Catalytic-dependent and independent functions of the histone acetyltransferase CBP promote pioneer factor-mediated zygotic genome activation [ATAC-seq]

Immediately after fertilization the genome is transcriptionally quiescent. Maternally encoded pioneer transcription factors reprogram the chromatin state and facilitate the transcription of the zygotic genome. In Drosophila, transcription is initiated by the pioneer factor Zelda. While Zelda-occupied sites are enriched with histone acetylation, a post-translational mark associated with active cis-regulatory regions, the functional relationship between Zelda and histone acetylation in zygotic genome activation remained unclear. We show that Zelda-mediated recruitment of the histone acetyltransferase CBP is essential for zygotic transcription and embryonic development. CBP catalytic activity is necessary for release of RNA Polymerase II (Pol II) into transcription elongation. However, CBP largely activates zygotic transcription independent of acetylation through Pol II recruitment. Neither acetylation nor CBP are required for the pioneering function of Zelda. Our data suggest that pioneer factor-mediated recruitment of CBP is a conserved mechanism required to activate zygotic transcription but that this role is separable from the function of pioneer factors in restructuring chromatin accessibility. Overall design: This data set contains ATAC-seq data from individual Drosophila melanogaster embryos precisely staged 15mins into nuclear cycle 14 during the maternal-to-zygotic transition. Single-embryo ATAC-seq was executed on GFP-CBP;his2AV-RFP and GFP-CBP;nos-deGrad/+;his2AV-RFP embryos to measure the effect CBP knockdown has on chromatin accessibility. Single embryo ATAC-seq was performed similarly on CRY2-CBP;his2avRFP and his2AV-RFP control embryos where both genotypes were subjected to either a blue light treatment precisely from NC10 to 15mins into NC14 or left in the dark. Blue light treatment inactivates CRY2-CBP histone acetyltransferase activity and therefore these experiments identify if catalytic activity of CBP is essential for chromatin accessibility. ATAC-seq in S2 cells was performed with control drug, DMSO, or a CBP catalytic inhibitor, A485, after induction of Zld from a CuSO4 inducible promoter to assay if H3K27ac is essential for chromatin accessibility at Zld pioneered regions.