2,062 serum samples, from participants in the National Health and Nutrition Examination Survey (NHANES) 2003-2004 aged 12 years and older, were analyzed for PBDEs and BB-153; stratified and regression analyses were used to examine levels among demographic groups. The congener with the highest serum concentration was 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) [geometric mean 20.5 ng/g lipid]; followed by 2,2',4,4',5,5'-hexaBDE (BDE-153) [5.7 ng/g lipid]; 2,2',4,4',5-pentaBDE (BDE-99) [5.0 ng/g lipid; a value equal to the highest limit of detection for an individual sample]; 2,2',4,4',6-pentaBDE (BDE-100) [3.9 ng/g lipid]; BB-153 [2.3 ng/g lipid]; and 2,4,4'-triBDE (BDE-28) [1.2 ng/g lipid]. For BDE-47, we observed no significant difference in the least-squares geometric mean (LSGM) by sex, but with age we found both a linear decrease (p = 0.01) and a positive quadratic trend (p = 0.01). Its LSGM, 27.9 ng/lipid, in the 12-19 year olds decreased to 17.2 ng/g lipid in the 40-49 year group, and then curved upward to 20.4 ng/g lipid in the > or =60 years olds. Mexican Americans had the highest LSGM of BDE-47 (24.5 ng/g lipid), which was significantly higher than that of non-Hispanic whites (19.7 ng/g lipid, p = 0.01). Adults 60 years and older were twice as likely as adults 20-59 years old to have a serum BDE-47 concentration above the 95th percentile (p = 0.02). These data provide needed exposure assessment data for public health decisions.

BackgroundThere is emerging evidence that background exposure to persistent organic pollutants (POPs) are important in the development of conditions predisposing to diabetes as well as of type 2 diabetes itself. We recently reported that low dose POPs predicted incident type 2 diabetes in a nested case-control study. The current study examined if low dose POPs predicted future adiposity, dyslipidemia, and insulin resistance among controls without diabetes in that study.Methodology/Principal FindingsThe 90 controls were diabetes-free during 20 years follow-up. They were a stratified random sample, enriched with overweight and obese persons. POPs measured in 1987-88 (year 2) sera included 8 organochlorine (OC) pesticides, 22 polychlorinated biphenyls (PCBs), and 1 polybrominated biphenyl (PBB). Body mass index (BMI), triglycerides, HDL-cholesterol, LDL-cholesterol, and homeostasis model assessment value for insulin resistance (HOMA–IR) were study outcomes at 2005-06 (year 20). The evolution of study outcomes during 18 years by categories of serum concentrations of POPs at year 2 was evaluated by adjusting for the baseline values of outcomes plus potential confounders. Parallel to prediction of type 2 diabetes, many statistically significant associations of POPs with dysmetabolic conditions appeared at low dose, forming inverted U-shaped dose-response relations. Among OC pesticides, p,p'-DDE most consistently predicted higher BMI, triglycerides, and HOMA-IR and lower HDL-cholesterol at year 20 after adjusting for baseline values. Oxychlordane, trans-nonachlor, and hexachlorobenzene also significantly predicted higher triglycerides. Persistent PCBs with ≥7 chlorides predicted higher BMI, triglycerides, and HOMA-IR and lower HDL-cholesterol at year 20 with similar dose-response curves.Conclusions/SignificanceSimultaneous exposure to various POPs in the general population may contribute to development of obesity, dyslipidemia, and insulin resistance, common precursors of type 2 diabetes and cardiovascular diseases. Although obesity is a primary cause of these metabolic abnormalities, POPs exposure may contribute to excess adiposity and other features of dysmetabolism.

BackgroundLow doses of some persistent organic pollutants (POPs) associate cross-sectionally with type 2 diabetes, whereas associations with high POP exposures are inconsistent.ObjectivesWe investigated whether several POPs prospectively predict type 2 diabetes within the Coronary Artery Risk Development in Young Adults (CARDIA) cohort.MethodsParticipants in this nested case–control study were diabetes free in 1987–1988. By 2005–2006, the 90 controls remained free of diabetes, whereas the 90 cases developed diabetes. Using serum collected in 1987–1988, we measured 8 organochlorine pesticides, 22 polychlorinated biphenyl congeners (PCBs), and 1 polybrominated biphenyl (PBB). We compared POP concentrations from CARDIA and the National Health and Nutrition Examination Survey (NHANES) in 2003–2004. We computed odds ratios (ORs) for incident diabetes using logistic regression analysis.ResultsChlorinated POPs in CARDIA in 1987–1988 were much higher than corresponding NHANES 2003-2004 concentrations. POPs showed nonlinear associations with diabetes risk. The highest risk was observed in the second quartiles of trans-nonachlor, oxychlordane, mirex, highly chlorinated PCBs, and PBB153—a finding that suggests low-dose effects. We concentrated risk by summing these POPs and isolated very low concentrations of multiple POPs in the lowest sextile of the sum. The adjusted OR in the second sextile vs. the lowest sextile was 5.3 overall and 20.1 for body mass index ≥ 30 kg/m2.ConclusionsSeveral POPs at low doses similar to current exposure levels may increase diabetes risk, possibly through endocrine disruption. Certain POPs may a play a role in the current epidemic of diabetes, which has been attributed to obesity.

A semiautomated extraction and cleanup method has been developed for the measurement of eight polybrominated diphenyl ethers (PBDEs), 2,2',4,4',5,5'-hexabromobiphenyl (BB-153) and 2,2',4,4',5,5'-hexachlorobiphenyl (CB-153). The method employs automated addition of internal standards ((13)C-labeled), addition of formic acid (denaturation agent), and dilution with water prior to automated overnight extraction using a modular solid-phase extraction (SPE) system. Removal of coextracted biogenic materials was performed on a two-layered 3-mL disposable cartridge containing activated silica gel and a mixture of silica gel and sulfuric acid. Sample cleanup was automated using the same modular SPE system. Reproducibility and precision of the liquid handler used for internal standard additions were shown to be 2 and 4%, respectively. Overall reproducibility during processing of eight batches of samples (N = 30/batch, including methods blanks) was below 10% for most analytes. Mean recoveries of the (13)C-labeled internal standards ranged from 69 to 95% for the seven monitored PBDEs; 76 and 98% were recovered for BB-153 and CB-153, respectively.