DV enhancers are not poised for future activation. (A) Histone modification levels at DV enhancers during the maternal-to-zygotic transition (Li et al. 2014) show that H3K27ac levels are accumulating early and gradually during development, and thus, some H3K27ac is present during enhancer priming by Zld at cell cycles 8 and 12. In contrast, H3K4me1 and H3K27me3, which mark poised enhancers, are only detectable after Dl-dependent transcription begins at stage 5 or cell cycle 14 (shaded in gray). Data are shown as average ChIP-seq signal in a 1-kb window centered on each enhancer. (B) Boxplots of DNase I hypersensitivity (DHS) at DV enhancers during embryogenesis show that all DV enhancers are most accessible during stages 5 and 9 when DV patterning takes place (shaded in gray), and become less accessible at subsequent stages. The DHS score is the average signal per enhancer region derived from the data by Thomas et al. (2011). Whiskers show 1.5 times the interquartile range, and outliers are shown as dots.