A gap in emission inventories of urban volatile organic compound (VOC) sources, which contribute to regional ozone and aerosol burdens, has increased as transportation emissions in the United States and Europe have declined rapidly. A detailed mass balance demonstrates that the use of volatile chemical products (VCPs)-including pesticides, coatings, printing inks, adhesives, cleaning agents, and personal care products-now constitutes half of fossil fuel VOC emissions in industrialized cities. The high fraction of VCP emissions is consistent with observed urban outdoor and indoor air measurements. We show that human exposure to carbonaceous aerosols of fossil origin is transitioning away from transportation-related sources and toward VCPs. Existing U.S. regulations on VCPs emphasize mitigating ozone and air toxics, but they currently exempt many chemicals that lead to secondary organic aerosols.
Beta-catenin-dependent or canonical Wnt signals are fundamental in animal development and tumor progression. Using Xenopus laevis, we report that the BTB/POZ zinc finger family member Kaiso directly represses canonical Wnt gene targets (Siamois, c-Fos, Cyclin-D1, and c-Myc) in conjunction with TCF/LEF (TCF). Analogous to beta-catenin relief of TCF repressive activity, we show that p120-catenin relieves Kaiso-mediated repression of Siamois. Furthermore, Kaiso and TCF coassociate, and combined Kaiso and TCF derepression results in pronounced Siamois expression and increased beta-catenin coprecipitation with the Siamois promoter. The functional interdependency is underlined by Kaiso suppression of beta-catenin-induced axis duplication and by TCF-3 rescue of Kaiso depletion phenotypes. These studies point to convergence of parallel p120-catenin/Kaiso and beta-catenin/TCF signaling pathways to regulate gene expression in vertebrate development and possibly carcinogenesis.
To investigate the role of DNA methylation during human development, we developed Methyl-seq, a method that assays DNA methylation at more than 90,000 regions throughout the genome. Performing Methyl-seq on human embryonic stem cells (hESCs), their derivatives, and human tissues allowed us to identify several trends during hESC and in vivo liver differentiation. First, differentiation results in DNA methylation changes at a minimal number of assayed regions, both in vitro and in vivo (2%-11%). Second, in vitro hESC differentiation is characterized by both de novo methylation and demethylation, whereas in vivo fetal liver development is characterized predominantly by demethylation. Third, hESC differentiation is uniquely characterized by methylation changes specifically at H3K27me3-occupied regions, bivalent domains, and low density CpG promoters (LCPs), suggesting that these regions are more likely to be involved in transcriptional regulation during hESC differentiation. Although both H3K27me3-occupied domains and LCPs are also regions of high variability in DNA methylation state during human liver development, these regions become highly unmethylated, which is a distinct trend from that observed in hESCs. Taken together, our results indicate that hESC differentiation has a unique DNA methylation signature that may not be indicative of in vivo differentiation.
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