Marking of the genome by H3K4 methylation prior to embryonic gene activation

Early zebrafish embryo development proceeds first from a maternally transcribed and stored mRNAs, and zygotic gene activation (ZGA) is initiated at the mid-blastula transition (MBT; 1000-cell stage), 3.3 h post-fertilization. Very little is known on how the zygotic genome is programmed for transcriptional activation at the MBT. To start addressing this issue, we have mapped by ChIP-chip genome-wide promoter histone methylation (H3K4me3, H3K9me3, H3K27me3, H3K36me3) and RNA Pol II profiles before ZGA (256-cell stage; 2.5 hpf), during ZGA (MBT; 3.5 hpf)) and after ZGA (Post-MBT; 5.3 hpf) . We used a custom 2.1M probe HD promoter array (Nimblegen) for ChIP and input DNA hybridization. Peak detection was done using MA2C with P=10e-4 as cutoff. ChIP-chip experiments were performed from chromatin prepared by sonication after formaldehyde cross-linking, from embryos are the indicated developmental stages and ChIP DNA was hybridized onto the aforementioned Nimbegen promoter arrays.