Valproic acid is widely used to treat epilepsy and bipolar disorder and is also a potent teratogen, but its mechanisms of action in any of these settings are unknown. We report that valproic acid activates Wntdependent gene expression, similar to lithium, the mainstay of therapy for bipolar disorder. Valproic acid, however, acts through a distinct pathway that involves direct inhibition of histone deacetylase (IC 50 for HDAC1 ‫؍‬ 0.4 mM). At therapeutic levels, valproic acid mimics the histone deacetylase inhibitor trichostatin A, causing hyperacetylation of histones in cultured cells. Valproic acid, like trichostatin A, also activates transcription from diverse exogenous and endogenous promoters. Furthermore, valproic acid and trichostatin A have remarkably similar teratogenic effects in vertebrate embryos, while non-teratogenic analogues of valproic acid do not inhibit histone deacetylase and do not activate transcription. Based on these observations, we propose that inhibition of histone deacetylase provides a mechanism for valproic acid-induced birth defects and could also explain the efficacy of valproic acid in the treatment of bipolar disorder.

Birds are the most species-rich class of tetrapod vertebrates and have wide relevance across many research fields. We explored bird macroevolution using full genomes from 48 avian species representing all major extant clades. The avian genome is principally characterized by its constrained size, which predominantly arose because of lineage-specific erosion of repetitive elements, large segmental deletions, and gene loss. Avian genomes furthermore show a remarkably high degree of evolutionary stasis at the levels of nucleotide sequence, gene synteny, and chromosomal structure. Despite this pattern of conservation, we detected many non-neutral evolutionary changes in protein-coding genes and noncoding regions. These analyses reveal that pan-avian genomic diversity covaries with adaptations to different lifestyles and convergent evolution of traits.

Sulfate aerosols exert profound impacts on human and ecosystem health, weather, and climate, but their formation mechanism remains uncertain. Atmospheric models consistently underpredict sulfate levels under diverse environmental conditions. From atmospheric measurements in two Chinese megacities and complementary laboratory experiments, we show that the aqueous oxidation of SO 2 by NO 2 is key to efficient sulfate formation but is only feasible under two atmospheric conditions: on fine aerosols with high relative humidity and NH 3 neutralization or under cloud conditions. Under polluted environments, this SO 2 oxidation process leads to large sulfate production rates and promotes formation of nitrate and organic matter on aqueous particles, exacerbating severe haze development. Effective haze mitigation is achievable by intervening in the sulfate formation process with enforced NH 3 and NO 2 control measures. In addition to explaining the polluted episodes currently occurring in China and during the 1952 London Fog, this sulfate production mechanism is widespread, and our results suggest a way to tackle this growing problem in China and much of the developing world.sulfate aerosol | severe haze | pollution | human health | climate

No abstract