Fig. 3.

Unifying model of sequential chromatin remodeling events preceding ZGA during early development. (1) Pioneer transcription factors (TF) can recognize a DNA sequence motif (green mark) and interfere with linker histone H1 (black). (2) DNA-bound pioneer TFs recruit chromatin remodeling complexes (CRC) that (3) remodel surrounding nucleosomes. This includes a repositioning of nucleosomes, post-translational modifications of histones, and leads to exposure of the transcription start site of the target gene (TSS, red mark). DNA methylation states on the promoters of developmentally regulated genes do not significantly change during the pre-ZGA to ZGA transition; these promoters are largely unmethylated, enabling a transcriptionally permissive state. (4) This remodeling is permissive for recruitment of the RNAPII complex, and transcription initiation at the time of ZGA. Dashed line represents a developmental time interval between two chromatin states